NONWOVEN FABRIC AND ASSOCIATED COMPOSITE AND METHODS OF MAKING

A nonwoven fabric useful for forming composite panels includes specific amounts of reinforcing fibers, a polyimide, and a block polyestercarbonate-polysiloxane. The nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter3, an areal density of 100 to 400 gram/meter2, and a tensile modulus of 50 to 1000 megapascals. Also described are a method of forming the nonwoven fabric, a composite formed from the nonwoven fabric, and a method of forming the composite.

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Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and U.S. Patent Application No. 62/671,429 filed 15 May 2018, and European Patent Application No. 18197230.8 filed 27 Sep. 2018, both of which are incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

Fiber-reinforced thermoplastics are increasingly used in the fabrication of interior parts for vehicles including aircraft, ships, and trains. For example, U.S. Patent Application Publication No. US 2012/0065283 A1 of Adjei et al. describes a nonwoven fabric prepared from reinforcing fibers, polyimide fibers, and polymeric binder fibers. Multiple layers of the nonwoven fabric are combined under elevated temperature and pressure to form a composite sheet that is optionally combined with a decorative film to form the vehicular interior part. Such parts exhibit advantageous properties including low weight, high flame retardancy, and low smoke generation. However, there is a desire for nonwoven fabrics that facilitate handling, as well as composite sheets that exhibit improved surface uniformity.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

One embodiment is a nonwoven fabric, comprising, based on the weight of the nonwoven fabric: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of a polyimide, and 5 to 20 weight percent of a block polyestercarbonate-polysiloxane; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of IV groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; wherein the nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter3, and an areal density of 100 to 400 gram/meter2; and wherein the nonwoven fabric has a tensile modulus of 50 to 1000 megapascals, determined according to ASTM D638-14 at a temperature of 23° C. and using a test speed of 50 millimeters/minute.

Another embodiment is a method of forming a nonwoven fabric, the method comprising: forming an aqueous suspension layer comprising water, 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of polyimide fibers, and 5 to 20 weight percent of binder fibers comprising a block polyestercarbonate-polysiloxane, wherein weight percent values are based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers; at least partially removing water from the aqueous suspension layer to form a fiber layer; and exposing the fiber layer to a temperature of 250 to 320° C., thereby melting the binder fibers, at least partially melting the polyimide fibers, and forming a nonwoven fabric; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units.

Another embodiment is a composite, comprising, based on the weight of the composite: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of a polyimide, and 5 to 20 weight percent of a block polyestercarbonate-polysiloxane; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; and wherein the composite has a density of 0.92 to 1.38 gram/centimeter3, and an areal density of 100 to 3000 gram/meter2.

Another embodiment is a method of forming a multilayer composite, the method comprising: exposing at least two layers of the nonwoven fabric in any of its variations to a temperature of 250 to 400° C. and a pressure of 300 to 1,500 kilopascals for a time of 60 to 600 seconds to yield a multilayer composite.

These and other embodiments are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a melt spinning apparatus.

FIG. 2 is a schematic illustration of a papermaking apparatus.

FIG. 3A is an image of a roll of 325 gram/meter2 non-consolidated nonwoven fabric; FIG. 3B is an image of a roll of 165 gram/meter2 pre-consolidated nonwoven fabric.

FIG. 4A is an optical micrograph of a cross-section of 325 gram/meter2 non-consolidated nonwoven fabric; FIG. 4B is an optical micrograph of a cross-section of 165 gram/meter2 pre-consolidated nonwoven fabric.

FIG. 5A is a surface profile derived from an optical micrograph of 325 gram/meter2 non-consolidated nonwoven fabric; FIG. 5B is a surface profile derived from an optical micrograph of 165 gram/meter2 pre-consolidated nonwoven fabric.

 DETAILED DESCRIPTION OF THE INVENTION

The present inventors have determined that nonwoven fabrics can be formulated to exhibit increased stiffness that facilitates handling of the fabrics as they are used to prepare composites. The formulation of the present nonwoven fabric also leads to better retention of reinforcing fibers during handling of the nonwoven fabric. And use of the present nonwoven fabric also improves the surface uniformity of composites prepared from it.

Thus, one embodiment is a nonwoven fabric, comprising, based on the weight of the nonwoven fabric: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of a polyimide, and 5 to 20 weight percent of a block polyestercarbonate-polysiloxane; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; wherein the nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter3, and an areal density of 100 to 400 gram/meter2; and wherein the nonwoven fabric has a tensile modulus of 50 to 1000 megapascals, determined according to ASTM D638-14 at a temperature of 23° C. and using a test speed of 50 millimeters/minute.

The nonwoven fabric includes reinforcing fibers. Reinforcing fibers include metal fibers, metallized inorganic fibers, metallized synthetic fibers, glass fibers, graphite fibers, carbon fibers, ceramic fibers, mineral fibers, basalt fibers, polymer fibers having a melting or glass transition temperature at least 150° C. higher than the glass transition temperature of polyimide, and combinations thereof. In some embodiments, the reinforcing fibers comprise glass fibers. As used herein, the term “fibers” refers specifically to fibers having a diameter of 5 to 125 micrometers, and a length of 5 to 75 millimeters. Within the range of 5 to 125 micrometers, the diameter can be 10 to 100 micrometers, or 10 to 50 micrometers, or 10 to 25 micrometers. Within the range of 5 to 75 millimeters, the fiber length can be 6 to 50 millimeters, or 7 to 40 millimeters, or 10 to 30 millimeters.

The nonwoven fabric includes the reinforcing fibers in an amount of 25 to 55 weight percent, based on the weight of the nonwoven fabric. Within this range, the amount of reinforcing fibers can be 30 to 50 weight percent.

In addition to the reinforcing fibers, the nonwoven fabric comprises a polyimide. A polyimide is a polymer comprising a plurality of repeating units having the structure

wherein U is independently at each occurrence a tetravalent linker selected from the group consisting of substituted or unsubstituted, saturated, unsaturated, or aromatic monocyclic and polycyclic groups having 5 to 50 carbon atoms, substituted or unsubstituted alkyl groups having 1 to 30 carbon atoms, and substituted or unsubstituted alkenyl groups having 2 to 30 carbon atoms; and R2 is independently at each occurrence a divalent group selected from the group consisting of substituted or unsubstituted divalent aromatic hydrocarbon moieties having 6 to 20 carbons, straight or branched chain alkylene moieties having 2 to 20 carbons, cycloalkylene moieties having 3 to 20 carbon atom, and divalent moieties of the general formula

wherein Q is selected from the group consisting of —O—, —S—, —C(O)—, —S(O)2—, —S(O)—, and —CyH2y— where y is 1 to 20. The number of repeating units in the polyimide can be, for example, 10 to 1,000, specifically 10 to 500.

Exemplary tetravalent linkers, U, include tetravalent aromatic radicals of the formula

wherein W is a divalent moiety such as —O—, —S—, —C(O)—, —SO2—, —SO—, —CyH2y— (y being an integer of 1 to 20), and halogenated derivatives thereof, including perfluoroalkylene groups, or a group of the Formula —O—Z—O— wherein the divalent bonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions, and wherein Z includes divalent moieties of the formula

wherein Q is divalent moiety that can be —O—, —S—, —C(O)—, —SO2—, —SO—, —CyH2y— wherein y is 1 to 8, or —CpHqFr— where p is from 1 to 8 and q is 0 to 15 and r is 1 to 16 and q+r=2p. In some embodiments the tetravalent linker U is free of halogens.

In some embodiments, the polyimide comprises a polyetherimide. Polyetherimides comprise repeating units of formula

wherein T is —O— or a group of the Formula —O—Z—O— wherein the divalent bonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions of the phthalimide groups, and wherein Z and R2 are defined as described above. In some embodiments, each occurrence of R2 is independently p-phenylene or m-phenylene, and T is a divalent moiety of the formula

Included among the many methods of making polyimides, including polyetherimides, are those disclosed in U.S. Pat. No. 3,847,867 to Heath et al., U.S. Pat. No. 3,850,885 to Takekoshi et al., U.S. Pat. Nos. 3,852,242 and 3,855,178 to White, U.S. Pat. No. 3,983,093 to Williams et al., and U.S. Pat. No. 4,443,591 to Schmidt et al.

In some embodiments, the polyimide comprises a polyetherimide comprising 10 to 1000 repeating units having the structure

wherein T is —O— or a group of the formula —O—Z—O— wherein the divalent bonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions, and wherein Z is selected from the group consisting of

wherein Q is divalent moiety selected from the group consisting of —O—, —S—, —C(O)—, —SO2—, —SO—, —CyH2y— where y is 1 to 8, and —CpHqEr- where p is from 1 to 8, q is 0 to 15, r is 1 to 16, and q+r=2p; and R2 is defined as described above.

In some embodiments, R2 is independently at each occurrence meta-phenylene or para-phenylene, and U has the structure

The repeating units of the polyimide are formed by the reaction of a dianhydride and a diamine. Dianhydrides useful for forming the repeating units include those having the formula

wherein U is as defined above. As mentioned above the term dianhydrides includes chemical equivalents of dianhydrides. In some embodiments, the dianhydride comprises an aromatic bis(ether anhydride). Examples of specific aromatic bis(ether anhydride)s are disclosed, for example, in U.S. Pat. No. 3,972,902 to Heath et al. and U.S. Pat. No. 4,455,410 to Giles. Illustrative examples of aromatic bis(ether anhydride)s include 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride, 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride, 4,4′-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4′-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride, 4,4′-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride, 4,4′-bis(2,3-dicarboxyphenoxy)diphenyl sulfone dianhydride, 4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl-2,2-propane dianhydride, 4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride, 4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride, and mixtures thereof.

Diamines useful for forming the repeating units of the polyimide include those having the formula


H2N—R2—NH2

wherein R2 is as defined above. Examples of specific organic diamines are disclosed, for example, in U.S. Pat. No. 3,972,902 to Heath et al. and U.S. Pat. No. 4,455,410 to Giles. Exemplary diamines include ethylenediamine, propylenediamine, trimethylenediamine, diethylenetriamine, triethylenetertramine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 1,12-dodecanediamine, 1,18-octadecanediamine, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 4-methylnonamethylenediamine, 5-methylnonamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 2,2-dimethylpropylenediamine, N-methyl-bis (3-aminopropyl) amine, 3-methoxyhexamethylenediamine, 1,2-bis(3-aminopropoxy) ethane, bis(3-aminopropyl) sulfide, 1,4-cyclohexanediamine, bis-(4-aminocyclohexyl) methane, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, m-xylylenediamine, p-xylylenediamine, 2-methyl-4,6-diethyl-1,3-phenylenediamine, 5-methyl-4,6-diethyl-1,3-phenylenediamine, benzidine, 3,3′-dimethylbenzidine, 3,3′-dimethoxybenzidine, 1,5-diaminonaphthalene, bis(4-aminophenyl) methane, bis(2-chloro-4-amino-3, 5-diethylphenyl) methane, bis(4-aminophenyl) propane, 2,4-bis(p-amino-t-butyl) toluene, bis(p-amino-t-butylphenyl) ether, bis(p-methyl-o-aminophenyl) benzene, bis(p-methyl-o-aminopentyl) benzene, 1, 3-diamino-4-isopropylbenzene, bis(4-aminophenyl) sulfide, bis (4-aminophenyl) sulfone, bis(4-aminophenyl) ether, 1,3-bis(3-aminopropyl) tetramethyldisiloxane, and mixtures thereof. In some embodiments, the diamine is an aromatic diamine, more specifically, m-phenylenediamine, p-phenylenediamine, sulfonyl dianiline, or a mixture thereof.

In general, polyimide-forming reactions can be carried out employing various solvents, e.g., o-dichlorobenzene, m-cresol/toluene, and the like, to effect a reaction between the dianhydride and the diamine, at temperatures of 100° C. to 250° C. Alternatively, the polyimide block can be prepared by melt polymerization or interfacial polymerization, e.g., melt polymerization of an aromatic bis(anhydride) and a diamine by heating a mixture of the starting materials to elevated temperatures with concurrent stirring. Generally, melt polymerizations employ temperatures of 200° C. to 400° C.

A chain-terminating agent can be employed to control the molecular weight of the polyimide. Monofunctional amines such as aniline, or monofunctional anhydrides such as phthalic anhydride can be employed.

In some embodiments, the polyimide has a melt index of 0.1 to 10 grams per minute, determined according to ASTM D 1238-04 at 350° C., using a 6.6 kilogram (kg) load. In some embodiments, the polyetherimide resin has a weight average molecular weight of 10,000 to 150,000 grams per mole, as determined by gel permeation chromatography using polystyrene standards. In some embodiments, the polyetherimide has a weight average molecular weight of 20,000 to 60,000. In some embodiments, the polyimide has an intrinsic viscosity greater than or equal to 0.2 deciliter per gram, specifically 0.35 to 0.7 deciliter per gram, measured by Ubbelohde viscometer in m-cresol at 25° C.

The nonwoven fabric includes the polyimide in an amount of 35 to 65 weight percent, based on the weight of the nonwoven fabric. Within this range, the amount of polyimide can be 40 to 60 weight percent.

In addition to the reinforcing fibers and the polyimide, the nonwoven fabric comprises a block polyestercarbonate-polysiloxane. A block polyestercarbonate-polysiloxane is a copolymer comprising at least one polyester block, at least one polycarbonate block, and at least one polysiloxane block. Specifically, the at least one polyester block comprises resorcinol ester units, each resorcinol ester unit having the structure

the at least one polycarbonate block comprises carbonate units, each carbonate unit having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and the at least one polysiloxane block comprises dimethylsiloxane units.

In some embodiments, the aromatic divalent groups are C6-C24 aromatic divalent groups. When not all R1 groups are aromatic, the remainder are C2-C24 aliphatic divalent groups. In some embodiments, each R1 is a radical of the formula

wherein each of A1 and A2 is independently a monocyclic divalent aryl radical, and Y1 is a bridging radical having one or two atoms that separate A1 from A2. Examples of A1 and A2 include 1,3-phenylene and 1,4-phenylene, each optionally substituted with one, two, or three C1-C6 alkyl groups. The bridging radical Y1 can be a C1-C12 (divalent) hydrocarbylene group. As used herein, the term “hydrocarbyl”, whether used by itself, or as a prefix, suffix, or fragment of another term, refers to a residue that contains only carbon and hydrogen unless it is specifically identified as “substituted hydrocarbyl”. The hydrocarbyl residue can be aliphatic or aromatic, straight-chain, cyclic, branched, saturated, or unsaturated. It can also contain combinations of aliphatic, aromatic, straight chain, cyclic, bicyclic, branched, saturated, and unsaturated hydrocarbon moieties. When the hydrocarbyl residue is described as substituted, it can contain heteroatoms in addition to carbon and hydrogen. In some embodiments, one atom separates A1 from A2. Illustrative examples of Y1 radicals are —O—, —S—, —S(O)—, —S(O)2—, —C(O)—, methylene (—CH2—; also known as methylidene), ethylidene (—CH(CH3)—), isopropylidene (—C(CH3)2—), neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene, adamantylidene, cyclohexylidene methylene, cyclohexylmethylene, and 2-[2.2.1]-bicycloheptylidene.

In some embodiments, the resorcinol ester units comprise resorcinol isophthalate/terephthalate units, and the carbonate units comprise resorcinol carbonate units and bisphenol A carbonate units.

The block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of the resorcinol ester units, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene (i.e., the carbonate units are resorcinol carbonate units), and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, which has the chemical structure

(i.e., the carbonate units are bisphenol A carbonate units). Within the range of 30 to 90 mole percent, the amount of resorcinol ester units can be 50 to 90 mole percent, or 70 to 90 mole percent. Within the range of 5 to 35 mole percent, the amount of resorcinol carbonate units can be 5 to 25 mole percent, or 5 to 15 mole percent. Within the range of 5 to 35 mole percent, the amount of bisphenol A carbonate units can be 5 to 25 mole percent, or 5 to 15 mole percent. The block polyestercarbonate-polysiloxane further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units. Within this range, the amount of dimethylsiloxane units can be 0.4 to 2 weight percent, or 0.5 to 2 weight percent.

In a very specific embodiment, the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of resorcinol isophthalate/terephthalate units, 5 to 15 mole percent of resorcinol carbonate units, and 5 to 15 mole percent of bisphenol A carbonate units, and further comprises dimethylsiloxane units in an amount, based on the total weight of the block polyestercarbonate-polysiloxane, of 0.5 to 2 weight percent.

There is no particular limit on the structure of end groups on the block polyestercarbonate-polysiloxane. An end-capping agent (also referred to as a chain stopping agent or chain terminating agent) can be included during polymerization to provide end groups. Examples of end-capping agents include monocyclic phenols such as phenol, p-cyanophenol, and C1-C22 alkyl-substituted phenols such as p-cumylphenol, resorcinol monobenzoate, and p-tertiary-butyl phenol; monoethers of diphenols, such as p-methoxyphenol; monoesters of diphenols such as resorcinol monobenzoate; functionalized chlorides of aliphatic monocarboxylic acids such as acryloyl chloride and methacryoyl chloride; and mono-chloroformates such as phenyl chloroformate, alkyl-substituted phenyl chloroformates, p-cumyl phenyl chloroformate, and toluene chloroformate. Combinations of different end groups can be used. In some embodiments, the block polyestercarbonate-polysiloxane has a weight average molecular weight of 15,000 to 55,000 grams/mole, as determined by gel permeation chromatography using polycarbonate standards. Within this range, the weight average molecular weight can be 18,000 to 50,000 grams/mole.

Methods for the preparation of block polyestercarbonate-polysiloxanes are known and described, for example, in U.S. Pat. No. 7,790,292 B2 to Colborn et al.

The nonwoven fabric comprises the block polyestercarbonate-polysiloxane in an amount of 5 to 20 weight percent, based on the weight of the nonwoven fabric. Within this range, the amount of block polyestercarbonate-polysiloxane can be 5 to 15 weight percent.

The nonwoven fabric can, optionally, further comprise an organophosphate ester flame retardant. Exemplary organophosphate ester flame retardants include phosphate esters comprising phenyl groups, substituted phenyl groups, or a combination of phenyl groups and substituted phenyl groups, bis-aryl phosphate esters based upon resorcinol such as, for example, resorcinol bis(diphenyl phosphate), as well as those based upon bisphenols such as, for example, bisphenol A bis(diphenyl phosphate). In some embodiments, the organophosphate ester is selected from tris(alkylphenyl) phosphates (for example, CAS Reg. No. 89492-23-9 or CAS Reg. No. 78-33-1), resorcinol bis(diphenyl phosphate) (CAS Reg. No. 57583-54-7), bisphenol A bis(diphenyl phosphate) (CAS Reg. No. 181028-79-5), triphenyl phosphate (CAS Reg. No. 115-86-6), tris(isopropylphenyl) phosphates (for example, CAS Reg. No. 68937-41-7), t-butylphenyl diphenyl phosphates (CAS Reg. No. 56803-37-3), bis(t-butylphenyl) phenyl phosphates (CAS Reg. No. 65652-41-7), tris(t-butylphenyl) phosphates (CAS Reg. No. 78-33-1), and combinations thereof. In some embodiments, the nonwoven fabric excludes flame retardants other than the organophosphate ester. For example, the nonwoven fabric can exclude brominated polycarbonate. In some embodiments, the organophosphate ester is halogen-free. In some embodiments, the organophosphate ester comprises an oligomeric phosphate ester, which can be a halogen-free oligomeric phosphate ester.

When the nonwoven fabric comprises the organophosphate ester flame retardant, it is present in an amount of 0.2 to 2 weight percent, based on the weight of the nonwoven fabric. Within this range, the amount of the organophosphate ester flame retardant can be 0.3 to 1 weight percent, or 0.4 to 0.9 weight percent.

The nonwoven fabric can, optionally, further comprise one or more additives known in the thermoplastics art. Suitable additives include, for example, stabilizers, mold release agents, lubricants, processing aids, drip retardants, nucleating agents, UV blockers, dyes, pigments, antioxidants, anti-static agents, blowing agents, mineral oil, metal deactivators, antiblocking agents, and combinations thereof. When present, such additives are typically used in a total amount of less than or equal to 1 weight percent, based on the weight of the nonwoven fabric. In some embodiments, additives are used in an amount of less than or equal to 0.5 weight percent, or less than or equal to 0.2 weight percent.

In some embodiments of the nonwoven fabric, the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and wherein the nonwoven fabric further comprises 0.2 to 2 weight percent of an organophosphate ester flame retardant.

In a very specific embodiment of the nonwoven fabric, it comprises, based on the weight of the nonwoven fabric, 30 to 50 weight percent of the reinforcing fibers, 40 to 60 weight percent of the polyimide, and 5 to 15 weight percent of the block polyestercarbonate-polysiloxane, and further comprises, based on the weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant; the reinforcing fibers comprise glass fibers; the polyimide comprises a polyetherimide; the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and the flame retardant comprises an oligomeric phosphate ester.

The nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter3. Density can be determined at 23° C. according to ASTM D792-13. Within the range of 0.03 to 0.2 gram/centimeter3, the density can be 0.033 to 0.17 gram/centimeter3.

The nonwoven fabric has an areal density of 100 to 400 gram/meter2. Areal density can be determined at 23° C. by weighing a 1.000 meter2 section of fabric. Within the range of 100 to 400 gram/meter2, the areal density can be 100 to 300 gram/meter2.

The nonwoven fabric has a tensile modulus of 50 to 1000 megapascals, determined according to ASTM D638-14 at a temperature of 23° C. and using a test speed of 50 millimeters/minute. Within the range of 50 to 1000 megapascals, the tensile modulus can be 150 to 600 megapascals.

One embodiment is a method of forming a nonwoven fabric, the method comprising: forming an aqueous suspension layer comprising water, 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of polyimide fibers, and 5 to 20 weight percent of binder fibers comprising a block polyestercarbonate-polysiloxane, wherein weight percent values are based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers; at least partially removing water from the aqueous suspension layer to form a fiber layer; and exposing the fiber layer to a temperature of 250 to 320° C., thereby melting the binder fibers, at least partially melting the polyimide fibers, and forming a nonwoven fabric; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units.

The method comprises forming an aqueous suspension layer comprising water, reinforcing fibers, polyimide fibers, and binder fibers. The aqueous suspension layer can be formed by depositing an aqueous suspension of fibers onto a screen that retains the fibers.

The aqueous suspension layer comprises water, which is the residual water after at least partially draining the liquid portion of the aqueous suspension through the screen. The water content of the aqueous suspension layer is typically 1 to 25 weight percent, based on the weight of the aqueous suspension layer, and depending on the degree of drainage.

The aqueous suspension layer further comprises reinforcing fibers. The reinforcing fibers are the same as those described above in the context of the nonwoven fabric. The aqueous suspension layer comprises the reinforcing fibers in an amount of 25 to 55 weight percent, based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers. Within this range, the amount of reinforcing fibers can be 30 to 50 weight percent.

The aqueous suspension layer further comprises polyimide fibers. The term “polyimide fibers” refers to fibers containing 95 to 100 weight percent polyimide, based on the weight of the polyimide fibers. When the polyimide content is less than 100 weight percent, the balance is typically an additive that facilitates production or handling of the polyimide fibers, such as, for example, a spin finish on the surface of the polyimide fibers. The polyimide of the polyimide fibers is the same as the polyimide described above in the context of the nonwoven article. Methods of forming polyimide fibers are described, for example, in U.S. Pat. No. 4,994,544 to Nagahiro et al., and U.S. Pat. No. 5,716,567 to Musina et al. Polyimide fibers are also commercially available as, for example, KURAKISSS™ polyimide fibers from Kuraray.

The aqueous suspension layer comprises the polyimide fibers in an amount of 35 to 65 weight percent, based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers. Within this range, the polyimide fiber amount can be 40 to 60 weight percent.

The aqueous suspension layer further comprises binder fibers comprising a block polyestercarbonate-polysiloxane. The block polyestercarbonate-polysiloxane is the same as that described in the context of the nonwoven fabric. In some embodiments, the binder fibers comprise 90 to 100 weight percent of the block polyestercarbonate-polysiloxane, based on the weight of the binder fibers.

In a very specific embodiment, the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; the binder fibers further comprise an oligomeric aromatic phosphate ester; and the binder fibers comprise, based on the weight of the binder fibers, 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10 weight percent of the oligomeric aromatic phosphate ester.

The aqueous suspension layer comprises the binder fibers in an amount of 5 to 20 weight percent, based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers. Within this range, the binder fiber amount can be 5 to 15 weight percent.

After the aqueous suspension layer is formed, the method comprises at least partially removing water from the aqueous suspension layer to form a fiber layer. Water can be removed by methods including gravity drainage through a screen on which the aqueous suspension layer can be formed, and passing the aqueous suspension layer through one or more sets of nip rollers.

After water is at least partially removed from the aqueous suspension layer, the method comprises exposing the fiber layer to a temperature of 250 to 400° C., thereby melting the binder fibers, at least partially melting the polyimide fibers, and forming a nonwoven fabric. The temperature range of 250 to 400° C. is effective to melt the binder fibers and at least partially melt the polyimide fibers. Within this range, the temperature can be 260 to 350° C., or 270-320° C.

In some embodiments, the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals. Within this range, the pressure can be 50 to 200 kilopascals.

In some embodiments, the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent, and the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent.

In a very specific embodiment of the method, the aqueous suspension layer comprises 30 to 50 weight percent of the reinforcing fibers, 40 to 60 weight percent of the polyimide fibers, and 5 to 15 weight percent of the binder fibers; the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent; the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent; the reinforcing fibers comprise glass fibers; the polyimide fibers comprise a polyetherimide; the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; the binder fibers further comprise an oligomeric aromatic phosphate ester; the binder fibers comprise, based on the weight of the binder fibers, 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10 weight percent of the oligomeric aromatic phosphate ester; and the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals.

Another embodiment is a composite, comprising, based on the weight of the composite: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of a polyimide, and 5 to 20 weight percent of a block polyestercarbonate-polysiloxane; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; and wherein the composite has a density of 0.92 to 1.38 gram/centimeter3, and an areal density of 100 to 3000 gram/meter2.

In some embodiments, the composite is prepared from multiple layers of the nonwoven fabric, with or without at least one scrim layer. The optional additional one or more scrim layer can include, for example, a woven glass scrim.

The composite comprises 25 to 55 weight percent of reinforcing fibers, based on the weight of the composite. Within this range, the amount of reinforcing fibers can be 30 to 50 weight percent. The reinforcing fibers are the same as those described in the context of the nonwoven fabric.

The composite further comprises 35 to 65 weight percent of a polyimide, based on the weight of the composite. Within this range, the amount of the polyimide can be 40 to 60 weight percent. The polyimide is the same as that described in the context of the nonwoven fabric.

The composite further comprises 5 to 20 weight percent of a block polyestercarbonate-polysiloxane, based on the weight of the composite. Within this range, the amount of block polyestercarbonate-polysiloxane can be 5 to 15 weight percent. The block polyestercarbonate-polysiloxane is the same as that described in the context of the nonwoven fabric.

In some embodiments of the composite, the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and the composite further comprises 0.2 to 2 weight percent of an oligomeric aromatic phosphate ester flame retardant.

The composite has a density of 0.8 to 1.5 gram/centimeter3. Density can be determined at 23° C. according to ASTM D792-13. Within the range of 0.8 to 1.5 gram/centimeter3, the density can be 0.9 to 1.4 gram/centimeter3, or 0.92 to 1.38 gram/centimeter3.

The composite has an areal density of 100 to 3000 gram/meter2. Areal density can be determined at 23° C. by weighing a 1.000 meter2 section of fabric. Within the range of 100 to 3000 gram/meter2, the areal density can be 200 to 2500 gram/meter2, or 300 to 2200 gram/meter2.

In a very specific embodiment of the composite, the composite comprises, based on the weight of the composite, 30 to 50 weight percent of the reinforcing fibers, and 40 to 60 weight percent of the polyimide, and 5 to 15 weight percent of the block polyestercarbonate-polysiloxane; the nonwoven fabric further comprises, based on the total weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant; wherein the reinforcing fibers comprise glass fibers; wherein the polyimide comprises a polyetherimide; the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and the flame retardant comprises an oligomeric aromatic phosphate ester.

Another embodiment is a method of forming a multilayer composite, the method comprising: exposing at least two layers of the nonwoven fabric in any of its above-described variations to a temperature of 250 to 400° C. and a pressure of 300 to 1,500 kilopascals for a time of 60 to 600 seconds to yield a multilayer composite.

Within the range of 250 to 400° C., the temperature can be 350 to 400° C.

Within the range of 300 to 1,500 kilopascals, the pressure can be 400 to 1,200 kilopascals, or 500 to 1000 kilopascals.

Within the range of 60 to 600 seconds, the time can be 80 to 300 seconds.

The invention includes at least the following embodiments.

Embodiment 1

A nonwoven fabric, comprising, based on the weight of the nonwoven fabric: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of a polyimide, and 5 to 20 weight percent of a block polyestercarbonate-polysiloxane; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; wherein the nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter3, and an areal density of 100 to 400 gram/meter2; and wherein the nonwoven fabric has a tensile modulus of 50 to 1000 megapascals, determined according to ASTM D638-14 at a temperature of 23° C. and using a test speed of 50 millimeters/minute.

Embodiment 2

The nonwoven fabric of embodiment 1, wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and wherein the nonwoven fabric further comprises 0.2 to 2 weight percent of an organophosphate ester flame retardant.

Embodiment 3

The nonwoven fabric of embodiment 2, wherein the organophosphate ester flame retardant comprises an oligomeric phosphate ester.

Embodiment 4

The nonwoven fabric of any one of embodiments 1-3, wherein the reinforcing fibers comprise glass fibers.

Embodiment 5

The nonwoven fabric of embodiment 1, wherein the nonwoven fabric comprises, based on the weight of the nonwoven fabric, 30 to 50 weight percent of the reinforcing fibers, 40 to 60 weight percent of the polyimide, and 5 to 15 weight percent of the block polyestercarbonate-polysiloxane; wherein the nonwoven fabric further comprises, based on the weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant; wherein the reinforcing fibers comprise glass fibers; wherein the polyimide comprises a polyetherimide; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and wherein the flame retardant comprises an oligomeric phosphate ester.

Embodiment 6

A method of forming a nonwoven fabric, the method comprising: forming an aqueous suspension layer comprising water, 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of polyimide fibers, and 5 to 20 weight percent of binder fibers comprising a block polyestercarbonate-polysiloxane, wherein weight percent values are based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers; at least partially removing water from the aqueous suspension layer to form a fiber layer; and exposing the fiber layer to a temperature of 250 to 320° C., thereby melting the binder fibers, at least partially melting the polyimide fibers, and forming a nonwoven fabric; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units.

Embodiment 7

The method of embodiment 6, wherein the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals.

Embodiment 8

The method of embodiment 6 or 7, wherein the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent; and wherein the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent.

Embodiment 9

The method of any one of embodiments 6-8, wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; wherein the binder fibers further comprise an oligomeric aromatic phosphate ester; and wherein the binder fibers comprise, based on the weight of the binder fibers, 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10 weight percent of the oligomeric aromatic phosphate ester.

Embodiment 10

The method of embodiment 6, wherein the aqueous suspension layer comprises 30 to 50 weight percent of the reinforcing fibers, 40 to 60 weight percent of the polyimide fibers, and 5 to 15 weight percent of the binder fibers; wherein the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent; wherein the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent; wherein the reinforcing fibers comprise glass fibers; wherein the polyimide fibers comprise a polyetherimide; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; wherein the binder fibers further comprise an oligomeric aromatic phosphate ester; wherein the binder fibers comprise, based on the weight of the binder fibers, 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10 weight percent of the oligomeric aromatic phosphate ester; and wherein the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals.

Embodiment 11

A composite, comprising, based on the weight of the composite: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of a polyimide, and 5 to 20 weight percent of a block polyestercarbonate-polysiloxane; wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; and wherein the composite has a density of 0.92 to 1.38 gram/centimeter3, and an areal density of 100 to 3000 gram/meter2.

Embodiment 12

The composite of embodiment 11, wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and wherein the composite further comprises 0.2 to 2 weight percent of an oligomeric aromatic phosphate ester flame retardant.

Embodiment 13

The composite of embodiment 11, wherein the composite comprises, based on the weight of the composite, 30 to 50 weight percent of the reinforcing fibers, and 40 to 60 weight percent of the polyimide, and 5 to 15 weight percent of the block polyestercarbonate-polysiloxane; wherein the nonwoven fabric further comprises, based on the total weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant; wherein the reinforcing fibers comprise glass fibers; wherein the polyimide comprises a polyetherimide; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and wherein the flame retardant comprises an oligomeric aromatic phosphate ester.

Embodiment 14

A method of forming a multilayer composite, the method comprising: exposing at least two layers of the nonwoven fabric of any one of embodiments 1-5 to a temperature of 250 to 400° C. and a pressure of 300 to 1,500 kilopascals for a time of 60 to 600 seconds to yield a multilayer composite.

All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. Each range disclosed herein constitutes a disclosure of any point or sub-range lying within the disclosed range.

The invention is further illustrated by the following non-limiting examples.

Examples

Materials used in these examples are summarized in Table 1.

TABLE 1 Component Description GF Glass fibers, having a diameter of about 16 micrometers, and a length of about 12 millimeters; obtained as OPTIFLOW ™ 790C from Owens Corning. PEIF Polyetherimide fibers, 8 denier per filament with a fiber length of about 12 millimeters; obtained as KURAKISSS ™ UP801 8.8 dtex × 12 mm from Kuraray. PEC-Si para-Cumylphenol endcapped block polyestercarbonate- polysiloxane with about 99 weight percent total of polyester blocks and polycarbonate blocks, and about 1 weight percent polysiloxane blocks; the polyestercarbonate portion contains about 80 mole percent 1,3-phenylene isophthalate-co-terephthalate units, about 9 mole percent resorcinol carbonate units, and about 11 mole percent bisphenol A carbonate units; the polysiloxane blocks have, on average, about 10 dimethylsiloxane units per block; the polyestercarbonate- polysiloxane has a weight average molecular weight of about 24,500 grams/mole and is preparable by the procedure of Example 2-14 of Method 2 as described in U.S. Pat. No. 7,790,292 B2 to Colburn et al., except that the p-cumylphenol level was adjusted to achieve a weight average molecular weight of about 24,500 grams/mole. OPE Oligomeric phosphate ester flame retardant; obtained in powder form as FYROLFLEX ™ SOL-DP flame retardant from ICL Industrial Products. TBPDP Tetrakis(2,4-di-tert-butylphenyl)4,4′- biphenyldiphosphonite, CAS Reg. No. 119345-01-6; obtained as IRGAFOS ™ P-EPQ from BASF.

The composition used to prepare block polyestercarbonate-polysiloxane containing fibers (PEC-Si fibers) is summarized in Table 2, where component amounts are expressed in weight percent based on the total weight of the composition. The composition was prepared by dry blending all components and adding the resulting mixture to the feed throat of a twin-screw extruder operating with zone temperatures ranging from 230 to 300° C. The extrudate was cooled in water before being pelletized.

TABLE 2 Component Amount PEC-Si 93.44 OPE 6.50 TBPDP 0.06

Pellets were dried at 80 to 120° C. for 6 to 12 hours before being fed to the hopper of a melt spinning apparatus. The melt spinning apparatus is schematically illustrated in FIG. 1, where melt spinning apparatus 1 comprises extruder 5, in which dried pellets are converted to a melt, melt pump 10, which conveys the melt to spin pack 15, where it is filtered, then to spinneret 20, where multiple fibers are formed from the filtered melt. The fibers are immediately conveyed to quench section 30, where they are air-cooled and solidified. The cooled fibers then enter spin finish section 40, where a spin finish can be applied to the surface of the fibers. The fibers then traverse a sequence of godet pairs comprising first godets 50, second godets 60, and third godets 70, where the fibers are drawn (stretched). The fibers then enter winder section 80, where contact roller 90 facilitates formation of wound fiber 100 around one of two winding cores 110.

In these experiments, the melt pump was operated at 10 centimeter3/revolution. Extruder and melt pump temperatures were 280 to 330° C. A 144-hole, single-position spinneret was used. Spinneret holes (nozzles) were circular with a diameter of 0.8 millimeters. The length-to-diameter ratio of each spinneret was 4:1. A 325 U.S. mesh (44 micrometer opening) screen filter was used in the spinpack for filtration of the composition melt. After fibers exited the nozzles, they were solidified by quenching with air at ambient temperature (about 23° C.). Individual filaments were combined to form multi-filament threads, then a spin finish (an acrylamide copolymer in an oil-in-water emulsion, obtained as LUROL™ PS-11744 from Goulston) was applied to the multi-filament threads before they contacted the first godet. The draw down ratio was 280 to 550. Draw down ratio, which is unitless, is defined as the ratio of speed (in meters/minute) at which the melt exits the spinneret nozzles to the speed (in meters/minute) of the fiber at the first godet. The apparent shear rate was 170 to 1700 second−1. Apparent shear rate (in units of second−1) is defined according to the equation


Apparent shear rate (second−1)=4Q/πR3ρ

wherein Q is the melt throughput per spinneret nozzle (in grams/second), R is the nozzle radius (in centimeters), and ρ is the polymer melt density (in grams/centimeter3). The mechanical draw ratio was 0.95 to 1.2. Mechanical draw ratio, which is unitless, is defined as the ratio of the first godet speed (in meters/minute) to the winder speed (in meters/minute). The resulting threads, containing fibers of 8 denier per filament, were chopped to a length of about 12 millimeters for use in preparation of a nonwoven fabric.

Formation of Nonwoven Fabric. A mixture of polyetherimide fibers (50 weight percent), PEC-Si fibers (10 weight percent), and chopped glass fibers (40 weight percent) was used to prepare a nonwoven fabric via a wet-laid papermaking) process. FIG. 2 is a schematic illustration of a papermaking apparatus 200, which includes mixing tank 210, run tank 220, headbox 230, wire former 240, dryer 250, and winder 260. A fiber dispersion was prepared by dispersing 200 kilograms total of the three ingredient fibers in 200 kilograms of an aqueous solution containing a viscosity modifying agent. The viscosity modifying agent was a poly(acrylamide-co-diallyldimethylammonium chloride) solution, 10 weight percent in water, and it was used in an amount effective to provide the aqueous solution with a viscosity of 50 to 200 centipoise. The fiber dispersion was fed onto the wire mesh of a paper-making machine to form an aqueous suspension layer, and aqueous solution was drained to form a fiber layer. The fiber layer was transferred to a water washing section where viscosity modifier was washed from the fiber layer. The washed fiber layer was then transferred to a tunnel dryer, and finally to a winding section. Water was essentially eliminated from the mat by the sequence of gravity drainage through holes in the wire mesh, squeezing through several pairs of nip rollers, and heating in an ambient-pressure tunnel dryer, where the temperature was set to 280-300° C. and the drier residence time was 120-180 seconds. In this temperature range, the PEC-Si fibers melted and the polyetherimide fibers at least partially melted. Both types of fibers flowed, losing their fiber shape. If the tunnel dryer temperature is less than 280° C., web tearing occurs. If it is less than 220° C., not only is there web tearing, but the binder (PEC-Si) fibers do not get fully activated, leading to a weak and locally torn fabric. This stage is referred to as binder activation, because the binder fibers melt, and the melted PEC-Si copolymer flows within the web to bind together the network of glass and polyetherimide fibers. This gives the network enough mechanical integrity to prevent it from falling apart in subsequent processing and handling. Using the above process steps, a 165 gram/meter2 nonwoven fabric web was produced at a speed of 5 meters/minute. The nonwoven fabric web was wound on a core. When the roll was fully wound, the edges were trimmed to meet the target width, and the nonwoven fabric web was re-wound to a new core.

As a comparison, a 325 gram/meter2 non-consolidated nonwoven fabric was produced from the same fiber mix (40% glass fiber, 50% polyetherimide fiber, and 10% PEC-Si fiber) and the same process, except that the fiber dispersion did not include a viscosity modifier, there was no water washing step, and the dryer temperature was 200° C.

Tensile properties for the 165 gram/meter2 nonwoven fabric and the 325 gram/meter2 non-consolidated nonwoven fabric were determined according to ASTM D638-14 at 23° C. using a test speed of 50 millimeters/second. The 165 gram/meter2 nonwoven fabric exhibited a tensile modulus of 293 megapascals, and a tensile strain at break of 1.6 percent. The 325 gram/meter2 non-consolidated nonwoven fabric exhibited a tensile modulus of 16 megapascals, and a tensile strain at break of 4.5 percent.

FIG. 3 provides images of rolls of (a) 325 gram/meter2 non-consolidated nonwoven fabric, and (b) 165 gram/meter2 nonwoven fabric. Note that the stiffer pre-consolidated nonwoven fabric assumes an essentially planar shape when unwound from the roll, while the less stiff non-consolidated nonwoven fabric hangs limply. The greater stiffness of the pre-consolidated nonwoven fabric provides advantages including ease of trimming, ease of shearing into complex shapes, shape retention without underlying support.

Additional advantages of the pre-consolidated nonwoven fabric relative to the non-consolidated nonwoven fabric are that it surrounds the reinforcing fibers with more resin, and that it has smoother and more uniform surfaces. Both of these advantages contribute to less fiber shedding during nonwoven fabric handling. FIG. 4 provides optical micrographs of (a) 325 gram/meter2 non-consolidated nonwoven fabric, and (b) 165 gram/meter2 pre-consolidated nonwoven fabric. These micrographs show that the pre-consolidated nonwoven fabric surrounds the reinforcing fibers with more resin than the non-consolidated nonwoven fabric. FIG. 5 provides surface profiles, derived from optical micrographs, of (a) 325 gram/meter2 non-consolidated nonwoven nonwoven fabric, and (b) 165 gram/meter2 nonwoven fabric. These surface profiles show that the pre-consolidated nonwoven fabric has smoother and more uniform surfaces than the non-consolidated nonwoven fabric.

The nonwoven fabric was used to form a consolidated multi-layer composite suitable for thermoforming. Seven or eight layers of the 165 gram/meter2 pre-consolidated nonwoven fabric were unwound from independently operating pay-off winders, stacked one over another, then topped with one layer of 10-20 gram/meter2 glass fiber woven fabric scrim obtained as BGF 104 from BGF Industries (Greensboro, N.C., USA). The combined layers were then passed through a consolidation apparatus. The consolidation apparatus was a steel double belt press obtained as Heather 5 from HELD Technologie GmbH (Trossingen, Germany). The nonwoven web was exposed to radiation from an infrared pre-heating device before it was fed to the double-belt press. The double-belt press consolidation simultaneously compressed the nonwoven fabrics and caused the polyetherimide fibers to melt and flow. A mold release agent, LOCTITE™ FREKOTE™ 700-NC from Henkel, was continuously applied to the steel belts to prevent sticking of the nonwoven webs to the steel belts. Typical consolidation conditions were 180 to 300 seconds at a temperature of 350 to 400° C., and a pressure of 800 kilopascals. Consolidation was followed by cooling while maintaining pressure. The cooled, consolidated composite had a continuous resin matrix containing strained glass fibers. The strained glass fibers release their residual stress and create “lofting” during a subsequent thermoforming process. The mass per unit area of the consolidated mat was 1,155 grams/meter2 for the seven-layer composite, and 1,320 grams/meter2 for the eight-layer composite. The thickness of the consolidated composite was 1.05 millimeters for a seven-layer composite, and 1.20 millimeters for the eight-layer composite. The width of the consolidated panel is variable and can be controlled, for example, using an in-line edge trimmer. The length of the consolidated panel is variable and can be controlled, for example, using a guillotine cutter on the consolidation apparatus.

Claims

1. A nonwoven fabric, comprising, based on the weight of the nonwoven fabric: a polycarbonate block comprising carbonate units having the structure wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units;

25 to 55 weight percent of reinforcing fibers,
35 to 65 weight percent of a polyimide, and
5 to 20 weight percent of a block polyestercarbonate-polysiloxane;
wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure
wherein the nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter3, and an areal density of 100 to 400 gram/meter2; and
wherein the nonwoven fabric has a tensile modulus of 50 to 1000 megapascals, determined according to ASTM D638-14 at a temperature of 23° C. and using a test speed of 50 millimeters/minute.

2. The nonwoven fabric of claim 1,

wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and
wherein the nonwoven fabric further comprises 0.2 to 2 weight percent of an organophosphate ester flame retardant.

3. The nonwoven fabric of claim 2, wherein the organophosphate ester flame retardant comprises an oligomeric phosphate ester.

4. The nonwoven fabric of claim 1, wherein the reinforcing fibers comprise glass fibers.

5. The nonwoven fabric of claim 1,

wherein the nonwoven fabric comprises, based on the weight of the nonwoven fabric, 30 to 50 weight percent of the reinforcing fibers, 40 to 60 weight percent of the polyimide, and 5 to 15 weight percent of the block polyestercarbonate-polysiloxane;
wherein the nonwoven fabric further comprises, based on the weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant;
wherein the reinforcing fibers comprise glass fibers;
wherein the polyimide comprises a polyetherimide;
wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and
wherein the flame retardant comprises an oligomeric phosphate ester.

6. A method of forming a nonwoven fabric, the method comprising: wherein weight percent values are based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers; a polycarbonate block comprising carbonate units having the structure wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units.

forming an aqueous suspension layer comprising water, 25 to 55 weight percent of reinforcing fibers, 35 to 65 weight percent of polyimide fibers, and 5 to 20 weight percent of binder fibers comprising a block polyestercarbonate-polysiloxane,
at least partially removing water from the aqueous suspension layer to form a fiber layer; and
exposing the fiber layer to a temperature of 250 to 320° C., thereby melting the binder fibers, at least partially melting the polyimide fibers, and forming a nonwoven fabric;
wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure

7. The method of claim 6, wherein the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals.

8. The method of claim 6,

wherein the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent; and
wherein the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent.

9. The method of claim 6,

wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units;
wherein the binder fibers further comprise an oligomeric aromatic phosphate ester; and
wherein the binder fibers comprise, based on the weight of the binder fibers, 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10 weight percent of the oligomeric aromatic phosphate ester.

10. The method of claim 6,

wherein the aqueous suspension layer comprises 30 to 50 weight percent of the reinforcing fibers, 40 to 60 weight percent of the polyimide fibers, and 5 to 15 weight percent of the binder fibers;
wherein the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent;
wherein the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent;
wherein the reinforcing fibers comprise glass fibers;
wherein the polyimide fibers comprise a polyetherimide;
wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units;
wherein the binder fibers further comprise an oligomeric aromatic phosphate ester;
wherein the binder fibers comprise, based on the weight of the binder fibers, 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10 weight percent of the oligomeric aromatic phosphate ester; and
wherein the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals.

11. A composite, comprising, based on the weight of the composite: a polycarbonate block comprising carbonate units having the structure wherein at least 60 percent of the total number of R1 groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; and

25 to 55 weight percent of reinforcing fibers,
35 to 65 weight percent of a polyimide, and
5 to 20 weight percent of a block polyestercarbonate-polysiloxane;
wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure
wherein the composite has a density of 0.92 to 1.38 gram/centimeter3, and an areal density of 100 to 3000 gram/meter2.

12. The composite of claim 11,

wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and
wherein the composite further comprises 0.2 to 2 weight percent of an oligomeric aromatic phosphate ester flame retardant.

13. The composite of claim 11,

wherein the composite comprises, based on the weight of the composite, 30 to 50 weight percent of the reinforcing fibers, and 40 to 60 weight percent of the polyimide, and 5 to 15 weight percent of the block polyestercarbonate-polysiloxane;
wherein the nonwoven fabric further comprises, based on the total weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant;
wherein the reinforcing fibers comprise glass fibers;
wherein the polyimide comprises a polyetherimide;
wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R1 is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R1 is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and
wherein the flame retardant comprises an oligomeric aromatic phosphate ester.

14. A method of forming a multilayer composite, the method comprising:

exposing at least two layers of the nonwoven fabric of claim 1 to a temperature of 250 to 400° C. and a pressure of 300 to 1,500 kilopascals for a time of 60 to 600 seconds to yield a multilayer composite.
Patent History
Publication number: 20190352821
Type: Application
Filed: Apr 23, 2019
Publication Date: Nov 21, 2019
Inventors: Sungkyun Sohn (Longmeadow, MA), Stanley Leroy Lawrence (Adams, MA)
Application Number: 16/391,754
Classifications
International Classification: D04H 3/011 (20060101); D04H 3/004 (20060101);