Soft and semi-hard polyimide-containing foams with excellent heat resistance

Abstract

The present invention relates to a reactive mixture and a method for forming soft and semi-hard polyimide-containing foams based on isocyanate, said foams having high temperature resistance and good acoustic properties.

Description

Technical Field

[0001] The present invention relates to a method for forming a soft / semi-rigid polyimide (PI)-containing foam made from polyisocyanate, monoanhydride and polyamine, which has excellent temperature resistance compared with conventional soft / semi-rigid polyurethane (PU)-containing foam made from polyisocyanate and polyol.

[0002] The invention also relates to a reactive mixture for producing the flexible / semi-rigid polyimide-containing foam according to the invention.

[0003] The flexible / semi-rigid polyimide-containing foams according to the present invention have predominantly open cells and low air flow resistance, which makes them ideal for sound insulation or sound absorption.

[0004] Furthermore, the invention relates to the use of the flexible / semi-rigid polyimide-containing foam according to the invention for sound absorption and / or sound insulation, more particularly for automotive applications. Background Art

[0005] Conventional flexible / semi-rigid polyurethane foams have limited temperature resistance, which greatly limits their range of available applications, excluding them from, for example, the specialty / high-performance market segments. They are generally not suitable for prolonged exposure to temperatures above 150-200°C, as this leads to a significant drop and degradation of their properties (mechanical properties, etc.).

[0006] Additional advantages of high temperature resistant foams include reduced risk of scorching during production and better fire protection properties.

[0007] Many solutions exist to improve foam temperature resistance, but these solutions are not always practical depending on the target application and foam properties and / or are too expensive to implement in a cost-competitive industry such as the automotive industry.

[0008] One of these solutions in the prior art involves extensive reformulation of the reactive mixture used to make flexible polyurethane foams, for example by incorporating more thermally stable raw materials, such as replacing polyether polyols with polyester polyols. However, the improvement in the temperature resistance of the foams is still limited.

[0009] Another possibility is to use isocyanate-based resins containing polycarboxylic acids or polyanhydrides that produce imide bonds. These resins are known to be useful for preparing foaming resins for insulation applications and for preparing lightweight flame-retardant structural foams for automobiles, aircraft, packaging, etc. Such resins can be prepared by reacting polyisocyanates with polycarboxylic acids or polyanhydrides, see for example US3314923; US3562189; US3644234 and US3772216.

[0010] US7541388 describes isocyanate-based resins containing aromatic dianhydrides which react with polyisocyanates to produce polyimide foams. The claims and examples are limited to the use of dianhydrides to obtain stable foams. However, dianhydride acids are very expensive and are only affordable in niche industries such as for use in aerospace.

[0011] In order to solve the above problems, it is necessary to produce cost-effective high temperature resistant flexible / semi-rigid foams. A specific example is the use in automobile engine compartment sound insulation.

[0012] Therefore, it is necessary to produce low density (less than 100 kg / m 3 ) of a soft or semi-rigid foam which is heat-resistant (exposure to temperatures above 150-200° C.) and has a predominantly open-cell structure, which maintains good sound insulation properties.

[0013] Purpose of the Invention

[0014] The ultimate goal would be to obtain a low density, predominantly open-cell, flexible or semi-rigid foam that:

[0015] have a predominantly open-cell structure (at least 50% open-cell content), and

[0016] Less than 100 kg / m2 measured according to ISO 845 3 , preferably less than 50kg / m 3 , more preferably less than 20kg / m 3 The apparent density of

[0017] Highly heat resistant (exposure to temperatures above 150-200°C), and

[0018] • Made using cost-competitive reactive mixtures and methods for making foams.

[0019] Furthermore, the foams according to the present invention should have suitable levels of air flow and cell openness (having an open cell content of preferably at least 80 vol%, more preferably at least 90 vol%, even more preferably at least 95 vol%, most preferably at least 98 vol%, based on the total volume of the foam and measured according to ASTM D6226-10), which makes them suitable for use in applications where good sound absorption and / or sound insulation is required.

[0020] Another object is to use polyisocyanates as starting materials and to improve the prior art polyurethane (PU)-containing flexible and semi-rigid foams. This object is achieved by producing polyimide-containing foams in which the conventionally used isocyanate-reactive polyol compounds are replaced by monoanhydrides and polyamines.

[0021] It was therefore an object of the present invention to develop reactive mixtures and processes for producing flexible or semirigid polyimide-containing foams having the properties described above.

[0022] Definitions and terminology

[0023] In the context of the present invention, the following terms have the following meanings:

[0024] 1) The "NCO value" or "isocyanate value" referred to herein is the weight percentage of reactive isocyanate (NCO) groups in an isocyanate, modified isocyanate or isocyanate prepolymer compound.

[0025] 2) The term "average nominal functionality" (or simply "functionality") is used herein to refer to the average number of functional groups per molecule in the composition.

[0026] 3) Unless otherwise indicated, the word "average" means mean.

[0027] 4) As used herein, the term "flexible foam" is used in its broad sense to refer to low-density cellular materials (apparent density <100 kg / m 3 ), which allows a certain degree of compression and rebound, providing a shock absorbing effect. Semi-rigid foams and semi-flexible foams are also part of the present invention.

[0028] 5) As used and referred to herein, the terms "polyurethane" and "materials comprising polyurethane" are not limited to those polymers that include only urethane bonds or urethane bonds. It is well understood by those of ordinary skill in the art of preparing polyurethanes that polyurethane polymers also include allophanates, carbodiimides, urea butadiene diones, isocyanurates, and other bonds in addition to urethane bonds.

[0029] 6) As used herein, the terms "polyimide-containing material" and "polyimide-containing foam" are not limited to those polymers that only include (poly)imide bonds. As required by the present invention, on top of polyisocyanates and monoanhydrides, polyamines and water are used as starting materials to produce a stable polyimide-containing foam as the final material, optionally with small amounts of other chemicals such as polyols, and those skilled in the art of preparing polymers will well understand that the following bonds may also be present in small amounts: amide, allophanate, carbodiimide, urea butadiene dione, urethane, isocyanurate and other bonds. However, the soft and semi-rigid polyimide-containing foams according to the present invention are polyimide-containing foams that contain a large number of imide bonds. Typically, at least 20%, preferably 30%, more preferably 40% of the isocyanate groups initially present in the reactive mixture are converted to imide bonds in the final foam product according to the present invention.

[0030] 7) As used herein, the expressions "reaction system", "reactive foam formulation" and "reactive mixture" refer to the combination of reactive compounds used to make the polyimide-containing foam of the present invention, wherein the polyisocyanate compound is generally maintained in one or more containers separate from the remaining formulation components (such as anhydrides, polyamines, surfactants, solvents, etc.).

[0031] 8) Unless otherwise indicated, the "weight percent" (expressed as % by weight or wt%) of a component in a composition refers to the weight of the component relative to the total weight of the composition in which the component is present, and is expressed as a percentage.

[0032] 9) Unless otherwise indicated, "parts by weight" of a component in a composition refers to the weight of the component used and is expressed as "pbw".

[0033] 10) "Density" of a foam refers to the apparent density measured on a foam sample by cutting a parallelepiped foam, weighing it and measuring its dimensions. Apparent density is the ratio of weight to volume measured according to ISO 845 and is expressed in kg / m 3 express.

[0034] 11) The term "open-cell foam" refers to a foam having cells that are not completely surrounded by a wall membrane and are open to the foam surface directly or by interconnection with other cells, so that liquid and air can easily pass through the foam. As used herein, the term open-cell foam refers to a foam having an open cell content of at least 50% by volume, such as 60 to 99.9% by volume or 75 to 99.5% by volume, based on the total volume of the foam and measured according to ASTM D6226-10 (open cell content measured by a pycnometer).

[0035] 12) "Physical blowing agents" herein refer to permanent gases such as CO2, N2 and air, and volatile compounds (low boiling point inert liquids) which expand the polymer by evaporation during polymer formation and are not formed by any chemical reaction during foaming. Examples of suitable volatile compounds include, but are not limited to, chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), hydrofluoroolefins (HFOs), hydrochlorofluoroolefins (HCFOs), and hydrocarbons such as pentane, isopentane and cyclopentane. The process of making bubbles / foam is irreversible and endothermic, i.e., it requires heat (e.g., from the release of heat from a chemical reaction) to volatilize the (low boiling point) liquid blowing agent.

[0036] 13) "Chemical blowing agents" include compounds that decompose under the processing conditions and expand the polymer by producing gases as a by-product. Examples include water (by reacting with isocyanates to form CO2) or even isocyanates in the presence of a suitable catalyst (such as a carbodiimide catalyst, where the carbodiimide releases CO2 when it is formed).

[0037] 14) "Sound absorption" or "sound insulation" herein is measured according to ASTM E1050-98.

[0038] 15) "Exotherm of reaction" refers herein to the temperature generated during the formation of the polymer, more specifically the maximum temperature reached during the foaming step of the process whereby, starting from the reactive (liquid) mixture according to the invention, a polyimide-containing polymer is manufactured. DETAILED DESCRIPTION

[0039] The present invention discloses a low density (<100kg / m 3 ) soft and semi-rigid polyimide-containing foams, which mainly have an open-cell structure (the open-cell content is at least 50 volume %, preferably at least 80 volume %, more preferably at least 90 volume %, even more preferably at least 95 volume %, most preferably at least 98 volume %, based on the total volume of the foam and measured according to ASTM D6226-10), which have high temperature resistance, more specifically, can be exposed to temperatures above 150-200°C for a long time.

[0040] Thus, the present invention discloses a reactive mixture for making low density soft and semi-rigid polyimide-containing foams having an open cell structure, the foam having an open cell content of at least 50% by volume as measured according to ASTM D6226-10 and having a density of less than 100 kg / m 3 The reactive mixture comprises the following ingredients to form a reactive mixture:

[0041] a) a polyisocyanate composition comprising at least one polyisocyanate compound, and

[0042] b) at least one monoanhydride compound, and

[0043] c) at least one aprotic polar solvent having a boiling point above 100° C. at normal pressure, and

[0044] d) at least one polyamine compound, and

[0045] e) a blowing agent composition comprising at least 50 mol % of water, based on the total molar amount of the blowing agent composition, and optionally comprising a physical blowing agent and / or a non-reactive chemical blowing agent having no isocyanate-reactive groups, and

[0046] f) an optional catalyst composition comprising at least one catalyst compound selected from the group consisting of a carbamate-forming catalyst compound, a urea-forming catalyst compound, an imide-forming catalyst compound, an amide-forming catalyst compound, a carbodiimide-forming catalyst compound and / or a trimerization catalyst compound, and

[0047] g) Optional other additives, such as surfactants, flame retardants, fillers, pigments and / or stabilizers.

[0048] According to an embodiment, the at least one aprotic polar solvent has a boiling point at atmospheric pressure above 140° C., preferably above 170° C., more preferably above the exotherm of reaction in the reactive mixture.

[0049] According to an embodiment, ingredients b) to g) are first combined and then reacted with the polyisocyanate composition.

[0050] According to an embodiment, the foam may be manufactured according to a free rise method, a molding method, a slabstock method, a lamination method, or a spraying method.

[0051] The ingredients may be fed separately to the mixing head of the foaming machine.The monoanhydride compound, polyamine, water, solvent and optional ingredients are preferably premixed before they are mixed with the polyisocyanate composition.

[0052] According to an embodiment, the low-density polyimide-containing foam according to the present invention is a free-rise soft / semi-rigid foam having a density of <40 kg / m 3 , preferably <15kg / m 3 , more preferably 4-10kg / m 3 density.

[0053] According to an embodiment, the low density polyimide-containing foam according to the present invention is a spray foam using prior art spray technology for polyurethane foaming.

[0054] According to an embodiment, a method for producing an isocyanate-based flexible or semi-rigid polyimide-containing foam having an open-cell structure is provided, the foam having an open-cell structure of at least 50% by volume, preferably at least 80% by volume, more preferably at least 90% by volume, even more preferably at least 95% by volume, most preferably at least 98% by volume, based on the total volume of the foam and measured according to ASTM D6226-10, and having a pressure below 100 kg / m 2 measured according to ISO 845. 3 The apparent density of

[0055] i. forming a reactive mixture by combining a polyisocyanate composition, at least one monoanhydride compound, at least one aprotic polar solvent, at least one polyamine compound, a blowing agent composition, and optionally a catalyst composition and / or other additives,

[0056] ii. causing the reactive mixture to foam and form a foam comprising polyurea ("polyurea pre-foam"), and

[0057] iii. post curing the polyurea pre-foam to obtain the final polyimide-containing foam.

[0058] According to an embodiment, the method for producing low-density soft and semi-rigid polyimide-containing foams according to the present invention comprises at least the following steps:

[0059] i. The ingredients of the reactive mixture (polyisocyanate, monoanhydride, polyamine, solvent, water, optional additives) are mixed, and then

[0060] ii. foaming the reactive mixture obtained in step i. and forming a foam containing polyurea ("polyurea pre-foam"), and then

[0061] iii. post-curing the polyurea pre-foam obtained in step ii. to obtain the final polyimide-containing foam.

[0062] According to an embodiment, the mixing step i. may include a premixing step, wherein the monoanhydride compound, polyamine, solvent, catalyst compound and optional blowing agent composition and other additives are first mixed before being combined with the polyisocyanate compound to form a reactive mixture.

[0063] According to an embodiment, the step of mixing the components of the reactive mixture is performed using a high pressure mixing system.

[0064] According to an embodiment, the step of mixing the components of the reactive mixture is performed using a dynamic mixing system.

[0065] According to embodiments, no external heat is added to the reactive mixture and the exotherm of reaction is sufficient to obtain a low density foamed structure.

[0066] According to the embodiment, the post-curing step iii can be carried out in a variety of ways, including application of heat (preferably in the range of 150-300°C for several hours), microwave radiation, IR radiation, etc. It can be carried out before commercialization, but can also be carried out in situ during the life of the foam when it is exposed to high temperatures during use.

[0067] According to an embodiment, the low-density polyimide-containing foam according to the present invention has an open cell content of ≥50% by volume, preferably at least 80% by volume, more preferably at least 90% by volume, even more preferably at least 95% by volume, and most preferably at least 98% by volume, based on the total volume of the foam and measured according to ASTM D6226-10.

[0068] Monoanhydride compounds

[0069] According to an embodiment, the monoanhydride compound is selected from maleic anhydride (I), phthalic anhydride (II), succinic anhydride (III), trimellitic anhydride (IV) and / or itaconic anhydride (V).

[0070]

[0071] According to an embodiment, the amount of monoanhydride in the reactive mixture is 10-60 wt%, preferably 15-50 wt%, more preferably 20-40 wt%, even more preferably 20-30 wt%, based on the total weight of the reactive mixture.

[0072] According to an embodiment, the monoanhydride may be pre-dissolved in a solvent / diluent prior to any further mixing with the isocyanate. The polyamine (primary or secondary, aliphatic or aromatic) may also be dissolved in the solvent solution, or added separately (i.e. as separate components / streams) to the reactive mixture.

[0073] According to an embodiment, monoanhydrides may also be present in the reactive mixture in their polymerized and / or copolymerized form, such as copolymers of maleic anhydride with ethylene, propylene, isobutylene or styrene (e.g. copolymers of maleic anhydride with styrene, which may be used as The monoanhydride may also be present in the reactive mixture when grafted as a pendant group onto a polymer backbone, such as onto polyethylene or polyisoprene.

[0074] Polyamine compounds

[0075] The presence of polyamines in the reactive mixture is essential for producing good quality (ie fine-celled, stable, non-collapsed, defect-free) foams. In other words, polyamines can be considered as processing aids, the presence of which allows excellent foam quality to be obtained.

[0076] According to an embodiment, the polyamine compound is selected from polyamine compounds having an amine functionality greater than or equal to 1 and is selected from primary amines or secondary amines.

[0077] Suitable examples of polyamines include DETDA (diethyltoluenediamine), MDA (diphenylmethanediamine, in monomeric or polymeric form), polyvinylamine, amine-modified PDMS (or other temperature-resistant polymers), and the like.

[0078] According to an embodiment, the amount of polyamine in the reactive mixture is less than 30 wt%, preferably less than 20 wt%, more preferably less than 10 wt%, based on the total weight of the reactive mixture.

[0079] Catalyst composition

[0080] According to embodiments, the catalyst compound, if used, is used in a catalytic amount sufficient to promote the formation of urea and ultimately the formation of imide bonds within the polymer.

[0081] According to an embodiment, the total amount of catalyst compounds in the reactive composition is at most 5 wt%, preferably at most 4 wt%, more preferably at most 3 wt%, based on the total weight of the reactive mixture. Advantageously, the amount of catalyst compounds is 0.5 wt% to 3 wt%, preferably 1 wt% to 2.5 wt%, based on the total weight of the reactive mixture.

[0082] According to an embodiment, the catalyst composition comprises the urea-forming catalyst compound in an amount of at least 50 wt%, preferably at least 75 wt%, more preferably at least 90 wt%, based on the total weight of all catalyst compounds in the catalyst composition.

[0083] According to an embodiment, at least one urea-forming catalyst is preferably selected from metal salt catalysts such as organic tin, and amine compounds such as triethylenediamine (TEDA), N-methylimidazole, 1,2-dimethylimidazole, N-methylmorpholine, N-ethylmorpholine, triethylamine, N,N'-dimethylpiperazine, 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine, 2,4,6-tris(dimethylaminomethyl)phenol, N-methyldicyclohexylamine, pentamethyldipropylenetriamine, N-methyl-N'-(2-dimethylamino)-ethyl-piperazine, tributylamine, pentamethyldiethylenetriamine, hexamethyltriethylenetetramine, heptamethyltetraethylenepentamine, dimethylaminocyclohexylamine, pentamethyldipropylenetriamine, triethanolamine, dimethylethanolamine, bis(dimethylaminoethyl)ether, tris(3-dimethylamino)propylamine, and any mixture thereof. Suitable commercially available catalysts are DPA, ZF10, Z130, NE300, NE1091 and NE1550.

[0084] Foaming agent composition

[0085] According to an embodiment, the reactive mixture contains at least water as blowing agent (in addition to possible other blowing agents) in an amount of greater than 0 wt.-% to 5 wt.-%, preferably 0.5-4 wt.-%, more preferably 1-3.5 wt.-%, and even more preferably 1.5-3 wt.-% water, based on the total weight of the reactive mixture.

[0086] According to an embodiment, no physical blowing agents and / or further chemical blowing agents other than water are added to the reactive mixture.

[0087] According to an embodiment, the blowing agent composition may contain (in addition to water) a physical blowing agent and / or a non-isocyanate reactive chemical blowing agent to further reduce the density of the foam. Suitable physical blowing agents may be selected from isobutylene, methyl formate, dimethyl ether, methylene chloride, acetone, tert-butyl alcohol, argon, krypton, xenon, chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), hydrofluoroolefins (HFOs), hydrochlorofluoroolefins (HCFOs) and hydrocarbons such as pentane, isopentane and cyclopentane and mixtures thereof.

[0088] According to a preferred embodiment, the blowing agent composition comprises at least 50 mol% of water, preferably at least 65 mol% of water, more preferably at least 70 mol% of water, even more preferably 90 mol% of water and most preferably at least 95 mol% of water, based on the total molar amount of all blowing agents in the blowing agent composition.

[0089]

[0066] Depending on the embodiment, the amount of water and / or other blowing agent (optionally) added to the reactive mixture may vary based on, for example, the intended use and application of the foam product and the desired foam stiffness and density.

[0090] Solvents

[0091] According to an embodiment, at least one aprotic polar solvent is present in the reactive mixture, the solvent having a boiling point at atmospheric pressure above 100°C, preferably above 140°C, more preferably above 170°C, even more preferably above the exothermic heat of reaction in the reactive mixture, and in an amount sufficient to at least partially dissolve / solubilize the monoanhydride. Suitable solvents are dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and triethyl phosphate (TEP). The solvent is used in an amount of 5-40% by weight, preferably 5-30% by weight, more preferably 7-20% by weight, even more preferably 7-15% by weight, based on the total weight of the reactive mixture.

[0092] During the post-curing step of the polyurea pre-foam, the solvent used will be removed together with other unreacted volatile materials.

[0093] Polyisocyanate composition

[0094] According to an embodiment, the polyisocyanate composition is used in an amount of 20-90 wt %, preferably 30-80 wt %, more preferably 40-70 wt %, even more preferably 45-65 wt %, based on the total weight of the reactive mixture.

[0095] According to an embodiment, the polyisocyanate compound in the reactive mixture is selected from isocyanate compounds with a functionality > 2, such as polymeric MDI or modified MDI compounds, such as uretonimine, biuret, allophanate, isocyanate trimer (polyisocyanurate). Commercial examples of isocyanate compounds with a functionality > 2 are available from Huntsman 5025, 2020 and 2185.

[0096] According to embodiments, high functionality polyisocyanate compounds such as polymeric MDI are preferred for improving foam stability during foaming.

[0097] According to an embodiment, the polyisocyanate composition may further comprise a polyisocyanate compound selected from the group consisting of difunctional isocyanates (diisocyanates), preferably selected from aliphatic diisocyanates selected from hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate and cyclohexane diisocyanate and / or aromatic diisocyanates, the aliphatic diisocyanate selected from the group consisting of toluene diisocyanate (TDI), naphthalene diisocyanate, tetramethylxylene diisocyanate, phenylene diisocyanate, toluidine diisocyanate and in particular diphenylmethane diisocyanate (MDI).

[0098] According to an embodiment, the polyisocyanate compound in the polyisocyanate composition can also be an isocyanate-terminated prepolymer, which is prepared by the reaction of an excess of polyisocyanate with a suitable polyol to obtain a prepolymer with the NCO value shown. Methods for preparing prepolymers have been described in the art. The relative amounts of polyisocyanate and polyol depend on their equivalent weights and the required NCO value, and can be easily determined by those skilled in the art. The NCO value of the isocyanate-terminated prepolymer is preferably higher than 5% by weight, more preferably higher than 10% by weight, and most preferably higher than 15% by weight.

[0099] Isocyanate-reactive compounds containing OH groups

[0100] According to an embodiment, the reactive mixture may further comprise (optionally) an isocyanate reactive compound (polyol) having a hydroxyl functionality of 1 to 8, the polyol being selected from polyether polyols, polyester polyols and / or polyether-polyester polyols. Preferably, the polyol is a high molecular weight polyol having a molecular weight of 500 to 20000 g / mol, more preferably 500 g / mol to 10000 g / mol, more preferably 500 g / mol to 5000 g / mol, most preferably 650 g / mol to 4000 g / mol. Suitable high molecular weight polyols have a molecular weight of 650 g / mol, 1000 g / mol and 2000 g / mol. Suitable high molecular weight polyols include hydroxyl terminated reaction products of dihydroxy alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 2-methyl-1,3-propanediol, 1,6-hexanediol or cyclohexanedimethanol or mixtures of these dihydroxy alcohols with dicarboxylic acids or their ester-forming derivatives such as succinic acid, glutaric acid and adipic acid or their dimethyl esters, sebacic acid, phthalic anhydride, tetrachlorophthalic anhydride or dimethyl terephthalate or mixtures thereof. Polycaprolactones and unsaturated polyester polyols are also contemplated. Polyesteramides can be obtained by introducing amino alcohols such as ethanolamine into the polyesterification mixture.

[0101] According to an embodiment, the reactive mixture may further comprise (optionally) a low molecular weight polyol having a hydroxyl functionality of 1-8, a molecular weight of <500 g / mol, preferably a molecular weight of 45 to 500 g / mol, more preferably 50 to 250 g / mol. Suitable examples include diols such as aliphatic diols, such as ethylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,2-propylene glycol, 1,3-butanediol, 2,3-butanediol, 1,3-pentanediol, 2-ethyl-butanediol, 1 , 2-hexanediol, 1,2-octanediol, 1,2-decanediol, 3-methylpentane-1,5-diol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 2,5-dimethyl-2,5-hexanediol, 3-chloro-propylene glycol, 1,4-cyclohexanediol, 2-ethyl-2-butyl-1,3-propanediol, diethylene glycol, dipropylene glycol and tripropylene glycol as well as 1,4'-butanediol and cyclohexanedimethanol. Other suitable examples include amino alcohols such as ethanolamine, triethanolamine, diethanolamine, N-methyldiethanolamine, etc. Glycerol is an example of a suitable triol.

[0102] Since the amount of temperature sensitive chemicals in the reactive mixture should be minimized to achieve the best possible foam temperature resistance, the amount of polyols is preferably avoided or minimized to a concentration of less than 20 wt %, preferably less than 10 wt %, more preferably less than 5 wt %, based on the total weight of the reactive mixture.

[0103] additive

[0104] According to an embodiment, conventional ingredients (additives and / or adjuvants) may be used to make the foam comprising polyimide according to the present invention. These ingredients include surfactants, flame retardants, fillers, pigments, stabilizers, etc. Suitable surfactants may be selected from silicon surfactants, such as commercially available DC 193, B8494, B8466 and B8416.

[0105] According to an embodiment, a free radical initiator may be added to the reactive mixture to accelerate the (free radical) polymerization of the monoanhydride compound during foam formation and / or during post-cure. Examples include dicumyl peroxide, AIBN or dibenzoyl peroxide.

[0106] According to an embodiment, the reactive mixture may further comprise solid polymer particles, such as styrene-based polymer particles. Examples of styrene polymer particles include so-called styrene-acrylonitrile "SAN" particles. Examples of commercially available polymer polyols are Polyol 1639, which is a polyether polyol modified with a styrene-acrylonitrile polymer (SAN) having a solids content of about 41 wt % (also referred to as a polymer polyol).

[0107] According to an embodiment, the reactive mixture may contain fillers such as wood chips, wood powder, wood chips, wood boards; shredded or layered paper and cardboard; sand, vermiculite, clay, cement and other silicates; ground rubber, ground thermoplastics, ground thermosets; honeycombs of any material such as cardboard, aluminum, wood and plastic; metal particles and plates; cork in granular form or in layers; natural fibers such as flax, hemp and sisal fibers; synthetic fibers such as polyamide, polyolefin, polyaramid, polyester and carbon fibers; mineral fibers such as glass fibers and rock wool fibers; mineral fillers such as BaSO4 and CaCO3; nanoparticles such as clay, inorganic oxides and carbon; glass beads, ground glass, hollow glass beads; expanded or expandable beads; untreated or treated waste such as ground, shredded, crushed or milled waste, and in particular fly ash; woven and non-woven fabrics; and combinations of two or more of these materials.

[0108] All reactants may be reacted at once, or may be reacted in a sequential manner by premixing all or part of the ingredients. The various ingredients used to make the foam according to the invention may be added in virtually any order. The process may be selected from a bulk process, a batch process including a casting process, or a continuous process.

[0109] According to an embodiment, the low-density polyimide-containing foam according to the present invention is a low-density foam having a predominantly open-cell structure, having an open-cell content of at least 50% by volume, preferably at least 80% by volume, more preferably at least 90% by volume, even more preferably at least 95% by volume, most preferably at least 98% by volume, based on the total volume of the foam and measured according to ASTM D6226-10.

[0110] The flexible and semi-rigid foams comprising polyimide according to the present invention have high temperature resistance, which means that these foams can be used in applications under oxidative or non-oxidative conditions, wherein they do not suffer significant degradation over time of the properties of interest for the relevant applications (e.g. mechanical properties, structural integrity, acoustic properties, etc.) when exposed to temperatures above 150°C, preferably above 175°C, more preferably above 200°C.

[0111] The flexible and semi-rigid foams according to the invention comprising polyimides have high temperature resistance and are therefore ideally suitable for use as lightweight sound insulation or as sound absorbing material in demanding automotive / transportation and aircraft / aerospace applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Figure 1 is a TGA graph under air showing the temperature resistance of both a comparative foam according to the prior art and a foam according to the invention.

[0113] Figure 2 is a TGA graph under nitrogen showing the temperature resistance of both a comparative foam according to the prior art and a foam according to the invention.

[0114] Example

[0115] Chemicals used:

[0116] Maleic anhydride: monoanhydride, from Huntsman

[0117] Diethyltoluenediamine (DETDA): aromatic diamine, from Lonza (NH2 value: 630 mg KOH / g)

[0118] · F435: Polyether polyol from Huntsman (OH value: 35 mg KOH / g)

[0119] PPG425: Polyether polyol from Covestro (OH value: 264 mg KOH / g)

[0120] · F526: Polyether polyol from Huntsman (OH value: 140 mg KOH / g)

[0121] · 200: Polyether polyol, from Sasol (OH value: 561 mg KOH / g)

[0122] DMSO: dimethyl sulfoxide. Solvent / diluent, from Acros Organics

[0123] · B8017: Silicon surfactant from Evonik (OH value: 67 mg KOH / g)

[0124] · DC193: Silicone surfactant from Evonik (OH value: 75 mg KOH / g)

[0125] · 29: Tin octanoate catalyst, from Evonik

[0126] Black 99430: Dispersion of carbon black in polyether polyol, from Repi (OH value: 21 mgKOH / g)

[0127] · 71B: Phosphate-based flame retardant from ICL Industrial Products

[0128] · 5057: Antioxidant, from BASF

[0129] · 1135: Antioxidant, from BASF

[0130] · 501: Cell opener, from PU Performance Additives (OH value: 2 mg KOH / g)

[0131] Water: Foaming agent (OH value: 6230mg KOH / g)

[0132] · 6057: Polymeric MDI from Huntsman (NCO value: 31.40%)

[0133] · 2085: Polymeric MDI from Huntsman (NCO value: 30.50%)

[0134] Test Method

[0135] Density: The density of the foam is measured on the sample (4×4×2.5cm 3 ) is measured by dividing the mass by the volume and is expressed in kg / m 3 Representation, as described in the ISO 845 standard.

[0136] • Thermogravimetric analysis (TGA): Thermograms were recorded on a TA Instruments Q5000 analyzer with a heating ramp of 20°C / min applied under air or nitrogen environment.

[0137] Example

[0138] Example 1: According to the invention: Polyimide foam based on maleic anhydride, containing a diamine (DETDA) in the reactive mixture

[0139] Example 1 foams (Table 1) were produced by mixing the isocyanate with the remaining ingredients of the formulation (maleic anhydride and DETDA were pre-dissolved in DMSO solvent, respectively) in a 400 mL cup under high shear for 7 seconds using a Heidolph mixer (about 3000 rpm) under free rise conditions. The polyurea pre-foam was stored in a fume hood overnight, post-cured in an oven at 200°C for 2 hours (to drive imide formation and remove residual traces of solvent and any unreacted volatiles) to obtain the final open-cell flexible polyimide-containing foam, and then cut for subsequent characterization.

[0140] Table 1. Example 1 Formulation

[0141] Chemicals Example 1 (pbw) Maleic anhydride 5.7 DETDA 1.16 DMSO 2.5 water 0.57 Dabco DC 193 0.2 Suprasec 2085 13 <![CDATA[Density (kg / m 3 )]]> 9

[0142] Comparative Example 1: Conventional polyurethane soft foam

[0143] Comparative Example 1 Flexible foam (Table 2) was produced by mixing the isocyanate with the polyol blend (previously prepared) under high shear with a Heidolph mixer (about 2000 rpm) for 10 seconds under free rise conditions, followed by mixing with the catalyst blend (previously prepared) for 10 seconds, and then pouring the resulting reactive foaming mixture into a 20×20×20 cm 3 The foams were stored in a fume hood overnight and then cut and characterized.

[0144] Table 2. Comparative Example 1 Polyurethane Foam Formulation

[0145]

[0146] Comparative Example 2: Polyimide foam based on maleic anhydride without any polyamine in the formulation.

[0147] Example 1 was repeated but without DETDA in the reactive mixture. The resulting foam was of very poor quality, partially collapsed, full of internal defects and with a rather coarse cell structure. No further analysis / characterization was performed.

[0148] Through the air ( Figure 1 ) and nitrogen ( Figure 2 ) under both conditions (Table 3), it was demonstrated that the polyimide-containing foam of Example 1 had excellent temperature resistance compared with the polyurethane foam of Comparative Example 1.

[0149] Table 3. TGA results

[0150]

Claims

1. A reactive mixture for making a low-density isocyanate-based flexible or semi-rigid polyimide-containing foam having an open cell content of at least 50% by volume measured according to ASTM D6226-10 and having a relative humidity of less than 100 kg / m2 measured according to ISO 845 3 The apparent density of the reactive mixture comprises the following components: a) a polyisocyanate composition comprising at least one polyisocyanate compound, and b) at least one monoanhydride compound, and c) at least one aprotic polar solvent having a boiling point above 100° C. at normal pressure, and d) at least one polyamine compound, wherein the polyamine compound is selected from polyamine compounds having an amine functionality greater than or equal to 1 and is selected from primary amines or secondary amines, and e) a blowing agent composition comprising at least 50 mol % of water, based on the total molar amount of all blowing agents in the blowing agent composition, and optionally a physical blowing agent and / or a non-reactive chemical blowing agent having no isocyanate-reactive groups, and f) an optional catalyst composition comprising at least one catalyst compound selected from the group consisting of a carbamate-forming catalyst compound, a urea-forming catalyst compound, an imide-forming catalyst compound, an amide-forming catalyst compound, a carbodiimide-forming catalyst compound and / or a trimerization catalyst compound, and g) Optional other additives, such as surfactants, flame retardants, fillers, pigments and / or stabilizers.

2. The reactive mixture according to claim 1, wherein the monoanhydride compound is selected from maleic anhydride (I), phthalic anhydride (II), succinic anhydride (III), trimellitic anhydride (IV) and / or itaconic anhydride (V):

3. The reactive mixture according to claim 1 or 2, wherein the amount of the monoanhydride compound contained is 10-60 wt%, preferably 15-50 wt%, more preferably 20-40 wt%, even more preferably 20-30 wt%, based on the total weight of the reactive mixture.

4. A reactive mixture according to any one of the preceding claims, wherein the total amount of catalyst compound in the reactive composition is 0.5 to 3 wt%, preferably 1 to 2.5 wt%, based on the total weight of the reactive mixture.

5. The reactive mixture according to any one of the preceding claims, wherein the amount of water is from greater than 0 wt.% to 5 wt.%, preferably 0.5-4 wt.%, more preferably 1-3.5 wt.% and even more preferably 1.5-3 wt.% water, based on the total weight of the reactive mixture.

6. The reactive mixture according to any one of the preceding claims, wherein the reactive mixture further comprises at least one polyol selected from polyether polyols, polyester polyols and / or polyether-polyester polyols, the polyol having a molecular weight of 500-20000 g / mol, more preferably 500 g / mol to 10000 g / mol, more preferably 500 g / mol to 5000 g / mol, most preferably 650 g / mol to 4000 g / mol.

7. A process for producing an isocyanate-based flexible or semi-rigid polyimide-containing foam having an open-cell structure, the foam having an open-cell content of at least 50% by volume, preferably at least 80% by volume, more preferably at least 90% by volume, even more preferably at least 95% by volume, most preferably at least 98% by volume, based on the total volume of the foam and measured according to ASTM D6226-10, and having a relative humidity of less than 100 kg / m2, measured according to ISO 845. 3 The apparent density of i. forming a reactive mixture according to any one of claims 1 to 6 by combining a polyisocyanate composition, at least one monoanhydride compound, at least one aprotic polar solvent, at least one polyamine compound, a blowing agent composition, and optionally a catalyst composition and / or other additives: ii. allowing the reactive mixture to foam and form a foam comprising polyurea ("polyurea pre-foam"), and iii. post-curing the polyurea pre-foam to obtain the final polyimide-containing foam.

8. The method according to claim 7, wherein a premixing step is performed prior to forming step i., wherein the at least one monoanhydride compound, the at least one polyamine compound, the aprotic polar solvent, the blowing agent composition and optionally the catalyst compound and / or other additives are first mixed and then combined with the polyisocyanate composition to form the reactive mixture.

9. The method according to any one of claims 7-8, wherein the post-curing step is performed by applying heat in the range of 150-300°C for several hours, applying microwave radiation or applying IR radiation.

10. The method according to any one of the preceding claims, wherein the density of the foam comprising polyimide is 4 to 40 kg / m 3 , more preferably 4-15kg / m 3 , even more preferably 4-10 kg / m 3 .

11. The method according to any one of the preceding claims, wherein the open cell content of the polyimide-containing foam is preferably at least 80 volume %, more preferably at least 90 volume %, even more preferably at least 95 volume %, most preferably at least 98 volume %, based on the total volume of the foam and measured according to ASTM D6226-10.

12. An isocyanate-based flexible or semi-rigid polyimide-containing foam obtained by the process according to any one of the preceding claims 7 to 11, the foam having: Less than 100 kg / m2 measured according to ISO 845 3 , preferably 4-40kg / m 3 , more preferably 4-15kg / m 3 , even more preferably 4-10 kg / m 3 The apparent density of - An open cell content of at least 50 vol%, preferably at least 80 vol%, more preferably at least 90 vol%, even more preferably at least 95 vol%, most preferably at least 98 vol%, based on the total volume of the foam and measured according to ASTM D6226-10.

13. Use of the foam according to claim 12 for sound insulation or sound absorption in automotive / transportation and / or aircraft / aerospace applications.

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