ASSEMBLY FOR THE FULL-SURFACE ADHESIVE BONDING OF SUBSTANTIALLY CONGRUENT ADHESIVE-BONDING SURFACES OF A FIRST AND A SECOND JOINING PARTNER

Abstract

The invention relates to an assembly for adhesively connecting substantially congruent gluing surfaces of a first and second joining partner over their full surface, comprising: the first joining partner (1); the second joining partner (2); an adhesive layer (3) of a polar, flowable adhesive applied to the gluing surface (1a) of the first joining partner (1); means (8) for holding the second joining partner (2) above the adhesive layer (1a) of the first joining partner (1), such that the gluing surface (2a) of the second joining partner (2) faces the adhesive layer (3) on the first joining partner (1) and is disposed so as to be spaced therefrom across an air gap (5), and the spacing defined by the air gap (5) between the first joining partner (1) and the second joining partner (2) is dimensioned in such a way that a capillary volume is formed; means (7) for generating an electric field (10) in order to cause, by means of electric influence, a local charge displacement (11) on and/or in the second joining partner (1), and the charge displacement (11) is suitable for attracting the polar adhesive in such a way that it wets the gluing surface (2a) of the second joining partner (2) first in the area of the local charge displacement (11), wherein the means for generating the electric field comprise an electrode (7), which is disposed on the side of the second joining partner (2) facing away from the gluing surface (2a) and is electrically insulated from said partner (2).

Claims

1. An assembly for adhesively connecting substantially congruent gluing surfaces of a first and second joining partner over their full surface, comprising: the first joining partner; the second joining partner; an adhesive layer of a polar, flowable adhesive applied to the gluing surface of the first joining partner; means for holding the second joining partner above the adhesive layer of the first joining partner, such that the gluing surface of the second joining partner faces the adhesive layer on the first joining partner and is disposed so as to be spaced therefrom across an air gap, and the spacing defined by the air gap between the first joining partner and the second joining partner is dimensioned in such a way that a capillary volume is formed; means for generating an electric field in order to cause, by means of electric influence, a local charge displacement on and/or in the second joining partner, and the charge displacement is suitable for attracting the polar adhesive in such a way that it wets the gluing surface of the second joining partner first in the area of the local charge displacement, wherein the means for generating the electric field comprise an electrode, which is disposed on the side of the second joining partner facing away from the gluing surface and is electrically insulated from said partner.

2. The assembly according to claim 1, wherein means for applying the adhesive to the gluing surface of the first joining partner are also provided.

3. The assembly according to claim 2, wherein the means for holding the second joining partner comprise a receiving portion defining a contact surface for the second joining partner, and the electrode is at least partially embedded in the receiving portion.

4. The assembly according to claim 3, wherein the receiving portion is made from a plastic, preferably a polymer, more preferably a polyetherketone, such as polyaryletherketone, a polyhaloolefin, such as polytetrafluoroethylene, and/or a polyoxymethylene, such as a polyoxymethylene homopolymer.

5. The assembly according to claim 1, wherein the electrode has a pointed end pointing towards the gluing surface of the second joining partner.

6. The assembly according to claim 1, wherein the second joining partner is transparent, and the adhesive of the adhesive layer cures or hardens in a transparent manner.

7. The assembly according to claim 1, wherein the first joining partner is a display device, and its gluing surface is defined by an outer layer covering a display surface of the display device.

8. The assembly according to claim 1, wherein the second joining partner is a flat structure.

9. The assembly according to claim 1, wherein the second joining partner has a layer of polymethylmetacrylate.

10. The assembly according to claim 1, wherein the adhesive of the adhesive layer, at least during application, has a viscosity selected from the range of 500 mPas and 5000 mPas.

11. The assembly according to claim 1, wherein the adhesive of the adhesive layer is a chemically hardening adhesive, preferably a polymerization adhesive, such as a methyl methacrylate adhesive or a cyanoacrylate adhesive, or a polyaddition adhesive, such as an adhesive based on silicone polymer.

12. The assembly according to claim 1, wherein the means for holding the second joining partner comprise a vacuum holding device.

13. The assembly according to claim 1, wherein means for partially curing and/or hardening the adhesive layer are furthermore provided.

14. A method for adhesively connecting substantially congruent gluing surfaces of a first and second joining partner over their full surface, comprising the following steps: providing the first and second joining partners; applying a polar adhesive as a flowable adhesive layer to the gluing surface of the first joining partner; disposing the second joining partner above the first joining partner using means for holding the second joining partner such that the gluing surface of the second joining partner faces the adhesive layer and is spaced therefrom across an air gap, wherein the spacing defined by the air gap between the first joining partner and the second joining partner is dimensioned in such a way that a capillary volume is formed; generating an electric field by an electrode, which is disposed on the side of the second joining partner facing away from the gluing surface and is electrically insulated therefrom, in order to cause, by means of electric influence, a local charge displacement on and/or in the second joining partner; first wetting of the gluing surface of the second joining partner in the region of the local charge displacement by the polar adhesive being attracted due to the charge displacement; full-surface spreading of the adhesive and full-surface wetting of the gluing surface of the second joining partner, starting from the location of the local wetting, by means of capillary force in the air gap; curing or hardening of the adhesive layer.

15. The method according to claim 14, wherein the step of generating an electric field precedes the wetting step.

16. The method according to claim 14, wherein the step of curing or hardening includes a first step of partially curing or hardening the adhesive layer and a second subsequent step of the further, preferably full-surface, curing or hardening of the adhesive layer, and that further, an intermediary removing step, i.e. a step interposed between the first and second steps, is provided, in which the composite of the first and second joining partners and the adhesive layer is removed from the means for holding the second joining partner and/or the electrode.

Description

[0035] The invention is explained in more detail with reference to the following FIGURE. The FIGURE is to be understood only as an example and merely represents a preferred embodiment. In the drawing:

[0036] FIG. 1 shows a schematic flow chart of the method according to the invention and of the assembly according to the invention for carrying out the method.

[0037] The method according to the invention and the assembly according to the invention shown in FIG. 1 serve for adhesively connecting substantially flat parallel gluing surfaces of a first joining partner 1 and a second joining partner 2. In a first step shown in FIG. 1a), the first joining partner 1 and the second joining partner 2 are provided, which are respectively shown in a sectional view. These are two planar flat structures, with 1 being a layer structure of an LCD or OLED display device. The second joining partner 2 is a transparent pane of a transparent plastic, such as PMMA or a silicate glass. The two flat structures 1, 2 are configured in such a way that the associated gluing surfaces 1a, 2a face each other. In addition, a receiving portion 8 made from polytetrafluoroethylene is provided against which the second joining partner 2 rests due to a vacuum holding device 9. Of the vacuum holding device 9, only the through-holes 9 in the receiving portion 8 are shown via which the second joining partner 2 is held by suction due to the generated vacuum. An electrode 7 for generating an electric field 10, as will be explained later in FIG. 1c, is embedded into the receiving portion 8 in such a way that there is no touching contact with the joining partner 2 and, due to the electrical insulating property of the material chosen for the receiving portion 8, in this case PTFE, also no electric contact with the second joining partner 2. The electrode 7 has a pointed end pointing perpendicularly in the direction of the gluing surface 2a of the second joining partner 2 for concentrating the field strength. In the present case, the electrode 7 is disposed centrally, i.e. above the geometrical center of the adhesive surface 2a on the far side of the second joining partner 2. In each case, the gluing surface 1a, 2a is configured to be planar.

[0038] The method according to the invention shown in FIG. 1a) further comprises the step of applying a flowable, transparently hardening adhesive, which is polar on a molecular level, as an adhesive layer 3 to the gluing surface 1a of the first joining partner 1. Preferably, the adhesive is applied in the shape of a bone, with full-surface spreading taking place due to an automatic subsequent running and spreading. In the automatic method or assembly shown, the adhesive is applied by means of a nozzle 4 moving across the gluing surface. The location, duration, quantity and the speed of the nozzle discharge during application is selected in such a way, for example, depending on the flowability (viscosity) of the adhesive, that the result is a uniform wetting of the gluing surface of the first joining partner 1 with adhesive, at least after a predetermined period of time. “Uniform” means a layer thickness of the resulting adhesive layer 3 that is continuously largely consistent, apart from a decrease in the area of the edges.

[0039] The method according to the invention comprises the step, shown in FIG. 1b), of arranging the first joining partner 1 and second joining partner 3 in such a way that the gluing surface 2a of the second joining partner 2 faces towards the adhesive layer 3 applied to the first joining partner 1, while a minimum spacing is maintained, i.e. no contact takes place, between the joining partners 1, 2, with a capillary volume 5 being formed. A parallel spacing between the second joining partner 2 and the adhesive layer 3 of the first joining partner 1 is provided, so that no wetting of the second joining partner 2 with adhesive takes place yet. A capillary volume 5 forms between the first joining partner 1 and the second joining partner 2 due to the selected minimum spacing.

[0040] According to the invention, a subsequent step shown in FIG. 1c) is provided in which an electric field 10 is generated by means of the electrode 7. As shown in FIG. 1d), this field 10 is supposed to be chosen such that a charge displacement 11 in and/or on the joining partner 2 is caused which in turn acts in an attracting manner on the polar adhesive layer 3. As FIG. 1d) further shows, the strength and polarity of this filed 10 are selected such that the charge displacement 11 in the second joining partner 2 is sufficient for attracting the polar adhesive located on the first joining partner 1 as an adhesive layer 3 in such a way that, overcoming its surface tension, it locally wets the gluing surface 2a of the second joining partner 2 without the adhesive layer 3 detaching from the first joining partner 1. For example, the electrode 7 is negatively charged with respect to the adhesive. The step shown in FIG. 1d) causes a spatially limited, i.e. local, wetting of the gluing surface 2a of the second joining partner 2. After the electrostatic field is switched off, an automatic full-surface spreading of the adhesive on the gluing surface 2a of the second joining partner 2 by means of capillary force occurs in the subsequent step shown in FIG. 1e). Thus, the local wetting 6 serves as a “seed” for the further full-surface wetting of the gluing surface 2a of the second joining partner 2. According to the invention, subsequent to the local wetting, a full-surface wetting of the gluing surface of the second joining partner 2 and spreading of the adhesive via the capillary volume 5 occurs due to the capillary force, starting from the location 6 of the local wetting, in order to form a composite 1, 2, 3 consisting of the first joining partner 1, the second joining partner 2 and the adhesive layer 3.

[0041] As shown in step 1f), a full-surface spreading filling the capillary volume 5 is obtained. As further shown in FIG. 1f), a first hardening step follows, in which the adhesive of the adhesive layer 3 hardens partially transparently by irradiation with UV light. The partial hardening, which is substantially limited to the edge region of the composite 1, 2, 3 is the result of the orientation of the UV emission of the UV light sources 13. This emission is directed towards the end faces, i.e. the narrow sides, of the composites and there substantially covers the exposed adhesive layer and thus, due to the partial hardening and solidification of the adhesive layer, prevents the adhesive from leaking out from the capillary volume without a full-surface hardening of the adhesive layer being required. After the “sealing of the edges” has taken place by hardening or curing the adhesive of the adhesive layer 3 located in the edge region of the composite 1, 2, 3, the composite 1, 2, 3 is removed from the receiving portion 8 and then, the adhesive of the adhesive layer 3 is hardened transparently and over its full surface by an irradiation with UV light 11 through the transparent joining partner 2. The radiation density of the UV light irradiation 11 is selected to be lower in the second step than in the first step in order not to jeopardize the optical properties of the adhesive of the adhesive layer 3 in the remaining part close to the center, outside the edge region irradiated in the first step.