Multilayer structural adhesive film

Abstract

The invention relates to the use of a structural adhesive film for bonding and sealing a hem flange connection between panels. The structural adhesive film comprises at least one adhesive layer and at least one layer with a porous structure. The adhesive layer comprise an epoxy compound as well as an epoxy curing agent.

Claims

1. A hem flange connection between panels to be bonded and sealed with a structural adhesive film, the structural adhesive film in its uncured state is an uncured film comprising: at least one adhesive layer having an adhesive major surface; and at least one porous layer with a porous structure and having a porous major surface, wherein the adhesive layer comprises an epoxy compound as well as an unreacted epoxy curing agent, and the adhesive major surface faces and contacts the porous major surface.

2. The hem flange connection between panels according to claim 1, wherein the at least one adhesive layer comprises an epoxy compound, an epoxy curing agent, a thermoplastic resin and optionally a toughening agent.

3. The hem flange connection between panels according to claim 1, wherein the at least one adhesive layer comprises an epoxy compound, a thermoplastic resin, an epoxy curing agent and in addition 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.

4. The hem flange connection between panels according to claim 1, wherein the at least one adhesive layer comprises an epoxy compound, an epoxy curing agent, and an acrylic polymer.

5. The hem flange connection between panels according to claim 1, wherein the at least one adhesive layer further comprises a toughening agent and/or a blowing agent.

6. The hem flange connection between panels according to claim 1, wherein the porous structure is selected from a woven or knit or non-woven fabric.

7. The hem flange connection between panels according to claim 1, wherein the porous structure is a spunlaced or hydroentangled fabric.

8. The hem flange connection between panels according to claim 1, wherein the porous structure is derived from cotton, glass, polyester, polyamide, polypropylene, carbide or aramid fibers or metal or a combination thereof.

9. The hem flange connection between panels according to claim 1, wherein the porous layer comprises a thickness in the range of 0.05 to 0.6 mm.

10. The hem flange connection between panels according to claim 1, wherein the porous layer comprises an area weight in the range of 5 to 200 g/m.sup.2.

11. The hem flange connection between panels according to claim 1, wherein the porous structure comprises a porosity in the range of 1000 to 7000 L/m.sup.2/s measured according to ISO 139, 2.sup.nd edition, 2005-01-15.

12. The hem flange connection between panels according to claim 1, wherein in the uncured film, the adhesive layer is positioned on one or on both sides of the porous layer.

13. The hem flange connection between panels according to claim 1, wherein the adhesive layer has a width and the porous layer has a width, and in the uncured film, either the porous layer extends along the entire width of the adhesive layer or the width of the adhesive layer is larger than the width of the porous layer.

14. The hem flange connection between panels according to claim 1, wherein in the uncured film, the adhesive layer is divided in two parts that are arranged on one side of the porous layer.

15. The hem flange connection between panels according to claim 3, wherein the at least one mineral filler is selected from the group consisting of metal oxides and metal hydroxides.

16. The hem flange connection between panels according to claim 1, wherein the at least one layer with a porous structure is a porous carrier layer.

17. The hem flange connection between panels according to claim 1, wherein the at least one layer with a porous structure is a malleable scrim or mesh.

18. The hem flange connection between panels according to claim 1, wherein the at least one layer with a porous structure is a wipe.

19. The hem flange connection between panels according to claim 18, wherein the at least one layer with a porous structure is a spunlaced wipe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail with reference to the following Figures exemplifying particular embodiments of the invention:

(2) FIG. 1 is an embodiment showing a cross-sectional view of an inner panel with a structural adhesive film applied thereto and an outer panel before joining it with the inner panel;

(3) FIG. 2 is a cross-sectional view of a metal penal assembly in accordance with one aspect of the invention;

(4) FIG. 3 is a cross-sectional view of one embodiment of a structural adhesive film used in the invention;

(5) FIG. 4 is a cross-sectional view of another embodiment of a structural adhesive film used in the invention;

(6) FIG. 5 is a cross-sectional view of another embodiment of a structural adhesive film used in the invention;

(7) FIG. 6 is a cross-sectional view of another embodiment of a structural adhesive film used in the invention;

(8) FIG. 7 is a cross-sectional view of another embodiment of a structural adhesive film according to the invention;

(9) FIG. 8 is a cross-sectional view of a metal panel assembly according to another aspect of the invention with a structural adhesive film shown in FIG. 5; and

(10) FIG. 9 is a cross-sectional view of a metal panel assembly according to another aspect of the invention with a structural adhesive film shown in FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS

(11) 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.

(12) FIG. 1 and FIG. 2 show the use according to the invention of a structural adhesive film for bonding and sealing a hem flange connection between metal panels.

(13) As shown in FIG. 1, an outer metal panel 10 comprises a body portion 11 with a flange 12 along a margin of the body portion near end 13 of the outer panel 10. As can be seen in FIG. 2 in the hem flange bonding process the flange 12 is folded over flange 22 of the inner panel 20. Flange 22 of the inner panel 20 is along a margin of body portion 21 of the inner panel near end 23. End 23 is adjacent flange 12 of the outer panel 10. A structural adhesive film 30 is located between the inner 20 and outer panel 10. A portion 32 near end 31 of the structural adhesive film 30 is located between body portion 11 of outer panel 10 and the flange 22 of inner panel 20. The structural adhesive film 30 is folded (hemming process) over inner panel 20 and hence portion 34 near end 33 of the structural adhesive film 30 is between flange 12 of the outer panel 10 and flange 22 of the inner panel 20. The structural adhesive film 30 bonds the two metal panels together at the joint or hem.

(14) In accordance with one aspect illustrated in FIG. 2, a metal part assembly in accordance with the present invention, for example as illustrated in FIG. 1, may be obtained by adhering the structural adhesive film 30 to the inner metal panel 20. However, it is also possible to instead adhere the structural adhesive film 30 to the outer panel prior to joining the metal panels (not illustrated). As shown in FIG. 2, the structural adhesive film 30 is adhered to the inner panel. In one particular aspect, the structural adhesive film 30 has a surface that is tacky at ambient temperature, typically about 20 C., and can be adhered to the inner panel via this tacky surface. The structural adhesive film may allow forming an adhesive bond sufficient to hold the metal parts together in the metal joint without requiring curing of the composition of the structural adhesive film. It is also possible that the structural adhesive film is heated before curing below the curing temperature to initiate the above mentioned tack.

(15) The outer panel may then be folded such that the flange 12 of the outer panel is folded over the flange 22 of the inner panel 20 and over portion 34 of the structural adhesive film 30. Accordingly, outer panel 10 will be folded over inner panel 20 with the structural adhesive film located between the two panels and thus a metal joint is obtained. In case the structural adhesive film 30 was adhered to the outer panel 10 instead of the inner panel 20, the structural adhesive film 30 will be folded in-between the panels during folding of the outer panel 10 over flange 22 of the inner panel 20.

(16) It is also possible, in case the structural adhesive film 30 is pre-formable, that the structural adhesive film 30 is pre-formed in for example a u-shaped form and afterwards applied to the first panel 20, thereby covering its outer edge 23, before the second panel 30 is folded around the outer edge 23 of the first panel.

(17) FIG. 3 is a cross-sectional view of a structural adhesive film 30 according to the invention with a first adhesive layer 1 and a second porous layer 2. First adhesive layer 1 and second porous layer 2 are positioned adjacent to each other, in the drawing the first adhesive layer is positioned on top of the second layer 2. FIG. 4 is a cross-sectional view of a structural adhesive film 30 with a first adhesive 1, a second porous layer 2 and a third adhesive layer 1, the two adhesive layers are positioned on both sides of the second porous layer 2. Adhesive layer 1 or adhesive layers 1 may extend over the same widths as the layer 2. It is also possibleas indicated in FIG. 5 that adhesive layer 1 has a larger width as the porous layer 2.

(18) It is also possible to provide the structural adhesive film 30 in several parts as indicated in FIGS. 6 and 7. FIG. 6 shows a cross-sectional view of another structural adhesive film 30 according to the invention with a first part 30a and a second part 30b. The first part 30a comprises a first adhesive layer 1 and a second porous layer 2. The second part 30b comprises only one adhesive layer 1. The embodiment shown in FIG. 7 differs from the embodiment shown in FIG. 6 in that the adhesive layer 1 in the part 30a is thicker as the adhesive layer in part 30b.

(19) The cross-sectional view of a metal panel assembly of FIG. 8 shows a hem flange connection with an outer 10 and an inner metal panel 20 and a structural adhesive film 30 as shown in FIG. 5 in between the two metal panels 10 and 20. The porous layer 2 of the structural adhesive tape 30 faces the body portion 11 of the outer panel 10. The adhesive layer 1 of the structural adhesive film 30 faces the flange portion 22 of the inner panel 20.

(20) The cross-sectional view of a metal panel assembly of FIG. 9 shows a hem flange connection with an outer 10 and an inner metal panel 20 and a structural adhesive film 30 as shown in FIG. 6 in between the two metal panels 10 and 20. The porous layer 2 of part 30b of the structural adhesive tape 30 faces the body portion 11 of the outer panel 10. The adhesive layer 1 of part 30b faces the flange portion 22 of the inner panel. The adhesive layer 1 of part 30a of the structural adhesive film 30 faces the other side of the flange portion 22 of the inner panel 20.

(21) As indicated in FIGS. 8 and 9, there may be some space 40 between the metal panels and the structural adhesive film 30 after the film has been applied and after the outer metal panel 10 has been folded over the inner metal panel. In some instances it is possible that the hemmed metal panel assembly, with an uncured and unexpanded structural adhesive film 30 according to the invention in between the two panels 10 and 20 passes a bath before being put into a curing oven. During this process step, liquid may enter the space 40 between the two panels next to the film 30. During curing, when heat gets applied, the liquid may get gaseous and try to escape along either path A or path B. In order to avoid that this process impacts the appearance of the cured structural adhesive film 30 the layer 2 is porous, therewith providing areas through which the gas may escape, without impacting the adhesive layer.

Examples

(22) Test Methods:

(23) The invention relates to the use of a structural adhesive film for bonding and sealing a hem flange connection between panels, e.g. metal panels. One important criteria for a car manufacture is the visual appearance of the film after the two panels are brought together and after the structural adhesive film was cured.

(24) The visual appearances 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.

(25) List of Materials for the Adhesive Layer:

(26) TABLE-US-00001 TABLE 1 Material Function Description Wt. % Epikote 828 Epoxy resin Trade designation of a liquid reaction product 54.5 or Epon 828 of epichlorohydrin and bisphenol A having an approximate epoxy equivalent weight of 184- 192 grams/equivalent, according to ASTM D 1652. Commercially available by Momentive Or Resolution Performance Products PK-HH Thermoplastic Trade designation of a phenoxy resin. 26.0 Or PK-HP resin Commercially available by InChem 200 Corporation. Paraloid Toughening agent Trade designation of a core-shell toughening 13.5 2650J agent based on butadiene rubber. Commercially available by DOW Amicure Primary Curative Trade designation of 2-cyanoguanidine 3.3 CG1200 (dicyandiamide), available from Air Products. Omicure Curative Trade designation of 4,4 methylene bisphenyl 1.5 U52M accelerator dimethyl urea, available from CVC Speciality Chemicals, USA. Eurocell 140 Particulate filler Trade designation of expanded perlite, 1.2 commercially available by Europerl, Germany.

(27) The epoxy-based compositions of the present invention are prepared by combining the ingredients from the list of materials of table 1 in a high speed mixer (DAC 150 FVZ Speed mixer, from Hauschild Engineering) Stirring at 3000 rpm. In Table 2, the concentrations are given as wt. %. In a first step the epoxy resin, the thermoplastic phenoxy resin and the core shell toughening agent are mixed together for 2 min. The mixture is then placed into an air-driven oven at temperature of 95 C. for about 1 h. The hot mixture is again stirred for 2 min at 3000 rpm in the speed mixer to ensure complete dispersion of the three ingredients. Then the mixer temperature is reduced to 60 C. and the two curatives (Amnicure CG1200 and Omnicure U52M) together with the physical blowing agent, and optionally the filler material and/or the glass beads, 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. By using a knife coater the mixer can be hot coated to a film.

(28) List of Materials for the Porous Layer/List of Examples:

(29) TABLE-US-00002 TABLE 2 Product Additional Porosity Name Material Information L/m.sup.2/s Comp. adhesive Example film without porous layer Example 1 polyester 3M Polyester 90 g/m.sup.2 78 woven RM1173100 0.2 mm Example 2 polyester Reemay 2016 Polyester 46 g/m.sup.2 3443 non woven 0.25 mm Example 3 spunlaced Spunlaced Polyester 42 g/m.sup.2 3763 wipe-non Sandler- 0.25 mm woven Sawatex 2058 Example 4 spunlaced Spunlaced Polyester 30 g/m.sup.2 6263 wipe-non Sandler- 0.25 mm woven Sawatex 2621 Example 5 spunlaced Spunlaced Polyester 60 g/m.sup.2 2670 wipe-non Sandler- 0.45 mm woven Sawatex 2621

(30) The above mentioned different porous layers were coated between 2 adhesive layers of 0.1 to 0.15 mm thickness so that the final sandwich is 0.5 mm thick. As a comparative example a 0.4 mm adhesive film without a porous layer is provided.

(31) The structural adhesive film according to the above described examples examples were applied on an edge of a metal panel so that the adhesive film was covering the edge and the adhesive surfaces stick on both sides of the panel. The metal panel was a 40 by 200 mm (metal galvanized steel DX 54 D+Z from supplier Thyssen Krupp) panel. Table 3 shows how the different examples behave during the application of the film. While the film without a mesh could easily be applied to the metal panels, examples 1 and 2 tended to pop of the both sides of the metal panel due to the stiffness of the used porous layer. Example 1 is so stiff that the bending on the metal edge is difficult to do, the adhesive film springs back to the original flat shape because of the stiffness of the woven fabric. Example 3, 4 and 5 with a spunlaced wipe were easy to apply and stayed on the metal panel after application, thanks to the softness of the wipe fabric.

(32) Afterwards a second metal panelsame geometry as the first panelwas brought together with the first metal panel a hemming process was conducted by manually hemming the two metal panels together with a press. The adhesive film was applied to the inner panel and a second outer panel was hemmed around the inner panel as described above.

(33) The hemmed metal construction with the tape was then treated in a water bath of 65 C. The construction was then cured in the oven, at 180 C. for 30 minutes.

(34) After curing the examples 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 example (adhesive without porous layer) provided a film after cure with a surface with bubbles. Example 1 shows a mesh after cure that was not formable in the oven. Therefore the cured adhesive shows a gap between the film and the panel. The structural adhesive film according to example 2 shows the same behaviour as from example 1. The structural adhesive film according to example 3 had a good visual appearance after cure. The porous layer absorbed the adhesive. There was enough free adhesive not retained on the wipe, able to flow and covers the edge of the panel (per gravity and capillarity). Examples 4 and 5 showed the same good results regarding the visual appearance as example 3.

(35) TABLE-US-00003 TABLE 3 Handling Visual Appearance Comp. adhesive film good Bubbling Example without porous layer Example 1 polyester woven Difficult to Mesh is too stiff, creates handle, to stiff, gap between adhesive pop up tape and panel Example 2 polyester Difficult to Mesh is too stiff, creates non woven handle, to stiff, gap between adhesive pop up tape and panel Example 3 Spunlaced wipe- good good non woven Example 4 Spunlaced wipe- good good non woven Example 5 Spun laced wipe- good good non woven