MXPA97000815A - Procedure for preparing non-woven fabrics depolibenza - Google Patents

Abstract

A continuous process for preparing non-woven fabrics of polybenzazole filaments, which comprises spinning at least two filaments of polybenzazole absorbing material from a spinning head (1), simultaneously, through an extinguishing chamber (2) on guide rollers (3), through a vacuum cleaner (4), and intermixing and depositing the filaments on a collection surface (5), substantially pl

Description

PROCEDURE FOR PREPARING NON-WOVEN FABRICS OF POLYBENZAZOL DESCRIPTION OF THE INVENTION This invention relates to polybenzazole polymer articles and, more specifically, to polybenzazole fiber fabrics. Non-woven fabrics are known materials, which comprise groups of textile fibers held together by mechanical entanglement in a random band or mat, melting thermoplastic fibers, or joining the fibers with a cementing medium such as starch, rubber, casein, rubber, Latex, derived from cellulose, or synthetic resins. The polybenzazole fibers are known fibers, which are prepared by extruding filaments of a polybenzazole absorbent material, extracting the filaments through an air gap, combining the filaments to form a multi-filament structure, and then, washing and drying the filaments. structure under sufficient conditions to remove the acid solvent and water from the filament. An efficient process for the preparation of non-woven fabrics of polybenzazole would be desirable. In one aspect, this invention is a continuous process for preparing nonwoven fabrics of polybenzazole filaments, which comprises spinning at least two filaments of polybenzazole absorbent material, simultaneously, and intermixing and depositing the filaments on a collection surface, substantially flat It has been discovered that the method of the invention provides means for preparing non-woven fabrics of polybenzazole in a continuous, in-line process, which allows the polybenzazole absorbent material to be extruded at a very high speed, since the speed of the process in line is not limited by the line speed, which may be necessary to wash and dry individual filaments in an online procedure. In addition, since the fabric moves through the washing and drying equipment at a rate of speed much slower than a single fiber, fewer washing and drying cabinets may be required to effectively wash and dry the fabric. These and other Advantages of the invention will be apparent from the description that follows. The understanding of the invention will be facilitated by referring to the attached drawings, Figures 1 and 2, which are schematic representations of two embodiments of the method of the invention. In the process of the invention, two or more filaments of polybenzazole absorbent material are extruded onto a substantially flat collection surface. The polybenzazole filaments used in the process of the invention can be obtained by spinning an absorbent material containing a polybenzazole polymer. As used herein, "polybenzazole" refers to polybenzoxazole homopolymers (PBO), polybenzothiazole homopolymers (PBT), and copolymerized, random, sequential, or block PBO and PBT polymer. The polybenzoxazole, polybenzothiazole, and the random, sequential, or block copolymerized polymers thereof are described, for example, in "Liquid Crystalline Polymer Compositions, Process and Products" ("Compositions, Processes and Products of Crystalline Polymer, Liquid") , by Wolfe and others, US patent 4,703,103 (October 27, 1987); "Liquid Crystalline Polymer Compositions, Process and Products" ("Compositions, Process and Products of Crystalline Polymer, Liquid "), U.S. Patent 4,533,692 (August 6, 1985);" Liquid Crystalline Poly (2,6-benzothiazole) Composition, Process and Products "(" Composition, Procedure and Products of Poly ( 2,6-benzothiazole) Crystalline, Liquid "), U.S. Patent 4,533,724 (August 6, 1985);" Liquid Crystalline Polymer Compositions, Process and Products "(" Compositions, Process and Products of Crystalline Polymer, Liquid "), patent US Pat. No. 4,533,693) August 6, 1985); "Thermooxidatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymers" ("Poly-p-Benzobisoxazole and p-Benzobistiazole Thermo-oxidatively Stable, Articulated Polymers"), by Evers, US Patent 4,539,567 (November 16, 1982); and "Method for aking Heterocyclic Block Copolymer" ("Method for Making a Block Copolymer, Heterocyclic"), by Tsai, US Patent 4,578,432 (March 25, 1986).

The structural units present in the PBZ polymer are preferably selected, so that the polymer is a liquid, lyotropic crystalline. Preferred monomer units are illustrated below in formulas I-VIII. The polymer most preferably consists of monomer units selected from those illustrated below, and preferably consists essentially of cis-polybenzoxazole, trans-polybenzoxazole, or trans-polybenzothiazole. cis-polybenzoxazole Poly [benzo (1,2-d: 5,4-d ') bisoxazole-2,6-diyl-1,4-phenylene] trans-polybenzoxazole Poly [benzo (1,2-d 4,5-d ') bisoxazole-2,6-diyl-1,4-phenylene] trans-polybenzothiazole cis-polybenzothiazole AB-PBO Poly (2,5-benzoxazole) twenty "> S Poli (2,5-benzothiazole) AB-PBO Poly (2,6-benzoxazole) Poly (2,6-benzothiazole).

Suitable polymers or copolymers of polybenzazole and absorbent materials can be synthesized by known methods, such as those described by Wolfe and other U.S. Pat. 4,533,693 (August 6, 1985); Sybert et al., Patent of E.U.A. 4,772,678 (September 20, 1988); Harris, U.S. Patent No. 4,847,350 (July 11, 1989); and Gregory et al., U.S. Patent. 5,089,591 (February 18, 1992). In summary, the suitable monomers are reacted in a solution of non-oxidizing and dehydrating acid (the acidic solvent) under a non-oxidizing atmosphere, with vigorous mixing and high shear, at a temperature which is increased in a stepped or ramp form from no more than 120 ° C to at least 190 ° C. Suitable solvents for the preparation of PBZ polymer absorbent material include cresols and non-oxidizing acids. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic acid, and highly concentrated sulfuric acid, or mixtures thereof. Preferably, the acidic solvent is polyphosphoric acid or methanesulfonic acid, but polyphosphoric acid is very preferred. The concentration of polymer in the solvent is preferably at least 7% by weight, preferably at least 10% by weight, and most preferably at least 13% by weight. The maximum concentration is limited by the practical factors of handling, such as the solubility of the polymer and the viscosity of the absorbent material. The concentration of the polymer normally does not exceed 30% by weight, and is preferably not more than about 20% by weight. Oxidation inhibitors, tarnish agents, coloring agents, and antistatic agents can also be added to the absorbent material. The solutions of polybenzazole polymers can be stored for a period before being spun. However, it is particularly desirable to conduct a direct spinning, continuous polymerization method, in which the polymerization is conducted continuously and a spinning absorbent material is supplied directly to a spinning device without prior storage. The process of the present invention is operated preferably in a continuous form, with a speed of rotation of at least about 50 meters / minute (m / min). The speed of rotation is preferably at least about 200 m / min, preferably at least about 400 m / min, and most preferably is at least about 600 m / min. Due to the high extensional viscosity of most of the polybenzazole absorbent materials, it is preferable to apply a stretching tension to the filament, in order to efficiently extrude the absorbent material. Stretch stress is preferably at least about 1 gram / denier, preferably at least about 3 grams / denier, but preferably is not more than about 10 grams per denier, most preferably not more than about 5 grams by denier Since it is difficult to obtain this level of tension with an air or gas aspirator, the filaments are preferably drawn using a vacuum cleaner, which uses the flow of a liquid to reduce the air pressure in the aspirator (hereinafter, "liquid aspirator"), and then deposited on the collection device. Alternatively, a group of drawing rollers, placed between the rotation die and the aspirator, can be used to stretch the filament, which can then be deposited on the collection device, using either a gas or liquid aspirator. Preferably, the aspirator moves in an oscillating movement relative to the collection device, in order to more effectively and uniformly disseminate the fiber on the surface of the device. After the filaments are extruded, they are intermixed and deposited on a substantially flat collection surface. The filaments can be intermixed by any suitable method, such as by passing the filaments through a device, which uses a vacuum to create turbulence and to stretch or transport the filaments therethrough to the collection surface. If a suction device is used, the temperature of the gas or liquid aspirator can be increased above ambient conditions to soften the absorbent material, if desired, which would cause the filaments to contact each other, to adhere . In such cases, when the filaments are subsequently washed and dried, the filaments will continue to adhere, creating a more rigid fabric than could be obtained otherwise. If hot liquid is to be used in the aspirator, it is preferably a liquid, which is not a solvent for the acid contained in the absorbent material, so that the acid is not removed before the filament is deposited on the surface of the absorber. harvest. If the fluid from the vacuum cleaner is a solvent for the acid, such as water, a portion of the solvent can be removed as the filament passes through the vacuum cleaner and the filament of the absorbent material will not adhere as effectively as after being deposited on it. the collection device. Examples of fluids that can be used, which are not solvents neither for the acid nor for the polybenzazole polymer, include alkyl glycos. The flow velocity of the fluid through the aspirator is preferably at least about 20 m / sec. The spun filament is deposited on a collecting surface, substantially flat. The filament first passes through a vacuum cleaner or other device, which can be used to direct the filament onto the collection surface, substantially flat. Although the pickup surface must be substantially flat and sufficiently level to hold the filaments of the extruded absorbent material, it may be made of a flexible material such as a net conveyor, but it is not a guide pulley or roller, as is typically used in a fiber spinning process. Any solid material can be used to make the collection surface, but is preferably one that is chemically resistant to the effect of the acid in the polybenzazole absorbing material and to any gas or liquid to which it can be exposed during the process. The polybenzazole filaments are preferably deposited on the collection device in quantities and under conditions sufficient to form a random network, having an average width of at least about 1 cm. However, it is more efficient, from the processing point of view, to prepare a random network having a much larger width, such as at least about 0.2 m, so that a correspondingly wider nonwoven web will be obtained. After the filament is deposited in the collection deviceIt can be washed and dried using methods, which are typically used in the manufacture of polybenzazole fibers. The filaments are preferably washed to remove approximately 80% of the acidic solvent present in the absorbent material, preferably at least about 90%, and most preferably at least about 95%. Examples of suitable washing fluids include water, methanol, and aqueous solutions of the acid solvent. If the acid solvent is polyphosphoric acid, the filaments are preferably washed at a residual phosphorus content of less than about 8,000 ppm, most preferably less than about 5,000 ppm. The filaments are preferably dried at a moisture content of less than 3.0% by weight, preferably less than 2.0% by weight, preferably less than 1.0% by weight, and most preferably less than 0.5% by weight, and any device can be employed suitable for drying. If desired, the filament may also be heat treated to improve its modulus to tension, as described, for example, in U.S. Patent 5,288,442. Referring now to Figure 1, there is shown an apparatus having a spinning head (1), which is spinning filaments through an extinguishing chamber (2), on a pair of guide rollers (3) coated with polytetrafluoroethylene , through a compressed air aspirator (4), and on a network conveyor (5), on which the filaments are collected. The filaments then pass through a series of wash baths (6), (7), and (9), and a neutralization bath (8). The washed filaments are then passed through a dryer (10) and the resulting nonwoven fabric is wound on a winder roller (11). Referring to Figure 2, there is shown an apparatus having a spinning head (12), which is spinning the filaments through an extinguishing chamber (13), through a water flow aspirator (14), and on a network conveyor (15), on which the filaments are collected. Then, the filaments pass through a series of wash baths (16), (17), and (19), and a neutralization bath (18). The washed filaments are then passed through a dryer (20) and the resulting nonwoven fabric is wound on a winder roller (21). The non-woven fabric obtained by washing and drying the filaments, which have been processed according to the invention, is a random strip or mat of polybenzazole filaments. As the filaments are deposited on the collection device at a high rate of speed, they are intermixed. They also intermix as they pass through the vacuum cleaner. The intermixing causes the filaments to mechanically interlock, and the filaments will remain intermixed as they are washed and dried. The stretching and intermixing process can cause the filaments to break periodically before or as they are deposited, although said rupture will not significantly affect the process. After the fabric is washed and dried, the mechanical entanglement of the filaments can be further increased, if desired, by the use of a needle punch, a water punch, or a calendering device designed for such purposes. If the filaments of the absorbent material are deposited at a temperature at which the absorbent material is softened, such as above about 80 ° C, the filaments will tend to adhere to each other, even after the filaments are washed and dried, which will also act to jointly hold the fabric. In addition, a binder can also be applied to the fabric, after it has been washed and dried, if desired. The non-woven fabric of polybenzazole, prepared by washing and drying the filaments according to the method of the invention, has advantageous properties of resistance to heat, power to tearing, resistance to tearing, resistance to insulation, wear, and resistance to flames. The tear strength of the filaments is preferably about 25 g / d, and the modulus at tension is preferably around 700 g / d. If the fabric is treated with heat, at a temperature of at least about 350 ° C, the modulus to the tension of the filaments can be increased to more than 1500 g / d. The following examples are presented to illustrate the invention and should not be construed as limiting in any way. Unless otherwise specified, all parts and percentages are given by weight.

EXAMPLE 1 A solution of polybenzoxazole in polyphosphoric acid was prepared from 4,6-diamino-1,3-benzenediol di-hydrochloride and terephthalic acid. The absorbent material had a phosphorous pentoxide content of 83.17% and an intrinsic viscosity of 24.4dL / g, as measured in methane sulphonic acid at 30 ° C, and was prepared using the method described in the US patent. 4,533,693. The absorbent material was passed through a metal screen filter and degassed in a twin screw extruder. The pressure was raised, and the absorbent material was transferred to a spinning head using a dosing pump and heated to 170 ° C. The absorbent material was spun through a spinner with 334 holes at 170 ° C, and then cooled to 60 ° C, in an extinguishing chamber. The filaments were extracted on a pair of driven guide rollers, which have a surface treated with polytetrafluoroethylene, at a speed of 200m / min. Then, the filaments were extracted through a vacuum cleaner, through which was fed compressed air, and were deposited on a network conveyor moving at a speed of 20 cm / min. The filament network was then washed in a 10% aqueous solution of polyphosphoric acid, maintained at a temperature of 22 ± 2 ° C. The filaments were subsequently washed in a water bath, and then immersed in a 0.1N solution of sodium hydroxide, to be neutralized. Then, the filaments were washed in a water bath, and dried for 5 minutes at 190 ° C. The resulting nonwoven fabric had a weight of 55 g / m2, and a water content of 0.8%. Twenty individual filaments of the fabric were removed, to determine their average physical properties, which are as follows: 1.5 denier filament, tensile strength of 35 g / denier (g / d), tension modulus 800 g / d, 4.5% elongation.

EXAMPLE 2 Polybenzoxazole filaments were prepared, using the procedure described in Example 1, except that the temperature of the extinguishing chamber was 80 ° C. The extruded filaments were extracted using a water aspirator, and then deposited on a network conveyor. Then, the filaments were washed, dried and neutralized using the procedure described in Example 1. Twenty individual filaments were removed from the fabric, to determine their average physical properties, which are as follows: 2.5 denier filament, resistance to the tension of 33 g / denier (g / d), tension module of 800 g / d, elongation of 4.4%.

Claims (3)

1. - A continuous process for preparing non-woven fabrics of polybenzazole filaments, which comprises spinning at least two filaments of polybenzazole absorbent material, simultaneously, and intermixing and depositing the filaments on a substantially flat collection surface.

2. The method of claim 1, wherein the polybenzazole is polybenzoxazole.

3. The method of claim 1, wherein the polybenzazole is polybenzothiazole. 4 - The method of claim 1, wherein the method comprises the additional steps of washing and drying the deposited filament. 5. The method of claim 1, wherein the spun filament is extracted with a liquid aspirator before being deposited on the collection surface. 6. The method of claim 1, wherein the spun filament is extracted with a pair of driven guide rollers before being deposited on the collection surface.