(19)
(11)EP 3 504 377 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
04.11.2020 Bulletin 2020/45

(21)Application number: 17755508.3

(22)Date of filing:  22.08.2017
(51)International Patent Classification (IPC): 
D21H 13/26(2006.01)
(86)International application number:
PCT/EP2017/071156
(87)International publication number:
WO 2018/037017 (01.03.2018 Gazette  2018/09)

(54)

METHOD FOR MANUFACTURING ARAMID PULP COMPRISING PVP

VERFAHREN ZUR HERSTELLUNG VON ARAMIDPULPE MIT PVP

PROCÉDÉ DE FABRICATION DE PÂTE ARAMIDE CONTENANT DU PVP


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 24.08.2016 EP 16185527

(43)Date of publication of application:
03.07.2019 Bulletin 2019/27

(73)Proprietor: Teijin Aramid B.V.
6824 BM Arnhem (NL)

(72)Inventors:
  • NIJHUIS, Walter
    7555 KZ Hengelo (NL)
  • TIECKEN, Jan-Cees
    6942 KK Didam (NL)
  • DIEDERING, Frank
    7413 CP Deventer (NL)

(74)Representative: CPW GmbH 
Kasinostraße 19-21
42103 Wuppertal
42103 Wuppertal (DE)


(56)References cited: : 
WO-A1-02/46527
WO-A1-2014/177328
WO-A1-96/10105
US-A- 5 399 431
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present invention is directed to a method for manufacturing aramid pulp comprising polyvinyl pyrrolidone (PVP).

    [0002] Poly(para-phenylene terephthalamide), also indicated as para-aramid, is known in the art for its high strength and fire resistance. Para-aramid pulp can be obtained by fibrillating short para-aramid fibers, also known as para-aramid short-cut. Para-aramid pulp is used in many applications where high strength and high heat resistance are required.

    [0003] To address specific requirements, modified aramid pulps have been described in the art.

    [0004] WO02/46527 describes a pulp manufacturing process wherein a blend of polymer materials is spun to form a fiber, floc is cut from the fibers and the floc is refined to form pulp. WO96/10105 describes a process for manufacturing a fibrous pulp of a combination of para-aramid and PVP wherein a para-aramid polymerization reaction is carried out in the presence of PVP, and pulp is prepared from the solution.

    [0005] US5399431 describes fiber materials from homogeneous blends of aromatic polyamides and PVP. The term homogeneous blends means that the components of the blend form an essentially uniform phase. The fiber materials are obtained by spinning (solutions of) the polymer blends. Pulp is mentioned as a possible use. US6303221 describes a high modulus elastomer composite comprising a fibrous pulp with is a uniform combination of, preferably para-aramid, and a further polymer such as PVP. The pulp is obtained by refining floc obtained by cutting fibers spun from a blend of component polymer materials.

    [0006] Thus, in the art, aramid pulp comprising PVP has been obtained either from a solution comprising para-aramid and PVP, wherein the para-aramid may be polymerized in the presence of the PVP, or by fibrillating fibers obtained from homogeneous blends of para-aramid and PVP. These processes have been found to result in pulp with attractive properties. However, there is need in the art for an improved process, in particular a process wherein a pulp with better dewatering properties is obtained, while maintaining good retention of PVP. Additionally, the processes described above have the disadvantage that they make use of relatively complex solutions, and are relatively complicated to integrate into existing para-aramid production.

    [0007] There is need in the art for a process for manufacturing aramid pulp comprising PVP which on the one hand results in a pulp of good quality, with improved dewatering characteristics while maintaining good retention of PVP, and on the other hand is easy to operate.

    [0008] The present invention provides such a process.

    [0009] The invention thus pertains to a process for manufacturing an aramid pulp comprising polyvinyl pyrrolidone (PVP), the method comprising the steps of
    • combining para-aramid short-cut having a length of at least 0.5 mm and at most 20 mm with PVP in an aqueous solution to form a mixture, the mixture comprising
    • 0.1-7 wt.% aramid short-cut, and
    • between 0.1 and 15 wt.% PVP, calculated based on the dry weight of the aramid short-cut;
    • subjecting the mixture to a refining step to form a para-aramid pulp comprising PVP.


    [0010] It has been found that the process according to the invention makes it possible to obtain aramid pulp comprising PVP in an efficient manner using an easy to operate process, namely without having to use the complicated process for manufacturing PVP-containing yarn. This is surprising since PVP has a high solubility in water. It would therefore be expected that a substantial amount of PVP would be lost during the refining process. This appears not to be the case. Interestingly, when PVP is added to an already existing pulp, PVP loss does take place.

    [0011] It has further been found that, at a certain fiber length, the PVP pulp prepared by the process according to the invention shows better dewatering properties (i.e. faster dewatering) than PVP pulp obtained from PVP-containing yarn at the same fiber length. This is attractive from a manufacturing point of view, and for use of the pulp in specific applications.

    [0012] It has further been found that refining of aramid pulp to a certain fiber length in the presence of PVP requires less energy than refining short-cut derived from an aramid-PVP blend yarn.

    [0013] Further advantages of the present invention and specific embodiments thereof will become clear from the further specification.

    [0014] The invention will be elucidated further below.

    [0015] In the context of the present specification aramid refers to an aromatic polyamide which is a condensation polymer of aromatic diamine and aromatic dicarboxylic acid halide. Aramids may exist in the meta- and para-form. Para-aramid is used in the present invention. In the context of the present specification the term para-aramid refers to aramid wherein at least 85% of the bonds between the aromatic moieties are para-aramid bonds. As typical members of this group are mentioned poly(paraphenylene terephthalamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylenedicarboxylic acid amide) and poly (paraphenylene-2,6-naphthalenedicarboxylic acid amide or copoly(para-phenylene/3,4'-dioxydiphenylene terephthalamide). The use of para-aramid wherein at least 90%, more in particular at least 95%, of the bonds between the aromatic moieties are para-aramid bonds is considered preferred. The use of poly(paraphenylene terephthalamide), also indicated as PPTA, is particularly preferred.

    [0016] Within the present specification the term para-aramid short-cut refers to para-aramid fibers cut to a length of at least 0.5 mm, in particular at least 1 mm, more in particular at least 2 mm, in some embodiments at least 3 mm. The length is at most 20 mm, in particular at most 10 mm, more in particular at most 8 mm. The thickness of the short-cut is, e.g., in the range of 5-50 micron, preferably in the range of 5-25 micron, most preferably in the range of 6-18 micron. Para-aramid fibers from which such short-cut can be prepared are commercially available, e.g., from Teijin Aramid®. The length of the shortcut refers to the LL0.25, which is a length-weighted average length wherein particles are included having a length > 250 µm, i.e. > 0.25 mm.

    [0017] PVP, polyvinyl pyrrolidone, is known in the art and commercially available. It may, e.g., have been obtained by linear polymerization of N-vinyl-2-pyrrolidone. The PVP used in the present invention generally has a weight average molecular weight in the range of 5 to 2500 kg/mol. It may be preferred for the PVP to have a weight average molecular weight of 8 to 1500 kg/mol. Lower molecular weights may be preferred, in particular to obtain improved PVP retention. Therefore, it may be preferred for the PVP to have a weight average molecular weight in the range of 10 to 1000 kg/mol, in particular 10-500 kg/mol, more in particular 10-200 kg/mol, in some embodiments 10-100 kg/mol, or even 10-60 kg/mol.

    [0018] In the first step of the process according to the invention, para-aramid short-cut is combined with PVP in an aqueous solution to form a mixture. This can be done in a variety of ways. For example, dry short-cut may be added to a solution or suspension of PVP in water, PVP may be added to a suspension of short-cut in water, or PVP and short-cut may be added together to an aqueous medium.

    [0019] The aramid short-cut is present in the mixture in an amount of 0.1-7 wt.%, in particular in the range of 1-5 wt.%. An amount in this range has been found suitable for a successful refining operation.
    The concentration of PVP in the mixture depends on the amount of PVP desired in the end product and on the amount of PVP that may be lost during operation. The amount of PVP in the end product is in the range of 0.1-10 wt.% PVP, calculated based on aramid dry weight, in particular 0.5-6 wt.%. The amount of PVP present in the aqueous mixture varies between 0.1 and 15 wt.%, calculated based on the dry weight of the aramid short-cut, in particular between 0.5 and 10 wt.%, calculated based on the dry weight of the aramid short-cut.

    [0020] The aqueous mixture comprising PVP and para-aramid short-cut is subjected to a refining step to form an aramid pulp comprising PVP. Refining processes are known in the art. In general, in refining, a short-cut slurry is subjected to a high shear environment, e.g., by passing it between discs which move with respect to each other. The effect of the refining step is to reduce the length of the short-cut, and to fibrillate the short-cut to form pulp. In fibrillation, fibrils will form on the short-cut, which will result in "stems" with fibrils connected thereto and loose fibrils. Further, the stems of the pulp may become kinked during the refining process.
    It is possible to carry out a single refining step, but is also possible to subject refined pulp to one or more further refining steps, which are carried out at the same or different conditions as the first refining step.

    [0021] The pulp slurry resulting from the refining process may be treated as desired. It can for example be provided to a dewatering step wherein the slurry is dewatered, generally by bringing it onto a sieve or other filtering material. This results in the formation of a dewatered pulp. Dewatered pulp generally has a water content in the range of 40-80 wt.%, specifically 50-70 wt.%. The dewatered pulp can be in the form of a cake (as it originated from the filter), or the cake can be broken to form individual pieces, also indicated as crumb.

    [0022] The dewatered pulp, in the form of cake or crumb or any other form, can be an end product, which can be further processed as desired. The dewatered pulp can also be dried.

    [0023] Drying of the dewatered pulp can take place in a conventional manner, e.g. by contacting it with a drying atmosphere, optionally at an elevated temperature, resulting in the formation of dried pulp. Dried pulp generally has a water content in the range of 2 to 20 wt.%, in particular 3 to 10 wt.%.

    [0024] The dried pulp can, if so desired, be subjected to an opening step. Pulp opening is known in the art. It encompasses subjecting the dried pulp to mechanical impact, e.g., using an impact mill, a mill using turbulent air, or a high shear/high agitating mixer. The pulp opening step decreases the bulk density of the pulp material (i.e., it makes it more "fluffy"). Opened pulp may be easier to disperse and therewith easier to apply. In general, the pulp opening step does not substantially change the properties of the pulp.

    [0025] The PVP-containing aramid pulp obtained by the method according to the invention generally has a length (LL0.25) in the range of 0.7 to 1.5 mm, in particular in the range of 0.9 to 1.5 mm, in some embodiments in the range of 0.9-1.3 mm. This parameter is determined by the Pulp Expert™ FS apparatus which is calibrated with samples of pulp with known lengths. The length weighted length LL0.25 [mm] is a length-weighted average length wherein particles are included having a length > 250 µm, i.e. > 0.25 mm.

    [0026] The PVP-containing aramid pulp obtained by the method according to the invention has a Schopper Riegler (SR) in the range of 15 to 80 °SR, in particular in the range of 20 to 60 °SR, more in particular in the range of 20 to 40 °SR. The SR is a parameter often used in the art of pulp and paper technology. It is a measure of the drainability of a pulp suspension in water. SR can be determined in accordance with ISO5267/1. As indicated above it has been found that the pulp obtained by the process of the invention has better dewatering properties, as evidenced by a lower SR, than a pulp with a comparable length obtained from refining short-cut containing both aramid and PVP (under the same refining conditions).

    [0027] The PVP-containing aramid pulp generally has a Canadian Standard Freeness (CSF) in the range of 15 to 700 mL, in particular in the range of 100 to 600 mL, more in particular in the range of 270 to 570 mL. The CSF is a parameter often used in the art of pulp and paper technology. It is a measure of the drainability of a pulp suspension in water. CSF can be determined in accordance with TAPPI T227. The improved dewatering properties of the pulp obtained by the process of the invention also appear from a higher CSF as compared with a pulp with a comparable length obtained from refining short-cut containing both aramid and PVP (under the same refining conditions).

    [0028] As will be evident to the skilled person, the various preferred embodiments as described above can be combined unless they are mutually exclusive.

    [0029] The invention will be elucidated with reference to the following Examples, without being limited thereto or thereby.

    Example 1: manufacture of PVP-aramid pulp according to the invention



    [0030] 4 kg of para-aramid chopped fibers of 6 mm in length (6 mm short-cut based on Twaron® type 1000 1680f1000 from Teijin Aramid BV, NL) was added to 200 liter of an aqueous solution of PVP. The PVP had a molecular weight of approximately 50 kg/mol. The resulting medium contained 2 wt.% of aramid short-cut and 0.1 wt.% of PVP. The resulting suspension was passed through a Sprout-Bauer 12" lab refiner until the desired fiber length was obtained. Intermediate samples were taken during the process. The refined suspension was dewatered on a sieve table to yield a dewatered cake. The dewatered cake was dried in an oven overnight at 105°C to yield a dried cake. Approximately 800 g of the dried cake was then opened in a Lödige high-shear mixer for 4 minutes resulting in an opened PVP pulp. The resulting dry pulp contained 5 wt.% PVP, determined from the amount of PVP present in the effluent. The properties of the pulp are discussed in Example 4 below.

    Example 2: manufacture of a comparative pulp from aramid fiber comprising PVP



    [0031] The starting material was a para-aramid fiber comprising 5 wt.% of PVP. The fiber was obtained by spinning of aramid in the presence of PVP. The fiber was chopped into short-cut with a length of 6 mm. The short-cut was added to water to form a suspension containing 2 wt.% of aramid-PVP fiber. The suspension was provided to a refiner as described in Example 1, and the resulting refined suspension was treated further as described there. The resulting dry pulp contained 5 wt.% PVP, determined from the amount of PVP present in the effluent. The properties of the pulp are discussed in Example 4 below.

    Example 3: manufacture of a comparative PVP-aramid pulp by adding PVP to aramid pulp



    [0032] 4 kg of para-aramid chopped fibers of 6 mm in length (6 mm short-cut based on Twaron® type 1000 from Teijin Aramid BV, NL) was added to 200 liter of water. The resulting medium contained 2 wt.% of aramid short-cut. The suspension was passed through a Sprout-Bauer 12" lab refiner as described in Example 1. PVP with a molecular weight of approximately 50 kg/mol was added to the resulting refined pulp suspension in an amount sufficient to obtain a PVP concentration of 0.1 wt.%. The mixture was mixed for 10 minutes and was then dewatered and treated further as described in Example 1. The resulting dry pulp contained 2-4 wt.% PVP, determined from the amount of PVP present in the effluent. The properties of the pulp are discussed in Example 4 below.

    Example 4: Comparison of PVP-aramid pulps



    [0033] The following was seen from the manufacture and analysis of the various pulp types.

    1. PVP retention



    [0034] PVP retention on the pulp was about 100% for the pulp of Example 1 according to the invention and the pulp from blend yarn for Example 2. Where the PVP was added to the pulp after refining (Example 3), only about 80% retention was obtained. These values of retention are based on analysis of the filtrates of the final refined suspension mentioned in examples 1 to 3. The filtrate was obtained by dewatering of the refined suspension on a Büchner funnel. This shows that the process according to the invention makes it possible to incorporate PVP into aramid pulp with low PVP loss, without having to spin the aramid in the presence of PVP, which is a more complicated process.

    2. Dewatering



    [0035] It appeared that the dewatering step for the comparative pulp obtained from the blend yarn (Example 2) took more time than the dewatering step for either the pulp of Example 1, or the comparative pulp with post-added PVP (Example 3), as evidenced by the freeness values in the table below (expressed both in °SR and mL CSF). A higher SR-value indicates slower dewatering, whereas a higher CSF-value indicates faster dewatering. The following table shows the SR and CSF values for the three types of pulp, normalized to a fiber length of 1 mm.
     Freeness [°SR]CSF [mL]
    Pulp of Example 1 (invention) 36 295
    Pulp of Example 2 (comparative) 69 42
    Pulp of Example 3 (comparative) 19 584

    3. Required energy for refining



    [0036] It appeared that the cumulative specific energy (CSE) to reach a certain fiber length is higher for the comparative pulp obtained from the blend yarn (Example 2) than the CSE for either the pulp from Example 1, or the comparative pulp with post-added PVP (Example 3, where the pulp before treatment with PVP is considered), as illustrated in the table below. The table shows the CSE values for the three types of pulp, normalized to a fiber length of 1 mm. This shows that it is less energy efficient to produce pulp from blend yarn in comparison to the pulp from example 1. In addition, in order to even be able to process the blend yarn mentioned in Example 2, the throughput of the refiner needed to be reduced.
     CSE [kJ/kg]
    Pulp of Example 1 (invention) 3349
    Pulp of Example 2 (comparative) 5965
    Pulp of Example 3 (comparative) 2788


    [0037] In conclusion, the process according to the invention makes it possible to obtain a PVP pulp with improved dewatering properties and energy consumption as compared to pulp obtained from PVP-containing yarn, while maintaining a high PVP retention.


    Claims

    1. Process for manufacturing an aramid pulp comprising polyvinyl pyrrolidone (PVP), the method comprising the steps of

    - combining para-aramid short-cut having a length of at least 0.5 mm and at most 20 mm with PVP in an aqueous solution to form a mixture, the mixture comprising

    - 0.1-7 wt.% aramid short-cut, and

    - between 0.1 and 15 wt.% PVP, calculated based on the dry weight of the aramid short-cut;

    - subjecting the mixture to a refining step to form a para-aramid pulp comprising PVP.


     
    2. Process according to claim 1, wherein the para-aramid is poly(paraphenylene terephthalamide).
     
    3. Process according to any one of the preceding claims, wherein the para-aramid short-cut comprises para-aramid fibers with a length of 1-10 mm.
     
    4. Process according to any one of the preceding claims, wherein the para-aramid short-cut has a thickness in the range of 5-50 micron, preferably in the range of 5-25 micron, most preferably in the range of 6-18 micron.
     
    5. Process according to any one of the preceding claims, wherein the PVP has a weight average molecular weight in the range of 5 to 2500 kg/mol.
     
    6. Process according to any one of the preceding claims, wherein the concentration of aramid short-cut in the mixture is in the range of 1-5 wt.%.
     
    7. Process according to any one of the preceding claims, wherein the amount of PVP present in the aqueous mixture varies between 0.5 and 10 wt.%, calculated based on the dry weight of the aramid short-cut.
     
    8. Process according to any one of the preceding claims, wherein the pulp slurry resulting from the refining step is subjected to a dewatering step, to form a dewatered pulp with a water content which generally is in the range of 40-80 wt.%, specifically 50-70 wt.%.
     
    9. Process according to claim 8, wherein the dewatered pulp is subjected to a drying step to form a dried pulp, with a water content which generally is 2 to 20 wt.%, in particular 3 to 10 wt.%.
     
    10. Process according to claim 8, wherein the dried pulp is subjected to an opening step.
     
    11. Para-aramid pulp comprising 0.1-10 wt.% PVP, calculated on aramid dry weight, obtainable by the process of any one of the preceding claims, wherein the para-aramid pulp has a Schopper Riegler (SR) in the range of 15 to 80 °SR.
     
    12. Para-aramid pulp comprising PVP according to claim 11, which comprises 0.5-6 wt.% PVP, calculated on aramid dry weight.
     
    13. Para-aramid pulp according to claim 11 or 12, which has a length (LL0.25) in the range of 0.7 to 1.5 mm.
     
    14. Para-aramid pulp comprising PVP according to any one of claims 11-13, which has a Schopper Riegler (SR) in the range of 15 to 60 °SR.
     
    15. Para-aramid pulp comprising PVP according to any one of claims 11-14, which has a Canadian Standard Freeness (CSF) in the range of 15 to 700 mL, in particular in the range of 100 to 570 mL.
     


    Ansprüche

    1. Verfahren zur Herstellung einer Aramid Pulpe, umfassend Polyvinylpyrrolidon (PVP), wobei das Verfahren die Schritte umfasst

    - Kombinieren von Para-Aramid-Kurzschnitt mit einer Länge von mindestens 0,5 mm und höchstens 20 mm mit PVP in einer wässrigen Lösung, um ein Gemisch zu bilden, wobei das Gemisch umfasst

    - 0,1-7 Gew.-% Aramid-Kurzschnitt, und

    - zwischen 0,1 und 15 Gew.-% PVP, berechnet auf der Basis des Trockengewichts des Aramid-Kurzschnittes;

    - Unterziehen des Gemisches einem Mahlschritt, um eine PVP umfassende Para-Aramid Pulpe zu bilden.


     
    2. Verfahren nach Anspruch 1, wobei das Para-Aramid Poly(paraphenylenterephthalamid) ist.
     
    3. Verfahren nach einem der vorstehenden Ansprüche, wobei der Para-Aramid-Kurzschnitt Para-Aramidfasern mit einer Länge von 1-10 mm umfasst.
     
    4. Verfahren nach einem der vorstehenden Ansprüche, wobei der Para-Aramid-Kurzschnitt eine Dicke im Bereich von 5-50 µm, vorzugsweise im Bereich von 5-25 µm, besonders bevorzugt im Bereich von 6-18 µm, aufweist.
     
    5. Verfahren nach einem der vorstehenden Ansprüche, wobei das PVP ein gewichtsmittleres Molekulargewicht im Bereich von 5 bis 2500 kg/Mol aufweist.
     
    6. Verfahren nach einem der vorstehenden Ansprüche, wobei die Konzentration von Aramid-Kurzschnitt in dem Gemisch im Bereich von 1-5 Gew.-% liegt.
     
    7. Verfahren nach einem der vorstehenden Ansprüche, wobei die Menge an PVP, die in dem wässrigen Gemisch vorhanden ist, zwischen 0,5 und 10 Gew.-% variiert, berechnet auf der Basis des Trockengewichts des Aramid-Kurzschnitts.
     
    8. Verfahren nach einem der vorstehenden Ansprüche, wobei die aus dem Mahlschritt resultierende Pulpenaufschlämmung einem Entwässerungsschritt unterzogen wird, um eine entwässerte Pulpe mit einem Wassergehalt zu bilden, der im Allgemeinen im Bereich von 40-80 Gew.-%, insbesondere 50-70 Gew.-%, liegt.
     
    9. Verfahren nach Anspruch 8, wobei die entwässerte Pulpe einem Trocknungsschritt unterzogen wird, um eine getrocknete Pulpe mit einem Wassergehalt zu bilden, der im Allgemeinen 2 bis 20 Gew.-%, insbesondere 3 bis 10 Gew.-%, beträgt.
     
    10. Verfahren nach Anspruch 8, wobei die getrocknete Pulpe einem Öffnungsschritt unterzogen wird.
     
    11. Para-Aramid Pulpe, umfassend 0,1-10 Gew.-% PVP, berechnet auf Aramid-Trockengewicht, erhältlich durch das Verfahren nach einem der vorstehenden Ansprüche, wobei die Para-Aramid Pulpe einen Schopper-Riegler (SR)-Grad im Bereich von 15 bis 80°SR aufweist.
     
    12. Para-Aramid Pulpe, umfassend PVP nach Anspruch 11, die 0,5-6 Gew.-% PVP, berechnet auf Aramid-Trockengewicht, umfasst.
     
    13. Para-Aramid Pulpe nach Anspruch 11 oder 12, die eine Länge (LL0,25) im Bereich von 0,7 bis 1,5 mm aufweist.
     
    14. Para-Aramid Pulpe, umfassend PVP, nach einem der Ansprüche 11-13, die einen Schopper-Riegler (SR)-Grad im Bereich von 15 bis 60°SR aufweist.
     
    15. Para-Aramid Pulpe, umfassend PVP, nach einem der Ansprüche 11-14, die einen Canadian Standard Freeness (CSF)-Wert im Bereich von 15 bis 700 ml, insbesondere im Bereich von 100 bis 570 ml, aufweist.
     


    Revendications

    1. Processus de fabrication d'une pâte d'aramide comprenant de la polyvinylpyrrolidone (PVP), le procédé comprenant les étapes consistant à

    - combiner du para-aramide court-coupé présentant une longueur d'au moins 0,5 mm et d'au plus 20 mm avec de la PVP dans une solution aqueuse pour former un mélange, le mélange comprenant

    - de 0,1 à 7 % en poids d'aramide court-coupé, et

    - entre 0,1 et 15 % en poids de PVP, calculée sur la base du poids sec de l'aramide court-coupé ;

    - soumettre le mélange à une étape de raffinage pour former une pâte de para-aramide comprenant de la PVP.


     
    2. Processus selon la revendication 1, dans lequel le para-aramide est du poly(paraphénylène téréphtalamide).
     
    3. Processus selon l'une quelconque des revendications précédentes, dans lequel le para-aramide court-coupé comprend des fibres de para-aramide avec une longueur de 1 à 10 mm.
     
    4. Processus selon l'une quelconque des revendications précédentes, dans lequel le para-aramide court-coupé présente une épaisseur dans la plage de 5 à 50 microns, de préférence dans la plage de 5 à 25 microns, le plus préférentiellement dans la plage de 6 à 18 microns.
     
    5. Processus selon l'une quelconque des revendications précédentes, dans lequel la PVP présente un poids moléculaire moyen en poids dans la plage de 5 à 2 500 kg/mol.
     
    6. Processus selon l'une quelconque des revendications précédentes, dans lequel la concentration en aramide court-coupé dans le mélange est dans la plage de 1 à 5 % en poids.
     
    7. Processus selon l'une quelconque des revendications précédentes, dans lequel la quantité de PVP présente dans le mélange aqueux varie entre 0,5 et 10 % en poids, calculée sur la base du poids sec de l'aramide court-coupé.
     
    8. Processus selon l'une quelconque des revendications précédentes, dans lequel la suspension de pâte résultant de l'étape de raffinage est soumise à une étape d'assèchement, pour former une pâte asséchée avec une teneur en eau qui est généralement dans la plage de 40 à 80 % en poids, spécifiquement de 50 à 70 % en poids.
     
    9. Processus selon la revendication 8, dans lequel la pâte asséchée est soumise à une étape de séchage pour former une pâte séchée, avec une teneur en eau qui est généralement de 2 à 20 % en poids, en particulier de 3 à 10 % en poids.
     
    10. Processus selon la revendication 8, dans lequel la pâte séchée est soumise à une étape d'ouverture.
     
    11. Pâte de para-aramide comprenant de 0,1 à 10 % en poids de PVP, calculée sur la base du poids sec d'aramide, pouvant être obtenue par le processus selon l'une quelconque des revendications précédentes, dans laquelle la pâte de para-aramide présente un Schopper-Riegler (SR) dans la plage de 15 à 80 °SR.
     
    12. Pâte de para-aramide comprenant de la PVP selon la revendication 11, qui comprend de 0,5 à 6 % en poids de PVP, calculée sur la base du poids sec d'aramide.
     
    13. Pâte de para-aramide selon la revendication 11 ou 12, qui présente une longueur (LL0,25) dans la plage de 0,7 à 1,5 mm.
     
    14. Pâte de para-aramide comprenant de la PVP selon l'une quelconque des revendications 11 à 13, qui présente un Schopper-Riegler (SR) dans la plage de 15 à 60 °SR.
     
    15. Pâte de para-aramide comprenant de la PVP selon l'une quelconque des revendications 11 à 14, qui présente un indice d'égouttage Canadian Standard (CSF) dans la plage de 15 à 700 ml, en particulier dans la plage de 100 à 570 ml.
     






    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description