Title:
Method for Producing Duroplastic Fine-Fiber Non-Wovens Having a High Flame-Retardant, Thermal Protective and Sound Insulating Effect
Kind Code:
A1


Abstract:
The invention relates to a method for producing duroplastic fine-fiber non-wovens, characterized in that: a) melts of reactive three-dimensionally cross-linkable, non-linear prepolymers are extruded by nozzles; b) the exiting melts are blown by means of hot air to form fine fibers; c) the fine fibers are separated by the flow of air and deposited to form a non-woven comprised of a fine-fiber weave; d) the non-woven is subsequently compacted, and; e) the non-woven is treated with a medium that initiates a three-dimensional cross-linking, and the fine fibers in the non-woven are inherently bonded and/or hardened in a subsequent thermal post-hardening. This enables duroplastic fine-fiber non-wovens to be economically produced that have both a high flame retardant effect as well as a high thermal protection, sound insulation and filtering capacity.



Inventors:
Riedel, Bernd (Unterwellenborn, DE)
Bucka, Hartmut (Eggendorf, AT)
Application Number:
11/909300
Publication Date:
08/28/2008
Filing Date:
03/21/2006
Assignee:
AMI AGROLINZ MELAMINE INTERNATIONAL GBMH (Linz, AT)
Primary Class:
International Classes:
D04H3/02; D04C1/00; D04H3/03
View Patent Images:



Primary Examiner:
SCHIFFMAN, BENJAMIN A
Attorney, Agent or Firm:
Workman Nydegger (Salt Lake City, UT, US)
Claims:
1. A process for producing thermoset microfibrous webs, comprising: a) melts of reactive, three-dimensionally crosslinkable, nonlinear prepolymers are pressed through dies, b) the exiting melts are attenuated by hot air to form microfibers, c) the microfibers are separated from the air stream and are deposited to form a web consisting of a microfibrous braid, d) the web is subsequently compacted, e) treated with a medium inducing a three-dimensional crosslinking and in a subsequent thermal postcure the microfibers in the web are self-bonded and/or cured off.

2. The process according to claim 1, wherein reactive, nonlinear prepolymers three-dimensionally crosslinkable by a condensation reaction are pressed through dies situated in the tip of cones.

3. The process according to claim 2, wherein the exiting melt is attenuated directly at the die outlet to form microfibers by the hot air, whose temperature is above the starting temperature of the condensation reaction, flowing at a high rate of speed along the tips of the die cones.

4. The process according to claim 2, wherein the microfibers are separated from the air stream and are deposited as an unconsolidated web (random-laid ply).

5. The process according to claim 4, wherein the unconsolidated web is subsequently compacted.

6. The process according to claim 4, wherein the unconsolidated web has air comprising a component catalyzing the crosslinking flowing through it at temperatures below the melting point of the prepolymer.

7. The process according to claim 4, wherein the unconsolidated web subsequently has an inert medium flow through it and, in the process, the catalyzing component is completely removed from the spaces between the fibers or if appropriate neutralized with a basic gas.

8. The process according to claim 4, wherein the unconsolidated web is self-bonded and/or cured off to a consolidated web by elevating the temperature.

9. The process according to claim 8, wherein the web has hot air flow through it and, in the process, is incrementally or continuously further heated.

10. The process according to claim 8 wherein the web is dwelled at high temperatures.

11. The process according to claim 1, wherein the reactive crosslinkable, nonlinear prepolymers consist of alcohol-etherified melamine-formaldehyde resins.

12. The process according to claim 11, wherein the alcohol-etherified melamine-formaldehyde resins consist of meltable 4- to 18-nucleus oligotriazine ethers in which the triazine segments contain R1=—NH2, —NH—CHR2—O—R3, —NH—CHR2—O—R4—OH, —CH3, —C3H7, —C6H5—OH, phthalimido-, succinimido-, —NH—CO-C5-C18-alkyl, —NH—C5-C18-alkylene-OH —NH—CHR2—O—R4—O—CHR2—NH—, —NH—CHR2—NH—, —NH—CHR2—O—C5-C18-alkylene-NH—, —NH—C5-C18-alkylene-NH—, —NH—CHR2—O—CHR2—NH—, R2═H, C1-C7-alkyl; R3=C1-C18-alkyl, H; R4=C2-C18-alkylene, —[CH2—CH2—O—CH2—CH2]n—, —[CH2—CH(CH3)—O—CH2—CH(CH3)]n—, —[—O—CH2—CH2—CH2—CH2—]n—, —[(CH2)2-8—O—CO-C6-C12-aryl-CO—O—(CH2)2-8—]n—, —[(CH2)2-8—O—CO-C6-C12-alkylene-CO—O—(CH2)2-8-]n—, where n=1 to 200; sequences containing siloxane groups, of the type C1-C4-alkyl C1-C4-alkyl, —(C1-C18)-alkyl-O—Si—O—[Si—]1-4—O—(C1-C18)-alkyl-, C1-C4-alkyl, C1-C4-alkyl polyester sequences containing siloxane groups, of the type -[(A)r-O—CO—(B)s—CO—O-(A)r]-, in which A={(CH2)2-8—O—CO—(C6-C14)-arylene-CO—O—(CH2)2-8—} or —{(CH2)2-8—O—CO—(C2-C12)-alkylene-CO—O—(CH2)2-8—}; C1-C4-alkyl C1-C4-alkyl B=—{(C6-C14)-arylene-CO—O-—({Si—O—[Si—O]y—CO—(C6-C14)-arylene-} C1-C4-alkyl C1-C4-alkyl or C1-C4-alkyl C1-C4-alkyl {O—CO—(C2-C12)-alkylene-CO—O—({Si—O—[Si—O], —CO—(C2-C12)-alkylene-CO—}; C1-C4-alkyl C1-C4-alkyl r=1 to 70; s=1 to 70 and y=3 to 50; polyether sequences containing siloxane groups, of the type C1-C4-alkyl C1-C4-alkyl —CH2—CHR2—O—({Si—O—[Si—O]y—CHR2—CH2— C1-C4-alkyl C1-C4-alkyl where R2═H; C1-C4-alkyl and y=3 to 50; sequences based on alkylene oxide adducts of melamine, of the type of 2-amino-4,6-di-C2-C4-alkyleneamino-1,3,5-triazine sequences; phenol ether sequences based on dihydric phenols and C2-C8 diols, of the type of —C2-C8-alkylene-O—(C6-C18)-arylene-O—(C2-C8)-alkylene-sequences; are linked by bridge members —NH—CHR2—O—R4—O—CHR2—NH— and —NH—CHR2—NH— and also, where appropriate, —NH—CHR2—O—CHR2—NH—, —NH—CHR2—O—C5-C18-alkylene-NH— and/or —NH—C5-C18-alkylene-NH— to form 4- to 18-nucleus oligotriazine ethers of linear and/or branched structure, the terminal triazine segments in the oligotriazine ethers forming triazine segments of the structure Y=—NH—CHR2—O—R3, —NH—CHR2—O—R4—OH and also if appropriate —NH— CHR2—O—C5-C18-alkylene-NH2, —NH—C5-C18-alkylene-NH2, —NH—C5-C18-alkylene-OH, R1=—NH2, —NH—CHR2—O—R3, —NH—CHR2—O—R4—OH, —CH3, —C3H7, —C6H5, —OH, phthalimido-, succinimido-, —NH—CO—R3, —NH—C5-C18-alkylene-OH, —NH—C5-C18-alkylene-NH2, R2=H, C1-C7-alkyl; R3=C1-C18-alkyl, H; R4=C2-C18-alkylene, —[CH2—CH2—O—CH2—CH2]n—,-[CH2—CH(CH3)—O—CH2—CH(CH3)]n—, —[—O—CH2—CH2—CH2—CH2—]n—, —[(CH2)2-8—O—CO-c6-c12-aryl-CO—O—(CH2)2-8-]n—, —[(CH2)2-8—O—CO-c6-c12-alkylene-CO—O—(CH2)2-8—]n—, where n=1 to 200; sequences containing siloxane groups, of the type C1-C4-alkyl C1-C4-alkyl, —(C1-C18)-alkyl-O—Si—O—[Si—]1-4—O—(C1-C18)-alkyl-, C1-C4-alkyl, C1-C4-alkyl polyester sequences containing siloxane groups, of the type -[(A)r-O—CO—(B)s—CO—O-(A)r]-, in which A={(CH2)2-8—O—CO—(C6-C14)-arylene-CO—O—(CH2)2-8—} or —{(CH2)2-8—O—CO—(C2-C12)-alkylene-CO—O—(CH2)2-8—}; C1-C4-alkyl C1-C4-alkyl B=—{(C6-C14)-arylene-CO—O—({Si—O—[Si—O]y—CO—(C6-C14)-arylene-} C1-C4-alkyl C1-C4-alkyl or C1-C4-alkyl C1-C4-alkyl {O—CO—(C2-C12)-alkylene-CO—O—({Si—O—[Si—O], —CO—(C2-C12)-alkylene-CO—}; C1-C4-alkyl C1-C4-alkyl r=1 to 70; s=1 to 70 and y=3 to 50; polyether sequences containing siloxane groups, of the type C1-C4-alkyl C1-C4-alkyl —CH2—CHR2—O—({Si—O—[Si—O]y—CHR2—CH2— —C1-C4-alkyl C1-C4-alkyl where R2═H; C1-C4-alkyl and y=3 to 50; sequences based on alkylene oxide adducts of melamine, of the type of 2-amino-4,6-di-C2-C4-alkyleneamino-1,3,5-triazine sequences; phenol ether sequences based on dihydric phenols and C2-Cdiolsa, of the type of —C2-C8-alkylene-O—(C6-C18)-arylene-O—(C2-C8)-alkylene-sequences; in the oligotriazine ethers the molar ratio of the substituents R3:R4=20:1 to 1:20, the proportion of the linkages of the triazine segments through bridge members —NH—CHR3—O—R4—O—CHR3—NH— is 5 to 95 mol %.

13. The process according to claim 11 wherein the alcohol-etherified melamine-formaldehyde resins contain further compounds influencing the reactivity of the prepolymers and the molecular structure of the cured polymers.

14. The process according to claim 1, wherein the reactive three-dimensionally crosslinkable, nonlinear prepolymers contain up to 20% by mass of further reactive polymers selected from the group consisting of ethylene copolymers, maleic anhydride copolymers, modified maleic anhydride copolymers, poly(meth)acrylates, polyamides, polyesters and polyurethanes.

15. The process according to claim 1, wherein the reactive three-dimensionally crosslinkable, nonlinear prepolymers contain up to 20% by mass of aliphatic diols of the HO—R—OH type and also up to 2% by mass of fillers, color pigments, stabilizers, UV absorbers and/or auxiliaries. The process according to at least one of the aforementioned claims, characterized in that the reactive three-dimensionally crosslinkable, nonlinear prepolymers are before processing in the form of cylindrical, lenticular, pastille-shaped or spherical particles having an average diameter of 0.5 to 8 mm.

16. The process according to claim 1, wherein the reactive, three-dimensionally crosslinkable, nonlinear prepolymers are melted at about 70° C. to 130° C. for spinning.

17. The process according to claim 1, wherein the dies have a diameter of 0.1 to 3 mm.

18. The process according to claim 17, wherein the dies have a diameter of 0.5 to 1 mm.

19. The process according to claim 1, wherein the dies are situated on and/or in the tips of cones and the hot air flows along the die cones at a high rate of speed.

20. The process according to claim 19, wherein the cones have an angle of 10 to 90°.

21. The process according to claim 1, wherein the hot air, in particular the hot air flowing along the tips of the die cones at a high rate of speed, has a temperature of 150° C. to 400° C.

22. The process according to claim 21, wherein the hot air, in particular the hot air flowing along the tips of the die cones at a high rate of speed, has a temperature of 180° C. to 300° C.

23. The process according to claim 1, wherein the resulting fibers, in particular microfibers, are filaments or have a diameter/length ratio of greater than 1:50.

24. The process according to claim 1, wherein the microfibers have an average diameter of 0.5 to 100 μm.

25. The process according to claim 24, wherein the microfibers have an average diameter of 1 to 7 μm.

26. The process according to claim 1, wherein the fibers have a disordered, small-scale crimped structure.

27. The process according to claim 1, wherein the microfibers are separated from the air stream using a wire grid or braid inserted into the air/microfiber stream and at the same time an unconsolidated web forms.

28. The process according to claim 27, wherein the wire grid or braid is in the form of an endless belt.

29. The process according to claim 27 wherein the air of the air/microfiber stream is aspirated away underneath the wire grid or braid.

30. The process according to claim 1, wherein the web is compacted to the desired density by mechanical pressure or by forming.

31. The process according to claim 1, wherein a three-dimensional crosslinking is induced or starts at temperatures below the microfiber melting point.

32. The process according to claim 1, wherein the component inducing the three-dimensional crosslinking, in particular the component catalyzing the condensation reaction, is gaseous HCl and/or gaseous HBr and/or formic acid neat or diluted with air or some other inert gas.

33. The process according to claim 32, wherein the microfibers in which the catalyzing components are sorbed self-bond in the temperature range between 100 and 120° C.

34. The process according to claim 1, wherein the thermal postcure of the web is effected by incremental or continuous heating with hot air and at the same time, the methanol released is discharged together with detached HCI and/or HBr.

35. The process according to claim 34, wherein the thermal postcure of the web is effected in the temperature range from 200° C. to 320° C. and preferably in the temperature range from 250° C. to 280° C. and the postcure time is between 15 min and 120 min and preferably between 20 min and 60 min.

36. The process according to claim 35, wherein the web is washed with water after the postcure.

Description:

This invention relates to a process for producing thermoset microfibrous webs.

The process of the present invention proceeds from reactive, three-dimensionally crosslinkable, nonlinear prepolymers, preferably from etherified melamine-formaldehyde resins. The melts of these prepolymers are pressed through dies, the exiting melts are attenuated by hot air to form microfibers, the microfibers are separated from the air stream and to form a microfibrous braid. The, in particular, unconsolidated web is subsequently compacted, treated with a medium inducing a three-dimensional crosslinking and then thermally postcured, causing the web fibers to self-bond and/or cure off. Web articles are formed which are widely used on account of their high flame protection effect and also their good thermally protecting, acoustically protecting and filtering ability.

It is particularly advantageous to deposit an unconsolidated web also known as a random-laid ply of loosely aggregated fibers.

Microfibrous webs, which are very useful for filtration and also thermal and acoustical protection, are produced in large amounts from meltable polymers by the familiar meltblown process. In the meltblown process, a low-viscosity molten jet of a thermoplastic polymer is extruded into a hot stream of air moving at a high rate of speed. The melt disintegrates into microfibers, which are cooled and laid down on a foraminous belt. The disadvantage of this economical process is that it is limited to thermoplastic polymers only, which have an inadequate flame protection effect. Flame-retardant, thermoset polymers have hitherto not been processible into fibers by such processes.

It is well known to use cotton webs consolidated with thermoset phenolic resin as acoustical and thermal protection in the automotive sector (Becker/Braun, Kunststoff-Handbuch: Duroplaste, page 763, Hanser Verlag Munich). The disadvantage of these webs is their high mass per unit area and their insufficient resistance to flames.

Also known are thermoset melamine resin fibers and webs produced therefrom, which have a very good flame protection effect. DE 19515277, DE 10133787 or DE 19753834 describe the production of fibers from aqueous melamine-phenol-formaldehyde precondensates. The aqueous precondensate solution is pressed through spinneret dies, the resulting fibers are subsequently dried and cured off at elevated temperature. The fibers can subsequently be processed by existing processes into nonconeustible webs. A significant disadvantage of such webs is that the fibers interentangle only insufficiently in the web-forming step and hence the strength of the webs is not sufficient. The addition of web-forming auxiliary fibers such as cotton is often necessary.

A further disadvantage is the separation of the process stages of “fiber production” and “web formation”, making the web-producing process unnecessarily complicated. It is further disadvantageous that hitherto only aqueous melamine resin precondensate solutions are used to produce the fibrous material, necessitating an energetically wasteful evaporation of the water during the filament-forming operation.

EP 1 403 405 A2 describes continuous filaments obtainable by melting amino resin polymers comprising oligo- and/or polytriazine ethers. The amino resin melts are spun by means of dies and are subsequently stretched into continuous filaments of a desired diameter while undergoing curing. The cured amino resin filaments can be wound up, bundled to form a strand or laid down to form a fabric. The disadvantage here is again the complicated web-producing process wherein it is necessary first to form the continuous filaments, then cut these into fibers and finally consolidate these fibers into a fabric.

It is an object of the present invention to develop a process whereby thermoset microfibrous webs possessing not only high flame protection effect but also a high thermally protecting, acoustically protecting and filtering ability are economically obtainable.

We have found that this object is achieved when melts of reactive, three-dimensionally crosslinkable, nonlinear prepolymers are pressed through dies, the exiting melts are attenuated by hot air to form microfibers, the microfibers are separated from the air stream and are deposited to form a web consisting of a microfibrous braid. The web is subsequently compacted, treated with a medium inducing a three-dimensional crosslinking and in a subsequent thermal postcure the microfibers are self-bonded and/or cured off.

It is particularly advantageous when the microfibers are separated from the air stream and are deposited as an unconsolidated web (random-laid ply).

Surprisingly, although the reactive, three-dimensionally crosslinkable, nonlinear prepolymers in the solid state are very brittle and are easy to crumb without particular exertion, the process of the present invention converts the melts of these prepolymers after departure from the die, despite the severe turbulences and frictional forces in the meltblown process air or to be more precise in the fiber/air stream, into microfibers which, without being crumbed into microfine particles, can be in particular laid down to form an unconsolidated web, which can be compacted or formed by application of force.

It is also surprising that the microfibers produced have a disordered, small-scale crimped structure which, however, is advantageous for web formation and web coherency.

It is further surprising that the microfibers produced can also be in the form of continuous filaments.

It is also surprising that the microfibers, after being exposed to the medium which induces the three-dimensional crosslinking, can self-bond to each other in the web at their contact surfaces without additional binders having been added.

The process is advantageously carried out when the reactive crosslinkable, nonlinear prepolymers consist of alcohol-etherified melamine-formaldehyde resins composed of meltable 4- to 18-nucleus oligotriazine ethers in which the triazine segments contain

    • R1=—NH2, —NH—CHR2—O—R3, —NH—CHR2—O—R4—OH, —CH3, —C3H7, —C6H5, —OH, phthalimido-,
      • succinimido-, —NH—CO-C5-C18-alkyl, —NH—C5-C18-alkylene-OH

      • —NH—CHR2—O—R4—O—CHR2—NH—, —NH—CHR2—NH—, —NH—CHR2—O—C5-C18-alkylene-NH—,
      • —NH—C5-C18-alkylene-NH—, —NH—CHR2—O—CHR2—NH—,
    • R2═H, C1-C7-alkyl;
    • R3═C1-C18-alkyl, H;
    • R4=C2-C18alkylene, —[CH2—CH2—O—CH2—CH2]n—, —[CH2—CH(CH3)—O—CH2—CH(CH3)]n—,
      • —[—O—CH2—CH2—CH2—CH2—]n—,
      • —[(CH2)2-8—O—CO-C6-C12-aryl-CO—O—(CH2)2-8—]n—,
      • —[(CH2)2-8—O—CO-C6-C12-alkylene-CO—O—(CH2)2-8—]n—,
      • where n=1 to 200;
    • sequences containing siloxane groups, of the type
    • C1-C4-alkyl C1-C4-alkyl, —(C1-C18)-alkyl-O—Si—O—[Si—]1-4—O—(C1-C18)-alkyl-, C1-C4-alkyl, C1-C4-alkyl
    • polyester sequences containing siloxane groups, of the type
    • —[(A)r-O—CO—(B)s—CO—O-(A)r]—, in which
    • A={(CH2)2-8—O—CO—(C6-C14)-arylene-CO—O—(CH2)2-8—} or
      • —{(CH2)2-8—O—CO—(C2-C12)-alkylene-CO—O—(CH2)2-8—};
      • C1-C4-alkyl C1-C4-alkyl
    • B=—{(C6-C14)-arylene-CO—O—({Si—O—[Si—O]y—CO—(C6-C14)-arylene-}
      • C1-C4-alkyl C1-C4-alkyl or
      • C1-C4-alkyl C1-C4-alkyl
      • {O—CO—(C2-C12)-alkylene-CO—O—({Si—O—[Si—O]Z—CO—(C2-C12)-alkylene-CO—};
      • C1-C4-alkyl C1-C4-alkyl
      • r=1 to 70; s=1 to 70 and y=3 to 50;
    • polyether sequences containing siloxane groups, of the type
    • C1-C4-alkyl C1-C4-alkyl
    • —CH2—CHR2—O—({Si—O—[Si—O]y—CHR2—CH2
    • C1-C4-alkyl C1-C4-alkyl
    • where R2═H; C1-C4-alkyl and y=3 to 50;
    • sequences based on alkylene oxide adducts of melamine, of the type of 2-amino-4,6-di-C2-C4-alkyleneamino-1,3,5-triazine sequences;
    • phenol ether sequences based on dihydric phenols and C2-C8 diols, of the type of —C2-C8-alkylene-O—(C6-C18)-arylene-O—(C2-C8)-alkylene-sequences;
    • are linked by bridge members —NH—CHR2—O—R4—O—CHR2—NH— and —NH—CHR2—NH— and also, where appropriate, —NH—CHR2—O—CHR2—NH—, —NH—CHR2—O—C5-C18-alkylene-NH— and/or —NH—C5-C18-alkylene-NH— to form 4- to 18-nucleus oligotriazine ethers of linear and/or branched structure,
    • the terminal triazine segments in the oligotriazine ethers forming triazine segments of the structure

    • Y=—NH—CHR2—O—R3, —NH—CHR2—O—R4—OH and also if appropriate
      • —NH—CHR2—O—C5-C18-alkylene-NH2,
      • —NH—C5-C18-alkylene-NH2, —NH—C5-C18-alkylene-OH,
    • R1=—NH2, —NH—CHR2—O—R3, —NH—CHR2—O—R4—OH, —CH3, —C3H7,
      • —C6H5, —OH, phthalimido-,
      • succinimido, —NH—CO—R3, —NH—C5-C18-alkylene-OH, —NH—C5-C18-alkylene-NH2,

    • R2=H, C1-C7-alkyl;
    • R3=C1-C18-alkyl, H;
    • R4=C2-C18-alkene, —[CH2—CH2—O—CH2—CH2]n—, —[CH2—CH(CH3)—O—CH2—CH(CH3)]n—, —[—O—CH2—CH2—CH2—CH2—]n—, —[(CH2)2-8—O—COC6-C12-aryl-CO—O—(CH2)2-8—]n—, —[(CH2)2-8—O—CO-C6-C12-alkene-CO—O—(CH2)2-8—]n—,
      • where n=1 to 200;
    • sequences containing siloxane groups, of the type
    • C1-C4-alkyl C1-C4-alkyl, —(C1-C18)-alkyl-O—Si—O—[Si—]1-4—O—(C1-C18)-alkyl-, C1-C4-alkyl, C1-C4-alkyl
    • polyester sequences containing siloxane groups, of the type
    • -[(A)r-O—CO—(B)S—CO—O-(A)r]—, in which
    • A={(CH2)2-8—O—CO—(C6-C14)-arylene-CO—O—(CH2)2-8-} or
      • —{(CH2)2-8—O—CO—(C2-C12)-alkylene-CO—O—(CH2)2-8-};
      • C1-C4-alkyl C1-C4-alkyl
    • B=—{(C6-C14)-arylene-CO—O—({Si—O—[Si—O]y—CO—(C6-C14)-arylene-}
      • C1-C4-alkyl C1-C4-alkyl or
      • C1-C4-alkyl C1-C4-alkyl
      • {O—CO—(C2-C12)-alkene-CO—O—({Si—O—[Si—O]z—CO—(C2-C12)-alkylene-CO—};
      • C1-C4-alkyl C1-C4-alkyl
      • r=1 to 70; s=1 to 70 and y=3 to 50;
    • polyether sequences containing siloxane groups, of the type
    • C1-C4-alkyl C1-C4-alkyl
    • —CH2—CHR2—O—({Si—O—[Si—O]y—CHR2—CH2
    • C1-C4-alkyl C1-C4-alkyl
    • where R2=H; C1-C4-alkyl and y=3 to 50;
    • sequences based on alkylene oxide adducts of melamine, of the type of 2-amino-4,6-di-C2-C4-alkyleneamino-1,3,5-triazine sequences;
    • phenol ether sequences based on dihydric phenols and C2-C8 diols, of the type of —C2-C8-alkylene-O—(C6-C18)-arylene-O—(C2-C8)-alkylene-sequences;
    • in the oligotriazine ethers the molar ratio of the substituents R3:R4=20:1 to 1:20,
    • the proportion of the linkages of the triazine segments through bridge members —NH—CHR3—O—R4—O—CHR3—NH— is 5 to 95 mol %.

Triazines herein are aromatic nitrogen heterocycles of the empirical formula C3H3N3 with three nitrogen atoms in a 6-membered ring. Triazine segments herein are parts of a network described herein which are derived from triazines.

The alcohol-etherified melamine-formaldehyde resins, as well as melamine and formaldehyde, may contain further compounds influencing the reactivity of the prepolymers and the molecular structure of the cured polymers, and also up to 20% by mass of further reactive polymers selected from the group consisting of ethylene copolymers, maleic anhydride copolymers, modified maleic anhydride copolymers, poly(meth)acrylates, polyamides, polyesters and polyurethanes and/or up to 20% by mass of aliphatic diols of the HO—R—OH type and also up to 2% by mass of fillers, color pigments, stabilizers, UV absorbers and/or auxiliaries.

Before being processed as a melt, the reactive, three-dimensionally crosslinkable, nonlinear prepolymers are in the form of cylindrical, lenticular, pastille-shaped or spherical particles having an average diameter of 0.5 to 8 mm.

To spin the reactive, three-dimensionally crosslinkable, nonlinear prepolymers they are melted at between 70 and 160° C. and in particular between 70° C. and 130° C.

The diameter of the dies is 0.1 to 3 mm and preferably 0.5 to 1 mm.

Preferably, the dies are situated in or on the tips of cones and the hot air flows along them at a high rate of speed. This makes it possible to elevate the temperature of the meltblown air, which disintegrates the melts into microfibers, far above the curing temperature of the reactive, three-dimensionally crosslinkable, nonlinear prepolymers, which makes particularly fine-denier fibers available without the dies becoming blocked.

It is further advantageous when the cones have an angle of 10 to 90°.

Preferably, the hot air has a temperature of 100 to 400° C. preferably 180 to 300° C.

The microfibers laid down to form a web can be filaments or have a diameter/length ratio of greater than 1:50. They have an average diameter of 0.5 to 100 μm and preferably of 1 to 7 μm.

The microfibers are separated from the air stream by means of a wire grid or braid inserted into the air/microfiber stream, the wire grid or braid advantageously taking the form of an endless belt. At the same time, in the process, the unconsolidated web forms as a deposited random-laid ply.

Advantageously, the air of the air/microfiber stream is aspirated away underneath the wire grid/braid, causing the very loosely aggregated microfiber web which forms to undergo a first compaction.

The unconsolidated web can further be compacted to a desired degree by mechanical pressure or by forming.

The three-dimensional crosslinking is effected by a condensation reaction. The condensation reaction is speeded (catalyzed) by, for example, gaseous HCl and/or gaseous HBr and/or gaseous formic acid neat or diluted with air or some other inert gas.

The sorption of the catalytically active components can advantageously induce three-dimensional crosslinking at temperatures below the microfiber melting point.

The thermal postcure, in which the microfibers in the web self-bond and/or cure off, is preferably carried out at temperatures of 60 to 320° C. and more preferably at 250 to 280° C. It is advantageous in this connection when the temperature is gradually raised from 60 to 280° C. and preferably from 80 to 280° C.

EXAMPLE 1

A prepolymer prepared by reaction of melamine with formaldehyde and subsequent etherification with methanol and polytetrahydrofuran Mn 250 and having a viscosity of 53 Pa*s at 135° C. is melted in a Rand Castel extruder at a block temperature of 135° C. and the melt is forced through a heated die at 150° C. which has a hole diameter of 1 mm. The die is situated in the tip of a cone having an angle of 20° C. The prepolymer melt exiting from the die is attenuated into microfibers by hot air (190° C., 0.4 bar) flowing along the die cone. The construction of the die used is depicted in FIG. 1.

The meltblown fiber stream is steered onto a wire sieve situated above an aspirating system. The microfibers laid down on the wire sieve form a loose random-laid web (unconsolidated web) which is compacted by a roll. To induce the curing reaction (particularly a catalyzed one), a mixture of 25% HCl and 75% air is sucked through the web. The web is cured off by the action of hot air (raising the temperature). The temperature in the process is raised from 60 to 210° C. over 30 minutes.

The fully cured microfibers forming the web have a length of 1 to 50 mm and a diameter of 4 to 20 μm.

The web obtained has a basis weight of 34 g/m2 coupled with a thickness of 2 mm. The structure of the web is documented in the scanning electron micrograph FIG. 2.

In a modification of this embodiment, the temperature is raised from 60 to 280° C. over 30 minutes. The web is dwelled at 280° C. for a further 45 minutes.

EXAMPLE 2

A prepolymer prepared by reaction of melamine with formaldehyde and subsequent etherification with methanol and butanediol and having a viscosity of 15 Pa*s at 135° C. is melted in a Rand Castel extruder at a block temperature of 145° C. and the melt is forced through a heated die at 150° C. which has a hole diameter of 1 mm. The die is situated on or in the tip of a cone having an angle of 20° C. The prepolymer melt exiting from the die is attenuated into microfibers by hot air (280° C., 0.8 bar) flowing along the die cone. The construction of the die used is depicted in FIG. 1.

The meltblown fiber stream is steered onto a moving endless wire sieve situated above an aspirating system. The microfibers laid down on the wire sieve form a stable unconsolidated web which is compacted by a roll. To induce, in particular to speed, the curing reaction, a mixture of 75% HCl and 25% air is sucked through the unconsolidated web.

The temperature is raised to start the condensation reaction. The methanol released in the course of the condensation reaction causes the microfibers to become tacky. They bond at their crossing points.

This creates a microfibrous web consolidated by self-bonding. The temperature is further raised from 80° to 200° C. over 30 minutes.

In an alternative embodiment, further from 100° C. to 250° C. over a period of 30 minutes.

The fully cured microfibers forming the, in particular, consolidated web obtained have a length of 1 to 50 mm and a diameter of 1 to 7 μm. They, as depicted in scanning electron micrograph FIG. 3, are self-bonded at their crossing points.

The web obtained has an envelope density of 9 kg/m3

EXAMPLE 3

A prepolymer prepared by reaction of melamine with formaldehyde and subsequent etherification with methanol and butanediol and having a viscosity of 20 Pa*s at 130° C. is melted in a Rand Castel extruder at a block temperature of 135° C. and the melt is forced through a heated die at 150° C. which has a hole diameter of 0.5 mm. The die is situated in the tip of a cone having an angle of 20° C. The prepolymer melt exiting from the die is attenuated into microfibers by hot air (280° C., 0.8 bar) flowing along the die cone.

The meltblown fiber stream is steered onto a moving endless wire sieve above an aspirating system. The microfibers laid down on the wire sieve form a stable unconsolidated web which is compacted by a roll. To speed the curing reaction, a mixture of 0.2% HCl and 99.8% air is sucked through the web.

Subsequently, further dry air is sucked through until HCl is no longer detectable (determined using moist indicator paper).

Hot air is flowed through the unconsolidated web to raise the temperature of the web. In the temperature range below the melting point of the prepolymer, the prepolymer is rendered tacky by the methanol eliminated in the course of the condensation reaction, and bonds at the crossing points.

Hot air is further flowed through the web to further raise the temperature. In the process, the temperature is raised from 80 to 280° C. over 30 minutes. The methanol released by the condensation in the course of curing is discharged together with residual HCl.

The fully cured microfibers forming the web have a length of 1 to 50 mm and a diameter of 1 to 7 μm.

The web obtained has a decomposition point of 390° C., determined by differential thermal gravimetry.

The web obtained has an envelope density of 9 kg/m3.

The web is subsequently if appropriate washed with water in a further operation (temperature of wash water: 30° C.). This raises the decomposition point of the web, as determined by differential thermal gravimetry, to 400° C.

LIST OF REFERENCE SYMBOLS FOR FIG. 1

  • Annular passage
  • MER melt
  • Meltblown air
  • Compressed air
  • Meltblown fiber stream