Method of making fire resistant sustainable aircraft interior panels

Abstract

The present invention relates to method of manufacturing an aircraft interior panel comprising a core sandwiched between first and second skins, wherein both of the first and second skins are formed from natural fibers containing non-halogenated fire-retardant and set within an inorganic thermoset resin, thereby forming a fire-resistant sustainable aircraft interior panel. The method comprises impregnating the natural fibers with non-halogenated fire retardant and an inorganic thermoset resin, and laying up the resin-impregnated natural fibers to sandwich the core. This stack is then cured by raising the temperature of the stack sufficient to initiate curing but without reaching the boiling point of water in the stack, holding the stack at that first temperature before raising the temperature again to reach the boiling point of water in the stack, before cooling the stack.

Claims

1. A method of manufacturing an aircraft interior panel comprising a core sandwiched between first and second skins, wherein both of the first and the second skins are formed from natural fibres containing a fire-retardant and set within an inorganic thermoset resin, thereby forming a fire-resistant sustainable aircraft interior panel, the method comprising: (a) impregnating the natural fibres with the fire retardant to form fire-resistant natural fibres; (b) impregnating the fire-resistant natural fibres with the inorganic thermoset resin to produce resin-impregnated natural fibres; (c) laying up the resin-impregnated natural fibres to sandwich the core, thereby forming a stack of the core sandwiched between the resin-impregnated natural fibres; and (d) curing the stack to form the fire-resistant sustainable aircraft interior panel that comprises the core sandwiched between the first and the second skins, wherein the curing comprises: (d1) raising the temperature of the stack to a first temperature that is equal to or greater than a minimum activation temperature of the inorganic thermoset resin that initiates a curing reaction and less than a boiling point of water in the stack; (d2) holding the stack at the first temperature; (d3) raising a temperature of the stack to a second temperature that is equal to or greater than the boiling point of water in the stack; and (d4) cooling the stack to reduce a temperature of the stack from the second temperature.

2. The method of claim 1, further comprising between steps (b) and (c): (b1) storing the resin-impregnated natural fibres as prepregs; and (b2) retrieving from storage the prepregs of the resin-impregnated natural fibres.

3. The method of claim 1, wherein the first temperature is between 75 C. and 90 C.

4. The method of claim 1, wherein step (d2) further comprises: holding the stack at the first temperature for between 5 minutes and 60 minutes.

5. The method of claim 1, wherein the second temperature is between 100 C. and 130 C.

6. The method of claim 1, wherein step (d3) further comprises: raising the temperature of the stack to the second temperature at a rate of between 1 C. per minute and 10 C. per minute.

7. The method of claim 1, wherein step (d4) further comprises: cooling the stack to reduce the temperature of the stack from the second temperature as soon as a temperature of the stack is measured to have reached the second temperature.

8. The method of claim 1, wherein step (d4) further comprises: cooling the stack to allow it to reach ambient temperature.

9. The method of claim 1, further comprising curing the stack in a press and wherein steps (c) and (d) further comprise: raising a temperature of dies of the press to the first temperature and holding the dies at the first temperature, then performing step (c) by laying up the stack within the press, closing the press such that the dies sandwich the stack, thereby raising the temperature of the stack to the first temperature; and cooling the stack, to reduce a temperature of the stack, by no longer heating the dies and allowing the stack to cool within the press.

10. The method of claim 2, wherein step (b1) further comprises storing the composite prepregs for over 1 day.

11. The method of claim 10, wherein step (b1) further comprises storing the composite prepregs at a temperature below 10 C.

12. The method of claim 1, further comprising passing the resin-impregnated natural fibres through drain rollers to achieve a fibre to resin mix ratio between 25% and 50%.

13. The method of claim 1, wherein step (b) further comprises impregnating the natural fibres with a resin mix comprising the inorganic thermoset resin in any combination with: a hardener; and an anti-shrinkage additive.

14. The method of claim 13, wherein the resin mix comprises substantially 80% by weight of an aluminium silicate derivative inorganic thermoset resin, substantially 15% by weight of an aluminium/copper phosphate hardener, and substantially 5% by weight of a metakaolin anti-shrinkage additive.

15. The method of claim 1, wherein the natural fibres comprise flax fibres.

16. The method of claim 1, wherein step (a) further comprises impregnating the natural fibres with a non-halogenated flame retardant.

17. A method of manufacturing an aircraft interior panel comprising a core sandwiched between first and second skins, wherein both of the first and the second skins are formed from natural fibres containing a fire-retardant and set within an inorganic thermoset resin, thereby forming a fire-resistant sustainable aircraft interior panel, the method comprising: (a) laying up resin-impregnated natural fibres to sandwich the core, thereby forming a stack of the core sandwiched between the resin-impregnated natural fibres; and (b) curing the stack to form the fire-resistant sustainable aircraft interior panel that comprises the core sandwiched between the first and the second skins, wherein the curing comprises: (b1) raising a temperature of the stack to a first temperature that is equal to or greater than a minimum activation temperature of the inorganic thermoset resin that initiates a curing reaction and less than a boiling point of water in the stack; (b2) holding the stack at the first temperature; (b3) raising a temperature of the stack to a second temperature that is equal to or greater than the boiling point of water in the stack; and (b4) cooling the stack to reduce a temperature of the stack from the second temperature.

18. A method of manufacturing an aircraft, the method comprising: manufacturing an aircraft interior panel comprising a core sandwiched between first and second skins, wherein both of the first and the second skins are formed from natural fibres containing a fire-retardant and set within an inorganic thermoset resin, thereby forming a fire-resistant sustainable aircraft interior panel, the method of manufacturing the aircraft interior panel comprising: (a) impregnating the natural fibres with the fire retardant to form fire-resistant natural fibres; (b) impregnating the fire-resistant natural fibres with the inorganic thermoset resin to produce resin-impregnated natural fibres; (c) laying up the resin-impregnated natural fibres to sandwich the core, thereby forming a stack of the core sandwiched between the resin-impregnated natural fibres; and (d) curing the stack to form the fire-resistant sustainable aircraft interior panel that comprises the core sandwiched between the first and the second skins, wherein the curing comprises: (d1) raising the temperature of the stack to a first temperature that is equal to or greater than a minimum activation temperature of the inorganic thermoset resin that initiates a curing reaction and less than a boiling point of water in the stack; (d2) holding the stack at the first temperature; (d3) raising a temperature of the stack to a second temperature that is equal to or greater than the boiling point of water in the stack; and (d4) cooling the stack to reduce a temperature of the stack from the second temperature; and installing the aircraft interior panel within the aircraft.

19. The method of claim 18, further comprising between steps (b) and (c): (b1) storing the resin-impregnated natural fibres as prepregs; and (b2) retrieving from storage the prepregs of the resin-impregnated natural fibres.

20. The method of claim 16, wherein the natural fibres comprise flax fibres.

Description

DRAWINGS

(1) In order that the present invention may be more readily understood, preferred embodiments will now be described, by way of example only, with reference to the following drawings in which:

(2) FIG. 1 is a perspective view of a sustainable aircraft interior panel according to a first embodiment of the current invention;

(3) FIG. 2 is a perspective view of a sustainable aircraft interior panel according to a second embodiment of the present invention;

(4) FIG. 3 is a schematic representation showing a method of manufacturing a fire resistant, sustainable aircraft interior panel according to a first embodiment of the present invention;

(5) FIG. 4 is a schematic representation of a method of impregnating natural fibres with an inorganic thermoset resin during manufacture of a sustainable aircraft interior panel;

(6) FIG. 5 is a schematic representation of a curing cycle that may be used in the method of FIG. 3 and that may be used in the method of FIG. 6;

(7) FIG. 6 is a schematic representation showing a method of manufacturing a fire resistant, sustainable aircraft interior panel according to a second embodiment of the present invention; and

(8) FIG. 7 is a schematic representation showing a method of manufacturing a fire resistant, sustainable aircraft interior panel according to a third embodiment of the present invention.

DESCRIPTION

(9) FIG. 1 shows a sustainable aircraft interior panel 20 according to a first embodiment of the present invention. The sustainable aircraft interior panel 20 comprises a core 22 sandwiched between an upper skin 24 and a lower skin 26.

(10) The core 22 is a fire resistant PVDF or PEI thermoplastic foam, typically a few mm thick. In alternative embodiments, the core 22 may comprise fire resistant balsa wood or a fire resistant paper honeycomb. Joined to the core 22 are the corresponding upper and lower outer skins 24, 26. Each skin 24, 26 comprises a natural composite material made from natural fibres (already protected against fire with non-halogenated flame retardants) set within an inorganic thermoset resin. In this embodiment, each skin 24, 26 comprises a single natural fibre fabric set within the resin. The skins 24, 26 are formed by curing the panel 20 such that the resin-impregnated natural fibres bond to the core 22 and form the skins 24, 26.

(11) The present invention is not limited to sustainable aircraft interior panel structures comprising only three layers. More than a single core layer 22 may be included, and more than a single skin layer 24, 26 may be included to any one side of the core 22, if thickness and weight are not prohibitive for the application.

(12) An example of a further sustainable aircraft interior panel 30 is shown in FIG. 2. The sustainable aircraft interior panel 30 comprises five layers that are stacked as follows, from top to bottom: an outer upper skin 34, an inner upper skin 38, a core 32, an inner lower skin 40 and an outer lower skin 36. The core 32 corresponds to the core 22 described in FIG. 1. Also, the skins 34, 36, 38, 40 correspond to the skins 24, 26 described in FIG. 1. Pairs of upper and lower skins 34, 38 and 36, 40 may be provided to increase strength, if thickness and weight are not prohibitive for the application. The skins may be laid up in an aligned manner, or with their plies rotated (e.g., the warp and weft of the outer upper skin 34 may have its warp and weft rotated through 90 degrees relative to those of the inner upper skin 38) to improve their mechanical properties.

(13) Methods of manufacture of fire-resistant sustainable aircraft interior panels according to the present invention will now be described. For the sake of simplicity, three-layer sustainable aircraft interior panels 20 will be described, although it will be readily appreciated that the method may be simply extended to panels having more than three layers.

(14) A method of manufacture is shown in FIGS. 3 and 4. At step 102, natural fibre fabrics 306 are immersed in non-halogenated flame retardants to ensure that the fibre fabrics have good fire resistance. In this example, the natural fibres are flax, although other natural fibres like hemp, sisal and jute may be used. At step 104, an inorganic thermoset resin 304 impregnates the fire-resistant natural fibre fabrics 306. As shown in FIG. 4, this is done by feeding the fire resistant natural fibre fabrics 306 through an impregnation bath 308 and then across drain rolls 310. The drain rolls 310 are operated to obtain a desired fabric to resin ratio of 33%.

(15) The impregnation bath 308 contains a resin mix 304 comprising an aluminium silicate derivative used as the inorganic thermoset resin, mixed with a hardener. In this embodiment, aluminium and copper phosphate mixtures are used as the hardener. In addition, an anti-shrinkage additive is used such as metakaolin. The mix in the impregnation bath is 80% wt resin, 15% wt hardener, and 5% wt anti-shrinkage additive.

(16) In this embodiment, the resin impregnated natural fibre fabrics 302 are used immediately to form an aircraft interior panel 20. In alternative embodiments, like that of FIGS. 6 and 7 described below, the resin impregnated natural fibre fabrics 302 are stored as composite prepregs for use later.

(17) At step 106, the resin impregnated natural fibre fabrics 302 are laid up on both sides of the core 22 to form a stack. The resin 304 in the natural fibre fabrics 302 provides adequate adhesion between the skins 24 and 26 and the core 22 as the panel 20 cures. In this embodiment, the core 22 comprises fire resistant PVDF or PEI thermoplastic foam.

(18) At step 108, the complete fire-resistant, sustainable aircraft interior panel 20 is formed by curing the stack in either a vacuum bag or in a hot press. This process is similar to the crush core process, and is now explained in further detail with reference to FIG. 5.

(19) A two-step curing cycle is used. First, at step 152, the temperature of the stack is raised to 80 C. This may be quickly, for example by exposing the stack to a surface pre-heated to this temperature. It will be noted that 80 C. is used as it is sufficiently high to activate the curing reaction, yet is below the boiling point of water. At step 154 the temperature of the stack is held at 80 C. for 15 minutes. This temperature has been found to promote polymerisation of the inorganic thermoset resin 304.

(20) At step 156, the temperature of the stack is raised to 100 C. at a rate of 4 C. per minute. This allows water removal and a complete curing of the inorganic thermoset resin 304. As soon as the temperature of the stack reaches 100 C., the stack is allowed to cool as shown at step 158. In this embodiment, the heat source is switched off such that the stack may cool back to ambient temperature.

(21) FIG. 6 shows a further embodiment of a method of manufacture according to the present invention. At steps 102 and 104, the natural fibres are immersed in fire retardant and then immersed in an inorganic thermoset resin as has been described for steps 102 and 104 of FIG. 3. The thus-formed fire-resistant, sustainable prepregs 302 are then stored at step 105. In this embodiment, the prepregs 302 are collected and folded with plastic sheets or by other means such as silicoated paper in between folds to avoid any resin 304 release from the fire-resistant, sustainable prepregs 302. The folded prepregs 302 are then sealed inside bags and stored at 20 C. for as long as 60 days, and have been found to show no signs of deterioration.

(22) When needed, the fire-resistant, sustainable prepregs 302 are retrieved from storage and, at step 106, the sustainable prepregs 302 are laid up on both sides of the core 22 to form the stack. At 108, the complete sandwich panel 20 may be formed by curing in a vacuum bag or a hot press. Step 106 in FIG. 5 is the same as step 106 in FIG. 3. Step 108 may comprise steps 152, 154, 156 and 158 of FIG. 5, although other curing methods may be used, such as those described in our patent application EP-A-2,463,083.

(23) A further embodiment of a method of manufacturing a fire-resistant, sustainable aircraft interior panel according to the present invention will now be described with reference to FIG. 7. Steps 102, 104 and 105 of FIG. 7 are as already has been described with respect to FIG. 6. Thus, at the end of step 105, pre-pregs of fire-resistant and resin impregnated natural fibre fabrics 302 have been formed and stored.

(24) When needed, the pre-pregs 302 are retrieved from storage. In this embodiment, the curing cycle is performed using a hot press. The hot press comprises a pair of opposed dies. The stack is formed between the dies, such that the dies may be closed. The dies are heated to elevate the temperature of the stack.

(25) At step 150, the dies are heated to a temperature of 80 C. and then held at that temperature. With the dies at 80 C., the method proceeds to step 106 where the stack is formed as previously described with respect to step 106 of FIG. 6. The stack is formed within the press. At step 152, the press is closed such that the dies sandwich the stack. As the stack is in thermal contact with the dies, the temperature of the stack soon rises to 80 C. At step 154, the temperature of the stack is held at 80 C. for 15 minutes by heating the dies appropriately. Either the stack may be held at 80 C. for minutes once the stack reaches 80 C. or, where 15 minutes may be allowed to pass after the press is closed. The latter alternative may be used where the temperature of the stack rises quickly.

(26) After 15 minutes, at step 156, the dies are further raised in temperature such that the temperature of the stack rises, for example at 4 C. per minute. This is maintained until the temperature of the stack is determined to be at 100 C. This may be determined directly by measuring the temperature of the stack, or indirectly by measuring the temperature of the dies. Once a temperature of 100 C. has been reached, heating of the dies is stopped such that the stack begins to cool. The stack is allowed to cool with the press closed. Once the stack has cooled to ambient temperature, the press is opened and the cured fire-resistant, sustainable aircraft interior panel is obtained.

(27) It will be clear to the skilled person that variations may be made to the above embodiments without necessarily departing from the scope of the invention that is defined by the appended claims.

(28) Further, the disclosure comprises embodiments according to the following clauses:

(29) Clause 1. A method of manufacturing an aircraft interior panel comprising a core sandwiched between first and second skins, wherein both of the first and second skins are formed from natural fibres containing fire-retardant and set within an inorganic thermoset resin, thereby forming a fire-resistant sustainable aircraft interior panel, the method comprising:

(30) (a) impregnating the natural fibres with fire retardant to form fire-resistant natural fibres;

(31) (b) impregnating the fire-resistant natural fibres with inorganic thermoset resin;

(32) (c) laying up the resin-impregnated natural fibres to sandwich the core thereby forming a stack of the core sandwiched between the resin-impregnated natural fibres; and

(33) (d) curing the stack to form the fire resistant sustainable aircraft interior panel that comprises the core sandwiched between the first and second skins, wherein the curing step comprises:

(34) (d1) raising the temperature of the stack to a first temperature that is equal to or greater than a minimum activation temperature of the inorganic thermoset resin that initiates the curing reaction and less than the boiling point of water in the stack;

(35) (d2) holding the stack at the first temperature;

(36) (d3) raising the temperature of the stack to a second temperature that is equal to or greater than the boiling point of water in the stack; and

(37) (d4) cooling the stack to reduce the temperature of the stack from the second temperature.

(38) Clause 2. The method of Clause 1, further comprising between steps (b) and (c):

(39) (b1) storing the resin-impregnated natural fibres as prepregs; and

(40) (b2) retrieving from storage the prepregs of resin-impregnated natural fibres.

(41) Clause 3. A method of manufacturing an aircraft interior panel comprising a core sandwiched between first and second skins, wherein both of the first and second skins are formed from natural fibres containing fire-retardant and set within an inorganic thermoset resin, thereby forming a fire-resistant sustainable aircraft interior panel, the method comprising:

(42) (a) impregnating the natural fibres with fire retardant;

(43) (b) impregnating the fire-resistant natural fibres with inorganic thermoset resin;

(44) (b1) storing the resin-impregnated natural fibres as prepregs;

(45) (b2) retrieving from storage the prepregs of resin-impregnated natural fibres;

(46) (c) laying up the resin-impregnated natural fibres to sandwich the core thereby forming a stack of the core sandwiched between the resin-impregnated natural fibres; and

(47) (d) curing the stack to form the fire resistant sustainable aircraft interior panel that comprises the core sandwiched between the first and second skins.

(48) Clause 4. The method of Clause 3, wherein the curing step comprises:

(49) (d1) raising the temperature of the stack to a first temperature that is equal to or greater than a minimum activation temperature of the inorganic thermoset resin that initiates the curing reaction and less than the boiling point of water in the stack;

(50) (d2) holding the stack at the first temperature;

(51) (d3) raising the temperature of the stack to a second temperature that is equal to or greater than the boiling point of water in the stack; and

(52) (d4) cooling the stack to reduce the temperature of the stack from the second temperature.

(53) Clause 5. The method of Clause 1, wherein step (d1) comprises:

(54) raising the temperature of the stack to the first temperature wherein the first temperature is between 75 C. and 90 C. and, optionally, is substantially 80 C.

(55) Clause 6. The method of Clause 1, wherein step (d2) comprises:

(56) holding the stack at the first temperature for between 5 minutes and 60 minutes, preferably between 10 and 30 minutes, more preferably between 10 and 20 minutes, and most preferably for substantially 15 minutes.

(57) Clause 7. The method Clause 1, wherein step (d3) comprises:

(58) raising the temperature of the stack to the second temperature wherein the second temperature is between 100 C. and 130 C. and, optionally, is substantially 100 C.

(59) Clause 8. The method of Clause 1, wherein step (d3) comprises:

(60) raising the temperature of the stack to the second temperature at a rate of between 1 C. per minute and 10 C. per minute, more preferably between 2 C. per minute and 5 C. per minute, and most preferably substantially 4 C. per minute.

(61) Clause 9. The method of Clause 1, wherein step (d4) comprises:

(62) cooling the stack to reduce the temperature of the stack from the second temperature as soon as the temperature of the stack is measured to have reached the second temperature.

(63) Clause 10. The method of Clause 1, wherein step (d4) comprises:

(64) cooling the stack to allow it to reach ambient temperature.

(65) Clause 11. The method of Clause 1, comprising curing the stack in a press and wherein steps (c) and (d) comprise:

(66) raising the temperature of dies of the press to the first temperature and holding the dies at the first temperature, then performing step (c) by laying up the stack within the press, closing the press such that the dies sandwich the stack thereby raising the temperature of the stack to the first temperature; and, optionally,
cooling the stack to reduce the temperature of the stack by no longer heating the dies and allowing the stack to cool within the press.

(67) Clause 12. The method of Clause 2, wherein step (b1) comprises storing the composite prepregs for over 1 day.

(68) Clause 13. The method of Clause 12, wherein step (b1) comprises storing the composite prepregs at a temperature below 10 C., optionally at a temperature of substantially 20 C.

(69) Clause 14. The method of Clause 1, further comprising passing the resin impregnated natural fibres through drain rollers to achieve a fibre to resin mix ratio between 25% and 50%, preferably between 30% and 35%, and more preferably substantially 33%.

(70) Clause 15. The method of Clause 1, wherein step (b) further comprises impregnating the natural fibres with a resin mix comprising the inorganic thermoset resin in any combination with:

(71) a hardener, optionally an aluminium/copper phosphate hardener; and

(72) an anti-shrinkage additive, optionally a metakaolin anti-shrinkage additive.

(73) Clause 16. The method of Clause 15, wherein the resin mix comprises substantially 80% by weight of an aluminium silicate derivative inorganic thermoset resin, substantially 15% by weight of an aluminium/copper phosphate hardener, and substantially 5% by weight of a metakaolin anti-shrinkage additive.

(74) Clause 17. The method of Clause 1, wherein the natural fibres comprise flax fibres, optionally woven as a fabric.

(75) Clause 18. The method of Clause 1, wherein step (a) comprises impregnating the natural fibres with a non-halogenated flame retardant.

(76) Clause 19. A method of manufacturing an aircraft comprising:

(77) manufacturing an aircraft interior panel in accordance with claim 1; and installing the aircraft interior panel within the aircraft.

(78) All mentioned documents are incorporated by reference as if herein written. When introducing elements of the present invention or exemplary aspects or embodiment(s) thereof, the articles a, an, the and said are intended to mean that there are one or more of the elements. The terms comprising, including and having are intended to be inclusive and mean that there may be additional elements other than the listed elements. Although this invention has been described with respect to specific embodiments, the details of these embodiments are not to be construed as limitations. Different aspects, embodiments and features are defined in detail herein. Each aspect, embodiment or feature so defined may be combined with any other aspect(s), embodiment(s) or feature(s) (preferred, advantageous or otherwise) unless clearly indicated to the contrary.