Flexible Core for Machine Processing or Production of Composite Parts or Materials

Abstract

The invention is directed to a core material, suitable for use in a closed mold system, based on at least one fibrous web containing a foam-structure within the web, said foam-structure being formed of a plurality of members that are separated from each other by channels, wherein said core material has a compression-resistance of greater than 40% at a pressure of 4 bar and at a temperature that is greater than or equal to 80 C.

Claims

1. Core material, suitable for use in a closed mold system, based on at least one fibrous web containing a foam-structure within the web, said foam-structure being formed of a plurality of members that are separated from each other by channels, wherein said core material has a compression-resistance of greater than 40% at a pressure of 4 bar and at a temperature that is greater than or equal to 80 C.

2. Core material according to claim 1 having a compression-resistance of greater than 40% at a pressure of 4 bar and a temperature that is greater than or equal to 120 C.

3. Core material according to claim 1, wherein said compression-resistance is greater than 60%.

4. Core material according to claim 1, wherein the members comprise microspheres having an activation temperature of at least 140 C.

5. Core material according to claim 1, wherein said fibrous web is impregnated with a thermosetting polymer.

6. Core material according to claim 1, having a free volume of less than 60%.

7. Core material according to claim 1, having a thickness of less than 1 mm.

8. Method for the preparation of a core material that is suitable for use in a closed mold system, said method comprising introducing unexpanded microspheres into a fibrous web using at least one binder, followed by expanding the introduced unexpanded microspheres while restricting the expansion of the microspheres in the direction orthogonal to the plane of the core material, which expanding of the introduced unexpanded microspheres comprises heating under pressure comprising calendaring.

9. Method according to claim 8, wherein the unexpanded microspheres are introduced into the fibrous web by screen printing, impregnation, scattering or a combination thereof.

10. Method according to claim 8, said method further comprising impregnating the fibrous web with a thermosetting polymer followed by heating the impregnated fibrous web above the thermosetting temperature of the thermosetting polymer.

11. Method according to claim 8, wherein the unexpanded microspheres are introduced as a blend with said binder, preferably as a blend comprising the binder and the unexpanded microspheres in a dry weight ratio of more than 12 to 1.

12. Core material claim 1, obtainable by a method comprising introducing unexpanded microspheres into a fibrous web using at least one binder, followed by expanding the introduced unexpanded microspheres while restricting the expansion of the microspheres in the direction orthogonal to the plane of the core material, which expanding of the introduced unexpanded microspheres comprises heating under pressure comprising calendaring.

13. Pre-preg product comprising the core material according to claim 1 and a curable resin.

14. Method for the preparation of a shaped article, said method comprising placing a mold that comprises a core material according to claim 1 with a curable resin, in an autoclave, followed by curing the curable resin in the autoclave.

15. Core material according to claim 2, wherein the temperature is greater than or equal to 140 C.

16. Core material according to claim 1, wherein the activation temperature is between 150 and 220 C.

17. Core material according to claim 16, wherein the activation temperature is between 155 and 175 C.

18. Core material according to claim 5, wherein the thermosetting polymer comprises polyacrylate.

19. Core material according to claim 6, wherein the free volume is less than 40%.

20. Core material according to claim 7, wherein the thickness is less than 0.9 mm.

21. Method of claim 11, wherein the dry weight ratio is more than 14 to 1.

22. Method of claim 21, wherein the dry weight ratio is more than 18 to 1.

23. Method for the preparation of a shaped article, said method comprising placing a mold that comprises a pre-preg product according to claim 13 in an autoclave, followed by curing the curable resin in the autoclave.

Description

EXAMPLE 1

High-Temperature Microspheres

[0071] A web was prepared consisting of about 80 wt. % polyester fibers and 20 wt. % binder (acrylate). A binder-microsphere blend was made by mixing 3 kg of high-temperature expandable microspheres (Expancel, AKZO-NOBEL) into 97 kg of acrylate binder. The dry solids content of the acrylate binder was about 52 wt. % and the dry weight ratio binder to microspheres was about 14.8 to 1.

[0072] The binder-microsphere mixture was applied to the web by rotary screen printing, wherein the mixture was pressed into the web. After printing the web was dried at about 110 C. and subsequently expanded to a thickness of about 2 mm at a temperature of about 220 C. Simultaneously the web was cured.

EXAMPLE 2

Impregnation with a Thermosetting Polymer

[0073] A web was prepared consisting of about 80 wt. % polyester fibers and 20 wt. % binder (acrylate).

[0074] A binder-microsphere blend was made by mixing 5 kg of expandable microspheres having an activation temperature of about 125 C. (Expancel, AKZO-NOBEL) into 95 kg of acrylate binder. The dry solids content of the acrylate binder was about 52 wt. % and the dry weight ratio binder to microspheres was about 11.6 to 1.

[0075] The binder-microsphere mixture was applied to the web by rotary screen printing, wherein the mixture was pressed into the web. After printing the web was dried at about 110 C. and subsequently expanded to a thickness of about 1.5 mm at a temperature of 200 C. Simultaneously the web was cured.

[0076] Next, the fibrous web was impregnated with a water-based polyacrylic acid polyol mixture.

[0077] After impregnation, the thermosetting polymer was cured at a temperature of about 150 C.

EXAMPLE 3

High-Temperature Microspheres and Impregnation with a Thermosetting Polymer

[0078] A core material was prepared as describe in Example 1 and was impregnated as described in Example 2 resulting in a material of about 1.7 mm.

EXAMPLE 4

High-Temperature Microspheres and Calendaring

[0079] A web was prepared consisting of 80 wt. % polyester fibers and 20 wt. % binder (acrylate).

[0080] A binder-microsphere blend was made by mixing 3 kg of high-temperature expandable microspheres (Expancel 980DU120, AKZO-NOBEL) into 97 kg of acrylate binder. The dry solids content of the acrylate binder was about 52 wt. % and the dry weight ratio binder to microspheres was about 14.8 to 1.

[0081] The binder-microsphere mixture was applied to the web by rotary screen printing, wherein the mixture was pressed into the web. After printing the web was dried at about 110 C. and subsequently expanded at a temperature of about 225 C. by restricting the expansion using a plate press to limit the thickness to about 1.8 mm. Simultaneously the web was cured.

EXAMPLE 5

High-Temperature Microspheres and Calendaring

[0082] Example 4 was repeated, but now the microspheres were expanded by restricting the expansion using a plate press to limit the thickness to about 1.4 mm.

EXAMPLE 6

[0083] Using a universal testing machine available from Zwick Roell AG being equipped with heating plates, the compression-resistance of the core materials obtained in Example 1-5 were analyzed at 80, 120 and 140 C. As a comparative example, Soric XF2 core material obtainable from Lantor, Veenendaal, the Netherlands was analyzed as well.

[0084] The results are provided in FIGS. 1, 2 and 3.

EXAMPLE 7

[0085] A web was used consisting of 100 wt. % polyester fibers, which was bonded by needle-punching (i.e. a needle-punched non-woven).

[0086] A binder-microsphere blend was made by mixing 2.3 kg high temperature expandable microspheres (Expancel 980DU120, AKZO-NOBEL) into 97.7 kg of acrylate binder. The dry solids content of the acrylate binder was about 50 wt. % and the dry weight ratio binder to microspheres was 21 to 1.

[0087] The binder-microsphere mixture was applied to the web by rotary screen printing, wherein the mixture was pressed into the web. The screen print pattern was designed as a hexagonal pattern, as described in EP1010793.

[0088] After printing, the web was dried at about 100 C. and subsequently expanded at a temperature of about 225 C. while restricting the expansion using a belt press and a calender to limit the thickness to about 1.1 mm. Simultaneously the web was cured.

EXAMPLE 8

[0089] A web was used consisting of 100 wt. % polyester fibers, which was bonded by needle-punching (i.e. a needle-punched non-woven).

[0090] A binder-microsphere blend was made by mixing 2,3 kg high temperature expandable microspheres (Expancel 980DU120, AKZO-NOBEL) into 97,7 kg of acrylate binder. The dry solids content of the acrylate binder was about 50 wt. % and the dry weight ratio binder to microspheres was 21 to 1. The screen print pattern was designed as a random dot pattern, as described in EP1542845

[0091] After printing, the web was dried at about 100 C. and subsequently expanded at a temperature of about 225 C. while restricting the expansion using a belt press and a calender to limit the thickness to about 1.1 mm. Simultaneously the web was cured.

EXAMPLE 9

[0092] Using a universal testing machine available from Zwick Roell AG being equipped with heating plates, the compression resistance of the core materials obtained in Example 7 and 8 were analyzed at 120 C. and 140 C. As a comparative example, Soric XF2 and TF1.5 core materials obtainable from Lantor, Veenendaal, the Netherlands, were analyzed as well. The results are provided in FIGS. 4 and 5.

EXAMPLE 10

[0093] A web was used consisting of 100 wt. % polyester fibers, which was bonded by needle-punching.

[0094] A binder-microsphere blend was made by mixing 2,7 kg high temperature expandable microspheres (Expancel 980DU120, AKZO-NOBEL) into 97,3 kg of acrylate binder. The dry solids content of the acrylate binder was about 50 wt. % and the dry weight ratio binder to microspheres was 18 to 1. The screen print pattern was designed as a random dot pattern, as described in EP1542845

[0095] After printing, the web was dried at about 100 C. and subsequently expanded at a temperature of about 225 C. while restricting the expansion using a belt press and a calender to limit the thickness to about 1.1 mm. Simultaneously the web was cured.

[0096] Using a universal testing machine available from Zwick Roell AG, the compression resistance of the core material obtained was analyzed until 20 bars at room temperature. Directly after terminating the test at 20 bar, and the pressure was released, the thickness of the test sample was measured at 3 time intervals: at 5 sec, at 1 minute and after 5 minutes. For this a universal thickness meter, available from Mitutoyo Corp. was used, equipped with a measuring stamp area of 38.5 cm.sup.2 and a standard load of 40.0 g/cm.sup.2. As a comparative example, Soric XF2 and TF1.5 core materials obtainable from Lantor, Veenendaal, the Netherlands, were analyzed as well. The results are provided in FIG. 6.