DE19523900C1 - Process for the pretreatment of a plastic surface to be glued - Google Patents

Description

State of the art

The invention relates to a method for pretreating at least one plastic surface to be glued according to the genus of the main claim.

To improve the strength and tightness properties of, for example, plastic / plastic or plastic / steel adhesive bonds, a number of conventional treatment processes are known, with which at least one surface to be bonded is pretreated. A mechanical treatment process can consist in roughening the adhesive surface to be treated with a sanded surface such as sandpaper or by sandblasting. Furthermore, a number of physical treatment methods are known, such as corona and low-pressure plasma discharge and pretreatment with an excimer laser (UV laser). R. Bütje, among others:
"Adhesive surface pretreatment of plastics by excimer laser", Laser und Optoelektronik 21 (1989) 6, pp. 62-66.

The ultraviolet radiation from the excimer laser is in Very strongly absorbed plastics. This emitted High intensity radiation causes high molecular weight  Substances, such as plastics, break the molecular chains through photochemical processes. This leads to Formation of polar groups on the surface, which in turn can have a positive effect on the adhesive properties.

DE 39 03 153 A1 describes a method for the treatment of surfaces to be bonded from fiber composite materials known in which generated by a CO₂ laser Laser radiation the cured polymer of the Fiber composite material to a defined depth is removed. The top fiber layer of the Laser composite is exposed, leaving the fibers but should not suffer any noticeable damage. By melting of the cured polymer on the surface is thus due to the surface Fiber structure creates a textured surface that is suitable as a primer for an adhesive.

Without removing the plastic on the surface comes the teaching of DE 42 28 040 A1. Here is by Irradiate the surface to be glued with UV radiation the molecular structure of the plastic material on the Split surface. A physical roughening of the Surface is not achieved with this process.

From US 4 925 523 a method for removing and Etching of substrates made of polymers is known, with the Removing or etching a pulsed UV laser radiation is used.

Advantages of the invention

The method according to the invention with the characteristic features of the main claim leads to a substantial improvement in Strength and tightness properties of the adhesive connections, by the effective by the inventive method Adhesive area is enlarged.

By at least partially melting and re-solidifying the surface of the plastic to be glued becomes rough Surface structure created essentially by pores and / or poses. At the same time, the through pretreated at least partially melting Plastic surface have undercuts that after the Melt the surface by solidifying the pretreated Plastic surface can arise.

This rough surface structure is particularly of Advantage if two to be glued together Plastic surfaces according to the inventive method have been pretreated. These undercuts can contribute significantly to the increase in adhesive strength as they when the adhesive connection is stressed by it acting forces as barbs or hooks can interlock at least partially and thus one result in higher adhesive strength.

Another advantage of the inventive method for Pretreatment of plastic surfaces to be glued lies in the improved climate and temperature changes  resistance. The rough solidified after melting Surface structure of the pretreated and to be glued The surface remains in its structure over a longer period Time period fully preserved without changing the Adhesive properties of the adhesive surface occurs.

Another advantage of the method according to the invention lies the fact that by using a laser a targeted and defined pretreatment is made possible. This allows preferably narrowly delimited adhesive surfaces are pretreated without that neighboring sensitive electrical or electronic Components are damaged.

An advantageous development of the method is Pretreat the plastic surface to be glued an at least partial thermal decomposition of the top one Edge layer of the adhesive surface. This leads to another Increasing the roughness of the pretreated Surface structure, so that the effective adhesive surface can be further enlarged. The adhesive strength can be a further measure can be increased.

Another advantageous embodiment of the method is the use of the laser in the infrared range between 780 nm to 1 mm, preferably 1.06 µm to 10.6 µm. In this Wavelength range can be achieved that the plastics in the top edge layer and one immediately underlying zone at least partially thermally decomposed be melted as well.

According to a further advantageous development of the The laser process becomes linear across the process adhesive surface led. Depending on the through the set parameters of the laser, such as Energy density, pulse duration or pulse frequency as well Feed rate can be the size of the generated or the resulting pores and / or poses the. With the linear guidance of the laser over the  pretreated surface thus creates a certain Track width. The location of the subsequent trace of the laser in opposite direction to the previously created track width is determined so that in the further, parallel pores and / or traces that run along this Poses almost immediately on the pores and / or Border on the previously generated track so that a Almost zero track overlap can be provided. So can the adhesive surface almost completely by the laser for example, scanned in line and pretreated will. The laser can be used in zigzag mode surface to be treated as well as only from one side to the others.

According to an advantageous development of the method provided that the poses and / or pores in a Lie in a row and form a track, also an overlap have almost zero, d. that is, the respective Posing adjacent to the next one. Thus at high processing speed the effective adhesive surface be greatly enlarged, leading to an improvement in Strength properties of the adhesive bond leads.

The laser can advantageously be pulsed onto the pretreat surface to be treated, before partly a Q-switch operation is provided for whose Q-switch frequency can be up to 50 kHz. Furthermore, it is advantageously provided that at least the surface to be glued embedded color pigments having. This can significantly increase the Absorption coefficient can be achieved, the effect of thermal decomposition and melting of the Favored surface. In particular, this is the case if Soot is stored in the plastic. The storage Such pigments can advantageously range from 0.02% by volume to 20% by volume. This allows using a relatively low energy and a short processing or Exposure time a relatively high surface roughness  be achieved. A chemical change in the surface plays a rather subordinate role in these processes.

A further advantageous embodiment of the method can are that glass fiber reinforced plastic is pretreated. It can be while working with the Laser onto the surface by the laser beam at least partial exposure of glass fibers take place after the Gluing two adhesive surfaces increases the interlocking effect can. This can further improve the Strength properties of adhesive bonds created will.

drawing

A preferred embodiment of the invention is in the Drawing shown and in the description below explained in more detail. Show it:

Fig. 1 is a schematic sectional view of a pre-treated according to the inventive method the surface of plastic,

Fig. 2 is a schematic sectional view of two pretreated plastic surfaces that form an adhesive connection and

Fig. 3 is a plan view of a partially pretreated adhesive surface.

Embodiment

Fig. 1 shows a sectional view of a plastic part 11 with a pretreated surface to be bonded 12 and a pretreated surface 13 of. The plastic part 11 can be made of a thermoplastic, thermoset or elastomer, preferably thermoplastic materials such as polyamide, polybutylene terephthalate, polyphenylene sulfide, polypropylene or the like are used.

The surface 12 to be glued is pretreated with a solid-state laser, which is advantageously operated with a wavelength in the infrared range between 780 nm to 1 mm. An Nd-YAG laser with a wavelength of 1.06 µm, with which a significant increase in the adhesive strength can be achieved, has proven to be particularly advantageous. A Q-switched laser, that is to say in Q-switch operation, can be used for the pretreatment, which is advantageously operated with a Q-switch frequency of up to 50 kHz. The pulsed energy can be introduced with an average power density of up to 10 MW / mm² and a pulse duration of 50 ns to 500 ns, whereby the average energy density can be between 0.005 J / mm² to 10 J / mm².

The pulsed laser beams acting on the surface 12 to be bonded cause an uppermost edge layer 14 to be at least partially thermally decomposed and an underlying zone 15 to be at least partially melted. This creates poses 16 which solidify immediately after melting and leave depressions or depressions behind. By means of a linear guiding of the laser, a large number of projections 16 are lined up in a track 26 ( FIG. 3). The formation of projections 16 produces a rough surface, through which the effective adhesive surface is increased and thus an improvement in the strength properties of the adhesive connection is achieved. In addition, this relatively coarse roughness of the surface 12 can be overlaid with a finer roughness 17 at least on the uppermost edge layer 14 . This can create a further improvement in the strength property of adhesive bonds 21 .

The projections 16 , which have solidified in a large number of different shapes, can also have undercuts 18 , which likewise improve the adhesion of the adhesive.

The plastic part 11 can in particular have colored pigments 19 embedded in the area of the surface 12 to be glued. The color pigments 19 can be provided in a proportion of 0.02% by volume to 20% by volume. Soot can advantageously be soot, since it has a high absorption coefficient when treated with a laser in the infrared range, as a result of which a relatively low energy is sufficient to produce the required or desired size of the projections 16 . A very short treatment time can advantageously be achieved. As a result, the cycle times for the pretreatment of plastic parts 11 can be reduced to a considerable extent, as a result of which the manufacturing costs can also be reduced.

In Fig. 2, an adhesive connection 21 from two plastic parts 11 , 11 'is shown in a schematic cross section. Between the two pretreated surfaces 12 , 12 ', adhesive 22 is introduced. For example, it is a 1-component epoxy adhesive. Furthermore, depending on the materials used for the adhesive connection 21, further suitable and known adhesives can be used. The undercuts 18 of the poses 16 formed after the melting by the laser rays during the solidification process have the effect that, for example, a higher strength between the adhesive and poses 16 is made possible, since this can already lead to a tangling effect. Furthermore, this interlocking effect can be achieved if, for example, two undercuts 18 , 18 'of the projections 16 , 16 ' can engage behind one another, so that an additional improvement in the strength property of the adhesive connection 21 can be created. Advantageously, the peaks and valleys of the projections 16 can at least partially interlock.

Furthermore, at least the surfaces to be bonded 12 , 12 'contain mineral fillers as well as glass fiber particles 23 , which can be introduced with a weight fraction of 5% to 75%. During the pretreatment process by at least partially thermal decomposition and melting of the surfaces to be bonded 12 , 12 ', the glass fibers 23 are at least partially exposed, so that they also contribute to the fact that a sticking effect occurs in the adhesive connection 21 .

In Fig. 3 a top view is shown on an adherend surface 12 of a plastic part 11. The laser beam is guided in a line over the surface 12 to be bonded, as a result of which line-shaped projections 16 are generated, the edge regions of which adjoin one another at an adapted Q-switch frequency and have an overlap of almost zero. As a result, the surface is almost completely processed and pretreated with the shortest possible processing time and leads to a substantial increase in the effective adhesive area. The poses 16 are shown round for the sake of simplicity and can occur in reality in further different forms.

For the pretreatment of the surface 12 to be glued, first a track 26 'of projections 16 along arrow direction 24 is formed by the linear guidance of the laser, which is followed by a next track 26 ' with arrow direction 25 . The projections 16 are advantageously arranged in such a way that when they approach a round diameter, they almost abut one another in the spaces 27 between them. At least, however, the second track 26 'running parallel to a first track 26 ' is designed such that a track overlap within the track 26 , 26 'is almost zero. The linear guidance of the laser can be performed both lengthways and crossways to a long side of a square or rectangular adhesive surface, for example. A circular or helical guide for pretreating the adhesive surface can also be provided.

A beam deflection to generate the track 26 , 26 ', 26 '', etc. takes place via a galvanometer scanner. As a result, a precise guidance of the laser beam can be achieved, which is precisely controlled and pretreated, in particular in the case of surfaces 12 to be bonded, which can lie in the sub-square millimeter range.

A comparison of different pretreatment processes shows that a significant increase in the adhesive strength has been achieved by the process according to the invention, this being particularly clear in the case of polypropylene. The comparison was based on a tensile shear test according to DIN 53 283 with an overlap of 5 mm, ie that the overlapping and pretreated surfaces 12 , 12 'overlap a width of 5 mm and thus form a 5 mm wide adhesive connection 21 . A 1-component epoxy adhesive was used for the adhesive connection 21 .

The adhesive connection 21 has been produced between two black joining parts.

PG-GF30 is practically not in the untreated state can be glued. The pretreatment of the plastic surfaces by Irradiation with Corona over a period of 3 seconds gave an adhesive strength of 0.5 N / mm². An improvement the adhesive strength, on the other hand, gave the radiation through Low pressure plasma over a period of between 60 seconds up to 120 seconds, resulting in an adhesive strength of 2.5 N / mm² was achieved. Pretreatment using an excimer laser increased the adhesive strength up to 5.2 N / mm². The Pretreatment of plastic surfaces with Solid-state lasers according to the inventive method resulted an adhesive strength of 9 N / mm². It gave similar results  for the materials PEEK-GF30, PBT-GF30, PA66-GF30 dry, PA66-GF30 moist.

It goes without saying that the method according to the invention can be used for an adhesive connection 21 , in which, for example, two plastic parts are glued together, a plastic part and a steel part, a plastic part and a part consisting of a further material. Furthermore, an adhesive connection can consist of a plastic part with a pretreated surface and another part with a pretreated or non-pretreated surface.

Claims (11)

1. A method for pretreating at least one surface to be bonded from plastic, the surface being irradiated with laser radiation, characterized in that the laser radiation is used in the infrared region with a wavelength of 780 nm to 1 mm such that the surface ( 12 ) to be bonded is at least partially melted on the surface. 2. The method according to claim 1, characterized in that an uppermost edge layer ( 14 ) of the surface to be bonded ( 12 ) is at least partially thermally decomposed and an underlying zone ( 15 ) is melted. 3. The method according to any one of the preceding claims, characterized in that the laser is guided linearly over the surface to be glued ( 12 ) with a track overlap of almost zero. 4. The method according to any one of the preceding claims, characterized in that the overlap formed between individual projections ( 16 ) in a track ( 26 ) depending on the relative movement of the laser to the surface to be glued ( 12 ) and a pulse duration within the track ( 26 ) is set to almost zero. 5. The method according to any one of the preceding claims, characterized in that the laser is in a Q-switch mode is pulsed, its Q-switch frequency up to 50 kHz is. 6. The method according to any one of the preceding claims, characterized in that the surface to be glued ( 12 ) has a proportion of 0.2 vol.% To 20 vol.% Of pigments, preferably carbon black. 7. The method according to any one of the preceding claims, characterized in that the surface to be glued ( 12 ) has a proportion of 5% by weight to 75% by weight of glass fiber ( 23 ). 8. The method according to any one of the preceding claims, characterized in that the surface to be glued ( 12 ) has a proportion of 5% by weight to 75% by weight of mineral fillers. 9. The method according to any one of the preceding claims, characterized in that the surface to be glued ( 12 ) is pretreated with an Nd-YAG laser with a wavelength of 1.06 µm. 10. The method according to any one of the preceding claims, characterized in that the laser is at a medium Energy density between 0.005 J / mm² to 10 J / mm² is set. 11. The method according to any one of the preceding claims, characterized in that the energy of the laser pulsed with an average power density up to 10 MW / mm² and a pulse duration of 50 ns to 500 ns becomes.