Composite structure for airbag cover

Abstract

The invention provides a composite structure containing a foam layer, an inner layer and an outer layer of a thermoplastic compact cover layer, and a lacquer layer in this order, and having a tensile strength according to DIN EN ISO 527-3 at 2000 mm/min and 23° C. of less than 5 MPa in both a first direction and a second direction perpendicular to the first direction, wherein the density of the foam layer is 40 to 150 kg/m3, the inner layer contains particles of an elastomer (polymer (F)) and at least 50 wt % of a thermoplastic polyolefin (polymer (E)) and is directly bonded to the outer layer, the outer layer differs from the inner layer in its composition and contains the following polymers (A) to (C) in a total amount of 100 parts by weight: 25 to 70 parts by weight of particles of an elastomer (polymer (A)), 0 to 40 parts by weight of a low-density polyethylene (polymer (B)), and 20 to 70 parts by weight of a thermoplastic polyolefin (polymer (C)) other than polymer (B). The invention provides the use of the composite structure in car interiors, in particular as airbag cover, a method for the production of the composite structure.

Claims

1. A composite structure comprising: a foam layer, an inner layer and an outer layer of a thermoplastic compact cover layer, and a lacquer layer, wherein the composite structure has a tensile strength according to DIN EN ISO 527-3 at 2000 mm/min and 23° C. of less than 5 MPa in both a first direction and a second direction perpendicular to the first direction, wherein a density of the foam layer is 40 to 150 kg/m.sup.3, wherein the inner layer contains the following polymers (D) to (F) in a total amount of 100 parts by weight: 5 to 35 parts by weight of particles of an elastomer (polymer (F)), 10 to 30 parts by weight of a linear low-density polyethylene (polymer (D)) and 40 to 80 parts by weight of a thermoplastic polyolefin (polymer (E)) other than polymer (D), wherein the inner layer is directly bonded to the outer layer, wherein the outer layer and the inner layer are made of different compositions, and wherein the outer layer contains the following polymers (A) to (C) in a total amount of 100 parts by weight: 25 to 70 parts by weight of particles of an elastomer (polymer (A)), 0 to 40 parts by weight of a low-density polyethylene (polymer (B)), and 20 to 70 parts by weight of a thermoplastic polyolefin (polymer (C)) other than polymer (B).

2. The composite structure according to claim 1, wherein the total of 100 parts by weight of polymers (A) to (C) consists of 25 to 70 parts by weight of polymer (A), 0 to 20 parts by weight of polymer (B), and 30 to 65 parts by weight of polymer (C).

3. The composite structure according to claim 1, wherein the total of 100 parts by weight of polymers (A) to (C) consists of 25 to 50 parts by weight of polymer (A), 20 to 40 parts by weight of polymer (B), and 20 to 45 parts by weight of polymer (C).

4. The composite structure according to claim 1, wherein the particles of the elastomer (polymer (A)) consists of 80 to 100 wt % of ethylene propylene diene monomer rubber and 0 to 20 wt % of ethylene propylene rubber.

5. The composite structure according to claim 1, wherein the weight content of particles of an elastomer in the outer layer is higher than in the inner layer.

6. The composite structure according to claim 1, wherein the outer layer of the cover layer is 1.5 to 3.0 times thicker than the inner layer.

7. The composite structure according to claim 1, wherein a thickness of the foam layer is more than 2.0 mm.

8. The composite structure according to claim 1, wherein a Shore A hardness of the outer layer is lower than that of the inner layer, and wherein the inner layer has a Shore A hardness of 75 to 95.

9. The composite structure according to claim 1, wherein a Shore A hardness of the outer layer is less than 75.

10. The composite structure according to claim 1, wherein a foam density [g/m.sup.3] multiplied by a foam thickness [mm] is in the range of 150 to 350.

11. The composite structure according to claim 1, which is an airbag cover.

12. The composite structure according to claim 1, which is useful as an interior part of cars.

13. A method for producing a composite structure of claim 1 comprising: a step (a) of preparing a molten mixture of a first raw material composition to form an outer layer containing the following polymers (A) to (C) in a total amount of 100 parts by weight: 25 to 70 parts by weight of particles of an elastomer (polymer (A)), 0 to 40 parts by weight of a low-density polyethylene (polymer (B)), and 20 to 70 parts by weight of a thermoplastic polyolefin (polymer (C)) other than polymer (B); a step (b) of preparing a molten mixture of a second raw material composition to form an inner layer containing the following polymers (D) to (F) in a total amount of 100 parts by weight: 5 to 35 parts by weight of particles of an elastomer (polymer (F)), 10 to 30 parts by weight of a linear low-density polyethylene (polymer (D)) and 40 to 80 parts by weight of a thermoplastic polyolefin (polymer (E)) other than polymer (D); a step (c) of coextruding the molten mixtures obtained in steps (a) and (b) to obtain the layers of the cover layer; a step (d) of laminating the layers of the cover layer on a foam layer having a density of 40 to 150 kg/m.sup.3; and a step (e) of providing a lacquer layer on the outer layer of the cover layer.

14. The method of claim 13, wherein the particles of the elastomer comprises an ethylene propylene diene monomer rubber and polypropylene.

Description

EXAMPLES

(1) This invention is further illustrated by the following examples.

(2) Measurement Methods

(3) In this invention, the following measurement methods were used to determine the parameters of the composite structure:

(4) (The norms and standards stated in this application refer to the latest versions at the filing date of this application unless otherwise indicated).

(5) Thickness: ISO 1923; Weight: ISO 2286-2:2016; Melting points (DSC): ASTM D 3418-15; elongation at break: ISO 13934-1:99; density: ISO 845; Hardness (Shore A, ShA): DIN 53505; resistance to tear: ISO-34-1; tensile strength: DIN EN ISO 527-3 at 2000 mm/min and 23° C.

(6) Gel content: Gel content measurement is based on ASTM D2765-16. The composite material is weighed (initial weight) and placed in xylene for 24 hours at 180° C., the dissolved material is separated and the weight of the remaining material is determined (final weight); gel content [%]=[(final weight)/initial weight)]×100

(7) The tear properties at airbag deployment were tested at −35° C., 23° C. and 85° C. Evaluation:

(8) ++: very good tear properties; the material is suitable for the use as airbag cover

(9) +: good tear properties, tearing occurs late; the material is still suitable for the use as airbag cover

Example 1

(10) The composite structure of example 1 has the following configuration:

(11) Layer 0: Paint based on silicone-containing aliphatic polyurethane, approx. 5 μm thick

(12) Layer 1: compact TPO layer (approx. 130 μm layer thickness)

(13) Layer 2: compact TPO layer (approx. 130 μm layer thickness)

(14) Layer 3: compact TPO layer (approx. 130 μm layer thickness)

(15) Layer 4: polypropylene foam (about 3.5 mm layer thickness)

(16) Layers 1 to 3 correspond to layers AA-B in Table 1.

Examples 2 to 5 and Comparative Examples 1 and 2

(17) The composite structures having configurations shown in Table 1 were prepared as described in Example 1.

(18) Table 1 also shows the results of Examples 1 to 5 and Comparative Examples 1 and 2 as well as the results of composite structures 1(V) and 5(V) of DE 10 2016 206 340 A1 (DE'340).

(19) In Examples 1 to 5 and Comparative Examples 1 and 2, TPV essentially consists of polypropylene and EPDM rubber and TPO is based on polypropylene.

(20) The composite structures of Comparative Examples 1 and 2 do not meet the feature that the inner layer contains at least 50 wt % of a thermoplastic polyolefin (polymer (E)) other than low-density polyethylene.

(21) TABLE-US-00002 TABLE 1 DE′340 Cmp. Cmp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 1(V) 5(V) Ex. 1 Ex. 2 Cover outer TPV pbw 60; 30 65 65 65 65 100 100 60; 30 65 layer layer mp (° C.) 157; 119/160 119/160 119/141 119/141 157; 157 formulation (AA) 119/160 119/160 ShA 50; 80 80 80 80 80 50; 80 50 LDPE pbw — 35 35 35 35 — — — 35 LLDPE pbw — — — — — — — — — TPO pbw 10 — — — — — — 10 — inner TPV pbw 20 20 20 20 20 90 0 65 65 layer mp (° C.) — — — — — 157 157 (B) ShA — — — — — 50 50 TPO pbw 60 60 60 60 60 — 40 — LLDPE pbw 20 20 20 20 20 — 20 — LDPE pbw — — — — — — 40 35 35 Cover layer thickness mm 0.4 0.5 0.4 0.6 0.6 0.8 0.8 0.4 0.4 Foam density kg/m3 50 100 100 67 100 67 67 50 50 Foam thickness mm 3.5 2.5 2.5 2.0 2.5 2 2 3.5 3.5 Tear property at airbag deployment ++ + + Elongation at long 264 343 242 469 356 break [%] cross 165 310 345 282 302 ratio (long/cross) 1.6 1.1 0.7 1.7 1.2 Tensile strength long 1.07 2.13 2.37 3.30 2.35 15 15 DIN EN ISO cross 1.19 2.56 2.02 2.36 2.98 18 18 527-3 ratio (long/cross) 0.9 0.8 1.2 1.4 0.8 0.8 0.8 Resistance long 8.6 16.9 15.4 22.3 19.6 8 25 to tear cross 8.2 16.7 16.6 17.7 18.7 11 62 ISO 34-1 ratio (long/cross) 1.0 1.0 0.9 1.3 1.1 0.7 0.4 Legend to Table 1: Ex. = Example; Cmp. Ex. = Comparative Example AA, B: configuration of the cover layer; layers AA make up ⅔ of the total thickness, layer B makes up ⅓ of the total thickness pbw = parts by weight; mp = melting point; ShA = Shore A hardness long = in extrusion direction (lengthwise); cross = perpendicular to extrusion direction (crosswise)

(22) The results show that the composite structures according to the present invention have advantageous properties such as low tensile strength and low resistance to tear. Therefore, the composite structures are suitable for the use as airbag covers. All composite structures are suitable for the use in airbags having H-shape geometry. Airbags having U-shape are more demanding and require a composite structure having isotropic properties resulting in an elongation at break that is similar in lengthwise and crosswise direction. LDPE confers isotropic properties. In addition, the foam density should be higher for the use in U-shaped airbags. Therefore, the composite structures of Examples 2, 3, and 5 are particularly suitable for the use in airbags having U-shape geometry.

(23) The composite structures of Examples 1 to 5 are thermoplastic and can be used in a thermoforming process.

(24) Because of the lower density of the foam layer, the composite structure of Example 1 is particularly suitable for being processed by cutting and sewing.