LATENTLY REACTIVE POLYURETHANE-BASED ADHESIVE FILM

Abstract

The present disclosure relates to a latently reactive conductive polyurethane-based adhesive film.

Claims

1. A latently reactive polyurethane-based adhesive film, comprising: up to 98 percent by weight of a crystalline or a crystalline and amorphous polyurethane component, or both, and 2 to 80 percent by weight of a conductive filler.

2. The latently reactive polyurethane-based adhesive film according to claim 1, wherein the adhesive film further comprises: a cross-linking agent, the cross-linking agent being an isocyanate-containing component dispersed into the polyurethane component.

3. The latently reactive polyurethane-based adhesive film of claim 1, wherein the adhesive film further comprises: up to 40 percent by weight of a cross-linking agent, up to 5 percent by weight of a thickening agent, and/or up to 5 percent by weight of a dispersing additive.

4. The latently reactive polyurethane-based adhesive film of claim 1, wherein the latently reactive conductive adhesive film has a quasi-static shear strength of at least 6 MPa on a polycarbonate.

5. The latently reactive polyurethane-based adhesive film of claim 1, wherein the conductive filler comprises conductive materials, the conductive materials being selected from the group consisting essentially of: metals, silver-enhanced metals, metal oxides, metal hydroxides, metal nitrides, carbon-containing materials, conductive polymers, magnetically soft materials, and magnetically hard materials.

6. A method comprising: applying the a latently reactive polyurethane-based adhesive film of claim 1 on an application site or a set of respective join partners, where the adhesive film reaches its final bond strength at an activation temperature of 70-120° C.

7. A method of manufacturing a latently reactive the polyurethane-based adhesive film of claim 1, comprising: mixing up to 98 percent by weight of a crystalline or a crystalline and amorphous polyurethane dispersion, or an admixture of both, with 2 to 80 percent by weight of a conductive filler; applying the polyurethane dispersion including the conductive filler dispersed into it onto a backing to create a compound, and drying the compound.

8. The latently reactive polyurethane-based adhesive film of claim 1, further comprising: 2 to 65 percent by weight of the conductive filler.

9. The latently reactive polyurethane-based adhesive film according of claim 2, wherein the adhesive film further comprises: up to 40 percent by weight of a cross-linking agent, up to 5 percent by weight of a thickening agent, and/or up to 5 percent by weight of a dispersing additive.

10. The latently reactive polyurethane-based adhesive film of claim 9, wherein the latently reactive conductive adhesive film has a quasi-static shear strength of at least 6 MPa on a polycarbonate.

11. The latently reactive polyurethane-based adhesive film of claim 9, wherein the conductive filler comprises conductive materials, the conductive materials being selected from the group consisting essentially of: metals, silver-enhanced metals, metal oxides, metal hydroxides, metal nitrides, carbon-containing materials, conductive polymers, magnetically soft materials, and magnetically hard materials.

12. The latently reactive polyurethane-based adhesive film of claim 10, wherein the conductive filler comprises conductive materials, the conductive materials being selected from the group consisting essentially of: metals, silver-enhanced metals, metal oxides, metal hydroxides, metal nitrides, carbon-containing materials, conductive polymers, magnetically soft materials, and magnetically hard materials.

13. The method of claim 7 wherein the polyurethane dispersion including the conductive filler dispersed into it further comprises: 2 to 65 percent by weight of the conductive filler.

14. The method of claim 7 wherein the backing comprises: a conductive backing.

15. The method of claim 7 wherein the backing comprises: a release liner.

16. The method of claim 7, wherein the polyurethane dispersion including the conductive filler dispersed into it further comprises: a cross-linking agent, the cross-linking agent being an isocyanate-containing component dispersed into the polyurethane component.

17. The method of claim 7, wherein the polyurethane dispersion including the conductive filler dispersed into it further comprises: up to 40 percent by weight of a cross-linking agent, up to 5 percent by weight of a thickening agent, and/or up to 5 percent by weight of a dispersing additive.

18. The method of claim 7, wherein the polyurethane dispersion including the conductive filler comprises conductive materials, the conductive materials being selected from the group consisting essentially of: metals, silver-enhanced metals, metal oxides, metal hydroxides, metal nitrides, carbon-containing materials, conductive polymers, magnetically soft materials, and magnetically hard materials.

19. The method of claim 8, wherein the polyurethane dispersion including the conductive filler dispersed into it further comprises: a cross-linking agent, the cross-linking agent being an isocyanate-containing component dispersed into the polyurethane component.

20. The method of claim 8, wherein the polyurethane dispersion including the conductive filler dispersed into it further comprises: up to 40 percent by weight of a cross-linking agent, up to 5 percent by weight of a thickening agent, and/or up to 5 percent by weight of a dispersing additive.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0056] What follows is a description of test examples.

[0057] In an embodiment, a latently reactive polyurethane-based adhesive film can be provided using the following basic materials. A polyurethane dispersion may include an aromatic cross-linking agent such as, e.g. toluylene-diisocyanate compounds (TDI compounds) and/or an aliphatic cross-linking agent such as, e.g. isophorone diisocyanate (IPDI). The following particles can, e.g. be used as electroconductive fillers: eConduct Aluminium 202000®, eConduct Aluminium 451500®, VP70308®, eConduct Glass 352000®, eConduct Glass 205002® and eConduct Copper 341000® all by the company ECKART GmbH. The average customary particle size in the tests performed has a diameter of 50 μm.

[0058] A general formulation of a polyurethane-based latently reactive conductive adhesive film may be provided as follows:

TABLE-US-00001 TABLE 1 Components Proportion Crystalline PU component up to 98 percent by weight Crystalline + amorphous PU component up to 98 percent by weight Conductive fillers 2 up to 80 percent by weight Cross-linking agent 0 up to 40 percent by weight Thickening agent 0 up to 5 percent by weight Dispersing additive 0 up to 5 percent by weight Other additives 0 up to 5 percent by weight

[0059] It derives from table 1 that the crystalline polyurethane component and the conductive fillers form the main components of the conductive, latently reactive adhesive film. A crystalline polyurethane component with conductive filler particles dispersed into it has high strength already after cooling down to room temperature. This is due to the re-crystallisation of the polyurethane components alone.

[0060] By adding a cross-linking agent such as, e.g. isocyanate, an additional cross-linking reaction is triggered by activation by heat treatment. There, the isocyanate groups react with the functional groups of the thermoplastic polyurethane and cross-link the system. Therefore, the adhesive film exhibits the relatively high strength values in excess of 6 MPa on PC also at higher ambient temperatures.

[0061] Finally, the following additives can be included as well: De-foaming agents, stabilisers, dyeing pigments, catalysts, antioxidants, light protection agents and further polymers for adjusting other adhesive properties.

[0062] For testing purposes, two latently reactive polyurethane-based adhesive films were manufactured. The two test adhesive films are referred to as System 1 and System 2 hereinafter. The following formulations correspond to the liquid polyurethane dispersion.

System 1

[0063]

TABLE-US-00002 TABLE 2 Components Proportion Crystalline PU component 54.1 percent by weight Cross-linking agent (isocyanate) 11.1 percent by weight Conductive filler (eConduct Aluminium 32.6 percent by weight 451500 ®) Thickening agent  1.4 percent by weight

[0064] When measuring conductivity in the z direction, i.e. perpendicular to the spatial adhesive layer, System 1 exhibits comparatively high conductivity in the range of 0.2-0.4 mOhm.

System 2

[0065]

TABLE-US-00003 TABLE 3 Components Proportion Crystalline PU component 66.4 percent by weight Cross-linking agent (isocyanate) 13.6 percent by weight Conductive filler (eConduct Copper 341000 ®) 17.3 percent by weight Thickening agent  1.4 percent by weight

[0066] When measuring conductivity in the z direction, i.e. perpendicular to the spatial adhesive layer, System 2 exhibits comparatively lower conductivity on copper substrates with resistance values in the range of 2-30 mOhm. This is due to the fact that the conductive filler used is platelet-shaped (eConduct Copper 341000®).

Manufacturing

[0067] Described hereinafter is the manufacture of a conductive, latently reactive adhesive film.

[0068] Liquid crystalline polyurethane is optionally homogenised with a cross-linking agent and the corresponding conductive particles in a speed mixer. The resulting dispersion is applied onto a substrate using a blade. The resulting film is dried at 50° C. for 5 minutes. Finally, a conductive, latently reactive adhesive film with a layer thickness of 100 μm is obtained.

[0069] The coating process can be repeated on the second side of the substrate, resulting in a two-sided latently reactive adhesive tape.

Test Set-Up

[0070] The tests as described hereinafter were carried out to determine quasi-static shear strength and electroconductivity depending on the adhesive film systems.

[0071] First, two copper sheets are cut, abraded and cleaned. The copper sheets are arranged in an overlapping position, with the overlapping surface amounting to 312.5 mm.sup.2 and wherein the adhesive tape described above is inserted between the two copper sheets. Finally, the two copper sheets and the adhesive tape are pressed together. This is carried out subject to 2.5 bar at 120° C. for 5 minutes. This is followed by a cold pressing step at 3.5 bar for 3 minutes.

[0072] In a next step the two exposed ends of the copper platelets are connected to an ohmmeter. The ohmmeter used is a Loresta-RX low impedance ohmmeter by the company NH-Instruments.

[0073] Apart from measuring the electrical resistance, a quasi-static shear strength test is carried out based on a surface of 312.5 mm.sup.2 on PC.

[0074] The tests showed the following results:

TABLE-US-00004 TABLE 4 Filler content in the Quasi-static shear Filler dry adhesive film strength on PC Electroconductivity Silver-enhanced 52 percent by weight 9.1 MPa (2827 0.19-0.4 mOhm aluminium (spherical) N/312.5 mm.sup.2) System 1 Silver-enhanced glass 42 percent by weight 6.4 MPa (2000 2.6-5.7 mOhm (platelets) N/312.5 mm.sup.2) Silver-enhanced 32 percent by weight 8.3 MPa (2588 2,057-31,400 mOhm copper (platelets) N/312.5 mm.sup.2) System 2

[0075] The tests showed that the quasi-static shear strength of the adhesive films is in excess of 6 MPa on PC regardless of the choice of conductive filler.

[0076] Systems with fillers based on silver-enhanced metals such as, e.g. silver-enhanced aluminium and silver-enhanced copper achieve shear strength values between 8 to 11 MPa on PC also at comparatively high filler levels (i.e. even with more than 50% fillers depending on the filler used).

[0077] For completeness' sake it should be noted that latent reactive adhesive films without fillers can achieve quasi-static shear strength values of greater than 12 MPa.