EP2917023A1

EP2917023A1 - Method for joining a joining partner made of a thermoplastic material to a joining partner made of glass

Info

Publication number: EP2917023A1
Application number: EP13789256.8A
Authority: EP
Inventors: Frank Brunnecker; Manuel Sieben; Tobias JAUS
Original assignee: LPKF Laser and Electronics AG
Current assignee: LPKF Laser and Electronics AG
Priority date: 2012-11-07
Filing date: 2013-11-06
Publication date: 2015-09-16
Also published as: DE102012220285A1; US20150298391A1; JP2016502475A; WO2014072322A1

Abstract

Disclosed is a method for joining a joining partner made of a thermoplastic material to a joining partner made of glass, characterised by the following method steps: producing a thermoplastic joining partner (2) made of a laser-absorbing thermoplastic material; producing a glass joining partner (1) made of a laser-transmissive glass material; superimposing the thermoplastic joining partner (2) and the glass joining partner (1) by applying a joining force (F) to the joining partners (1, 2); heating the glass joining partner (1), in particular using radiation (15); and applying a laser processing beam (3) onto the boundary surface (20) of the thermoplastic joining partner (2)through the glass joining partner (1) into a joining zone (18) so as to melt the thermoplastic joining partner (2) and so as to form a bond between the two joining partners (1, 2) in the joining zone (18) in conjunction with the cooling thereof.

Description

Method for joining a joining partner made of a thermoplastic material with a glass joining partner

The content of German Patent Application 10 2012 220 285.4 is incorporated herein by reference.

The invention relates to a method for joining a joining partner made of a thermoplastic material with a joining partner of glass. To the background of the invention it should be noted that usually currently glass-plastic compounds are realized by the use of adhesives. As an exemplary application here can be named glass displays glass displays, which are connected to a PC or PC / ABS housing. In a first step, the adhesive is applied, in a second step, the glass pane is placed. In this process, there is a great risk that leaking adhesive will "short-circuit" the ITO layers on the glass, thus irreversibly destroying the touch display In addition to this risk of reject production, this technique has the disadvantage that the joints may become opaque. table does not look appealing and must be covered by a black print on the display.

Other applications for this adhesive technology may be glazing in the automotive industry, such as sun roofs in a plastic carrier. In this area, PP is mainly used today as a material for the thermoplastic joining partner for economic reasons. Due to its non-polar structure, PP can only be glued after appropriate pretreatments, resulting in additional costs. A third application is ECUs / frequency converters which are applied directly to the back of a substrate wafer of photovoltaic solar panels. EP 1 763 431 B1 relates to a method for laser welding a thermoplastic polymer material with a second material permeable to the laser light used, wherein for the laser welding the laser light is directed at the weld by the second material onto the first material and at least the first material the weld softens under the action of the laser light. The second material according to EP 1 763 431 B 1 may be a non-softening material to which the softened first material adheres after solidification. For example, by the method according to EP 1 763 431 B 1 for laser welding, a thermoplastic polymer material (first material) can be bonded to glass.

DE 10 2009 034 226 A1 relates to a manufacturing method for a lamp having an at least partially transparent part and a plastic part, which forms a lamp housing or a lamp base. At least one connection point is produced by melting at least the plastic part by means of a laser beam, a cohesive or positive connection between the plastic part and the at least partially transparent part. In one embodiment of DE 10 2009 034 226 AI, the at least partially transparent part of the lamp consists of glass. By melting the at least one connection point of the plastic part, a positive connection between the plastic part and the glass part is generated. In the method according to DE 10 2009 034 226 AI durch- penetrates the at least partially transparent part during melting of the laser beam and initially heated substantially the plastic part. The plastic part is preferably made of polycarbonate, polypropylene, acrylonitrile-butadiene-styrene or polybutylene terephthalate.

JP 201 1-207 056 A relates to a method for bonding a thermoplastic with a glass substrate. The carrier material is welded in its edge region with the plastic base body. In this case, a laser radiates through the carrier material and heats a contact surface of the plastic. According to JP 201 1-207 056 A, the plastic body serves as a base body and the carrier material made of glass as a cover. In a region in which the carrier material is not welded to the plastic body, a semiconductor material is arranged between the base body and the carrier material.

Although the above-mentioned documents consistently disclose the principle of laser-induced melt-bonding of a thermoplastic joining partner with a glass joining partner. Experiments with the Applicant have shown in this context, however, that the basic technique suffers in particular with regard to the resulting in the cooling of the joining partners stresses in the two different materials, namely a thermoplastic and glass, the hot melt adhesive bond in their strength. On this basis, the invention is based on the object to provide a method for joining a joining partner of a thermoplastic material with a joining partner made of glass, which leads by simple process engineering means to a reliable thermoplastic glass connection without the use of adhesives. This object is achieved according to the characterizing part of claim 1 by the following method steps:

Providing a thermoplastic joining partner of a laser-absorbing, thermoplastic material,

Providing a glass joining partner of a laser-transmissive glass material,

Positioning the thermoplastic joining partner and the glass joining partner to one another while subjecting the joining partners to a joining force,

- Heating the glass joining partner by means of a radiation, and

- Injecting a laser machining beam on the boundary surface of the thermoplastic joining partner through the glass joining partner into a joining zone while melting the thermoplastic joining partner and forming an adhesive bond between the two joining partners in the joining zone with their cooling.

The method according to the invention is thus based on fundamentally known laser transmission welding, in which the processing beam radiates through a laser-transmissive joining partner onto the laser-absorbing joining partner, which melts and, in the case of a transmissive joining partner consisting of glass, adheres to the latter in the melt region.

According to the current state of knowledge, such adhesion compounds involve three different mechanisms of action. On the one hand, secondary valence bonds form in the adjacent molecular layers. The effective distance of this effect, which is mainly based on hydrogen bonding, is approximately 0.5 nm. Therefore, one of the connecting elements must inevitably be fused partner to bridge surface irregularities. In addition, it is necessary for this molten joining partner to spread on the surface of the fixed partner, ie the surface tension should be as low as possible. On the other hand, this mechanism of action requires a polarity of the molten medium, this requirement excludes a surface tension of 0. It is therefore in the optimal case only the essential part of the polar surface energy. A second, independent of the polarity mechanism of action is the mechanical Verkrallung the plasticized material in the surface structure of the solid present joining partner. This mechanism is independent of the polarity of the materials, but also requires a low surface energy, so that it can lead to the fullest possible spreading of the molten joining partner.

The third potential mechanism is covalent bonding. This type of bond promises high adhesive forces, but in many cases it requires functionalization of the plastic surface. On the side of the glass usually Si (silicon) molecules are available, which offer the formation of covalent bonds to SiOH (silanol). This in turn means that H (hydrogen) molecules must be available for this reaction on the surface of the thermoplastic. These molecules can either be naturally contained in the plastic or they can be introduced by functionalization.

All the above-mentioned mechanisms of action suffer from the fact that, due to the fact that they are significantly lower than the thermoplastic, Geren thermal expansion coefficient of glass, the melt adhesion or adhesive bond between the thermoplastic and the glass by the strong contraction of the former material in the joint zone, so usually occur in the produced hot melt seam, Nahteigenspannun- gene. These tensions overlap and reduce the attained adhesive forces. For some compounds even complete separation could be observed, suggesting that the seam tensions exceed the achieved bond strengths. This problem is mitigated by the further procedurally intended heating of the glass joining partner. By this measure, its temperature is increased in accordance with the heating of the thermoplastic joining partner, so that both joining partners show a more uniform cooling behavior with significantly reduced internal stress build-up. Corresponding experiments show that reliable connections between the two mentioned joining partners can be produced with high strength.

In the dependent claims preferred developments of the inventive method are given. Thus, the material of the thermoplastic joining partner may be selected from one or more of the following thermoplastic materials: polypropylene (PP), polyethylene (PE), acrylonitrile-butadiene-styrene (ABS), acrylic ester-styrene-acrylonitrile (ASA), polymethyl methacrylate (PMMA) , Polycarbonate (PC), polyethylene terephthalate (PC), polyetherimide (PEI), polyamide (PA) or cycloolefm copolymer (COC).

Borosilicate glass, quartz glass, magnesium fluoride, tempered glasses, produced by the preferred materials for the glass joining partner Ion exchange method or tempered glasses mainly borosilicate glass exposed.

The laser machining beam is preferably an infrared laser beam, in particular having a wavelength of 808 nm or 2000 nm, which can be provided with a laser power of 10 W to 200 W. For this purpose, conventional laser beam processing equipment can be used, as described by the applicant. manufactured and sold for laser transmission welding.

A preferred radiation source for the heating of the glass joining partner can be formed by at least one halogen emitter which emits, for example, a short-wave I radiation and whose power is between 500 W and 2000 W, preferably 1000 W. By this relatively broadband secondary radiation, which can be applied to the glass joining partner before and / or simultaneously with the laser processing beam, intensive heating of the glass material is achieved. A further optimization of the strength of the connection between the thermoplastic and glass joining partner can be achieved by surface activating the thermoplastic joining partner, at least in the region of the joining zone, by plasma treatment or flame treatment. In this plasma treatment, air, oxygen or nitrogen can preferably be used as the process gas. In the plasma treatment process, OH groups are enriched on the surface of the plastic joining partner. These OH groups are then available as partners for the formation of hydrogen bonds in the downstream connection process. Superimposed on the formation of these secondary valence bonds There is a covalent bond between the Si molecules in the glass and the OH groups on the functionalized surface of the plastic. A further increased strength of the connection can be expected if the surface of the glass joining partner is roughened at least in the region of the joining zone. As a result of this structuring introduced, for example, by means of ultrashort pulse lasers with a pulse duration <10 ns, the surface involved in the bonding process is increased many times, which structures the clinker effect of the molten thermoplastic material in these surface microstructures and thus the joint strength of the joint increases.

As a further preferred method measure the Setzweg occurring during joining of the two joining partners is measured. This benefits the reproducibility of the joining process.

As an advantageous parameter for the production of a seam-like joining zone, the laser machining beam is guided over the boundary surface of the thermoplastic joining partner at a feed rate of 2 mm / s to 100 mm / s. The joining force, which is applied to the two joining partners, can be between 200 N and 800 N, preferably 400 N. Some essential advantages of the invention can again be summarized as follows:

- No consumables, in particular a separate adhesive, is necessary;

- The joining process is easy to control; - only one process step is necessary

- Fine, demarcated structures can be created; and

- An online process control can be integrated into the joining apparatus.

Further features, details and advantages of the invention will be apparent from the following description, are explained in more detail in the embodiments with reference to the accompanying drawings. Show it:

Fig. 1 is a schematic, broken perspective view of a

Laser joining device with the two joining partners,

2 is a plan view of the joining partners with an intact adhesive

Adhesive seam, and

Fig. 3 is a plan view of the thermoplastic joining partner after a violent separation of the adhesive adhesive seam.

1 shows two joining partners to be bonded, namely a first glass joining partner 1, and a second thermoplastic joining partner 2. For this bonding, a device is used which is also used for laser transmission welding processes. The upper glass joining partner 1 is transmissive to the laser processing beam 3, the lower thermoplastic joining partner 2 is absorptive for it. Incidentally, the laser transmission welding is known and requires no further discussion.

The laser machining beam 3 is guided via a processing head designated as a whole by 4 from a stationary laser beam source via a fiber optic to the focusing optics 5. Laser source and fiber optics are omitted for clarity in the drawings. The Focusing optics 5 is seated on a support 6 of the machining head 4, which is flanged, for example, on the manipulation arm of an industrial robot. A tensioning roller 10 is mounted laterally next to the optical axis 9 of the laser processing beam 3 via a cantilever 8 and rolls with its circumference on the upper glass joining partner 1 and thus in the region of the gluing to be joined the two joining partners 1, 2 by applying a corresponding joining force F braced together. A corresponding counter-holder for the roller below the welding contour is also not shown in FIG. 1 for the sake of clarity.

Furthermore, an IR halogen emitter 14 is attached to the support 6 of the machining head 4, which generates a short-wave, infrared secondary radiation 15. The IR halogen emitter 14 is seated in a secondary beam reflector 16 on the carrier 6. Due to the reflector 16, the secondary radiation 15 is focused on the joining zone 18. As is clear from FIG. 1, the focal region 19 of the secondary radiation 15 is widened with respect to the focus 21 of the laser beam 3, so that in the joining zone 18 concentrically around the focus 21 the secondary radiation 15 heats the upper glass joining partner 1 ,

With the joining device described above, the method according to the invention can be realized as follows:

The thermoplastic joining partner 2 is prepared by plasma-activating its boundary surface 20 to be melted. The plasma used is a compressed air plasma, although it is not certain which constituents of the air are generated during plasma generation 2

ionized / radicalized. Presumably, these are O ^" ions, which form OH groups (OH, COOH, CHO, CONH ₂ ) on the plastic surface, which, on the one hand, increases the surface tension and, on the other hand, the OH groups for the bil - Formation of covalent bonds available.

The two joining partners 1, 2 are then clamped in the device shown in Fig. 1. The machining head 4 moves now under the action of the two joining partners 1, 2 with the tensioning roller 10, the joining contour K, which is to form an adhesive or adhesive joint between the two joining partners, in the feed direction 13, wherein in the respective joining zone 18 via the secondary radiation 15, the upper glass joining partner 1 is locally heated. At the same time the laser machining beam 3 is directed to the glass joining partner 1 facing boundary surface 20 of the thermoplastic joining partner 2 through the glass joining partner 1 and there leads to a local melting of the thermoplastic joining partner 2. This is an intimate contact under Formation of hydrogen bonds and a micro-clawing between see the two joining partners 1, 2 achieved and thus a melting

Attachment between the two joining partners 1, 2 caused. The Setzweg occurring between them in this joining of the two joining partners 1, 2 is measured as meaningful parameters for the melting process and included in the process control. After cooling of the two joining partners 1, 2, which leads to negligible internal stresses within the joint zone 18 due to the heating of the glass joining partner 1, a stable thermoplastic glass-Schmelzklebe- connection between two joining partners 1, 2 is formed. Based on FIGS. 2 and 3, test results with the joining method according to the invention are to be presented. Thus, FIG. 2 shows the plan view of the two joining partners 1, 2 after producing a joining contour K in the form of a short hot-melt adhesive seam, which is a uniform, glossy black seam surface in the boundary surface 20 of the lower thermoplastic joining partner 2 presents. It is a strong attachment to determine between two joining partners 1, 2 so there is a stable adhesive bond. FIG. 3 shows the boundary surface 20 of the thermoplastic joining partner 2 after the violent tearing off of the upper glass joining partner 1. Eruptions in the thermoplastic material can be seen which indicate the strength of the seam bonding.

In the case discussed above, the glass joining partner 1 consisted of standard glass BK7 with a thickness of 5 mm, the thermoplastic joining partner 2 of a material combination PC / ABS. The laser power was 28 W, the power of the secondary radiation 1000 W. The feed rate v of the laser beam was set to 7 mm / s, the joining force F to 400 N. In the following table are successful attempts to produce hot melt adhesive seams between various thermoplastics and glass (BK7, thickness 5 mm) with the appropriate materials and parameters documented:

Thermoplastic Laser Halogen Feed Joining Force Material Power Power Speed

PC / PET 28 W 1000 W 7 mm / s 400 N

PC / ABS 28 W 1000 W 7 mm / s 400 N

PP 14 W 1000 W 3 mm / s 400 N

PA (Grilamid) 24 W 1000 W 5.25 mm / s 400 N In the experiment with the thermoplastic material combination PC / PET were otherwise carried out temperature change experiments with the bonded joining partners 1, 2. Thus, after three temperature changes within 30 to 60 minutes in a temperature range of -20 ° C to 60 ° C no tearing of the adhesive seam could be observed.

Claims

claims

1. A method for joining a joining partner of a thermoplastic material with a joining partner made of glass, characterized by the following method steps:

Providing a thermoplastic joining partner (2) made of a laser-absorbent, thermoplastic material,

Providing a glass joining partner (1) of a laser-transmissive glass material,

- Positioning of the thermoplastic joining partner (2) and the glass joining partner (1) to each other under the action of the joining partners (1, 2) with a joining force (F),

- Heating the glass joining partner (1) in particular by means of a radiation (15), and

- irradiation of a laser machining beam (3) onto the boundary

Surface (20) of the thermoplastic joining partner (2) through the glass joining partner (1) into a joining zone (18) while melting the thermoplastic joining partner (2) and forming an adhesive bond between the two joining partners (1, 2) in the Joining zone (18) with its cooling.

2. The method according to claim 1, characterized in that the material of the thermoplastic joining partner (2) is selected from one or more of the following thermoplastic materials: polypropylene (PP), polyethylene (PE), acrylonitrile-butadiene-styrene (ABS), acrylic esters -

Styrene-acrylonitrile (ASA), polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PC), polyetherimide (PEI), polyamide (PA) or cycloolefin copolymer (COC).

3. The method according to claim 1 or 2, characterized in that the

Material of the glass joining partner (1) is selected from one or more of the following glass materials: borosilicate glass, quartz glass, magnesium fluoride, tempered glasses, produced by Ionenaustauschverfah- ren or tempered glasses mainly borosilicate glass.

4. The method according to any one of the preceding claims, characterized in that the laser machining beam (3) is an infrared laser beam, in particular with a wavelength of 808 nm or 2000 nm.

5. The method according to any one of the preceding claims, characterized in that the laser machining beam (3) is provided with a laser power of 10 W to 200 W.

6. The method according to any one of the preceding claims, characterized in that the radiation for the heating of the glass joining partner (1) by at least one halogen emitter (14) is generated.

7. The method according to claim 6, characterized in that the power of the halogen radiator (14) between 500 W and 2000 W, preferably 1000 W, is.

8. The method according to any one of the preceding claims, characterized in that the thermoplastic joining partner (2) is surface-activated at least in the region of the joining zone (18) by a plasma treatment or flame treatment.

9. The method according to claim 8, characterized in that in the

Plasma treatment of air, in particular compressed air, oxygen or nitrogen substance can be used as process gas.

10. The method according to any one of the preceding claims, characterized in that the surface of the glass joining partner (1) is roughened at least in the region of the joining zone (18).

1 1. A method according to claim 10, characterized in that the roughening of the glass joining partner (1) by a laser irradiation, in particular by ultra-short-time laser pulses with a pulse duration <10 ns, made.

12. The method according to any one of the preceding claims, characterized in that the Setzweg occurring during joining of the two joining partners (1, 2) is measured.

13. The method according to any one of the preceding claims, characterized in that for producing a seam-like joining zone of the laser machining beam (3) at a feed rate of 2 mm / s to 10 mm / s over the boundary surface (20) of the thermoplastic - Joining partner (2) is performed.

14. The method according to any one of the preceding claims, characterized in that the joining force (F) between 200 N and 800 N, preferably 400 N is.