Metal-polyamide/polyethylene-metal laminate

Abstract

The invention concerns a metal laminate comprising between two outer metal sheets an adhesive polymer layer, characterized in that the adhesive polymer layer comprises polyamide, a copolymer of ethylene and an unsaturated carboxylic acid and/or a derivative thereof and a reactive copolymer. The invention further concerns a process for the manufacture of such a metal laminate and the use of such metal laminates for the manufacture of automotive body parts.

Claims

1. A metal laminate comprising between two outer metal sheets an adhesive polymer layer, characterized in that the adhesive polymer layer comprises a single polymer component, wherein the single polymer component consists of a polyamide, a copolymer of ethylene and an unsaturated carboxylic acid and/or a derivative thereof, a reactive copolymer comprising a styrene-maleic acid anhydride copolymer having a molecular weight of 1400 to 10,000, and an optional epoxy resin.

2. The metal laminate according to claim 1, wherein the surface dimensions of the first outer metal sheet is greater than the surface dimensions of the second outer metal sheet.

3. The metal laminate according to claim 1, wherein the outer metal sheets are made of steel or aluminum.

4. The metal laminate according to claim 1, wherein the polyamide comprises polyamide 6.

5. The metal laminate according to claim 1, wherein the adhesive polymer layer comprises 20 to 95% in weight of polyamide.

6. The metal laminate according to claim 5, wherein the adhesive polymer layer comprises 45 to 65% in weight of polyamide.

7. The metal laminate according to claim 1, wherein the copolymer of ethylene and an unsaturated carboxylic acid is a copolymer of ethylene and an unsaturated carboxylic acid containing 1 to 6 carboxylic groups and/or the derivative thereof.

8. The metal laminate according to claim 1, wherein the adhesive polymer layer comprises a polyamide continuous phase.

9. The metal laminate according to claim 1, wherein the adhesive polymer layer comprises 0.5 to 10% in weight of the reactive copolymer.

10. The metal laminate according to claim 1, wherein the adhesive polymer layer further comprises a flame retardant agent.

11. A metal laminate according to claim 1, wherein the adhesive polymer layer comprises 2 to 6% of styrene-maleic anhydride.

12. The metal laminate according to claim 1, wherein the copolymer of ethylene and an unsaturated carboxylic acid and/or a derivative thereof is a grafted polyethylene.

13. The metal laminate according to claim 12, wherein the grafted polyethylene is grafted with maleic acid and/or a derivative thereof.

14. The metal laminate according to claim 12, wherein the grafted polyethylene is grafted with maleic acid anhydride.

15. The metal laminate according to claim 12, wherein the adhesive polymer layer comprises 5 to 80% in weight of the grafted polyethylene.

16. The metal laminate according to claim 15, wherein the adhesive polymer layer comprises 30 to 50% in weight of the grafted polyethylene.

17. The metal laminate according to claim 12, wherein the grafted polyethylene nonlinear grafted polyethylene.

18. A process for the manufacture of a metal laminate according to claim 1 comprising the steps consisting in: a. Providing a first and a second metal sheet; b. Applying a polymer composition comprising a single polymer component, wherein the single polymer component consists of a polyamide, grafted polyethylene, a reactive copolymer onto the first metal sheet, wherein the reactive copolymer comprising a styrene-maleic acid anhydride copolymer having a molecular weight of 1400 to 10,000, and an optional epoxy resin; c. Applying the second metal sheet onto the polymer layer applied onto the first metal sheet to obtain a metal laminate; and d. Heating the metal laminate to complete the adhesion.

19. The process according to claim 18, wherein the polymer composition is previously extruded to form a polymer film.

20. The process according to claim 18, wherein the polymer film is directly extruded onto the first metal sheet.

21. A method of manufacture of an automotive body part comprising molding the metal laminate of claim 1.

Description

EXAMPLE 1: POLYMER LAYER ACCORDING TO THE INVENTION

(1) A. Preparation of the Polyethylene Component

(2) The polyethylene component was prepared by extruding with a double screw extruder, a mixture of 89 parts of ethylene based octene plastomer (Exact 8203, available from Exxon Mobil), 9.05 part of linear low-density polyethylene (Escorene LL 6101 RQ, available from Exxon Mobil), 1.5 parts of maleic acid anhydride, 0.15 parts of organic peroxide (Interox DHBP from SOVAY) and 0.3 part of antioxidant Irganox 1330 (available from Ciba Geigy).

(3) The mixture was then subjected to melt devolatilisation, that is extrusion under vacuum in order to eliminate excess of maleic acid anhydride before granulation.

(4) The extrudate is then granulated. The composition of the polyethylene component is resumed in Table 1 hereunder.

(5) TABLE-US-00001 TABLE 1 Composition of the polyethylene component Parts per 100 Ethylene based octane plastomer 89 LLDPE 9.05 Maleic acid anhydride 1.5 Organic peroxide 0.15 Antioxidant 0.3
B. Preparation of the Adhesive Polymer Composition

(6) The adhesive polymer composition was prepared by extruding in a double screw extruder 55.75 parts of polyamide PA6 (Ultramid B3 from BASF) with 40 parts of the grafted polyethylene component obtained according to the preceding section, 2 parts of microfine talc (talc Naintsch A3 from Naintsch), 0.15 parts of antioxidant (Irganox 1098 available from Ciba), and 0.1 parts of another antioxidant (Irgafos 168 available from Ciba).

(7) To this mixture were added by way of a first side feeder 2 parts of styrene maleic acid anhydride copolymer (SMA 1000P from Atofina).

(8) The extrudate was then subjected to melt devolatilisation, that is extrusion under vacuum in order to eliminate volatile components, and then subjected to granulation.

(9) The obtained granules were dried at 70 C. for about 6 hours before storing away from moisture.

(10) The composition is summarised in Table 2 hereunder.

(11) The adhesive polymer composition presented a melt flow index at 275 C./49 N [measured according to the method of ASTD-1238] of 7 g/10 minutes.

(12) The adhesive polymer composition was then extruded to form a film.

(13) TABLE-US-00002 TABLE 2 Composition of the adhesive polymer composition Parts per 100 PA 6 55.75 Grafted Polyethylene 40 Styrene maleic acid anhydride copolymer 2 Processing aid 2 Antioxidant 0.15 Antioxidant 0.1

EXAMPLE 2: POLYMER PAYER ACCORDING TO THE PRIOR ART

(14) The metal laminate comprising a polypropylene core is prepared by laminating a polypropylene film (Appryl 3020, MFI 1.9, density 0.905, available from Atofina) between two metal sheets, which were previously coated with a thin layer of an epoxy primer comprising grafted polypropylene.

(15) The different adhesive polymer compositions were characterized by measuring the ductility and tensile modulus. The test procedures are described hereafter.

(16) a. Ductility

(17) The ductility of the polymer composition is measured using a standard elongation test (according to NF EN ISO 527).

(18) The polymer film is cut into samples having a total length of 150 mm and a width of 20 mm at the extremities, the central part of a length of 80 mm having a width of 10 mm.

(19) The sample is placed between the jaws of an elongation measuring apparatus INSTRON 45.05. The apparatus imparts a traction at a constant speed of 50 mm/min. The respective elongation of the sample at break indicates the ductility of the material.

(20) The ductility is considered satisfying when it is at least equal to the ductility of steel, that is typically 40%.

(21) b. Tensile Modulus at 220 C.

(22) The tensile modulus indicates the stiffness of the polymer film. It is measured using a dynamic mechanical and thermal analysis apparatus (Rheometric MKII).

(23) A sample of the polymer film of 4.75 cm0.5 cm is inserted between the jaws of the apparatus. Then, a tensile stress is imparted to the sample, which is sufficiently low to ensure elastic deformation. The force opposed by the film to restore its initial form is measured. This test is repeated by cycles, generally of 1 Hz, while heating the sample at a rate of 2 C./min to measure the values for a temperature range of 50 to 250 C.

(24) C. Preparation of the Laminate

(25) The metal laminate was prepared by heat laminating an extruded film of the adhesive polymer composition onto the metal sheet made of an interstitial free titanium steel sheet which was subjected to a chromatation treatment (granodine 1415AD, available from Henkel) having a thickness of 0.25 mm at a temperature of 190 C.

(26) D. Tests of the Metal Laminates

(27) The obtained metal laminates were tested in order to determine the adhesion strength between the adhesive polymer layer and the outer metal sheets. Further, the laminates were subjected to a standard deep drawing test.

(28) a. Adhesion Test

(29) The adhesion between the adhesive polymer layer and the outer metal sheets was evaluated using a standard T peeling test (NF T 76112). This test was carried out as follows.

(30) A sample of 250 mm25 mm is cut out of the metal laminate. Each of the two outer metal sheets is inserted between the jaws of an apparatus for measuring the elongation (model 4505 from INSTRON) capable of measuring the force necessary for a predetermined displacement. The peeling force necessary for a displacement of the jaws at a constant speed of 100 mm/min is read on the apparatus.

(31) b. Deep Drawing Test

(32) A circular sample of the metal laminate having a diameter of 150 mm is mounted into a clamp ring having an internal diameter of 85 mm of an industrial press having a force of 0.8 MN. The force applied on the clamp ring is 80 kN.

(33) A spherical punch with a diameter of 37.5 mm is applied to the center of the sample with a force of between 30 and 35 kN. The maximal penetration depth of the punch into the laminate before break is determined.

(34) The laminate of the example presents a penetration depth before break identical to the one of the metal sheets alone.

(35) The results of the tests of the polymer compositions and the metal laminates are resumed in Table 3 hereunder.

(36) TABLE-US-00003 TABLE 3 Properties of the polymer compositions and the metal laminate Maximum Deep elongation Tensile modulus Adhesion drawing Sample [%] at 200 C. [MPa] [daN/cm] [mm ] Example 1 500 53 7 As steel Example 2* 1000 0 10 As steel *prior art

(37) It follows from the results that a metal laminate according to the invention presents a heat resistance compatible with subsequent treatments such as cataphoresis combined with satisfactory adhesion properties and excellent tensile modulus, even at high temperature.

(38) The properties of metal laminates according to the invention are thus very satisfactory and allow their use, notably in the automotive industry for the manufacture of automotive body parts, but also in other industries such as in particular construction.