Papers Having High Average Specific Modulus and Ultimate Tensile Strength

Abstract

A paper comprising polymeric fibers and a binder, wherein the polymeric fibers comprise first fibers and second fibers, the first fibers comprising an aramid copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer, the second fibers comprising poly(para-phenylene terephthalate) homopolymer, and the binder comprising a third polymer that is either an aramid homopolymer or aramid copolymer; the paper having an ultimate tensile strength of 21 N-m/g or greater and average specific modulus of 4950 Pa-m.sup.3/g or greater.

Claims

1. A paper comprising polymeric fibers and a binder, wherein the polymeric fibers comprise first fibers and second fibers, the first fibers comprising a first polymer, wherein the first polymer is an aramid copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer, the second fibers comprising poly(para-phenylene terephthalate) homopolymer, and the binder comprising a third polymer that is either an aramid homopolymer or aramid copolymer; wherein the paper comprises 85 to 40 parts by weight polymeric fibers and 15 to 60 parts by weight binder, based on the combined weight of said polymeric fibers and said binder in the paper, the polymeric fibers comprising 12.5 to 75 parts by weight first fibers and 25 to 87.5 parts by weight second fibers, based on the combined weight of said first and said second fibers in the polymeric fibers, and wherein the paper has an ultimate tensile strength of 21 N-m/g or greater and average specific modulus of 4950 Pa-m.sup.3/g or greater.

2. The paper of claim 1 wherein the polymeric fibers comprise 12.5 to 60 parts by weight first fibers and 40 to 87.5 parts by weight second fibers, based on the combined weight of said first and said second fibers.

3. The paper of claim 2 wherein the polymeric fibers comprise 12.5 to 50 parts by weight first fibers and 50 to 87.5 parts by weight second fibers, based on the combined weight of said first and said second fibers.

4. The paper of claim 1 comprising 80 to 50 parts by weight of the polymeric fibers and 20 to 50 parts by weight of the binder, based on the combined weight of said polymeric fibers and said binder.

5. The paper of claim 1, wherein the benzimidazole monomer of the first polymer is 5(6)-amino-2-(p-aminophenyl) benzimidazole.

6. The paper of claim 1, wherein the para-oriented diamine monomer of the first polymer is paraphenylene diamine.

7. The paper of claim 1, wherein the para-oriented aromatic acid monomer of the first polymer is terephthaloyl dichloride.

8. The paper of claim 1, wherein the binder includes non-granular polymer fibrids that are fibrous, film-like or a mixture thereof.

9. The paper of claim 1, wherein the third polymer is poly(meta-phenylene isophthalamide) homopolymer.

10. The paper of claim 1, wherein the third polymer is an aramid copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer.

11. The paper of claim 10, wherein the third polymer comprises benzimidazole monomer that is 5(6)-amino-2-(p-aminophenyl) benzimidazole, para-oriented diamine monomer that is paraphenylene diamine, and para-oriented aromatic acid monomer that is terephthaloyl dichloride.

12. The paper of claim 1, wherein the ultimate tensile strength is 22 N.Math.m/g or greater.

13. A process for making a paper, comprising the steps of a) forming an aqueous slurry comprising 85 to 40 parts by weight polymeric fibers and 15 to 60 parts by weight binder, based on the combined weight of said polymeric fibers and said binder, wherein the polymeric fibers comprise first fibers and second fibers, the first fibers comprising a first polymer, wherein the first polymer is an aramid copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer, the second fibers comprising poly(para-phenylene terephthalate) homopolymer, and the binder comprising a third polymer that is either an aramid homopolymer or aramid copolymer; and the polymeric fibers comprising 12.5 to 75 parts by weight first fibers and 25 to 87.5 parts by weight second fibers, based on the combined weight of said first and said second fibers; b) removing water from the slurry on a paper machine to form a wet paper composition; c) drying the wet paper composition to form a dried sheet; and d) thermally consolidating the dried sheet in one or more steps between nipped rolls heated to a surface temperature of 260 C. or more, using a nip pressure of 700 to 5000 lbs./inch (125 to 894 kg/cm); to form a paper having an ultimate tensile strength of 21 N-m/g or greater and average specific modulus of 4950 Pa-m.sup.3/g or greater.

14. The process of claim 13, wherein the polymeric fibers comprise 12.5 to 60 parts by weight first fibers and 40 to 87.5 parts by weight second fibers, based on the combined weight of said first and said second fibers.

15. The process of claim 14, wherein the polymeric fibers comprise 12.5 to 50 parts by weight first fibers and 50 to 87.5 parts by weight second fibers, based on the combined weight of said first and said second fibers.

16. The process of claim 13 comprising 80 to 40 parts by weight of the polymeric fibers and 20 to 60 parts by weight of the binder, based on the combined weight of said polymeric fibers and said binder.

17. The process of claim 13, wherein the first polymer comprises benzimidazole monomer that is 5(6)-amino-2-(p-aminophenyl) benzimidazole, para-oriented diamine monomer that is paraphenylene diamine, and para-oriented aromatic acid monomer that is terephthaloyl dichloride.

18. The process of claim 13, wherein the binder includes non-granular polymer fibrids that are fibrous, film-like or a mixture thereof.

19. The process of claim 13, wherein the third polymer is poly(meta-phenylene isophthalamide) homopolymer.

20. The process of claim 13, wherein the third polymer is an aramid copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer.

21. The process of claim 20, wherein the third polymer comprises benzimidazole monomer that is 5(6)-amino-2-(p-aminophenyl) benzimidazole, para-oriented diamine monomer that is paraphenylene diamine, and para-oriented aromatic acid monomer that is terephthaloyl dichloride.

22. The process of claim 13, wherein step a) the first fibers have a 2 theta (2) x-ray diffraction angle peak of 25 (+/0.5) degrees

23. The process of claim 13, wherein step a) the first fibers have not been exposed to any environment of 260 C. or higher

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is an illustration of a representative x-ray diffraction angle tracing of either a paper and fiber having a 2 theta (2) x-ray diffraction angle peak at 25 (+/0.5) degrees as designated by 1; and a representative x-ray diffraction angle tracing of paper and fiber having a 2 theta (2) x-ray diffraction angle peak at 20.2 (+/0.5) degrees as designated by 2.

DETAILED DESCRIPTION OF THE INVENTION

[0017] This invention relates to an aramid paper having an ultimate tensile strength of 21 N-m/g or greater and average specific modulus of 4950 Pa-m.sup.3/g or greater. The paper comprises polymeric fibers and a binder, wherein the polymeric fibers comprise fibers made with an aramid copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer. The paper further comprises fibers comprising poly(para-phenylene terephthalate) (PPD-T) homopolymer. Finally, the polymeric fibers in the paper are bound in the paper by the use of a binder, that binder comprising an aramid homopolymer or aramid copolymer.

[0018] The paper comprises 85 to 40 parts by weight of the polymeric fibers, and 15 to 60 parts by weight of the binder, those amounts being based on the combined weight of those polymeric fibers and binder. In some embodiments, the paper comprises 80 to 40 parts by weight of the polymeric fibers, and 20 to 60 parts by weight of the binder, those amounts being based on the combined weight of those polymeric fibers and binder. In some embodiments, the paper comprises 80 to 45 parts by weight of the polymeric fibers, and 20 to 55 parts by weight of the binder, those amounts being based on the combined weight of those polymeric fibers and binder. In some embodiments, the paper comprises 80 to 50 parts by weight of the polymeric fibers, and 20 to 50 parts by weight of the binder, those amounts being based on the combined weight of those polymeric fibers and binder.

[0019] Specifically, the polymeric fibers comprise 12.5 to 75 parts by weight of the aramid copolymer fibers previously described, and 25 to 87.5 parts by weight of the (PPD-T) homopolymer fibers previously described, based on the combined weight of said those two types of fibers. In some embodiments, the polymeric fibers comprise 12.5 to 60 parts by weight of the aramid copolymer fibers previously described, and 40 to 87.5 parts by weight the (PPD-T) homopolymer fibers previously described, based on the combined weight of those two types of fibers. In some other embodiments, the polymeric fibers comprise 12.5 to 50 parts by weight of the aramid copolymer fibers previously described, and 50 to 87.5 parts by weight the (PPD-T) homopolymer fibers previously described, based on the combined weight of those two types of fibers.

[0020] It is believed that certain resins, such as phenolic resins, have more affinity to aramid copolymer fiber than for PPD-T homopolymer fiber; therefore, it is believed that the use of some aramid copolymer floc in aramid papers comprising PPD-T floc could improve adhesion of such resins to the paper.

[0021] By paper, it is meant a planar sheet, made from one or more plies or layers of polymeric fibers incorporating a polymeric binder, that is prepared by paper-making processes; the polymeric fibers can be in the form of fibers, floc, or pulp. Such paper-making processes typically involve depositing an aqueous slurry or dispersion of fibrous material (preferably both fibers and binder) on a screen or mesh to form one or more fibrous layer(s) or ply (plies) and removing liquid to form a de-watered sheet. Representative devices and machinery that can be used to make plies or layers include continuous-processing equipment such as, for example without limitation to, a Fourdrinier, inclined wire, or other papermaking machine; or batch-processing equipment that, for example, makes a paper in a sheet mold containing a forming screen. The de-watered sheet is then typically dried on the surface of drying cans or in an oven to make the sheet a formed paper. This formed paper is also known as uncalendered paper. As used herein, formed paper or uncalendered paper is a planar sheet that has not been exposed to temperatures of 260 C. or higher. This formed or uncalendered paper generally does not have high strength properties; therefore, uncalendered paper is then typically thermally consolidated with heat and pressure to form bonds or linkages between the fibrous materials in the paper. This thermal consolidation can be done by pressing the dried sheet between two surfaces maintained at a high temperature, such as in a heated plate press; but for practical commercial production, the thermal consolidation can be performed in a continuous manner by pressing the dried sheet in the nip between two heated rolls. This process is known as calendering, and the rolls are known as calendering rolls. Thermally consolidated paper is therefore made by the application of high pressure and heat as described herein, by some sort of process such as by use of a heated press or heated set of calender rolls. As used herein, a thermally consolidated or calendered paper is a planar sheet that has been exposed to 260 C. or higher under a pressure of at least 700 lbs./inch (125 kg/cm); and further, the terms calendered paper and thermally consolidated paper are used interchangeably herein. It is understood that several plies with the same or different compositions can be combined together into the final paper structure during forming and/or calendering.

[0022] Polymeric fiber means fiber made from a polymer or copolymer. Fiber means a relatively flexible, unit of matter having a high ratio of length to width across its cross-sectional area perpendicular to its length. Herein, the term fiber is used interchangeably with the term filament. The cross section of the filaments described herein can be any shape but are typically circular or bean shaped. Fibers or filaments spun onto a bobbin in a package without any prior cutting is referred to as continuous fiber. Fiber can be cut into short lengths called staple fiber. Fiber can be cut into even smaller lengths called floc.

[0023] The preferred polymeric fiber can include floc. The term floc, as used herein, means fibers that are cut to a short length and that are customarily used in the preparation of papers. Typically, floc has a length of from about 3 to about 20 millimeters. A preferred length is from about 3 to about 7 millimeters. Floc is normally produced by cutting continuous fibers into the required lengths using well-known methods in the art.

[0024] The polymeric fiber can include pulp. Pulp as used herein comprises fibrillated fibrous structures, which are particles of material having a stalk, and fibrils extending therefrom; wherein the stalk is generally columnar and about 10 to 50 microns in diameter and the fibrils are hair-like members only a fraction of a micron or a few microns in diameter attached to the stalk and about 10 to 100 microns long.

[0025] The paper comprises polymeric fibers comprising a first polymer, also referred to herein as first fibers wherein the first polymer is a copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer. In some preferred embodiments, the copolymer is an aramid copolymer including a benzimidazole group.

[0026] The terms polymer or copolymer as used herein, mean a material prepared by polymerizing monomers, end-functionalized oligomers, and/or end-functionalized polymers whether of the same or different types. The term aramid, as used herein, means aromatic polyamide, wherein at least 85% of the amide (CONH) linkages are attached directly to two aromatic rings.

[0027] The term aramid copolymer including a benzimidazole group as used herein refers to copolymers polymerized from aromatic diacid monomers and aromatic diamine monomers, wherein there are at least two different aromatic diamine monomers present; preferably a para-aromatic diamine monomer and a benzimidazole monomer. The two different aromatic diamine monomers can be polymerized with a stoichiometric amount of at least one para-oriented aromatic diacid monomer. By copolymer it is meant the monomers are copolymerized in some fashion to form individual polymer chains having residues of the para-oriented aromatic diamine monomer, the benzimidazole monomer, and the para-oriented aromatic diacid monomer. In some embodiments, the monomers form a random copolymer; that is, the para-oriented aromatic diamine monomer and benzimidazole monomer residues are located randomly in the polymer chain.

[0028] In some embodiments, the para-oriented aromatic diamine is paraphenylene diamine. Other para-oriented aromatic diamines are possible. In some embodiments, the benzimidazole is 5(6)-amino-2-(p-aminophenyl) benzimidazole (DAPBI). Other benzimidazoles are possible. In some embodiments, the para-oriented aromatic diacid is terephthaloyl dichloride. Other para-oriented aromatic diacids are possible. In some preferred embodiments, the aramid copolymer is made by polymerizing the monomers 5(6)-amino-2-(p-aminophenyl) benzimidazole, one or more para-aromatic diamine(s), and one or more para-aromatic diacid-chloride(s). In some most preferred embodiments, the aramid copolymer is made by polymerizing the specific monomers 5(6)-amino-2-(p-aminophenyl) benzimidazole, paraphenylene diamine, and terephthaloyl dichloride.

[0029] In some embodiments, the molar ratio of benzimidazole monomer, such as 5(6)-amino-2-(p-aminophenyl) benzimidazole, to the para-aromatic diamine monomer, such as paraphenylene diamine, is 50/50 to 80/20, and in some embodiments the molar ratio is 50/50 to 70/30. In some embodiments, the benzimidazole monomer is 50 mole percent or greater of the total moles of benzimidazole and the para-aromatic diamine present.

[0030] In some specific embodiments, the aramid copolymer including a benzimidazole group includes a residue of 5(6)-amino-2-(p-aminophenyl) benzimidazole and a residue of paraphenylene diamine, wherein the molar ratio of the residue of 5(6)-amino-2-(p-aminophenyl) benzimidazole to the residue of paraphenylene diamine is 50/50 to 80/20. In some specific embodiments, the aramid copolymer including a benzimidazole group includes a residue of 5(6)-amino-2-(p-aminophenyl) benzimidazole and a residue of paraphenylene diamine, wherein the molar ratio of the residue of 5(6)-amino-2-(p-aminophenyl) benzimidazole to the residue of paraphenylene diamine is 50/50 to 70/30. In still other embodiments, the residue of the benzimidazole, such as 5(6)-amino-2-(p-aminophenyl) benzimidazole, is 50 mole percent or greater of the total moles of benzimidazole and the para-aromatic diamine residues.

[0031] As used herein, stoichiometric amount means the amount of a component theoretically needed to react with all of the reactive groups of a second component. For example, stoichiometric amount refers to the moles of terephthaloyl dichloride needed to react with substantially all of the amine groups of the amine components. It is understood by those skilled in the art that the term stoichiometric amount refers to a range of amounts that are typically within 10% of the theoretical amount. For example, the stoichiometric amount of terephthaloyl dichloride used in a polymerization reaction can be 90-110% of the amount of terephthaloyl dichloride theoretically needed to react with all of the amine groups.

[0032] In some embodiments, all of monomers can be combined together and reacted to form the polymer or copolymer. In some embodiments, the monomers or various amounts of the monomers can be reacted sequentially to form oligomers which can be further reacted with additional monomer(s) or oligomer(s) to form polymers or copolymers. By oligomer, it is meant polymers or species eluting out at <3000 MW with a column calibrated using poly(paraphenylene terephthalamide) homopolymer.

[0033] As used herein, the term residue of a chemical species refers to the moiety that is the resulting product of the chemical species in a particular reaction scheme or subsequent formulation or chemical product, regardless of whether the moiety is actually obtained from the chemical species. Thus, a copolymer comprising residues of paraphenylene diamine refers to a copolymer having one or more units of the formula:

##STR00001##

[0034] And a copolymer having residues of terephthaloyl dichloride contains one or more units of the formula:

##STR00002##

[0035] Similarly, a copolymer comprising residues of a benzimidazole contains one or more units of the formula:

##STR00003##

[0036] And specifically, a copolymer comprising residues of DAPBI contains one or more units of the formula:

##STR00004##

[0037] Therefore, in some embodiments, the aramid copolymer includes a residue of a benzimidazole, and in some embodiments the aramid copolymer includes a residue of 5(6)-amino-2-(p-aminophenyl).

[0038] After copolymerization, the copolymer can preferably be isolated from the polymerization solvent and then redissolved in another solvent, typically sulfuric acid, to form a polymer solution suitable for spinning fibers. Preferably, the polymeric fibers are spun from the polymer solution, preferably via air-gap or dry-jet spinning into a coagulation bath to remove the solvent, followed by processing steps that can include various treatment steps, including washing, drying, drawing, and heat treating steps, to develop the desired high tenacity.

[0039] With regards to filaments of aramid copolymer including a benzimidazole group, it is known that to attain yarns having the highest yarn tenacity and highest yarn modulus, the fiber has to be exposed to a temperature above the glass transition temperature of the polymer, a temperature that is normally chosen to be 260 C. or higher. Such fibers that have been exposed a temperature of 260 C. or higher to are referred to herein as heat-treated fibers.

[0040] Aramid copolymer fibers that have not been exposed to a temperature of 260 C. or higher are referred to herein as dried fibers. Therefore, these dried fibers have only been exposed to temperatures lower than 260 C. prior to their use in papermaking. The term dried fibers is used because the drying of the aramid copolymer fiber is a typical processing step that might expose the fibers to some heat prior to any heat treating step of about 260 C. or greater.

[0041] Further, while the aramid copolymer dried fibers have much lower tenacity and tensile modulus than the heat treated fibers, it has been found that when heat-treated aramid copolymer fiber yarns and dried aramid copolymer fiber yarns are each cut into floc, and each separately used to make thermally-consolidated paper, the thermally-consolidated paper made with the lower tenacity/lower modulus dried fibers have surprisingly high dielectric strength, high density, and high stiffness as represented by high average specific modulus.

[0042] Both the dried and heat-treated polymeric fibers, when used to make formed papers, preferably have a relatively round or solid-circular cross-section prior to any thermal consolidation of the dried sheet. It is believed, however, that if the dried sheet is made with dried fibers as defined herein, and is then thermally consolidated under heat and pressure, the majority of the dried fibers in the thermally consolidated paper are deformed or flattened, which contribute to the surprising properties of this inventive paper. It is further believed that if the dried sheet is made with heat treated fibers as defined herein, and is then thermally consolidated under heat and pressure, the majority of the heat treated fibers retain their round structure, which contributes the lower density exhibited by those thermally consolidated papers. It is believed that since the heat treated fibers have already been exposed to temperatures of 260 C. or higher, which increases their crystallinity prior to paper making, the heat treated fibers better retain their round fiber structure when the paper is subsequently consolidated with heat and pressure. Since the dried fibers have not been exposed to such temperatures, these dried fibers are more deformable when the paper is subsequently consolidated with heat and pressure, providing a paper that has higher density.

[0043] The paper also comprises polymeric fibers comprising a second polymer, also referred to herein as second fibers, the second fibers comprising poly(para-phenylene terephthalate) (PPD-T) homopolymer. By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. Other diamines and other diacid chlorides can be used in amounts up to as much as about 10 mole percent of the p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups which interfere with the polymerization reaction. Additives can be used with the para-aramid in the fibers and it has been found that up to as much as 10 percent, by weight, of other polymeric material can be blended with the aramid or that copolymers can be used having as much as 10 percent of other diamine substituted for the diamine of the aramid or as much as 10 percent of other diacid chloride substituted for the diacid chloride of the aramid.

[0044] Poly(p-phenylene terephthalamide) fibers are generally spun by extrusion of a polymer solution of the PPD-T through a capillary into a coagulating bath. The solvent for the solution is generally concentrated sulfuric acid, and the extrusion is generally through an air gap into a cold, aqueous, coagulating bath. Such processes are generally disclosed in U.S. Pat. Nos. 3,063,966; 3,767,756; 3,869,429, & 3,869,430. PPD-T fibers are available commercially as Kevlar fibers, which are available from DuPont, and Twaron fibers, which are available from Teijin, Ltd. The homopolymer PPD-T fibers used herein have a different chemical structure to the aramid copolymer fibers described herein, PPD-T homopolymer having been described as a rigid-rod polymer. Therefore, as described in U.S. Pat. No. 3,767,756 cited above, the modulus of PPD-T yarns can be increased by heat treating at temperatures of 150 to 550 C. but yarn tenacity is not significantly changed; although can be reduced after treatment at 450 C. of more. Therefore, the discussion of differences between the dried and heat-treated aramid copolymer fibers provided herein, and the effect high temperatures has on those aramid copolymer fibers, does not apply to the second fibers comprising PPD-T homopolymer. It is believed the PPD-T fibrous component in the inventive papers is not appreciably changed during thermal consolidation due to the PPD-T fiber's chemical structure.

[0045] The paper further comprises binder for the polymeric fibers, the binder comprising a third polymer that is either an aramid homopolymer or aramid copolymer. By binder it is meant a polymeric binding agent that effectively binds together at least some parts of the polymeric fibers together in the sheet. The inclusion of the binder typically increases the strength and other properties of the paper. The polymeric binder is preferably activated by the application of heat and pressure. In a preferred embodiment, the sole added binder in the paper is the polymeric binder made with the third polymer. The third polymer can be the same or different as either the first polymer, which is an aramid copolymer; or the second polymer, which is an aramid homopolymer.

[0046] Like the first polymer, the third polymer can be a copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer.

[0047] In some embodiments, the third polymer can have one or more of the same specific monomers as the first polymer or aramid copolymer previously described herein; and the specific aramid copolymer monomers can be present in the same molar ratios and amounts and residues as previously discussed herein. In some embodiments, the benzimidazole monomer of the second polymer is 5(6)-amino-2-(p-aminophenyl) benzimidazole. In some embodiments, the second polymer further comprises a para-oriented diamine monomer that is paraphenylene diamine, and in some embodiments the para-oriented aromatic acid monomer is terephthaloyl dichloride. In some preferred embodiments, the second polymer is the same as the first polymer. In some preferred embodiments, the monomers of both the first and second polymers is as follows; the benzimidazole monomer is 5(6)-amino-2-(p-aminophenyl) benzimidazole, the para-oriented diamine monomer is paraphenylene diamine, and the para-oriented aromatic acid monomer is terephthaloyl dichloride. The molar ratio of the monomers in the first and second polymer can be different; however, in some preferred embodiments both the first polymer and the second polymer have the same the molar ratio of the residue of 5(6)-amino-2-(p-aminophenyl) benzimidazole to the residue of paraphenylene diamine.

[0048] In some embodiments the third polymer of the binder can comprise an aramid homopolymer. In some embodiments, that aramid polymer is a meta-aramid. The aramid polymer is considered a meta-aramid polymer when the two rings or radicals are meta oriented with respect to each other along the molecular chain. The preferred meta-aramid is poly(meta-phenylene isophthalamide) (MPD-I). U.S. Pat. Nos. 3,063,966; 3,227,793; 3,287,324; 3,414,645; and 5,667,743 are illustrative of useful methods for making aramid materials.

[0049] In some preferred embodiments, the polymeric binder can be in the form of fibrids. The term fibrids, as used herein, means very small, nongranular, fibrous or film-like particles, with at least one of their three dimensions being of minor magnitude relative to the largest dimension. These particles can be prepared by precipitation of a solution of polymeric material using a non-solvent under high shear. Representative of such known methods include using an apparatus such as disclosed in U.S. Pat. No. 3,018,091. Preferably, the fibrids have a melting point or decomposition point above 320 C.

[0050] Fibrids generally have a largest dimension length in the range of about 0.1 mm to about 1 mm with a length-to-width aspect ratio of about 5:1 to about 10:1. The thickness dimension is on the order of a fraction of a micron, for example, about 0.01 to about 1.0 micrometer. While not required, it is preferred to incorporate aramid fibrids into the paper during paper forming while the fibrids are in a never-dried state. For example, the wet fibrids, before being dried, can be incorporated into a headbox slurry and deposited on a screen with the polymeric binder physically entwined with and about the floc component of the laid paper.

[0051] In some embodiments, the polymeric binder of the paper includes non-granular polymer fibrids that are fibrous, film-like or a mixture thereof, made from the first polymer as described herein. That is, the fibrids are non-granular film-like particles of aramid copolymer including a benzimidazole group having a melting point or decomposition point above 320 C. Preferably, such fibrids have residues of a benzimidazole monomer, such as 5(6)-amino-2-(p-aminophenyl) benzimidazole; a para-oriented diamine monomer, such as paraphenylene diamine; and a para-oriented aromatic acid monomer, such as terephthaloyl dichloride.

[0052] In some embodiments, the polymeric binder of the paper includes non-granular polymer fibrids that are fibrous, film-like or a mixture thereof, made from the second polymer as described herein. That is, the fibrids are non-granular film-like particles of aramid homopolymer having a melting point or decomposition point above 320 C. Preferably, such fibrids are made from poly(metaphenylene isophthalamide), which is made by reacting a meta-oriented diamine monomer, such as metaphenylene diamine; and a meta-oriented aromatic acid monomer, such as isophthaloyl dichloride.

[0053] The thermally consolidated paper has a dielectric strength of 10.2 kV/mm or greater. In some embodiments, the thermally consolidated paper has a dielectric strength of 13.0 kV/mm or greater. In some embodiments, the thermally consolidated paper has a dielectric strength of 21.0 kV/mm or less. In some embodiments, the thermally consolidated paper has a dielectric strength of 10.2 to 20.0 kV/mm.

[0054] The thermally consolidated paper has an average specific modulus of 4950 Pa-m.sup.3/g or higher. In some embodiments, the thermally consolidated paper has an average specific modulus of 5100 Pa-m.sup.3/g or higher. In some embodiments, the thermally consolidated paper has an average specific modulus of 6000 Pa-m.sup.3/g or less. In some embodiments, the thermally consolidated paper has an average specific modulus of 5700 Pa-m.sup.3/g or less. In some embodiments, the thermally consolidated paper has an average specific modulus of 4950 to 6000 Pa-m.sup.3/g, and in some other embodiments, the thermally consolidated paper has an average specific modulus of 5100 to 5700 Pa-m.sup.3/g.

[0055] The thermally consolidated paper has an ultimate tensile strength of 21 N-m/g or greater. In some embodiments, the paper has an ultimate tensile strength of 22 N-m/g or greater; while in some embodiments the paper has an ultimate tensile strength of 40 N-m/g or greater.

[0056] The thermally consolidated paper has a density of 0.74 grams per cubic centimeter (g/cm.sup.3) or greater. In some embodiments, the thermally consolidated paper has a density of 0.76 g/cm.sup.3 or greater. In some embodiments, the thermally consolidated paper has a density of 1.1 g/cm.sup.3 or less. In some embodiments, the thermally consolidated paper has a density of 0.74 g/cm.sup.3 to 1.1 g/cm.sup.3, and in some other embodiments, the thermally consolidated paper has a density of 0.76 g/cm.sup.3 to 0.80 g/cm.sup.3.

[0057] In some embodiments, the thermally consolidated paper has a total thickness in both the machine and cross direction of 0.030 to 0.070 mm. In some embodiments, the thermally consolidated paper has a total thickness in both the machine and cross direction of 0.035 to 0.065 mm; preferably a total thickness in both the machine and cross direction of 0.040 to 0.055 mm.

[0058] In some embodiments, the thermally consolidated paper has a total basis weight in both the machine and cross direction of 15 to 100 grams per square meter (gsm). In some embodiments, the thermally consolidated paper has a total basis weight in both the machine and cross direction of 25 to 75 gsm; preferably a basis weight in both the machine and cross direction of 30 to 60 gsm.

[0059] In one preferred embodiment, it is believed that after thermal consolidation in a paper, the first fibers in the paper, those fibers comprising a copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer, have an x-ray diffraction angle tracing showing a 2 theta (2) x-ray diffraction angle peak of 20.2 (+/0.5) degrees, and the integrated intensity of said x-ray diffraction angle peak is 4 percent or less of the total diffraction pattern intensity, after background subtraction.

[0060] It has been found that an x-ray diffraction angle tracing showing a 2 theta (2) x-ray diffraction angle peak of 25 (+/0.5) degrees, with the integrated intensity of that x-ray diffraction angle peak being 25 percent or more of the total diffraction pattern intensity, after background subtraction, is representative of the previously-described first fibers made with an aramid copolymer comprising an imidazole group that have not been exposed to any environment of 260 C. or higher (called dried fibers or dried copolymer fibers herein). Tracing 1 of FIG. 1 is an illustration of representative x-ray diffraction angle tracings of paper and fiber having a 2 theta (2) x-ray diffraction angle peak at 25 (+/0.5) degrees. Further, it has been found that when formed papers comprising these dried aramid fibers made from the first polymer; that is, the copolymer described above, using a polymeric binder that is also made from that same aramid copolymer; and the papers are then thermally consolidated or calendered, the resulting papers and fibers exhibit a 2 theta (2) x-ray diffraction angle peak of 20.2 (+/0.5) degrees, and the integrated intensity of that x-ray diffraction angle peak is 4 percent or less of the total diffraction pattern intensity, after background subtraction. Tracing 2 of FIG. 1 is an illustration of representative x-ray diffraction angle tracings and of paper and fiber having a 2 theta (2) x-ray diffraction angle peak at 20.2 (+/0.5) degrees.

[0061] This is in contrast with the previously described heat-treated polymeric fibers, which exhibit an x-ray diffraction angle tracing showing a 2 theta (2) x-ray diffraction angle peak of 20.2 (+/0.5) degrees, wherein the integrated intensity of said x-ray diffraction angle peak is greater than 4 percent of the total diffraction pattern intensity, after background subtraction. Since such heat-treated fibers have already been exposed to an environment of 260 C. or higher, and when formed papers comprising those heat-treated fibers made from the first polymer; that is, the copolymer described above, and polymeric binder made from the second polymer; that is, the copolymer described above, are then thermally consolidated or calendered, the resulting papers exhibit a x-ray diffraction angle peak and intensity similar to the heat-treated fibers; that is, such papers made from heat-treated fibers exhibit an x-ray diffraction angle tracing showing a 2 theta (2) x-ray diffraction angle peak of 20.2 (+/0.5) degrees, and wherein the integrated intensity of that peak is greater than 4 percent of the total diffraction pattern intensity, after background subtraction. Again, tracing 2 of FIG. 1 is an illustration of representative x-ray diffraction angle tracings and of paper and fiber having a 2 theta (2) x-ray diffraction angle peak at 20.2 (+/0.5) degrees, which is representative of both the heat-treated fibers and papers made from such heat-treated fibers. The X-ray peaks and intensities of the different of the fibers and papers made from aramid copolymer comprising an imidazole group are summarized in the Reference Table.

TABLE-US-00001 Reference Table X-Ray Peak Intensity Forms of Aramid Copolymer Fibers (+/0.5) (%) Dried Fiber 25 >/=25 Uncalendered Paper w/Dried Fiber 25 >/=25 Calendered Paper w/Dried Fiber 20.2 4 Uncalendered Paper w/HT Fiber 20.2 >4 Calendered Paper w/HT Fiber 20.2 >4

[0062] It is believed the use of the dried aramid copolymer fibers in the formation of the papers can provide a thermally consolidated paper that has fiber components that are more efficiently bonded or bound together. The result is a paper having a preferred higher density along with high average specific modulus with good ultimate tensile index, versus papers made the same way with heat treated aramid copolymer fibers.

[0063] This invention also relates to a process for making a paper, comprising the steps of: [0064] a) forming an aqueous slurry comprising 85 to 40 parts by weight polymeric fibers and 15 to 60 parts by weight binder, based on the combined weight of said polymeric fibers and said binder, [0065] wherein the polymeric fibers comprise first fibers and second fibers, [0066] the first fibers comprising a first polymer, wherein the first polymer is an aramid copolymer having a structure derived from the reaction of para-oriented aromatic diamine monomer and benzimidazole monomer with a para-oriented aromatic diacid monomer, [0067] the second fibers comprising poly(para-phenylene terephthalate) homopolymer, and [0068] the binder comprising a third polymer that is either an aramid homopolymer or aramid copolymer; and [0069] the polymeric fibers comprising 12.5 to 75 parts by weight first fibers and 25 to 87.5 parts by weight second fibers, based on the combined weight of said first and said second fibers; [0070] b) removing water from the slurry on a paper machine to form a wet paper composition; [0071] c) drying the wet paper composition to form a dried sheet; and [0072] d) thermally consolidating the dried sheet in one or more steps between nipped rolls heated to a surface temperature of 260 C. or more, using a nip pressure of 700 to 5000 lbs./inch (125 to 894 kg/cm);
to form a paper having an ultimate tensile strength of 21 N-m/g or greater and average specific modulus of 4950 Pa-m.sup.3/g or greater.

[0073] The aqueous slurry of polymeric fibers used in step a) preferably contains dried fibers as defined herein made from the first polymer, which is the aramid copolymer comprising an imidazole group. These dried fibers have not been exposed to any environment of 260 C. or higher. Consequently, these dried fibers have a 2 theta (2) x-ray diffraction angle peak of 25 (+/0.5) degrees. In some embodiments, these first polymer dried fibers have an x-ray diffraction angle tracing showing a 2 theta (2) x-ray diffraction angle peak of 25 (+/0.5) degrees, and the integrated intensity of said x-ray diffraction angle peak is 25 percent or more of the total diffraction pattern intensity, after background subtraction.

[0074] The thermal consolidation in step d) exposes the fibrous material in the formed paper to high temperatures (260 C. or more) and pressure (700 to 5000 lbs./inch (125 to 894 kg/cm)), creating a paper having an ultimate tensile strength of 21 N-m/g or greater and average specific modulus of 4950 Pa-m.sup.3/g or greater. It is believed that after thermal consolidation of the paper under this high temperature and pressure, the first polymer fibers in the paper have an x-ray diffraction angle tracing showing a 2 theta (2) x-ray diffraction angle peak of 20.2 (+/0.5) degrees, the integrated intensity of said x-ray diffraction angle peak being 4 percent or less of the total diffraction pattern intensity, after background subtraction. In other words, it is believed that both the x-ray diffraction angle peak and the integrated intensity of the first polymer fibers in the formed paper changes as a result of thermal consolidation which involves exposure to temperatures of 260 C. or more.

[0075] Conversely, the heat-treated first polymer fibers have already been exposed to high temperatures (260 C. or more) in the manufacture of those fibers prior to their use in papermaking. As shown in the Reference Table, those heat-treated fibers have an x-ray diffraction angle tracing showing a 2 theta (2) x-ray diffraction angle peak of 20.2 (+/0.5) degrees, and the integrated intensity of said x-ray diffraction angle peak is more than 4 percent of the total diffraction pattern intensity (after background subtraction), and the formed paper made with the heat treated fibers has essentially this same x-ray diffraction angle peak and the integrated intensity. Additionally, as also shown in the Reference Table, because the heat-treated fibers have already been exposed to high temperatures, thermal consolidation of the formed paper with high temperatures (260 C. or more) and pressure does not have the same effect on those fibers in the paper, and an x-ray diffraction angle tracing of such paper retains the 2 theta (2) x-ray diffraction angle peak of 20.2 (+/0.5) degrees, and while the integrated intensity of said x-ray diffraction angle peak changes slightly, it is maintained at more than 4 percent of the total diffraction pattern intensity, after background subtraction.

[0076] In some embodiments, an aqueous slurry containing the desired paper composition is supplied to a screen or wire mesh belt, where the solid materials in the slurry form a wet laid web, or what is sometimes known as a waterleaf, and the water is removed by gravity, vacuum, and/or pressing. The wet laid web, when dried using a conventional papermaking dryer section (typically on dryer rolls or in an oven at temperatures greater than 100 C. generally up to about 150 C., but significantly below 260 C.), becomes a dried paper (or dried sheet or formed paper as used interchangeably herein).

[0077] Reference may be made to Gross, (U.S. Pat. No. 3,756,908) and Hesler et al. (U.S. Pat. No. 5,026,456) for illustrative known processes for forming the dried sheet or formed paper. Once the dried sheet is formed, it can be thermally consolidated using a plate press, but for practical commercial production the thermal consolidation can be performed in a continuous manner by calendering the dried sheet in a nip between two heated calendering rolls, which applies high temperature and pressure to the dried sheet. If desired, several plies of the dried sheet with the same or different compositions can be combined together and thermally consolidated into the final paper structure.

[0078] The thermal consolidation of the dried sheet can be accomplished in one or more steps between heated surfaces, such as the nipped calender roll surfaces or a press plate surface, heated to a surface temperature of 260 C. or more, using a nip pressure of 700 to 5000 lbs./inch (125 to 894 kg/cm). In some embodiments, the nip pressure is 1500 to 5000 lbs./inch (268 to 894 kg/cm). In some embodiments, the nip pressure is 1500 to 3000 lbs./inch (268 to 535 kg/cm). In some embodiments, the surface can be heated to a surface temperature can be 260 C. to 450 C. In some embodiments, the surface can be heated to a surface temperature of 300 C. to 425 C. In some embodiments, the surface can be heated to a surface temperature of 350 C. to 425 C.

[0079] All of the additional features, elements, compositions, and properties of the paper or ingredients of the paper previously described herein; for example, dielectric strength, average specific modulus, tensile modulus, density, thickness, etc., apply to the features, elements, and properties recited for the process for making the paper.

[0080] Specifically, as previously discussed herein, the process for making the paper utilizes polymeric fibers, comprising first polymer fibers and second polymer fibers, as previously described herein, and polymeric binder comprising a third polymer as previously described herein. That first polymer can comprise benzimidazole monomer that is 5(6)-amino-2-(p-aminophenyl) benzimidazole, para-oriented diamine monomer that is paraphenylene diamine, and para-oriented aromatic acid monomer that is terephthaloyl dichloride. Likewise, the second polymer can comprise benzimidazole monomer that is 5(6)-amino-2-(p-aminophenyl) benzimidazole, para-oriented diamine monomer that is paraphenylene diamine, and para-oriented aromatic acid monomer that is terephthaloyl dichloride. The second polymer comprising PPD-T homopolymer, and the third polymer can be an aramid copolymer or aramid homopolymer and can be the same or different from the first or second polymer. Preferably, the third polymer is either MPD-I or an aramid copolymer comprising an imidazole group. In some embodiments, the binder includes non-granular polymer fibrids that are fibrous, film-like or a mixture thereof, made from the third polymer.

[0081] The aqueous slurry comprises 85 to 40 parts by weight of the polymeric fibers, and 15 to 60 parts by weight of the binder, preferably in water; those amounts being based on the combined weight of those polymeric fibers and binder. In some specific embodiments, the aqueous slurry has 80 to 40 parts by weight of the polymeric fibers and 20 to 60 parts by weight of the binder, based on the combined weight of those polymeric fibers and binder. In some embodiments, the aqueous slurry comprises 80 to 45 parts by weight of the polymeric fibers, and 20 to 55 parts by weight of the binder, those amounts being based on the combined weight of those polymeric fibers and binder. In some embodiments, the aqueous slurry comprises 80 to 50 parts by weight of the polymeric fibers, and 20 to 50 parts by weight of the binder, those amounts being based on the combined weight of those polymeric fibers and binder.

[0082] In some embodiments, the polymeric fibers in the aqueous slurry comprise 12.5 to 75 parts by weight of the aramid copolymer fibers previously described, and 25 to 87.5 parts by weight of the (PPD-T) homopolymer fibers previously described, based on the combined weight of said those two types of fibers. In some embodiments, the polymeric fibers in the aqueous slurry comprise 12.5 to 60 parts by weight of the aramid copolymer fibers previously described, and 40 to 87.5 parts by weight the (PPD-T) homopolymer fibers previously described, based on the combined weight of those two types of fibers; and in some other embodiments, the polymeric fibers in the aqueous slurry comprise 12.5 to 50 parts by weight of the aramid copolymer fibers previously described, and 50 to 87.5 parts by weight the (PPD-T) homopolymer fibers previously described, based on the combined weight of those two types of fibers.

[0083] The inventive papers also have very good mechanical properties that are useful in composite applications including such things as honeycomb and other types of core material. The inventive papers have good electrical insulative properties and are also suitable for use as electrical insulation; along with any number of other applications that require a thermally stable high performance paper.

Test Methods

[0084] Average specific modulus. The Average specific modulus of a paper is the calculated average of the MD specific modulus and the XD specific modulus, reported in Pa-m.sup.3/g. The density of each of a MD paper sample and a XD paper sample is measured, and then the Young's Modulus in the machine direction (MD) and the Young's Modulus in the cross direction (XD) is determined. The MD specific modulus is then the Young's Modulus in the machine direction (MD) divided by the density of the MD paper sample; and the XD specific modulus is the Young's Modulus in the cross direction (XD) divided by the density of the XD paper sample. The MD specific modulus and the XD specific modulus are then averaged to calculate the average specific modulus.

[0085] Ultimate Tensile Index. Tensile Index was measured according to ASTM D 828-97 with 2.54 cm wide test specimens and a gage length of 18 cm and reported in N.Math.m/g.

[0086] Dielectric Strength. Dielectric Strength was measured according to ASTM D149-97A and reported in V/mil or kV/mm using 20.3 cm by 20.3 cm (8 by 8) test specimens pre-conditioned at 23 deg C. and 50% RH and tested with 5.08 cm (2) flat electrodes at 20.6 deg C. and 60% RH. Some specimens have also been tested with 6.35 mm (0.25) flat electrodes.

[0087] MD/XD Strength, MD/XD Modulus, & MD/XD Elongation. Tensile Strength, Young's Modulus, and Elongation in both the machine direction (MD) and the orthogonal cross direction (XD) were measured according to ASTM D 828-97 with 2.54 cm wide test specimens and a gage length of 18 cm and reported in MPa or N/cm and converted to GPa.

[0088] Density. Density was measured according to ASTM D792-20 and reported in kg/m.sup.3 and converted to g/cm.sup.3.

[0089] X-Ray Diffraction. The molecular structure of papers and fibers was assessed with x-ray diffraction, using a Malvern Panalytical Materials Powder Diffractometer (MPD). Data were fit using an automated script written in MATLAB. Fiber samples were read on low background silicon wafers to avoid background discrepancies between samples. Data were first read in, then a scan of an empty sample holder was subtracted, such that the baseline on either side of the diffraction pattern was level after subtraction. Baseline leveling points were 7 and 59 two theta for meridional fiber data, 7.2 and 44 for equatorial fiber data. Next, a linear background was subtracted using the same endpoints to bring the baseline down to zero counts.

[0090] Thickness. Thickness was measured according to ASTM D374-99 (2004) and reported in mils and converted to millimeters.

[0091] Base Weight. Basis Weight was measured according to ASTM D 646-96 and reported in g/m.sup.2.

EXAMPLES

[0092] The aramid copolymer floc used in Example 1 was made as follows. The monomers 5(6)-amino-2-(p-aminophenyl) benzimidazole (DAPBI) and paraphenylene diamine (PPD), in amounts suitable for forming a copolymer having a DABPI/PPD monomer ratio of 70/30, were combined with a stoichiometric amount of terephthaloyl dichloride (TCI) in a solvent system comprising N-methyl-2-pyrrolidone (NMP) solvent and 4.5 weight percent calcium chloride (CaCl2) as a solubility enhancer. The monomers polymerized to form a copolymer. After the polymerization was complete, the copolymer crumb was recovered, ground, and washed with sodium hydroxide to neutralize byproduct hydrochloric acid. The crumb was then filtered and dried. The copolymer that had an inherent viscosity of about 6.45 dl/g. As reference, other known method of making the copolymer are disclosed in U.S. Pat. Nos. 9,988,514; 9,994,974; 10,400,082; 10,400,357; and 11,279,800.

[0093] The dried aramid copolymer floc use in the papers of the examples was made in the following manner. A portion of the dried aramid copolymer crumb was redissolved in sulfuric acid, to form a polymer solution suitable for spinning fibers. An aramid copolymer yarn of polymeric filaments was then spun from the polymer solution by extruding the polymer solution through a spinneret for form dope filaments, followed by air-gap spinning the dope filaments into a coagulation bath to remove sulfuric acid and form a yarn of filaments having nominal individual linear densities of 1.25 denier (1.39 dtex) per filament, followed by washing and drying of the yarn, using known techniques such as disclosed, for example, in U.S. Pat. Nos. 9,988,514; 9,994,974; 10,400,082; 10,400,357; and 11,279,800. The aramid copolymer yarn used in the example contained dried fibers made by drying the aramid copolymer filament yarn only slightly above 100 C. and not subjecting the yarn to any additional heat treating; that is, the aramid copolymer yarn was made without exposure to a temperature of 260 C. or greater. The aramid copolymer yarn was then cut into 3 mm aramid polymer floc using a Lummus cutter (available from DM&E Corporation) for use in the paper examples.

[0094] The poly (metaphenylene isophthalamide) (MPD-I) fibrids used in the example papers were made as follows. A polymer solution of MPD-I polymer in a DMAc/CaCl.sub.2) solvent system is first made, followed by precipitation of the MPD-I polymer in water while under vigorous agitation, using a fibridator, which is the apparatus disclosed in U.S. Pat. No. 3,018,091. The apparatus shears the precipitating solution to form filmy fibrous structures. The resulting fibrids were then washed in water to remove DMAc and calcium chloride. Other known techniques for making fibrids, such as disclosed in U.S. Pat. Nos. 2,999,788 and 3,756,908 could be used.

Example 1

[0095] In the examples that follow, the thermally consolidated paper samples were made using aramid copolymer floc, PPD-T floc, and MPD-I fibrids. The aramid copolymer floc had a nominal floc cut length of 3 mm and a linear density of 1.25 denier (1.39 dtex) per filament. The PPD-T floc was obtained from commercially available Kevlar 49 yarn having filaments with a linear density of 1.5 denier (1.65 dtex) per filament. The PPD-T filament yarn was prepared by the known processes of U.S. Pat. Nos. 3,767,756 and 3,869,429; such yarns typically have filament tenacities of at least 18 gpd, (15.9 dN/tex), breaking elongation of at least 3.5 percent, and filament modulus of at least 400 gpd (353 dN/tex). The PPD-T filament yarn was then cut into 3 mm floc using a Lummus cutter for use in the paper samples.

[0096] Specifically, the paper samples had the compositions as described in Table 1A, where the percentages of the flocs and fibrids in the paper samples are provided; and the calculated percentage of each type of floc in the polymeric fibers used in each paper sample, excluding the fibrids, is also provided.

[0097] Each paper sample was a handsheet prepared from a slurry of the floc and fibrids in water. Prior to combining the floc to the fibrids, the fibrids were dispersed in about 2 liters of water by shear mixing in a high shear laboratory mixer for 1 minute. Separately, the floc was dispersed in about 4 liters of water by shear mixing in a high shear laboratory mixer for 5 minutes. The fibrid slurry was then added to floc slurry and further mixed for 5 more minutes to achieve a slurry having uniformly dispersed solids in about 6 liters of water. The slurry was then added to the tank of paper hand-sheet equipment (TechPap model FDA Automated Dynamic Handsheet Former) while maintaining mixing, and a paper sample handsheet measuring 1036 inches (25.4 cm91.44 cm) was prepared. The handsheet was then removed, placed between two pieces of blotting paper and hand-couched with a rolling pin to remove excess water, and then dried in a hand sheet dryer at 150 C. for 10 minutes. The handsheets were then conditioned an oven at 80 C. for 8 hours to remove moisture before densification. Each of the handsheets was then densified (thermally consolidated) by pressing between nipped rollers at a temperature of 330 C. and a pressure of 800 lbs/in.sup.2 (5.510.sup.6 N/m.sup.2).

[0098] In this and all other examples, handsheet paper samples were made, cut into testing samples as needed (e.g., machine direction (MD) and cross direction (XD), etc.), and individually tested. Various properties of various compositions of the paper samples are summarized in Tables 1B & 1C. Inventive papers (1-1 to 1-8) contained various proportions of dried aramid copolymer floc, PPD-T floc, and MPD-I fibrids, and illustrate these papers have claimed combination of high average specific modulus with good ultimate tensile strength. Comparative papers A-1 to A-3 illustrate compositions with too little binder do not provide the claimed combination of properties. Comparative papers A-4 and A-5 illustrate composition containing only the aramid copolymer floc or PPD-T floc and lower levels of fibrids do not provide the claimed combination of properties.

TABLE-US-00002 TABLE 1A Percentage in the Percentage in the Paper Polymeric Fibers Aramid Aramid Copolymer PPD-T MPD-I Copolymer PPD-T Floc Floc Fibrids Floc Floc Item (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) 1-1 10 70 20 12.5 87.5 1-2 20 60 20 25 75 1-3 30 50 20 37.5 62.5 1-4 40 40 20 50 50 1-7 10 40 50 20 80 1-8 25 25 50 50 50 A-1 A-3 90 10 0 100 A-2 1-5 10 80 10 11.1 88.9 A-3 1-6 45 45 10 50 50 A-4 A-1 80 20 0 100 A-5 A-2 80 20 100

TABLE-US-00003 TABLE 1B Aramid Ultimate Copol- Average Tensile ymer PPD-T MPD-I Dielectric Specific Strength Floc Floc Fibrids Strength, Modulus Index Item (wt. %) (wt. %) (wt. %) (kV/mm) (Pa .Math. m.sup.3/g) (N .Math. m/g) 1-1 10 70 20 11.8 4966 22.3 1-2 20 60 20 10.7 5133 23.0 1-3 30 50 20 10.9 5132 23.3 1-4 40 40 20 10.2 5331 23.3 1-7 10 40 50 17.5 5302 45.9 1-8 25 25 50 19.3 5673 48.7 A-3 90 10 10.1 3623 14.8 1-5 10 80 10 9.6 3677 14.0 1-6 45 45 10 8.4 3655 8.8 A-1 80 20 10.0 4084 20.7 A-2 80 20 8.0 5993 17.6

TABLE-US-00004 TABLE 1C Basis Breaking Mod- Direc- Weight Thickness Strength ulus tion- Den- MD/XD MD/XD MD/XD MD/XD ality sity Item (gsm) (mm) (N/cm) (GPa) (ratio) (g/cm.sup.3) 1-1 37.2/37.2 0.047/0.047 10.5/6.1 5.1/2.7 1.7 0.79 1-2 38.9/38.9 0.049/0.049 11.5/6.4 5.5/2.8 1.8 0.80 1-3 39.6/39.1 0.052/0.052 11.1/7.2 4.9/2.9 1.5 0.76 1-4 37.3/37.6 0.049/0.049 10.4/7.0 5.2/3.0 1.5 0.77 1-7 39.5/39.4 0.050/0.050 20.4/15.8 4.9/3.5 1.3 0.79 1-8 40.0/39.7 0.053/0.053 22.0/16.8 5.2/3.4 1.3 0.76 A-3 39.8/39.5 0.048/0.048 8.1/3.7 4.3/1.8 2.2 0.83 1-5 38.4/38.5 0.047/0.047 6.6/4.2 3.9/2.1 1.6 0.82 1-6 38.3/38.6 0.054/0.054 4.2/2.6 3.4/1.8 1.6 0.72 A-1 37.6/38.3 0.045/0.046 10.3/5.4 4.6/2.2 1.9 0.83 A-2 31.9/31.9 0.045/0.044 6.8/4.4 5.0/3.5 1.5 0.71

Comparison Example

[0099] A number of paper samples were made as a comparison in the manner as described in Example 1. The samples were made solely with PPD-T floc and MPD-I fibrids or made solely with MPD-I floc and MPD-I fibrids. The MPD-I floc was made from MPD-I fiber, which was made using known techniques and apparatus such as disclosed in, for example, U.S. Pat. No. 3,756,908. The MPD-I fiber was obtained by dry spinning yarns of MPD-I filaments having a linear density of 2.2 denier (2.44 dtex) and subsequently exposing the MPD-I filament yarns to temperatures above the glass transition temperature of the MPD-I polymer, which formed crystallized MPD-I yarns. The MPD-I filament yarn was then cut into 3 mm floc using a Lummus cutter.

[0100] Various properties of various compositions of the paper samples were then measured and summarized in Tables 2A & 2B. Comparison items A and B used MPD-I fibrids combined with MPD-I floc, while Comparison items C and D used MPD-I fibrids combined with PPD-T floc. All of the items A through D were thermally consolidated.

[0101] Comparative papers A through C did not have the claimed combination of properties. Comparative paper D illustrated a paper with PPD-T floc and MPD-I fibrids can obtain the claimed properties, but since no aramid copolymer floc is present in the paper, it is believed this paper would not have the desired benefit of potentially improved adhesion to certain resins that the aramid copolymer floc provides.

TABLE-US-00005 TABLE 2A Ultimate Avg. Tensile Dielectric Specific Strength Floc, Fibrid, Fibrid Strength, Modulus Index Item wt. % wt. % Floc Type Type (kV/mm) (Pa .Math. m.sup.3/g) (N .Math. m/g) A 80 20 MPD-I MPD-I 9.0 3054 40.6 B 50 50 MPD-I MPD-I 17.3 3134 51.3 C 80 20 PPD-T MPD-I 10.0 4084 20.7 D 50 50 PPD-T MPD-I 16.0 5008 44.4

TABLE-US-00006 TABLE 2B Basis Breaking Weight Thickness Strength Modulus MD/XD MD/XD MD/XD MD/XD Directionality Density Item (gsm) (mm) (N/cm) (GPa) (ratio) (g/cm.sup.3) A 41.0/41.4 0.059/0.061 25.3/8.1 3.3/0.92 3.1 0.69 B 41.0/41.0 0.054/0.054 29.6/12.5 3.0/1.7 2.4 0.76 C 37.6/38.3 0.045/0.046 10.3/5.4 4.6/2.2 1.9 0.83 D 40.5/40.3 0.047/0.047 21.6/14.2 5.5/3.3 1.5 0.86