PEI or PEI-PEEK- particle foams for lightweight applications

Abstract

To provide a composition for producing novel foams for use in aircraft construction.SOLUTION: The present invention provides a polymer mixture comprising polyetherimide (PEI) and polyether ether ketone (PEEK) and also at least one nucleating agent for the production of foams having a density of 40 to ≤200 kg / m3 and a glass transition temperature of 140 to 230°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] A polymer mixture for producing foams comprising a polyetherimide, a polyetheretherketone, and at least one nucleating agent.

[0002] Polymer foams based on blends of polyetherimide (PEI) and polyetheretherketone (PEEK) meet the legal requirements imposed by the aviation industry for aircraft interiors and exteriors. Here, the requirements on fire behavior, media stability and mechanical properties are of particular importance. According to the prior art, suitable polymer foams are produced as semi-finished products. Post-processing to molded articles is uneconomical in terms of time and material used, for example because of the large amounts of sawing waste that result. The present invention solves this problem by making it possible in principle to process suitable materials to particle foam molded articles. These molded articles can be produced without post-processing, with short cycle times and therefore economically. Furthermore, this gives rise to new options in terms of functional integration and design freedom, for example by incorporating inserts directly into the foam.

[0003] prior art Foam materials suitable for installations in the aeronautical industry are well known. However, the majority of foams described for this purpose consist exclusively of pure PMI (polymethacrylimide), PPSU (polyphenylenesulfone) or PES (polyethersulfone). There are also PI (polyarylimides) in the literature, which are unsuitable from a toxicological point of view. All these materials have so far only been used as block or slab materials.

[0004] Other materials have been described as slab materials for installation in the aeronautical industry, but in less detail. Thus, poly(oxy-1,4-phenylsulfonyl-1,4-phenyl) (PESU) is an example of such a material. It is sold, for example, by DIAB under the product name Divinycell F. However, further processing of these extruded foam boards produces uneconomical amounts of waste material.

[0005] An economical way to avoid cutting waste in the production of three-dimensional foamed mouldings is to use foam particles (bead foams) rather than slabstock foams. All particle foams available in the prior art have drawbacks when used at high temperatures or overall non-optimal mechanical properties, especially at these high temperatures. Furthermore, there are very few known foams that are not highly flammable and can be installed as is, for example, in the interiors of road vehicles, rail vehicles or aircraft. Thus, for example, particle foams based on polypropylene (EPP), polystyrene (EPS), thermoplastic polyurethane elastomers (E-TPU) or PMI (ROHACELL Triple F) have insufficient flame retardancy, while all inherently flame-retardant polymers that are in principle suitable, such as PES, PEI, PEEK or PPSU, are only processed into slabstock foams in the prior art.

[0006] assignment The problem addressed by the present invention with respect to the prior art was to provide a composition for producing novel foams for use in aircraft construction. The foams obtained should have a good combination of usability at high temperatures, good mechanical properties, especially with respect to elongation at break, and flame retardancy, at least sufficient for many applications in vehicle and aircraft construction. Moreover, the foams should be feasible from the compositions produced, by a wide variety of different methods, in a wide range of three-dimensional shapes, and with only little or no waste material being generated in the production of the final parts.

[0007] Further implicit objectives will be apparent from the description, claims or examples herein, even if not explicitly stated herein for this purpose.

[0008] solution These objectives are met by providing novel compositions for the production of thermally stable foamed materials with low flammability for use in the aviation industry. In particular, these objectives are met by providing novel compositions with a density, measured according to DIN EN ISO 1183, between 40 and ≦200 kg / m 3 The problem is solved by the provision of a polymer mixture comprising polyetherimide (PEI), polyetheretherketone (PEEK) and further at least one nucleating agent for producing foams having a glass transition temperature of 140-230°C measured according to DIN EN ISO 6721-1. A suitable polymer mixture is characterized in that it comprises 50-99.999% by weight of PEI, 0-49.999% by weight of PEEK, 0.001-2% by weight of a nucleating agent, 0-25% by weight of a blowing agent and 0-20% by weight of additives. A particularly suitable polymer mixture consists of 60-79.999% by weight of PEI, 20-39.999% by weight of PEEK and 0.001-20% by weight of a blowing agent. A polymer mixture comprising 0.1-17% by weight of a blowing agent is preferred. The choice of blowing agent is relatively free and is determined by the skilled artisan, inter alia, the selected foaming method, its solubility in the polymer, and the foaming temperature. Suitable examples are alcohols, such as isopropanol or butanol, ketones, such as acetone or methyl ethyl ketone, alkanes, such as isobutane, n-butane, isopentane, n-pentane, hexane, heptane or octane, alkenes, such as pentene, hexene, heptene or octene, CO 2 , N 2 , water, an ether, such as diethyl ether, an aldehyde, such as formaldehyde or propanal, a hydro(chloro)fluorocarbon, a chemical blowing agent, or a mixture of several of these substances.

[0009] Chemical blowing agents are substances of low or no volatility that undergo chemical decomposition under foaming conditions to form the actual blowing agent. A very simple example is tert-butanol, which forms isobutene and water under foaming conditions. A further example is NaHCO 3 , citric acid, citric acid derivatives, azodicarbonamide (ADC) and / or compounds derived therefrom, toluenesulfonylhydrazine (TSH), oxybis(benzosulfohydroazide) (OBSH) or 5-phenyltetrazole (5-PT).

[0010] In addition, the foams usually contain various additives. Depending on the nature of the additive, 0-20% by weight of the additive is added to the polymer mixture. The additives are flame retardants, plasticizers, pigments, UV stabilizers, nucleating agents, impact modifiers, adhesion promoters, rheology modifiers, chain extenders, fibers, platelets 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 widely known to the person skilled in the art. For this purpose, generally HALS compounds, Tinuvins or triazoles are used. The impact modifiers used are generally polymer particles comprising an elastomeric phase and / or a soft / flexible phase. These are often core-(shell-)shell type particles with a slightly weakly crosslinked outer shell by themselves, which as pure polymers will show at least minimal miscibility with PEI or blends of PEI and PEEK. As pigments, in principle all known pigments can be used. Of course, in particular in relatively large amounts, as with all other additives used in amounts above 0.1% by weight, the effect on the foaming process must be investigated, which can be done by the skilled artisan with relatively little effort.

[0011] Suitable plasticizers, rheology modifiers and chain extenders are generally known to the skilled person from the production of sheets, films or mouldings from PEI, PEEK or their blends and accordingly can be transferred with minimal expenditure to the production of foams from the compositions according to the invention. The fibres optionally added are generally known fibrous materials which can be added to polymer compositions. In a particularly preferred embodiment of the invention, the fibres are PEI fibres, PEEK fibres, PES fibres, PPSU fibres or blend fibres, the blend fibres being composed of the polymer choices mentioned.

[0012] Nanoparticles may be, for example, tubes, platelets, rods, spheres or other known shapes, and are generally inorganic materials. They can simultaneously perform different functions in the finished foam. For example, these particles can act as nucleating agents during foaming. Furthermore, these particles can affect the mechanical properties and also the (gas) diffusion properties of the foam. Furthermore, these particles also help to make the foam less flammable.

[0013] In addition to the mentioned nanoparticles, it is also possible to add microparticles or poorly miscible phase-separating polymers as nucleating agents. When considering the composition, the described polymers need to be seen separately from other nucleating agents, because they mainly affect the mechanical properties of the foam, the melt viscosity of the composition, and thus the foaming conditions. The ability of the phase-separating polymer to act as an additional nucleating agent is an additional desirable effect of this component, but not the main effect in this case. Therefore, these additional polymers are listed separately from other additives in the above overall balance.

[0014] These polymer mixtures are processed into foams by known processes. The conventional process is extrusion. According to the invention, the foams are prepared by subjecting the mixtures to a density of 40 to ≦200 kg / m3, measured according to DIN EN ISO 1183. 3The foams are produced by extrusion. It is preferred to produce the foaming agent-filled particles by underwater pelletization. The foaming agent-filled particles can be provided in various shapes. Advantageously, ellipsoidal particles are produced having a weight of 0.5-15 mg, preferably 1-12 mg, more preferably 3-9 mg. Ellipsoid is a term that describes a three-dimensional shape based on an ellipse (two dimensions). If the semiaxes are the same, the ellipsoid is a sphere, if the two semiaxes correspond, the ellipsoid is a spheroid (rugby ball), and if all three semiaxes are different, the ellipsoid is a triaxial body. A particularly preferred variant provides a method for producing a particle foam, in which a composition consisting of 50-99.999% by weight PEI, 0-49.999% by weight PEEK, and 0.001-2% by weight nucleating agent is compounded in an extruder by underwater pelletization or strand pelletization and processed into pellets. The resulting pellets are then swollen with 0.001-20% by weight, preferably 0.1-17% by weight, of a blowing agent in a suitable container, e.g. drum, tank or reactor, and the swollen particles are separated on a sieve and dried. The resulting blowing agent-filled particles are pre-expanded by heating. Heating is carried out by infrared radiation, a fluid (e.g. steam), electromagnetic waves, heat conduction, convection or a combination of these methods. By heating the blowing agent-filled particles, foam particles are obtained. These foam particles have a bulk density, measured according to DIN EN ISO 1183, of 40 to ≦200 kg / m 3 and preferably 30 to 90 kg / m 3 The average cell size of the particle foam is preferably ≦500 μm, more preferably less than 250 μm. The size of the cells can often be easily measured, for example using a microscope. This is particularly applicable when the cell wall between two cells is easily discernible.

[0015] The particle foam according to the invention as a foamed material has a glass transition temperature of 140°C to 230°C, preferably 180 to 225°C. The stated glass transition temperatures are, unless otherwise specified, according to the invention measured by DSC (differential scanning calorimetry). The skilled person is aware that DSC is sufficiently informative only if, after a first heating cycle to a temperature at least 25°C above the highest glass transition or melting temperature of the material and at least 20°C below the lowest decomposition temperature of the material, the material sample is kept at this temperature for at least 2 minutes. The sample is then cooled to a temperature at least 20°C below the determined lowest glass transition or melting temperature, where the cooling rate should be 20°C / min or less, preferably 10°C / min or less. After this, after a further waiting period of a few minutes, the actual measurement is carried out, in which the sample is heated to a temperature at least 20°C above the highest melting or glass transition temperature, generally with a heating rate of 10°C / min or less. The obtained foam particles are processed into a molded body by using a molding die and inputting energy to sinter the pre-foam particles, and the sintering pressure is 40 to ≦200 kg / m 3 A molding is formed having a density of 10 ...

[0016] More preferably, the foam particles produced are then adhesively bonded, sewn or welded to the cover material, regardless of the method used. By "welded" in this invention is meant heating a member to create a cohesive bond (adhesion) between the foam core and the cover material.

[0017] The cover material may include wood, metal, decorative films, composites, prepregs, or other known materials. For example, there may be a foam core with a thermoplastic or crosslinked cover layer. The prior art discloses various methods of manufacturing composite members.

[0018] A preferred method of making the composite member is characterized in that a particle foam made according to the invention is expanded in the presence of a cover material so as to be bonded thereto by adhesive bonding or welding.

[0019] In a process variant in which the foaming agent filling takes place in the extruder, the blend of PEI and PEEK can also be processed into a semi-finished product at the exit of the extruder, optionally combined with a cover material, alternatively using a suitable nozzle. Alternatively, the composition can be foamed in a foaming injection device directly at the same time as it is molded (foaming injection molding).

[0020] Regardless of the variant used, it is possible to provide inserts in the particle foam or composite material during foaming and / or to incorporate channels in the particle foam. It is also very surprising that all the necessary material properties, which are prerequisites for use in aircraft interiors, are met by the particle foam according to the invention just as they are met by the corresponding foam in slab form. In the case of PMI, for example, this relationship does not exist, since in the case of this polymethacrylimide, the sheet material produced from slabstock foam meets the conditions, whereas the particle foam does not receive approval.

[0021] The foam according to the invention preferably has a degree of foaming, which is equivalent to a reduction in density, compared to the unfoamed material, of 1 to 98%, preferably 50 to 97%, more preferably 70 to 95%. The foam preferably has a density of 20 to 1000 kg / m 3 , preferably 40 to 200 kg / m 3 has a density of

[0022] In addition to the particle foams according to the present invention, the present invention also includes methods for their production.

[0023] There are in principle two preferred methods for producing the particle foam according to the invention. In the first method variant, a composition consisting of 50-99.999% by weight of PEI, 0-49.999% by weight of PEEK, 0.001-2% by weight of nucleating agent, 0.001-20% by weight of blowing agent and optionally up to 20% by weight of additives is processed into foamed pellets by means of an extruder with a perforated plate. The temperature between the intake zone and the screw tip is preferably in the range of 320-400 ° C. Moreover, the temperature in this distance is usually not uniform, for example there is a temperature gradient with an increasing temperature in the direction of the feed of the polymer melt. The temperature of the perforated plate is 250-350 ° C, the melt temperature at the exit through the perforated plate is 230-360 ° C. The filling of the blowing agent is generally carried out in the extruder. The pellets are then expanded on leaving the perforated plate. The pellets thus expanded are then preferably further expanded to obtain a particle foam.

[0024] In one variation of this embodiment, the composition can be directed to an underwater pelletizer upon exiting the extruder, which is designed to employ a combination of temperature and pressure to prevent such foaming from occurring. This method provides pellets loaded with foaming agent, which can then be expanded with new energy input to a desired density and / or optionally shaped and further processed into particulate foam workpieces.

[0025] In a second variant of the method for producing a particle foam, a suitable composition as described for the first variant is likewise first processed into pellets by means of an extruder with a perforated plate, but without the filling of a blowing agent. Here too, the temperature between the intake zone and the screw tip is in the range of 320-400 ° C, which is also not necessarily uniform. The temperature of the perforated plate is likewise 250-350 ° C, and the melt temperature at the outlet through the perforated plate is 230-360 ° C. In this case, the pellets are then filled with a blowing agent in an autoclave so that they contain 0.001-20% by weight, preferably 0.1-17% by weight, of the blowing agent. The pellets filled with the blowing agent can then be expanded by expansion into a particle foam and / or by heating to a temperature above 200 ° C.

[0026] For the preparation of the blends of PEI and PEEK used according to the invention, it is possible in principle to use preferably 50-99.999% by weight of PEI and 0.001-49.999% by weight of PEEK, similar to the two methods described above for the pure particle foams. Since PEEK is crystalline and has a high melting temperature of around 335°C, if it is intended to include more than 25% by weight of PEEK, the temperatures mentioned above for the individual process steps must be adjusted by the skilled person according to the exact composition of the blend. It is assumed that the temperatures selected here tend to be somewhat higher than those of blends containing less than 25% by weight of PEEK.

[0027] As regards the actual foaming, it is known in principle to the skilled artisan that various methods for foaming polymer compositions are applicable to the compositions of the invention, in particular as regards methods for thermoplastic foams. For example, the composition can be foamed at temperatures between 150 and 250°C and pressures between 0.1 and 2 bar. If the actual foaming does not follow directly from extrusion, it is preferably carried out at temperatures between 180 and 230°C in a standard pressure atmosphere.

[0028] In a variant in which the filling of the blowing agent is carried out later, the composition not yet containing the blowing agent is added with the blowing agent in an autoclave at a temperature of, for example, 20 to 120° C. and a pressure of, for example, 30 to 100 bar, and then foamed in the autoclave by lowering the pressure and raising the temperature to the foaming temperature. Alternatively, the composition with the blowing agent is cooled in the autoclave and removed from the autoclave after cooling. The composition can then be foamed by heating to the foaming temperature. This can be done, for example, in parallel with further molding or in combination with other elements such as inserts or cover layers.

[0029] The foam according to the invention or the foam produced by the method according to the invention can be used in spacecraft or aircraft construction, in shipbuilding, in railcar construction or in vehicle construction, in particular in the interior or exterior thereof. This can include particle foams, whether or not produced by the method according to the invention, and also composites realized therefrom. More particularly, due to their low flammability, the foam according to the invention can also be placed in the interior of the aforementioned vehicles. The invention further likewise provides for the use of the cited materials in shipbuilding, in vehicle construction or in railcar construction.

[0030] The particle foams based on blends of PEI and PEEK are particularly suitable for incorporation into aircraft interiors. Besides jets or light aircraft, aircraft also include, in particular, helicopters or spacecraft. Examples of such installations in aircraft interiors include, for example, foldable tablets behind passenger seats, infills for seats and interior partitions, and for example installations in interior doors.

[0031] The particle foams based on blends of PEI and PEEK are furthermore particularly suitable for being incorporated into the exterior of aircraft, where "exterior" means not only the filling of the exterior surface of the aircraft, but also in particular the filling of the nose, tail, wings, exterior doors, rudders or rotors of the aircraft.

Claims

1. Density measured according to DIN EN ISO 1183: 40 to ≦200 kg / m ３ and a glass transition temperature, measured according to DIN EN ISO 6721-1, of 140 to 230° C., said polymer mixture comprising a polyetherimide, a polyetheretherketone and at least one nucleating agent.

2. 2. The polymer blend of claim 1, wherein the polymer blend comprises 50-99.999 wt.% PEI, 0-49.999 wt.% PEEK, 0.001-2 wt.% nucleating agent, 0-25 wt.% blowing agent, and 0-20 wt.% additives.

3. 2. The polymer mixture of claim 1, wherein 0.001 to 20% by weight of a blowing agent is added.

4. 2. The polymer mixture of claim 1, wherein 0.1 to 10% by weight of an additive is added.

5. 25~≦100kg / m ３ 4. The polymer blend of claim 3, wherein the foam having a density of

6. 4. The polymer mixture of claim 3, wherein the blowing agent filled particles are produced by underwater pelletization.

7. 7. The foaming agent filled particles of claim 6, wherein ellipsoidal particles having a weight of 0.5 to 15 mg, preferably 1 to 12 mg, more preferably 3 to 9 mg are produced.

8. 3. The polymer mixture of claim 2, wherein the particles are produced by underwater pelletizing or strand pelletizing and then charged with the blowing agent in a suitable container.

9. 9. A foamed particle, characterized in that the foamed particle is a foamed agent-filled particle according to any one of claims 6 to 8, which is pre-expanded by heating.

10. The foam particles have a compressive strength of 25 to ≦100 kg / m ３ The foam particles of claim 9 having a bulk density of

11. A molded body, which is obtained by sintering the foam particles according to claim 10 using a molding die and inputting energy, and has a strength of 25 to ≦100 kg / m ３ A molded article, characterized in that a molded foam having a density of

12. 12. A molded article, characterized in that the foaming process according to claim 11 is carried out by infrared radiation, heat input from a fluid, thermal conduction, or electromagnetic waves.

13. 11. A molding, characterized in that the foam particles according to claim 10 are adhesively bonded using a molding tool and additives.

14. Use of a PEI / PEEK foam obtainable according to claim 5 or a PEI / PEEK particle foam according to any one of claims 11 to 13 in the aeronautical industry, in shipbuilding, in rail vehicle construction or in vehicle construction.