METHOD OF BONDING PANELS TO A PANEL ASSEMBLY AND PANEL ASSEMBLY

Abstract

The invention relates to a method of bonding panels together to form a panel assembly, comprising the following steps: providing a first panel (10) with a body portion (11) and an end portion (12) and a second panel (20) with a body portion (21) and an end portion (22); providing a first structural adhesive film (30) and a second structural adhesive film (31); applying the first structural adhesive film (30) on an upper side of the end portion (22) of the second panel (20) and applying the second structural adhesive film (31) on a lower side of the end portion (22) of the second panel (20); bringing the two panels (10 and 20) together and folding the end portion (12) of the first panel (10) around the end portion (22) of the second panel (10) such that the end portion (12) extends essentially parallel to the body portion (11) of the first panel (10) thereby enclosing the end portion (22) of the second panel and such that the first structural adhesive film (30) is positioned between the upper side of the end portion (22) of the second panel (20) and the end portion (12) of the first panel (10) and that the second structural adhesive film (31) is positioned between the lower side of the end portion (22) of the second panel (20) and the body portion (11) of the first panel (10); heating the assembly above the activation temperature of the first (10) and second structural adhesive tape (20); wherein the first structural adhesive film (10) differs from the second structural adhesive film (20).

Claims

1. Method of bonding panels together to form a panel assembly, comprising the following steps: providing a first panel with a body portion and an end portion and a second panel with a body portion and an end portion; providing a first structural adhesive film and a second structural adhesive film; applying the first structural adhesive film on an upper side of the end portion of the second panel and applying the second structural adhesive film on a lower side of the end portion of the second panel; bringing the two panels together and folding the end portion of the first panel around the end portion of the second panel such that the end portion extends essentially parallel to the body portion of the first panel thereby enclosing the end portion of the second panel and such that the first structural adhesive film is positioned between the upper side of the end portion of the second panel and the end portion of the first panel and that the second structural adhesive film is positioned between the lower side of the end portion of the second panel and the body portion of the first panel; heating the assembly above the activation temperature of the first and second structural adhesive tape; wherein the first structural adhesive film differs from the second structural adhesive film.

2. Method according to claim 1, wherein the first structural adhesive film differs from the second structural adhesive film in its thickness, its width, its chemical composition and/or its construction.

3. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film comprise(s) at least one epoxy compound and at least one curing agent.

4. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) a thermoplastic resin and optionally a toughening agent.

5. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) a thermoplastic resin and at least one component comprising at least one epoxy moiety and at least one linear or branched alkyl group and/or at least one mineral filler, wherein the at least one mineral filler is capable of absorbing water.

6. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) at least one acrylic polymer.

7. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) a toughening agent and/or a blowing agent.

8. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) at least one layer of porous structure.

9. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film are tacky at room temperature.

10. Method according to claim 1, wherein the first structural adhesive film and/or the second structural adhesive film are elastic at room temperature.

11. Method according to claim 1, wherein the first structural adhesive film and the second structural adhesive film get applied simultaneously.

12. System for bonding two panels together by using the method according to any of the claims 1, wherein the system comprises a first structural adhesive film; a second structural adhesive film; wherein the first structural adhesive film differs from the second structural adhesive film.

13. Panel assembly comprising: a first panel with a body portion and an end portion and a second panel with a body portion and an end portion; a first structural adhesive film and a second structural adhesive film; wherein the end portion of the first panel is folded around the end portion of the second panel such that the end portion extends essentially parallel to the body portion of the first panel thereby enclosing the end portion of the second panel and wherein the first structural adhesive film is positioned between the upper side of the end portion of the second panel and the end portion of the first panel and that the second structural adhesive film is positioned between the lower side of the end portion of the second panel and the body portion of the first panel; wherein the first structural adhesive film differs from the second structural adhesive film.

14. Method according to claim 3, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) a thermoplastic resin and optionally a toughening agent.

15. Method according to claim 14, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) at least one acrylic polymer.

16. Method according to claim 15, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) a toughening agent and/or a blowing agent.

17. Method according to claim 16, wherein the first structural adhesive film and/or the second structural adhesive film further comprise(s) at least one layer of porous structure.

18. Method according to claim 17, wherein the first structural adhesive film and/or the second structural adhesive film are tacky at room temperature.

19. Method according to claim 18, wherein the first structural adhesive film and/or the second structural adhesive film are elastic at room temperature.

20. Method according to claim 19, wherein the first structural adhesive film and the second structural adhesive film get applied simultaneously.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The invention will now be described in more detail with reference to the following Figures exemplifying particular embodiments of the invention:

[0059] FIG. 1 is a three dimensional view of a structural adhesive film used in the method according to the invention;

[0060] FIG. 2 is a cross-sectional view of the film shown in FIG. 1 along the line II-II;

[0061] FIG. 3 is a three dimensional view of a structural adhesive film used in the method according to the invention;

[0062] FIG. 4 is a cross-sectional view of the film shown in FIG. 3 along the line IV-IV in Film;

[0063] FIG. 5 is a cross-sectional view of a first panel with a first structural adhesive film;

[0064] FIG. 6 is a cross-sectional view of the first panel of FIG. 5 with a second structural adhesive film;

[0065] FIG. 7 is a cross-sectional view of the first panel of FIGS. 5 and 6 with a second panel next to it;

[0066] FIG. 8 is a cross-sectional view of the first panel of FIGS. 5 to 7 with an end of the second panel bend around an end of the first panel;

[0067] FIGS. 9 to 11 are cross-sectional views of further a panel assemblies according to the invention with two different structural adhesive films before cure and

[0068] FIG. 12 is a cross-sectional view of a panel assembly with two different structural adhesive films after cure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0069] Herein below various embodiments of the present invention are described and shown in the drawings wherein like elements are provided with the same reference numbers.

[0070] FIG. 1 is a three-dimensional view of a structural adhesive film 30. The film 30 has an extension in its longitudinal direction y that is longer than its extension in its cross direction x. The structural adhesive film 30 may for example be provided as a film on a roll. Or it may be provided as a pre-cut die-cut. The structural adhesive film 30 comprises one layer of polymeric material. FIG. 2 is a cross sectional view of the film shown in FIG. 1 along the line II-II. One layer of an adhesive, e. g. a layer of a polymeric material, can be seen in this Figure.

[0071] FIG. 3 is a three-dimensional view of a structural adhesive film 30. The film 30 has an extension in its longitudinal direction y that is longer than its extension in its cross direction x. The structural adhesive film 30 may for example be provided as a film on a roll. Or it may be provided as a pre-cut die-cut. The structural adhesive film 30 comprises two layers 30a and 30b. The layers may be two layers of different or the same polymeric material. It is also possible that one of the layers comprise a porous material like a net or scrim or the like. FIG. 4 is a cross sectional view of the film shown in FIG. 1 along the line IV-IV. The two layers 30a and 30b are positioned on top of each other and extend parallel to each other.

[0072] The following Figures show the single steps of one embodiment of a method according to the invention.

[0073] FIG. 5 is a cross-sectional view of an inner panel (second panel) 20 that provides a body portion 21 and an end portion 22 with an edge 23, wherein the edge 23 extends perpendicular to the extension of the end portion 22. The inner panel 20 may be for example a metal panel, a plastic panel or a panel made out of a composite material. It may for example be used to make a panel assembly for a closure or a door for a vehicle. A structural adhesive film 30as shown in FIGS. 1 and 2is applied on the upper side of the end portion 22 of the inner panel 20. The adhesive film extends from the edge 23 towards the body portion 21 of the inner panel 20.

[0074] FIG. 6 is a cross-sectional view of the inner panel 20 of FIG. 5 with the first structural adhesive film 30 applied on the upper side of the end portion 22. A second structural adhesive film 31 is applied on the lower side of the end portion 22 of the panel 20. The adhesive film extends from the edge 23 towards the body portion 21 of the panel 20. The two films 30 and 31 extend essentially parallel to each other on both sides of the end portion 22 of the panel 20. The first structural adhesive film 30 differs from the second structural adhesive film 31 in its extension in the cross direction. The extension of the first structural adhesive film 30 is shorter than the extension of the second structural adhesive film 31. The first structural adhesive film 30 and the second structural adhesive film 31 may also vary in other properties from each other like in their thickness, their chemical composition and/or their construction. This will be described in more detail below.

[0075] FIG. 7 is a cross-sectional view of the inner panel 20 of FIG. 6 with the first 30 and the second structural adhesive film 31 applied to its end portion 22. FIG. 7 also shows a further outer panel (first panel) 10 with a body portion 11 and an end portion 12. The outer panel 10 may be for example a metal panel, a plastic panel or a panel made out of a composite material. For a hem flange connection the outer panel may preferably be a metal panel. The end portion 12 of the outer panel 10 ends in and edge 13, which extends perpendicular to the extension of the end portion 12. The outer panel 10 is brought in contact with the second structural adhesive film 31 on the lower side of the end portion 22 of the inner panel 20 such that the end portion 12 of the outer panel 10 extends over the edge 23 of the end portion 22 of the inner panel 20 with the structural adhesive films 30 and 31 on both sides.

[0076] FIG. 8 is a cross-sectional view of the two panels (outer and inner or first and second) 10 and 20 with the two structural adhesive films 30 and 31. FIG. 8 differs from FIG. 7 in that the end portion 12 of the outer panel 1 is bend or folded around the end portion 22 of the inner panel 20 to build a so-called hem flange connection between the two panels.

[0077] In order to reliably seal the hem flange connection it may be required that after curing of the structural adhesive films 30 and 31 the outer edge 13 of the outer panel 10 is completely covered by structural adhesive film. In order to fulfill this requirement, the first structural adhesive film 30 needs to expand during cure such that it extends covers the entire outer edge 13. This will be described in detail with reference to FIG. 12.

[0078] FIG. 9 is a cross-sectional view of two panels (outer and inner) 10 and 20 with two different structural adhesive films 30 and 31. The structural adhesive films 30 and 31 not only differ in their extension in the cross direction. They also differ in their thickness. The first structural adhesive film 30 is thicker than the second structural adhesive film 31. This may for example be necessary for example in order to reliably fulfill the above described requirements of covering the outer edge 13.

[0079] FIG. 10 is a cross-sectional view of the two panels (outer and inner or first and second) 10 and 20 with two different structural adhesive films 30 and 31. In this embodiment the first structural adhesive film 30 is a one layer film and the second structural adhesive film 31 provides two layers 31a and 31b. FIG. 11 is a further cross-sectional view of two panels (outer and inner) 10 and 20 with two different structural adhesive films 30 and 31. Both structural adhesive films provide two layers. The first structural adhesive film 30 provides a first layer 30a and a second layer 30b. The second structural adhesive film 31 provides a first layer 31a and a second layer 31b.

[0080] FIG. 12 shows a panel assembly with an outer panel 10 and an inner panel 20 with two different structural adhesive films 30 and 31 after curing the structural adhesive films, wherein the outer 10 and the inner panel 20 are connected over a hem flange connection. During the curing process the structural adhesive films 30 and 31 expands. Therefore the volume of the structural adhesive film 30 and 31 is bigger after cure as before. The shape of the first structural adhesive film 30 changed such that it covers the entire edge 13 of the outer panel 10. The structural adhesive 31 expanded a little bit out of the gap between the outer 10 and the inner panel 20. In FIG. 12 it is not indicated if and how many layers the structural adhesive films provide. All the above mentioned options are possible and others as well, like for example a first structural adhesive film 30 and/or a second structural adhesive film 31 with three layers etc.

EXAMPLES

[0081] The following examples are provided to illustrate certain embodiments but are not meant to be limited in any way.

Test Methods

[0082] The invention relates to a method of bonding panels together to form a panel assembly by providing a first structural adhesive film and a second structural adhesive film. One important criteria for a car manufacture is the visual appearance of the film in the panel assembly after the two panels are brought together and after the structural adhesive film is cured.

[0083] The visual appearance is tested by looking at the cured film in the hem flange connection. An experienced person can decide if the visual appearance is good or not good. A good visual appearance can be defined as a film surface that has a surface that extends essentially linear and essentially parallel to the edges of the panels it is bonding together, thereby covering the outer edge of the outer panel of the hem flange connection. In addition, to the linear and parallel extension of the film a film with a good appearance has a smooth surface that is essentially free from irregularities like bubbles or entrapped gas.

List of Raw Materials for Structural Adhesive Films

[0084] The raw materials used for the epoxy-based structural adhesive films are listed below in table 1.

TABLE-US-00001 TABLE 1 Material Function Description Epikote 828 Epoxy resin Trade designation of a liquid reaction product of epichlorohydrin and bisphenol A having an approximate epoxy equivalent weight of 184-190 grams/equivalent. Commercially available by Momentive. Epon 828 Epoxy resin Trade designation of a solid reaction product of epichlorohydrin and bisphenol A having an approximate epoxy equivalent weight of 185-192 grams/equivalent according to ASTM D 1652. Commercially available by Resolution Performance Products. D.E.R 671 Epoxy resin Trade designation of a solid reaction product of epichlorohydrin and bisphenol A having an approximate epoxy equivalent weight of 475-550 grams/equivalent according to ASTM D 1652. Commercially available by Dow Chemical Co. PK-HH Thermoplastic Trade designation of a phenoxy resin. Commercially resin available by InChem Corporation. Epodil 757 Flexibilizing and Trade designation of a glycidyl ether of cyclohexane wetting agent dimethanol. Commercially available by Air Products and Chemicals, Inc. Paraloid 2650J Thoughening Trade designation of a core-shell toughening agent based agent on butadiene rubber. Commercially available by Dow. Cardura E10P Reactive diluent Trade designation of glycidyl ester of Versatic Acid, a synthetic saturated monocarboxylic acid of highly branched C.sub.10 isomers. Commercially available by Hexion. Amicure Primary Curative Trade designation of 2-cyanoguanidine (dicyandiamide), CG1200 available from Air Products. Omicure U52M Curative Trade designation of 4,4 methylene bisphenyl dimethyl accelerator urea, available from CVC Speciality Chemicals, USA. Micropearl Physical blowing Trade designation of a thermoexpandable microcapsule F48D agent produced by encapsulating volatile hydrocarbon with acrylic copolymer. Commercially available by Pierce & Stevens Chemical Corp. MinSil 20 Fused Silica Trade designation of fused silica commercially available by Minco, Inc., USA Aerosil R202 Silica filler/ Trade designation of a fumed silica aftertreated with a hydrophobizing polydimethysiloxane, available commercially by Degussa agent AG, Germany. Eurocell 140 Particulate filler Trade designation of expanded perlite, commercially available by Europerl, Germany. CaO WFK super Filler absorbing Weissfeinkalk Omya 40 water Glasperlen Particulate spacer Trade designation of glass beads (average grain size 90.Math. m), commercially available by Kominex Mineralmahlwerk, GmbH.

[0085] The raw materials used for the epoxy-acrylate based adhesive films are listed below in table 2.

TABLE-US-00002 TABLE 2 Raw Short Trade name and material name Description Category/Function supplier Dimethyl- DMAA High Tg UV DMAA, Kojin acrylamide reactive monomer, Co. compatability to epoxy & phenoxy resin Dicyclopentenyl FA-511AS High Tg acrylic FA-511AS; acrylate monomer, low Hitachi polarity for low Chemical surface energy adherent Glycidyl- GMA Methacryl monomer, GMA; Kyoeisha methacrylate compatability to Chemical Co. epoxy monomer 2-Ethyl- 2EHA Acrylic monomer, EHA, hexylacrylate Tg control Nihonshokubai Co. Photo initiator Irg 651 UV photo initator Irgacure 651; BASF (Ciba) Phenoxy resin YP-50S Tape forming YP-50S; Nippon (support of acrylic Steel & Sumikin polymer) and higher Chemical adhesion Bis A liquid Bis-A Main heat curable YD-128; Nippon epoxy resin epoxy resin Steel & Sumikin Chemical Bis F liquid Bis-F Main heat curable YDF-170; Nippon epoxy resin epoxy resin Steel & Sumikin Chemical Core shell BTA731 Shock resistance BTA 731; Rohm impact improvement & Haas modifier Dicyandiamide DICY Epoxy resin EH3636AS, hardener ADEKA Epoxy hardener 2MZA-PW Promotes hardener's 2MZA-PW, catalyst reaction at lower Shikoku-Kasei temperatures Co. Epoxy hardener 2PHZ-PW Promotes hardener's 2PHZ-PW, catalyst reaction at lower Shikoku-Kasei temperatures Co. Blowing agent FN-80GSD Expandable blowing FN-80GSD; agent Matsumoto Yushi-Seiyaku Blowing agent FN-100SD Expandable blowing FN-100SD; agent Matsumoto Yushi-Seiyaku

[0086] Most of the structural, epoxy-based adhesive films used for testing additionally contained a porous structure (mesh) as listed in table 3:

TABLE-US-00003 TABLE 3 Additional Porosity Type Product Name Information L/m.sup.2/s Polyamide 3M RM1173100 Style 90 g/m.sup.2 78 10 woven 5302 Nylon clothes 53 0.2 mm thick inch, Gehring Textiles INC.
Preparation of Epoxy Based Compositions (Examples 1-2) for the Making of Structural Adhesives Films) and Preparation of the Structural Adhesive Films with or Without Porous Structure:

[0087] The epoxy-based compositions of the structural adhesive films utilized in the present disclosure are listed in table 4 and are later referred to as examples 1 and 2. The resulting structural adhesive films with or without porous structure are listed in table 5. The epoxy-based compositions are prepared by combining the ingredients from the list of materials of table 1 in a high speed mixer (DAC 150 FVZ Speedmixer, from Hauschild Engineering) stirring at 3000 rpm.

[0088] In a first step the epoxy resin, the thermoplastic phenoxy resin and the core shell toughening agent are mixed together for 10 minutes. This mixture is then placed into an air-driven oven at a temperature of 95 C. for about 1 hour. The hot mixture is again stirred for 2 minutes at 3000 rpm in a speed mixer to ensure the complete dispersion of all three ingredients. The mixture temperature is reduced then to 70 C.; the two curatives together with the further ingredients are added to the mixture, followed by mixing for an additional 2 minutes under vacuum. The resulted mixture is a paste having a uniform consistency.

TABLE-US-00004 TABLE 4 Epoxy-based compositions in wt. % Raw Material Example 1 Example 2 Epon 828 22 Epikote 828 40 D.E.R 671 30 Paraloid EXL 2650J 14 9.8 PK-HH 16 19.0 Glass beads Amicure CG 1200 3.2 2.06 Omicure U52M 1.5 1.03 Epodil 757 4 1.72 Cardura E10P 3.43 Glasperlen 90 mm 1 0.99 Micropearl F48D 0.5 Eurocell 140 3 Aerosil R202 5 MinSil 20 17.15 Calcium oxide 4.29 Graphite flakes 1.72 Total 100

[0089] By using a pre-warmed knife coater at 80 C., the mixture is hot coated in order to obtain a structural adhesive film having the desired thickness. The formed adhesive film is soft and homogenous when cooled down.

[0090] The porous structure (mesh) was then laminated into the preformed adhesive film by using a calender also pre-warmed at 80 C. The thickness of the construction was set by calipering the calender gap.

[0091] The structural, epoxy-based adhesive films used for visual appearance testing in hemmed metal assemblies are listed in table 5. All samples are referred to in this table as SAF1-SAF5 and comprise as porous structure the mesh from table 3 with the only exception being that sample SAF5 was mesh free. Samples SAF1 through SAF 5 are based on the structural, epoxy-based compositions from table 4.

TABLE-US-00005 TABLE 5 Based on SAF 1 SAF 2 SAF 3 SAF 4 SAF 5 Example 1 With mesh, With mesh, total total thickness thickness 0.4 mm 0.2 mm Example 2 With mesh, With mesh, Mesh free; total total total thickness thickness thickness 0.2 mm 0.4 mm 0.45 mm
Preparation of Epoxy-Acrylate Based Compositions (Examples 3 and 4) for the Making of Structural Adhesive Films and Preparation of the Resulting Structural Adhesive Films with or Without Porous Structure:

[0092] The epoxy-acrylate based compositions (examples 3 and 4) of the structural adhesive films were prepared by compounding the components at the amounts shown in table 6.

TABLE-US-00006 TABLE 6 Epoxy-acrylate based compositions Example 3 Example 4 Monomer components DMMA 11.3 11.4 FA-511AS 11.3 11.4 BA 2EHA 2.3 2.3 GMA 4.5 3.4 HD-N Photoinitiator Irg651 0.3 0.3 Phenoxy resin YP-50S 9.0 9.1 Epoxy resin YD-128 5.7 YDF-170 41.9 34.9 Impact modifier BTA731 14.4 16.3 Thermosetting agent DICY 3.2 3.2 Curing aid 2MZA-PW 0.3 2PHZ-PW 0.6 Foaming agent FN-100SD 1.1 FN-100MD FN-80GSD 1.7 0.3 Filler R-972

[0093] The resulting structural adhesive films based on examples 3 and 4 (with or without porous structure) used for visual appearance testing in hemmed assemblies are listed later in table 7.

[0094] For the making of the adhesive films each of the adhesive compositions was molded into a sheet shape between PET films that had been subjected to light peeling treatment. Alternatively, in case of films with porous structure: each of the adhesive composition was molded into a sheet shape onto the porous structure and between PET films so that the mixture embedded the porous structure. This construction had been subjected to light peeling treatment. The thickness of the construction was set by calipering the molding gap.

[0095] The molded sheets were subjected to irradiation of ultraviolet light at 1 mW from a light source using an ultraviolet fluorescent lamp (VC7692 T12 bulb, manufactured by Sylvania Corp.) for three minutes, and thereafter were subjected to irradiation at 5 mW for three minutes. The monomer components copolymerized due to the ultraviolet light and sheet shape adhesives (adhesive sheets) were obtained.

TABLE-US-00007 TABLE 7 Based on SAF 6 SAF 7 Example 3 Mesh free, total thickness 0.4 mm Example 4 With mesh, total thickness 0.2 mm

Metal Test Assembly Preparation:

[0096] For test assembly preparation a first structural adhesive film as listed in table 5 or table 7 was applied on the upper side of the end portion of the second (inner) panel and the second structural film according to table 5 or table 7 was applied on the lower side of the end portion of the same panel. The selected metal panel was a 40 by 200 mm (metal galvanized steel DX 54 D+Z from supplier Thyssen Krupp) panel.

[0097] Afterwards the first (outer) metal panelcomprising the same geometry as the second (inner) metal panelwas brought together with the second (inner) metal panel and a hemming process was conducted by manually hemming the two metal panels together with a press. Hereby the end portion of the first metal panel was folded around the end portion of the second metal panel such that the end portion of the first panel extended parallel to the body portion of the second panel hereby enclosing the end portion of the second panel. Further hereby the first adhesive film was positioned between the upper side of end portion of the second metal panel and the end portion of the first panel. The second adhesive film example was positioned between the lower side of the end portion of the second (inner) metal panel and the body portion of the first (outer) metal plate (see FIGS. 8 to 11).

[0098] The resulting hemmed metal test assemblies comprising two differing adhesive films, with the exception of the comparative examples, were then treated in a water bath at 65 C. The construction was finally cured in the oven, at 180 C. for 30 minutes.

[0099] All test assemblies tested for visual appearance are listed in table 8 and will be referred to as TA 1 through TA 4. Additionally two comparative test assemblies were made differing from TA1 through TA 4 in such a way that both selected structural adhesive films had the same thickness. Hereby in table 8 the first adhesive film is always applied to the upper side of the inner plate and the second adhesive film to the lower side of the inner plate prior to hemming the metal test assembly.

TABLE-US-00008 TABLE 8 Adhesive Comp. Comp. Film used TA 1 TA 2 TA 3 TA-4 TA 1 TA 2 SAF 1 First First First adhesive adhesive adhesive film film film SAF 2 Second First & adhesive second film adhesive film SAF 3 Second Second adhesive adhesive film film SAF 4 Second adhesive film SAF 5 First adhesive film SAF 6 First adhesive film SAF 7 Second adhesive film

[0100] After curing the test assemblies were visually inspected by an experienced person in the area of structural adhesive films and the visual appearance of the structural adhesive film after cure was evaluated. The comparative examples provided a film after cure with a surfaces showing insufficient visual appearance.

[0101] In the case of comparative example TA1 the structural adhesive film on the upper side of the inner panel was selected too thin, whereas in the case of comparative example TA2 the second adhesive film positioned on the lower side of the inner panel was selected too thick resulting in access adhesive film pushing out of the hemmed test assembly. All test results on the visual appearance of metal test assemblies are shown in table 9. Results indicated as OK passed the visual inspection; results indicated as NOK did not meet the visual inspection criteria.

TABLE-US-00009 TABLE 9 Test assembly Visual appearance TA 1 OK TA 2 OK TA 3 OK TA 4 OK Comparative TA 1 NOK Comparative TA 2 NOK