Relating to thermosetting adhesive films

Abstract

Flexible films of thermosetting adhesive materials which are non-tacky to the touch are storage stable at room temperature and can be cured at elevated temperature with a short cure time and can be cured to produce a tough flexible adhesive layer including bonding to oily surfaces, the materials are particularly useful in bonding together dissimilar substrates.

Claims

1. An article comprising: a curable thermosetting epoxy resin based adhesive film, a coating of liquid, tacky epoxy resin free of a curing agent applied to the adhesive film, and a release liner disposed on the coating so that the article is adapted for reeling and unreeling at room temperature, wherein the adhesive film is; i) non-tacky to the touch at room temperature: ii) flexible prior to cure: and iii) storage stable; wherein the adhesive film is derived from a mixture of: a.) phenoxy resin; b.) an elastomer/epoxy resin adduct; c.) a core shell material; and d.) a curing agent; wherein the adhesive film is configured to form an adhesive bond with a metal surface having a corrosion preventive oi; wherein the adhesive bond has a shear strength of no less than about 90% or more of an adhesive bond between the adhesive film and a metal surface free of corrosion preventive oil when the metal surface is provided with a layer of about 3 g/m.sup.2of the corrosion preventive oil, and wherein the coating is configured to be cured by the curing agent of the adhesive film.

2. The article according to claim 1, wherein the adhesive film can be cured in no more than 45 minutes at a temperature no higher than 190 C.

3. The article according to claim 2, wherein the adhesive film is foamable.

4. The article according to claim 1, wherein the adhesive film can be cured at a temperature in the range 130 C. to 190 C.

5. The article according to claim 4, wherein the adhesive film has an uncured thickness between 0.2 and 3.0 mm.

6. The article according to claim 4, wherein the adhesive film has a density of from 1.1 to 1.5 g/ml.

7. The article according to claim 1, wherein the adhesive film contains from 15 to 40 wt % of the phenoxy resin, from 5 to 40 wt % of the elastomer epoxy resin adduct, and from 5 to 25 wt % of the core shell material.

8. The article according to claim 7, wherein the article is supported by a carrier.

9. The article according to claim 8, wherein the carrier is a fibrous carrier or fleece selected from: a woven mat, a knit mat, or a random mat; and wherein the fibrous carrier or fleece is derived from: glass, polyester, polyimide, carbon, or aramid fibers.

10. The article according to claim 9, wherein the adhesive film is an uncured film and the article is on one or both sides of the fibrous carrier.

11. The article according to claim 7, wherein the adhesive film is a cured adhesive film derived from the curable adhesive film.

12. The article according to claim 11, wherein the article includes a fibrous carrier.

13. The article according to claim 12, wherein the cured adhesive film has a lap sheer resistance greater than 20 mPa.

14. A laminar structure comprising a metal substrate and a fiber reinforced resin substrate, wherein the cured adhesive film of the article according to claim 11 is released from the release liner and bonds the metal substrate and the fiber reinforced resin substrate together.

15. The article according to claim 7, wherein the adhesive film contains 0.001 to 7% by weight of the curing agent.

16. The article according to claim 15, wherein the curing agent includes a curing agent accelerator.

17. The article according to claim 1, wherein the coating is a bisphenol-A or bisphenol-F based epoxy resin.

18. The article according to claim 1, wherein the coating is applied to only one surface of the adhesive film.

19. The article according to claim 1, wherein the coating is applied to opposing surfaces of the adhesive film.

20. A process for the manufacture of the article of claim 1, comprising extruding the adhesive film at a temperature in the range 70 to 120 C. and calendering the extrudate to a thickness in the range 0.3 to 2 mm.

Description

EXAMPLE 1

(1) An adhesive film was prepared by blending the following materials.

(2) TABLE-US-00002 Component % CTBN modified epoxy resin (1600 g/Eq) 6.00% Epoxy resin (900 g/Eq) 5.00% Micronized grade of dicyandiamide (<50 micrometers) 5.00% Aromatic substituted urea (latent accelerator for the 0.60% dicyandiamide cure of epoxy resins) Calcium oxide (<70 micrometers) 5.00% Calcium carbonate (<70 micrometers) 18.40% Epoxy resin (200 g/Eq) 16.00% Methacrylate-butadiene-styrene (MBS) Coreshell impact 16.00% modifier: crosslinked poly (butadiene/styrene) core with a grafted polymethyl methacrylate shell Epoxy Phenol Novolac Resin 8.00% Phenoxy Resin 15.00% Silica (<50 nanometers: 40%) reinforced bisphenol F based 5.00% epoxy resin

(3) The formulation was extruded from a twin-screw then calendared to make a film as illustrated in FIG. 1 hereto.

(4) The temperatures in the different extruder zones were:

(5) TABLE-US-00003 Zone 1 30 Zone 2 60 Zone 3 85 Zone 4 110 Zone 5 100 Zone 6 100 Zone 7 90 Zone 8 80 Zone 9 80 Zone 10 80 Zone 11 80

(6) The temperature of the calendar cylinder is between 80 and 90 C.

(7) The calendared film had a thickness between 0.3 and 2 mm.

(8) The adhesive film was used to bond two steel plates. The curing conditions was heating at 165 C. for 20 minutes.

(9) Lap shear strength: 30 MPa/Cohesive failure

EXAMPLE 2

Tape Manufacturing

(10) A tacky film (a tape) was made by applying a liquid epoxy resin on at least one of the two surfaces of the Adhesive Film of Example 1.

(11) The liquid resin used for the tacky coat can be a Bisphenol-A based epoxy resin or a Bisphenol-F based epoxy resin

(12) The liquid resin can also be: the same than then liquid resin used in the formula of the Adhesive film. Different from the liquid resin used in the formula of the Adhesive film.

(13) Example 2A: the liquid resin is a Bisphenol-A based epoxy resin and is the same as the liquid resin used in the formula of the Adhesive film.

(14) Example 2B: the liquid resin is a Bisphenol-A based epoxy resin and is different from the liquid resin used in the formula of the Adhesive film.

(15) The mechanical performances of bonded assemblies using the Adhesive Films of Examples or the Adhesive Tapes of Examples 2A and 2B are almost the same. The Adhesive Tapes have a slightly higher lap shear strength and a slightly lower peel strength.

(16) The manufacture of films according to the present invention is illustrated by reference to the accompanying drawing II in which FIG. 1 shows the manufacturing line comprising an extruder (1) to which the first thermosetting resin system (2) is fed. The first thermosetting resin system is extended at about 80 C. and passes into a calendaring system (3) where it is calendared by passage through pressure rollers (4) to the required thickness.

(17) Optionally, the calendared extrudate may then pass to a laminate system where it is laminated to a fibrous layer (5) provided from reels (6). As a further option the laminate may then be passed to a coating system where it is coated with a second tacky thermosetting resin (7) supplied from tanks (8) from which it passes to a cutting system (9) where a release liner (10) can be provided on the tacky surface and the film or tape can be cute by a knife (11) into sections (12) of the desired length.

(18) When the film is to be used without a supporting fibrous layer and without a tacky layer it may pass directly to the cutting station. Similarly if a laminate with a fibrous layer is required without a tacky layer the laminate may pass directly to the cutting station after lamination.