HK40025691A - Pei particle foams for applications in aviation interiors - Google Patents

Description

PEI particle foam for aircraft interior trim

Technical Field

Polyetherimide (PEI) -based polymer foams meet the legal requirements of the aerospace industry for aerospace interior trim. In particular, the requirements for fire protection properties, medium resistance and mechanical properties constitute a great challenge here. According to the prior art, suitable polymer foams are produced as semi-finished products. For example, due to the large amount of cutting waste, the reprocessing into moldings is uneconomical in terms of time and material utilization. The invention solves this problem by making it possible to process materials which are suitable in principle into granulated foam moldings. These moldings can be produced in a short cycle time without further processing and are therefore produced economically. Furthermore, this opens up new possibilities for functional integration, for example by the direct introduction of inserts or the like in the foam, and in terms of design freedom.

Background

Foam materials suitable for installation in the aerospace industry are well known. However, most of the foams described for this purpose are only foams composed of pure PMI (polymethacrylimide), PPSU (polyphenylsulfone) or PES (polyethersulfone). Pi (polyarylimid) is also found in the literature, although it is not suitable from a toxicological point of view. All these materials have hitherto only been used as block or plate-shaped materials.

There are also other materials that are described in less detail as plate-like materials for installation in the aerospace industry. For example, poly (oxy-1, 4-phenylsulfonyl-1, 4-Phenyl) (PESU) is such a material. This is sold, for example, by the company DIAB under the product name divanycell F. However, in the further processing of these extruded foam boards, uneconomically large amounts of scrap are produced.

An economical way of avoiding cutting waste in the production of three-dimensional foam moldings is to use foam particles (bead foam) instead of slabstock foam. All the particulate foams available according to the prior art have disadvantages in the case of use at high temperatures or, in general, non-optimal mechanical properties, especially at these high temperatures. Furthermore, only a few foams are known to be non-flammable and can therefore be installed, for example, inside roads, rails or air vehicles. For example, particle foams based on polypropylene (PP), polystyrene (EPS), thermoplastic polyurethane elastomer (E-TPU) or pmi (rohaceltriple f) have an insufficient flame retardancy, while in principle all inherently flame-retardant polymers which are suitable, for example PES, PEI or PPSU, are processed according to the prior art only to form slabstock foams.

Disclosure of Invention

Problem(s)

In view of the prior art, the problem to be solved by the present invention is to provide a composition for producing a novel foam or composite material for aircraft construction, which composite material may be, for example, a foam core with a thermoplastic or crosslinked cover layer. The foams obtained should here have a good combination of usability at high temperatures, good mechanical properties, in particular sufficient elongation at break, and at least sufficient flame retardancy for many applications in the field of automotive and aircraft construction.

More particularly, the foam should have a high resistance to various liquids (acidic, basic or hydrophobic liquids) and to emulsions.

Furthermore, the foam should be achievable from the composition to be developed by various methods and in a wide variety of three-dimensional shapes and produce as little or only very little scrap as possible in the production of the final component.

Other non-obvious problems may be apparent from the description, claims or examples herein, which are not explicitly set forth herein.

Solution scheme

These problems are solved by providing novel compositions for the production of non-flammable thermally stable foams used in the aerospace industry, especially in aircraft construction. Such inventive composition for producing a foam is characterized in that it is a particulate foam based on Polyetherimide (PEI). The particulate foam according to the invention has a glass transition temperature of 180 to 215 ℃ here as foamed material and wherein the average cell diameter of the particulate foam is less than 2mm, preferably less than 1mm, more preferably less than 500 μm, most preferably less than 250 μm.

This is particularly surprising since the actual glass transition temperature of PEI is 215 to 217 ℃, so that this material cannot be processed into a granular foam according to the prior art, for example by means of underwater pelletization.

According to the present invention, the term "cell" describes a region of the foam which is free of any matrix material but is at least partially surrounded by it. The cells are also referred to herein as pores. Ideally, in rigid foams, these pores or cells are closed, which in turn means that the cells are completely surrounded by the matrix material of the foam. In the case of softer foams, open cells are present at least in part. These can still be identified as individual cells by incomplete wall arrangements or in the extreme case of bridging structures. It is therefore also possible to determine the size of such openings. The cell size can in many cases be measured in a simple manner, for example by means of a microscope. Also taking these factors into account, it is simple for the skilled person to maintain the maximum cell size in the foam.

Foam particles are understood according to the invention to mean regions in the particle foam which are defined by the expansion of individual unexpanded or pre-expanded particles. The boundaries between the individual foam particles bound to each other may be readily visible to the naked eye or may be determined under an optical microscope. This is particularly true when the interface between two foam particles is apparent. However, as the situation is not necessarily so, the present invention uses a simplified approach: for this purpose, the theoretical mean diameter of the foam particles is calculated in a simple manner from the diameter of the unexpanded particles, the total volume of the unexpanded particles and the volume of the finished foam part. The person skilled in the art knows that in the case of particle foam, a regular size distribution of the foam particles can be achieved in such a way that only small deviations occur in the edge regions of the foam piece. Another advantage of the invention is that the volume fraction around the gap between the individual foam particles is so small that it is hardly reflected in the volume measurement of the finished foam piece. Preferably, these foam particles in the finished foam are less than 1cm, more preferably less than 0.7 cm.

According to the invention, the reported glass transition temperatures are measured by means of DSC (differential scanning calorimetry), unless otherwise indicated. In this regard, one skilled in the art knows that DSC is sufficiently convincing only when a sample of the material is held at this temperature for at least 2 minutes after a first heating cycle up to a temperature that is at least 25 ℃ above the highest glass transition or melting temperature, but at least 20 ℃ below the lowest decomposition temperature of the material. Thereafter, the sample is cooled again back to a temperature which is at least 20 ℃ below the lowest glass transition or melting temperature to be determined, wherein the cooling rate should be not higher than 20 ℃/min, preferably not higher than 10 ℃/min. After waiting a further period of several minutes, the actual measurement is taken, wherein the sample is heated to at least 20 ℃ above the maximum melting or glass transition temperature at a heating rate of typically 10 ℃/min or less.

Preferably, in a first alternative embodiment of the invention, the composition of the invention for producing a particulate foam consists of 80 to 99.5% by weight of PEI. Furthermore, such compositions comprise from 0.5% to 10% by weight, preferably from 1% to 9% by weight, of blowing agent. It may further contain, inter alia, from 0% to 10% by weight, preferably from 1% to 5% by weight, of additives.

The additives may be, inter alia, flame retardants, plasticizers, pigments, uv stabilizers, nucleating agents, impact modifiers, adhesion promoters, rheology modifiers, chain extenders, fibers, and/or nanoparticles.

The flame retardants used are generally phosphorus compounds, in particular phosphates, phosphines or phosphites. Suitable UV stabilizers and/or UV absorbers are well known to those skilled in the art. HALS compounds, Tiuvine or triazoles are commonly used for this purpose. The impact modifiers used are generally polymeric particles comprising an elastomeric and/or flexible phase. They are often core- (shell-) shell particles with an outer shell which is at most lightly crosslinked by itself and exhibits at least minimal miscibility with PEI as a neat polymer. As pigments, in principle any known pigments can be used. In particular for larger amounts, their effect on the foaming operation is of course to be tested, as is the case with all other additives used in larger amounts of more than 0.1% by weight. This can be implemented with less cost and complexity for the skilled person.

Suitable plasticizers, rheology modifiers and chain extenders are well known to those skilled in the art of producing foils, films or moldings from PEI or PEI-containing blends and can therefore be transferred at low cost and complexity to the production of foams from the compositions according to the invention.

The optionally added fibres are generally known fibre materials which can be added to the polymer composition. In a particularly suitable embodiment of the invention, the fibers are PEI fibers, PES fibers, PPSU fibers or blend fibers, the latter being selected from the mentioned polymers.

Nanoparticles, which may be present, for example, in the form of tubes, flakes, rods, spheres, or in other known forms, are typically inorganic materials. They can simultaneously perform various functions in the final foam. For example, these particles partly act as nucleating agents in the foaming operation. The particles may additionally influence the mechanical properties of the foam, as well as the (gas) diffusion properties. The particles additionally contribute to the flame resistance.

In addition to the nanoparticles listed, it is also possible to add microparticles or less miscible phase-separating polymers as nucleating agents. In terms of composition, the polymers must be considered separately from the other nucleating agents here, since the latter primarily influence the mechanical properties of the foam, the melt viscosity of the composition and thus the foaming conditions. The additional effect of the phase separated polymer as a nucleating agent is an additional desired effect of this component, but is not a major effect in this case. Thus, these additional polymers are further listed in the aggregate separately from the remaining additives.

It is optionally also possible to include up to 9% by weight of additional polymer components in the additives to adjust the physical properties. The additional polymer may be, for example, a polyamide, a polyolefin, in particular PP, a polyester, in particular PET, a sulfur-based polymer, such as PSU, PPSU, PES or poly (meth) acrylimide.

The choice of blowing agent is relatively free and depends inter alia on the person skilled in the artThe foaming method, the solubility in the polymer and the foaming temperature are selected. Suitable examples are alcohols, for example isopropanol or butanol, ketones, for example acetone or methyl ethyl ketone, alkanes, for example isobutane or n-butane, or isopentane or n-pentane, hexane, heptane or octane, alkenes, for example pentene, hexene, heptene or octene, CO₂、N₂Water, ethers such as diethyl ether, aldehydes such as formaldehyde or propionaldehyde, fluoro (chloro) hydrocarbons, chemical blowing agents or mixtures of two or more of these.

Chemical blowing agents are less volatile or completely nonvolatile substances which, under the foaming conditions, undergo chemical decomposition and form the actual blowing agent there. Tert-butanol is a very simple example for this, which forms isobutene and water under foaming conditions. A further example is NaHCO₃Citric acid, citric acid derivatives, Azodicarbonamide (ADC) and/or compounds based thereon, Tosylhydrazide (TSH), oxybis (benzenesulfonylhydrazide) (OBSH), or 5-phenyltetrazole (5-PT).

Preferably, the granular foam according to the present invention has a tensile strength according to ISO1926 of more than 0.5MPa, an elongation at break according to ISO1926 of 8% to 12%, a shear modulus at room temperature according to ASTM C273 of more than 8MPa, a shear strength at room temperature according to ASTM C273 of more than 0.45MPa, a compression modulus at room temperature according to ISO 844 of more than 13MPa and a compression strength at room temperature according to ISO 844 of more than 0.4 MPa. In the case of the production of granular foams using the process described below, it is a simple matter for the person skilled in the art to maintain these mechanical properties while maintaining the glass transition temperature and the cell size according to the invention. Furthermore, it has also been found that, surprisingly, the particulate foam according to the invention can be used while meeting fire protection codes or fire protection properties according to FAR 25.852, which are important for use in the aviation industry, in particular for aircraft interiors.

It is also very surprising that the particle foam according to the invention, just like the corresponding slabstock foam, satisfies all the material properties necessary for use in aircraft interiors. For PMI, for example, there is no such correlation, since such polymethacrylimide sheets obtained from slabstock foams meet these conditions, whereas granular foams often have poorer mechanical properties than slabstock foams. A particularly surprising advantage which has additionally been found is that such granular foams, unlike slabstock foams, have no significant to no cell orientation at all. This in many cases gives the granular foam advantageous isotropic mechanical properties, whereas the corresponding block foams often have anisotropic mechanical properties, so that they differ in one region and in an axis perpendicular to this region. Depending on the specific application, isotropic mechanical properties may be quite advantageous, especially when the pressure stresses from various different directions are equal.

Preferably, the degree of foaming of the foam according to the invention corresponds to a density reduction with respect to the unfoamed material of from 1% to 98%, preferably from 50% to 97%, more preferably from 70% to 95%. The foam preferably has a density of 20 to 1000kg/m³Preferably 40 to 250kg/m³Particularly preferably from 50 to 150kg/m³The density of (c).

In addition to the granulated foam according to the invention, the production process thereof is also an integral part of the invention.

In principle, there are two preferred methods for producing the PEI particle foam according to the invention. In a first process variant, a composition consisting of 80 to 99.5% by weight of PEI, 0.5 to 10% by weight of blowing agent and 0 to 10% by weight of additives is processed by means of an extruder with an orifice plate to produce foamed or foamable pellets. Here, the temperature between the feed zone and the screw tip is preferably in the range of 320 to 400 ℃. Furthermore, there is generally no uniform temperature over this section of the path, but rather, for example, a gradient with an increasing temperature in the direction of conveyance of the polymer melt. The temperature of the perforated plate is here between 250 and 350 ℃ and the temperature of the material leaving through the perforated plate is between 230 and 360 ℃. The extruder is usually charged with blowing agent. The pellets then foam as they exit the orifice plate when the pressure in the underwater pelletization is below the expansion force of the blowing agent. The thus foamed pellets are then preferably further processed to form a granular foam.

In a variation of this embodiment, the composition exiting the extruder may be directed to an underwater pelletizer. Such underwater pelletizers are designed here with a combination of temperature and pressure that prevents foaming. This procedure results in pellets loaded with blowing agent, which can later be further processed into a granular foam workpiece by renewed supply of energy to the desired density and/or by optional shaping. The energy input required for prefoaming can be achieved in a radiation-based manner by means of contact heating, for example in an air-circulating oven, or by means of infrared or microwave radiation.

In a second method variant for producing PEI particle foams, a composition consisting of 90 to 100 wt.% PEI and 0 to 10 wt.% additive is first processed to produce pellets, likewise by means of an extruder with an orifice plate, but here without a blowing agent. The temperature between the feed zone and the screw tip is here also in the range of 320 to 400 ℃, which again is not necessarily uniform. The temperature of the perforated plate is likewise between 250 and 350 ℃ and the temperature of the material leaving through the perforated plate is between 230 and 360 ℃. Here, the pellets are subsequently loaded with blowing agent in an autoclave so that they then contain 0.5 to 10% by weight of blowing agent. The pellets loaded with blowing agent can then be foamed by depressurization and/or by heating to a temperature exceeding 200 ℃ to obtain a granular foam.

In respect of the actual foaming, various methods of foaming the polymer composition are known in principle to the person skilled in the art, which are suitable for the compositions according to the invention, in particular in respect of the methods used for thermoplastic foams. For example, the composition may be foamed at a temperature of from 150 to 250 ℃ and a pressure of from 0.1 to 2 bar. Preferably, the actual foaming, if not after extrusion, is carried out in an atmosphere of standard pressure at a temperature of from 180 to 230 ℃.

In a variant in which the blowing agent is loaded later, the composition still free of blowing agent is mixed with the blowing agent in an autoclave at a temperature of, for example, 20 to 120 ℃ and a pressure of, for example, 30 to 100 bar, and is subsequently foamed in the autoclave by reducing the pressure and increasing the temperature to the foaming temperature. Alternatively, the composition mixed with the blowing agent is cooled in an autoclave and taken out after cooling. Such compositions may be subsequently foamed later by heating to a foaming temperature. This can also be done, for example, with further shaping or in combination with other elements, such as inserts or coverings.

Particularly preferably, the produced granular foam-whatever the method used-is subsequently glued, sewn or welded to the covering material. By "welding" is meant herein that heating of the assembly results in cohesion or adhesion between the materials, for example by partial filling of open cells of the foam surface with a covering material.

The cover material may be wood, metal, decorative foil, composite material, prepreg or other known materials.

In the case of later foaming of the material used, for example after loading of the foaming agent in an autoclave, the produced particle foam can alternatively also be foamed in the presence of the covering material, so that the covering material is bonded to the particle foam by means of gluing or welding.

In a variant of the method of loading the blowing agent in the extruder, the PEI may alternatively be added to the optionally heated mould optionally containing a covering material, when leaving the extruder. In this case, foaming is effected simultaneously with shaping to produce a particulate foam or composite material. Alternatively, the composition exiting the extruder may be directed to a foam spray device. In this device, the foaming is then carried out directly at the same time as the shaping.

Regardless of the variant used, inserts may be provided for the particle foam or composite material during foaming and/or channels may be introduced into the particle foam.

The foam according to the invention or the foam produced by the process according to the invention can be used in the construction of spacecraft or aircraft, in particular in the interior or exterior thereof. This may include a particulate foam, whether made by the method of the present invention or not, and also composite materials so achieved. More particularly, the foams of the present invention may also be installed in the interior of such vehicles due to their flame resistance.

More particularly, pure PEI particle foams are particularly suitable for introduction into the interior of an aircraft. Aircraft here includes, in addition to jet aircraft or small aircraft, in particular helicopters or even spacecraft. Examples of installations in the interior of such aircraft are, for example, small table panels, seat fillings or interior partitions which can be folded down on the back of seats of passenger aircraft, and, for example, interior doors.

Particulate foams based on blends containing PEI are furthermore also suitable for incorporation outside aircraft. "external" is understood here not only as a filler in the outer skin of the aircraft, but also in particular in the nose, tail region, wing, outer door, control surface or rotor blade.

Claims (13)

1. Use of PEI particulate foam in aircraft construction, characterized in that the foamed PEI has a glass transition temperature of 180 to 215 ℃ and the average cell diameter of the particulate foam is less than 2 mm.
2. 2. Use of a particulate foam according to claim 1, characterized in that the particulate foam is obtained from a composition consisting of 80 to 99.5% by weight PEI, 0.5 to 10% by weight blowing agent and 0 to 10% by weight additive.
3. 3. Use of a particulate foam according to claim 1 or 2, characterized in that the additive is a flame retardant, a plasticizer, a pigment, a uv stabilizer, a nucleating agent, an impact modifier, an adhesion promoter, a rheology modifier, a chain extender, a fiber and/or a nanoparticle.
4. 4. Use of a cellular foam according to at least one of the claims 1 to 3, characterised in that the blowing agent is an alcohol, a ketone, an alkane, an alkene, CO2, N2, water, an ether, an aldehyde, a chemical blowing agent or a mixture of two or more of these.
5. 5. Use of a granulated foam according to at least one of claims 1 to 4, characterized in that the granulated foam has a tensile strength according to ISO1926 of more than 0.5MPa, an elongation at break according to ISO1926 of 8% to 12%, a shear modulus at room temperature according to ASTM C273 of more than 8MPa, a shear strength at room temperature according to ASTM C273 of more than 0.45MPa, a compression modulus at room temperature according to ISO 844 of more than 13MPa and a compression strength at room temperature according to ISO 844 of more than 0.4 MPa.
6. 6. Use of a particulate foam according to at least one of claims 1 to 5, characterized in that the particulate foam is installed inside an aircraft.
7. 7. Use of a particulate foam according to at least one of claims 1 to 6, characterized in that the average cell diameter of the particulate foam is less than 500 μm.
8. 8. Method for producing PEI particle foams for the use according to at least one of claims 1 to 7, characterized in that a composition consisting of 80 to 99.5 wt. -% PEI, 0.5 to 10 wt. -% foaming agent and 0 to 10 wt. -% additives is processed by means of an extruder with a perforated plate to produce foamed pellets, wherein the temperature between the feed zone and the screw tip is in the range of 180 to 380 ℃, the temperature of the perforated plate is between 250 to 350 ℃ and the material temperature upon exit through the perforated plate is between 230 to 360 ℃, and the foamed pellets are subsequently further foamed into a particle foam.
9. 9. Method for producing PEI particle foams for the use according to at least one of claims 1 to 7, characterized in that a composition consisting of 90 to 100 wt. -% PEI and 0 to 10 wt. -% additives is processed by means of an extruder with a perforated plate to produce pellets, wherein the temperature between the feed zone and the screw tip is in the range of 180 to 380 ℃, the temperature of the perforated plate is between 300 to 350 ℃ and the temperature of the mass upon exit through the perforated plate is between 250 to 360 ℃, and the pellets are subsequently loaded with blowing agent in an autoclave such that they thus contain 0.5 to 10 wt. -% blowing agent, and the pellets loaded with blowing agent are subsequently foamed by expansion and/or by heating to a temperature of more than 200 ℃ to obtain a particle foam.
10. 10. Method for producing a composite part, characterized in that a particle foam produced by means of the method according to claim 8 or 9 is glued, stitched or welded to a covering material.
11. 11. Method for producing a composite part, characterized in that a particle foam produced by means of the method according to claim 8 or 9 is foamed in the presence of a covering material, so that the covering material is bonded to the particle foam by means of gluing or welding.
12. 12. Process according to claim 8, characterized in that the PEI is introduced after leaving the extruder into an optionally heated mould optionally containing a covering material and is foamed while shaping to produce a particulate foam or composite.
13. 13. Method according to at least one of claims 8 to 12, characterized in that the inserts and/or channels are introduced into the particle foam during the foaming process.