KR0178360B1 - Process for preparing subdenier fibers, pulplike short fibers, fibrids, rovings and mats from isotropic polymer solutions - Google Patents

Abstract

A process for preparing subdenier fibers and structures thereof from isotropic polymer solutions is disclosed. The process comprises extruding a stream of the polymer solution into a chamber, introducing a pressurized gas into the chamber, directing the gas in the flow direction of and in surrounding contact with the stream within the chamber, passing both the gas and the stream into a zone of lower pressure at a velocity sufficient to attenuate the stream and fragment it into fibers, and contacting the fragmented stream in the zone with a coagulating fluid.

Description

[Name of invention]

Process for producing subdenier fibers, pulp short fibers, fibrids, rovings and mats from isotropic polymer solutions

Detailed description of the invention

This application is part of US Patent Application No. 07 / 555,194 of July 20, 1990, which is part of US Patent Application No. 07 / 304,461 of February 1, 1989. .

[Background of invention]

[Field of Invention]

The present invention relates to a method for producing subdenier fibers which can be concentrated in the form of pulp-like short fibers, fibrids, rovings and mats from an isotropic polymer solution. The present invention also contemplates and includes a product having a novel subdenier fiber structure made according to the method described above.

[Description of Prior Art]

Different methods are known in the art for producing sheet structures and nonwovens of discontinuous thermoplastic fibers.

As an example, US Pat. No. 3,849,241 to Butin et al. And European Patent Application Publication No. 0166830 disclose a method of feeding a gas stream directly to a polymer for forming fibers in a molten state and then concentrating the fibers on a screen. It is.

Also known in the art is a method of flash extruding a continuous fibrillated polymer structure and tearing the structure by feeding the fluid stream in a reverse direction to the flow direction of the structure at the time of its formation. US Patent No. 4,189,455 to Ragato et al.

However, the aforementioned references do not present a jet-attenuating process for producing subdenier fibers from isotropic solutions.

Morgan, US Patent No. 2,999,788, discloses its use in the manufacture of fibrids of various synthetic organic polymers and in the production of synthetic sheet structures such as paper. Such papers are useful for electrical applications when made from poly (meth-phenylene isophthalamide) fibrids, in particular papers such as fibrids and poly (meth-phenylene isophthalamide) short fibers (floc). When prepared from mixtures of, it can be more useful for electrical applications. As disclosed in US Pat. No. 3,756,908 to Gros, poly (meth-phenylene isophthalamide) fibrids used in the art act as flock binders and provide good electrical properties. Particles. However, this fibrid has the drawback that fibrids excessively seal the paper to reduce porosity. Porosity is a very important property because it serves to modify and improve the physical properties of the paper that can be used in electrical applications by promoting the coating and saturation of the paper with varnishes and resins in a manner well known in the art. to be.

It is an object of the present invention to produce new pulp poly (meth-phenylene isophthalamide) fibrids. The pulp-like fibrids can be used to make sheet structures, such as paper, with improved porosity and electrical properties, which can be used to make laminates and composite structures.

[Overview of invention]

The present invention provides a method of making subdenier fibers from an isotropic polymer solution. The method involves (1) extruding an isotropic solution stream of polymer into the chamber through a spinneret orifice, (2) introducing compressed gas into the chamber, and (3) directing the gas in the chamber in the direction of flow of the stream. (4) feeding the gas and the stream together, into the low pressure zone through the opening at a rate sufficient to refine the stream and fragment it into fibers, and (5) in the zone Contacting the fragmented stream with a solidifying fluid. The gas suitable for contacting the extruded stream inside the chamber is air, and the low pressure zone through which the gas and stream pass together may be air under atmospheric pressure. Preferably, the coagulating fluid is water, dimethyl sulfoxide or dimethylacetamide.

Preferred embodiments of the present invention include polyacrylonitrile; Poly (m-phenylene isophthalamide); Copolymers of 3,4'-diaminodiphenyl ether with isophthaloyl-bis- (caprolactam); And spinning isotropic polymer solutions comprising a mixture of poly (m-phenylene isophthalamide) and a copolymer of 3,3'-diaminodiphenyl ether and isophthaloyl-bis- (caprolactam). Can be.

Fragmented streams of subdenier fibers may be concentrated in the form of pulp-like short fibers, fibrids, rovings or mats, and such products are also considered part of the present invention.

In one embodiment of the invention, the fibrid on poly (m-phenylene isophthalamide) pulp is spun by polymer solution containing about 12 to 19% by weight of a poly (m-phenylene isophthalamide) polymer. Are manufactured. Hot air with a pressure of about 6 kg / cm ² or more is introduced into the chamber. Suitable solvents for the poly (m-phenylene isophthalamide) polymer include dimethylacetamide and a mixture of dimethylacetamide and dimethyl sulfoxide.

The invention also includes pulp-like fibrids prepared by the process. This pulp-like fibrid is about 0.1 to 50 micrometers in diameter, about 0.2 to 2 millimeters in length, has a freeness value of about 100 to 2000 milliliters, and uses 100% by weight of this fibrid. A poly (m-phenylene isophthalamide) porous sheet can be formed. This wet-laid porous sheet preferably has a porosity of about 0.1 to 200 seconds, more preferably about 0.1 to 2.0 seconds per 100 cubic centimeters. The sheet has a dielectric strength of at least about 300 volts per ounce per square yard, typically about 300 to 700 volts.

Wet laid sheets, which consist of about 5 to 95 weight percent of said poly (m-phenylene isophthalamide) pulp-like fibrids, are also considered part of the present invention. Such wet laid sheets can be composed of the above pulp fibrids, poly (m-phenylene isophthalamide) film fibrids and poly (m-phenylene isophthalamide) staple flocs.

[Brief Description of Drawings]

1 through 6 are cross-sectional schematic diagrams of an apparatus for carrying out the invention, mainly a spin-cell.

Detailed description of the invention

Several isotropic polymer solutions well known in the art can be used in the present invention. Such solutions include nylon 66, polyacrylonitrile, such as acrylonitrile, methyl acrylate and DEAM (diethylaminoethyl methacrylate) in a solvent of dimethyl sulfoxide, dimethylacetamide or dimethylformamide in sulfuric acid or formic acid. Co- and terpolymers; Polyether-urea-urethane polymers such as polymers made of polytetramethylene glycol, methylene-bis- (p-phenylene isocyanate), ethylene diamine and 1,3-cyclohexane diamine reactant in dimethylacetamide solvent; Polyimides such as terpolymers of oxydianiline, hexafluoropropylidene-bis-phthalic anhydride and sulfone dianiline in N-methylpyrrolidone solvents; Copolymers of aramids capable of melt treatment, such as 3,4'-diaminodiphenyl ether and isophthaloyl-bis- (carrolactam) in sulfuric acid; Poly (m-phenylene isophthalamide) in dimethylacetamide; And polyvinylidene fluoride with dimethylacetamide. In addition, other suitable isotropic polymer solutions for fiber formation that are well known in the art may also be used. If desired, one or more polymers may be incorporated into the same isotropic solution to form a suitable polymer blend. Isotropic polymer solutions for use in the present invention can be prepared by methods known in the art.

The isotropic polymer solution is extruded through the spinneret orifice into the chamber, generally near the convergent-walled aperture, through which it exits the chamber. In addition, compressed gas inert to the isotropic polymer solution is introduced into the chamber near the opening to make contact while surrounding the solution stream. The pressure when the gas, preferably air, is fed into the chamber is from 1.7 to 7.2 kg / cm ² and the temperature is from 20 ° to 300 ° C. The rate of gas is the rate at which the stream can be subdivided and fragmented when it is discharged through the opening in the chamber.

The gases and streams exiting the chamber enter the low pressure zone, preferably air, under atmospheric pressure. In this zone, the stream is in contact with the solidifying fluid before or after focusing. Suitable coagulating fluids include water, alcohols and mixed solvents thereof. Various products can be obtained depending on the type of solidifying fluid used and the method of contacting the stream with the solidifying fluid.

To produce the mat, the fragmentation stream is contacted with a spray of solidifying fluid, such as water, at a distance of, for example, 15 to 30 cm from the opening. Injection water solidifies and disperses the stream, and the dispersion stream treated with the injection water can be focused as a mat on a screen belt that moves transversely relative to the stream.

If the stream consists of an acid solution of the polymer, contact with water dilutes the acid and leaves the polymer out of the form of the solution. The focused material can be washed again or neutralized with dilute base by methods known in the art while the material is on the screen belt. The resulting mat is formed by irregular laydown of subdenier discontinuous fibers oriented while being spun with water spray, which has a wide variety of shapes. This mat can be formed at a dimensionally stable sheet structure by sticking at the fiber intersections.

To produce the pulp-like product, the coagulating fluid is contacted with the outlet solution stream at the opening and the product is focused onto a pool of coagulating fluid. This pulp-like product consists of oriented subdenier short fibers up to 15.0 mm long and varying in shape.

Finally, to produce a roving or sliver, the solidifying fluid is sprayed in the reverse direction to the fragmentation stream about 1.0 to 10.0 cm away from the opening, and the solidified product is sprayed on a screen moving at a relatively high speed. Although it consists of focusing, in this case, an injection of the coagulating fluid is used that does not have sufficient force to disperse the product before it is focused.

The structure of the solidified product is essentially a uniaxial laydown of oriented subdenier discontinuous fibers with a wide variety of morphological changes with essentially no adhesion or bonding between the fibers.

Hereinafter, a suitable apparatus and a driving method are explained in more detail.

FIG. 1 is a schematic cross-sectional view showing a spin cell with a tubular one-hole spinneret 4 in which the outlet 3 extends into the chamber 9 of the cylindrical manifold 6. The manifold has an inlet 8 and a nozzle 10, which has a converging mural opening 11 that acts as an outlet from the cell. In operation, an isotropic solution of polymer is introduced into the chamber 9, metered through the spinneret 4, and in contact with the compressed gas entering the inlet 8 through the chamber 9. The gas refines and breaks the polymer solution into the elongated fragments as the polymer solution exits the chamber through the opening 11 where both walls are concentrated in a narrower gap. As the stream of elongated fragments exits the opening 11, it is in contact with the solidifying fluid. Various products can be obtained depending on how the contact is made and what kind of solidifying fluid is used.

FIG. 2 shows the fluid of spray jet nozzle 20 which acts to solidify and diffuse fragment 30 of the stream where elongated fragments or fibers exiting spin cell 6 are slightly below the opening 11. 26), the process of depositing as a nonwoven sheet on the moving screen 32 is shown. If necessary, a series of such jet nozzles can be used. This fragment is a subdenier fiber with significantly different cross sections, up to 10 cm in length, up to 10 microns in diameter, and a ratio of length to diameter of at least 1000. Washing, drying and winding on bobbins (not shown) for the fibers on the screen can be done in a continuous process.

3 illustrates another method of making a roving or sliver by contacting the stream exiting the opening 11 with a solidifying fluid. In this case, the atomizing jet of the solidifying fluid 28 from the spray jet nozzle 24 impinges on the stream exiting the opening 11 at a maximum of 10 cm below the opening. The fibers in the stream have a greater momentum than the atomizing jets of the solidifying fluid, resulting in less deflection of the stream and less fiber dispersion. Under these conditions, the subsequent step, the fiber deposition on the moving screen 32, is essentially deposited in one direction, and the product is suitable for slivers and rovings. In a similar manner, the prevention of diffusion of the stream exiting the opening 11 can be achieved by enclosing the stream with a film of solidifying fluid flowing in the same direction. The coagulation fluid membrane initiates coagulation of the fibers and prevents them from spreading.

In another case, the stream containing the solidified fibers is blocked by a moving screen conveyor belt that causes the fibers to be deposited essentially in one axial direction on the screen. The formed sliver or roving may be wound into bobbins (not shown).

The fibers are similar to those of the nonwoven mat described above.

4 shows a method for producing pulp short fibers. 4 shows a spin cell 40 similar to that of FIG. 1 except that it has a conical nozzle 30 and a jet 35 embedded in the spin cell housing. The solidifying fluid from the jet 35 impinges on the outer surface of the nozzle 30 and flows down to the opening 12 along the inclined surface of the nozzle 30 to contact the discharge stream. According to this method, a short length of solidified pulp-shaped fragment is formed, which can be diffused on a moving screen or recovered in a receptacle (not shown) located below the spin cell.

5 shows a spin cell 50 having an inlet 51 for introducing a hot air for heating the spinneret to prevent clogging of the spinneret, and an inlet 52 for introducing air for cooling treatment to be introduced in the second step. It is shown. The seal 54 prevents hot air from mixing with cold air in the spin cell. The spent hot air can be removed from the chamber through the outlet 53. The polymer solution and cold air are discharged through the discharge opening 55.

FIG. 6 illustrates spin cell 150 through which hot air flows through inlet 151 to heat spinneret 104 to promote flow characteristics of the solution. The hot air then escapes through the narrow annular gap 154 before drag is applied to the solution discharged from the outlet of the spinneret 103. This air refines and breaks the filament when the air exits the chamber through the opening 130. The opening 130 is a gap having a constant diameter and a limited length. As the broken filament exits the opening 130, it is in immediate contact with the solidifying fluid entering the opening area through the hole 152. For the production of tangled pulp-like fibrid samples, the polymer solution, exhaust air and coagulant are collected in a water bath.

It will be apparent to one skilled in the art that various modifications can be made to the device. Thus, if necessary, a plurality of spin cells arranged side by side in a linear manner can be used to obtain a laydown of significant width and uniform sheet. Likewise, the diverging channel formed by the walls arranged and arranged parallel to the outlet of the opening 11 diffuses the exhaust stream into a wider stream as it exits the spinning cell.

There are several important process parameters in the production of high quality pulp fibrids using the process of the present invention, especially where the fibrids must have the necessary properties for the production of improved porous paper. Preferably, a spinneret arrangement similar to that shown in FIG. 6 is used. Important process variables include solution viscosity, solution extrusion rate, pressure of hot air flowing into the cell, holes in the air openings 130, and lengths of air gaps (the length of which is the outlet and opening 130 of the spinneret 103). ) Is measured as the distance between the outlets.

Solution viscosity is controlled by the solution temperature and the polymer concentration in the solution. For the work described herein, the solution viscosity was controlled through the adjustment of the polymer concentration. The solution extrusion rate was controlled by the nitrogen back pressure applied to move the solution forward. The air pressure can simply be adjusted via a regulator.

The polymer concentration in the poly (m-phenylene isophthalamide) solution (solvent = dimethylacetamide / dimethylsulfoxide) was varied between about 12% and 19% by weight so that the solution viscosity affected the quality of the pulp-like fibrids. The impact was investigated. Fibrid diameter decreases as the solution viscosity decreases, but the concentration of large particulate defects increases significantly at lower polymer concentrations. In order to achieve the desired goal of obtaining a fine diameter fibrid containing a minimum amount of particulate defects, a solution having a solids content of 16% by weight was determined to provide the best results. The optimal polymer concentration will vary depending on the specific polymer / solvent mixture used. Other possible solvents for the poly (m-phenylene isophthalamide) polymers are known in the art, for example dimethylacetamide itself.

The solution extrusion rate was controlled by nitrogen back pressure. High nitrogen pressures lead to high extrusion rates, which are desirable in terms of productivity, but often involve high concentrations of large particulate defects. For a 16 wt% poly (m-phenylene isophthalamide) (MPD-I) solution spun using a 0.004 inch (0.102 mm) spinneret, a nitrogen back pressure of 500 psig or less, preferably 400 psig or less In order to obtain high quality pulp fibrids.

Air pressure determines the air velocity and speed change near the capillaries and openings. The inventors have found that the best fibrid quality is achieved when the air pressure is set to about 80 psig (6.65 kg / cm ² ), which is the highest pressure that can be set for the device shown in FIG. 6 with the dimensions described in Examples 6-16. This result was found from this work.

The pulp MPD-I fibrids of the present invention have different properties and properties from the fibrids known in the art. For example, MPD-I fibrids, reported in the art, are flat film-like materials that are refined to various lengths and typical dimensions of 0.1 micrometers thick and 100 micrometers wide. The fibrous nature of these fibrids results in a low porosity by sealing the paper containing them.

In contrast, the improved pulp-like fibrids of the present invention have a basically round cross section with irregular fibril shapes. Unlike film-like fibrids in the art, the pulp-like MPD-I fibrids of the present invention have refined fibrid appearance, openness and paper processing capability without refining the fibrids. The pulp-like fibrids of the present invention do not seal the paper containing them. Therefore, when pulp-like fibrids consisting of aromatic polyamides such as MPD-I are used to produce electrical paper, improved combinations of electrical properties and porosity compared to similar papers in the art in which film-like fibrids are incorporated Is obtained.

In the end use of electrical paper or other high quality paper, the preferred dimensions for pulp-like fibrids are 0.1-50 micrometers in diameter and 0.2-2.0 mm in length. More preferably, the pulp-like fibrids have a diameter of 0.2-5.0 micrometers and a length of 0.2-1.3 mm. The pulp-like fibrids of the present invention also have a high freeness value. It is preferable that the freeness value measured with the Choppler Riegler apparatus is 100-2000 ml. More preferably, pulp-like fibrids have a freeness value of 500-1000 ml.

The MPD-I pulp-like fibrids of the present invention can be used alone or as a blend with film-like fibrids and staple flocs to produce paper having good electrical properties. The term staple flock or flock herein means that the fibers are in the form of short fibers. Preferably, the flock consists of fibers less than 2.54 cm in length and the optimal flock length is about 0.6 cm. Suitable yarns or tows of polyamide are cut to the desired floc length, for example by a suitable method using a spiral saw cutter. Suitable fibers are fibers having a denier of about 0.5 to about 10 or more. Denier less than about 5 is preferred. Most preferred are fibers having a denier of about 1 to about 3.

Of the poly (m-phenylene isophthalamide) pulp of the present invention and the poly (m-phenylene isophthalamide) film fibrid in the art, and poly (m-phenylene) isophthalamide staple floc In producing the electrical paper using the blend, the preferred composition of the blend is 5 to 100% by weight of pulp-like fibrids, 0 to 60% by weight of fibrous fibrids, and 0 to 90% by weight of staple flocs. More preferably, blends of 10 to 60% by weight of pulp-like fibrids, 0 to 33% by weight of fibrous fibrids and 10 to 50% by weight of staple flocs are used.

[Test Methods]

The denier of the sample fiber should be calculated before measuring the tensile properties. As described above, a method for measuring deniers of non-circular and various diameters is known, and examples thereof include specific surface area measurement, scanning electron microscopy, and direct measurement of sample fiber groups under an optical microscope.

Instron 1123 was used to measure tear strength and modulus according to ASTM D2101 Section 10.6 (10% strain). For a sample length of 1.0 inch, clamps (6/16 inch x 6/16 inch sized neoprene face grips) are secured 1-1 / 4 inch to 1-1 / 2/2 spaced apart, and 0.1 inch / Run at a crosshead speed of min. On the other hand, for a sample length of 0.25 inch, the clamp was fixed at 0.75 inch between the faces and operated at a crosshead speed of 0.025 inch / minute.

Each end of the filament sample was taped to the opposite end of a rectangular tab with rectangular cutouts (holes) of specification length (1 inch or 0.25 inch). This taping was located away from the hole and some fiber relaxation was allowed. An adhesive drop was placed near the edge of the tab hole to adhere the specified length of the filament to the length of the tab hole. The tab was installed in the upper clamp of the Instron, and one side of the tab was cut. The opposite end of the tab was then installed in the lower clamp and the other side of the tab was cut away leaving the filament elongated across the gap between the clamps. The tensile properties were evaluated by running the Instron and inputting the filament's stress-strain relationship directly into the computer.

Dielectric strength was measured according to ASTM D-149.

Porosity was measured using the Air Resistance of paper of TAPPI Test Method T460 om-88 paper. The results of this test are recorded in seconds, which is the number of seconds it takes for the 567 g mass to pass 100 cc of air through 6.4 square centimeters (1 square inch) of paper under test. Means. The larger the value (second) of the test result, the lower the porosity of the paper.

The average fiber length for pulp material is based on the Kajaani Model FS 100 device manufactured by Kajaani Electronic Ltd. of Kazani, Finland, as described in Kajaani FS100 Standard Procedure for Analysis, Document T3501.0-e, Copyright , September 1985].

Fibrid's sample is 2.0 grams of pad weight and according to the International Organization for Standardization (ISO) standard ISO 5267 / 1-1979 (E), Pulps-Determination of Drainability Part I-Schoppler-Riegler Freeness Tester. The freeness of this sample was tested using a temperature of about 20 ° to 25 ° C.

[Unit conversion]

1 in = 2.54 cm

1 oz / yd ² = 33.9 gm / m ²

The following examples are intended to illustrate the invention without limitation. In the examples below, parts and percentages are by weight unless otherwise indicated.

Example 1

A terpolymer of acrylonitrile having a composition of 91% acrylonitrile, 6% methyl acrylate and 3% DEAM (diethylaminoethyl methacrylate) and having an intrinsic viscosity of 1.4 in a 25% concentration solution in dimethylsulfoxide solution Made with. This solution was prepared by placing a polymer powder and a solvent in a resin kettle and dissolving the polymer in a solvent by stirring. The solution was then pushed into a spin cell similar to that shown in FIG. 4 by hydrostatic pressure and spun through a one-hole spinneret according to the conditions shown in Table 1. This spinneret was 0.004 inches (0.1016 mm) in diameter and had a ratio of length to diameter, that is, an L / D ratio of 3.0. In connection with FIG. 4, the spin cell measures 0.176 inch (4.47 mm) from the outlet 3 of the spinneret to the narrowest diameter (or neck) of the opening 12 of the nozzle 30 of the spin cell. Had an air gap. The narrowest diameter of the opening 12 was 0.062 inch (1.57 mm). The converging wall of the opening 12 was at an angle of 40 degrees with respect to the axis of the spinneret making a conical angle of 80 degrees. Air heated to 80 ° C. and pressurized at 80 psig (6.7 kg / cm ² ) was applied to the spin cell to refine and fragment the newly extruded polymer.

The discontinuous fibers exiting the spin cell contacted the tap water stream on the screen conveyor belt moving 17.375 inches (44.1 cm) away from the tip of the opening 12 to produce fibers having a length of up to 8 cm.

The fibers were placed on a moving screen conveyor belt, forming a random web and moved from the spinning chamber to the cleaning chamber along the conveyor belt. In this wash chamber, the web was washed to remove trace amounts of residual solvent, then transferred to a drying chamber to dehydrate the washed web, partially dry and then wound onto a bobbin (or roll).

The fibers on the bobbin (or roll) exhibited the appearance of carded slivers and could soon be used to make yarn. The physical properties of this fiber were tested and the results are shown in Table 1.

Alternatively, the discontinuous fibers exiting the spin cell were contacted with a tap water stream at the tip of the opening 12 to produce fibers having a length of less than 15 mm. These medium length fibers were concentrated in a water bath and water was then separated from the fibers by standard filtration. Finally, the fibers were washed to remove residual solvent. The fibers can be wet laid by conventional methods known in the art to produce paper.

Example 2

A solution of 20% concentration of poly (m-phenyleneisophthalamide) in dimethylacetamide solvent was hydraulically pushed into a spin cell similar to that shown in FIG. 4 and through a one-hole spinneret according to the conditions of Table 2 Spun. The one-hole spinneret had a diameter of 0.004 inches (0.1016 mm) and an L / D ratio of 3.0. Alternatively, the one-hole spinneret had a diameter of 0.010 inches (0.254 mm) and an L / D ratio of 3.0. The solution was spun from two types of spinneret.

With respect to FIG. 4, the spin cell measures the distance from the outlet 3 of the spinneret to the narrowest diameter (or neck) of the opening 12 of the nozzle 30 of the spin cell, resulting in 0.176 inch (4, 47 mm) air gap. The narrowest diameter of the opening 12 was 0.062 inch (1.57 mm). The converging wall of the opening was at an angle of 40 degrees with respect to the spinneret axis creating a conical angle of 80 degrees.

The discontinuous fibers exiting the spin cell contacted the tap water jet about 11 inches (28 cm) away from the tip of the opening 12 and focused on a stainless steel moving screen. A web of subdenier fibers was formed on the screen. The physical properties of one fiber were tested and the results are shown in Table 2. X-ray analysis of the fiber showed an amorphous structure. The washed, dried web could be used as an inner layer for making laminates with similar layers of poly (p-phenyleneterephthalamide) and for high temperature insulation.

Example 3

In this example, 160 grams of a 20% solution of poly (m-phenylene isophthalamide) in dimethylacetamide was diluted with 40 grams of dimethyl sulfoxide solvent. This mixture was hydraulically pushed into a spin cell similar to that shown in FIG. 4 and spun through a one-hole spinneret according to the conditions of Table 2. This one-hole spinneret had a diameter of 0.004 inches (0.1016 mm) and an L / D ratio of 3.0. The spin cell had an air gap of 0.176 inches (4.47 mm) as measured from the outlet 3 of the spinneret to the narrowest diameter (or neck) of the opening 12 of the nozzle 30 of the spin cell. The narrowest diameter of the opening 12 was 0.062 inch (1.57 mm). The converging wall of the opening was at an angle of 40 degrees with respect to the spinneret axis creating a conical angle of 80 degrees.

The discontinuous fibers exiting the spin cell contacted the tap water jet at the tip of the opening 12 and focused on a water bath (not shown). The fibers were filtered, washed and slurried in water using a Waring blender to further reduce the fiber length. The product was a subdenier pulp having a fiber length of up to 5 mm. This subdenier pulp was useful as a binder for poly (p-phenylene terephthalamide) paper and as a midpoint agent for the production of high quality paper.

Example 4

A solution of 30% concentration was prepared by dissolving a copolymer of (3,4'-diamino diphenyl) ether and isophthaloyl-bis- (caprolactam) in dimethylacetamide. This solution was then hydraulically pushed into a spin cell similar to that shown in FIG. 4 and spun through a one-hole spinneret. This one-hole spinneret had a diameter of 0.004 inches (0.1016 mm) and an L / D ratio of 3.0. The air gap was 0.176 inches (4.47 mm) as a result of measuring from the outlet 3 of the spinneret to the narrowest diameter (or neck) of the opening 12 of the nozzle 30 of the spin cell. The narrowest diameter of the opening 12 was 0.062 inch (1.57 mm). The converging wall of the opening was at an angle of 40 degrees with respect to the spinneret axis creating a conical angle of 80 degrees. Heated to 80 ° C., 83 psig (6.9 kg / cm ) Compressed air was introduced into the spin cell as the fluid for refinement. The discontinuous fibers discharged from this spin cell were contacted with tap water jet about 11 inches (28 cm) away from the tip of the opening 12 and focused on a moving screen. Subdenier fiber webs were formed on the screen.

Alternatively, the discontinuous fibers exiting the spin cell were contacted with tap water at the tip of the opening 12 and focused on a water bath as described in Example 3. The product in this case was a subdenier fiber, which can be used, for example, as a substitute for asbestos in papermaking or as a binder between poly (p-phenylene terephthalamide) layers for high temperature applications.

Example 5

A polymer blend of 70% poly (m-phenylene isophthalamide) and 30% by weight of a copolymer of 3,4'-diaminodiphenyl ether and isophthaloyl-bis- (caprolactam) in dimethylacetamide It was dissolved to make a solution of 20% concentration. This solution was then spun using a spin cell of a type similar to that shown in FIG. 4, with a one-hole spinneret of 0.004 inches (0.1016 mm) in diameter. The solution was also spun using a spin cell of the same type with spinnerets 0.010 inches (0.254 mm) in diameter. Both types of spinneret had an L / D ratio of 3.0. The spin cell measured from the outlet 3 of the spinneret to the narrowest diameter (or neck) of the opening 12 of the nozzle 30 of the spin cell, and had an air gap of 0.125 inches (0.175 mm). The narrowest diameter of the opening 12 was 0.062 inch (1.57 mm). The converging wall of the opening was at an angle of 40 degrees with respect to the spinneret axis forming a conical angle of 80 degrees. 90 ° C. and 60 psig (5.3 kg / cm ) Hot air was introduced into the spin cell as the fluid for refinement.

Discontinuous fibers exiting the spin cell were focused on the water bath described in Example 3 in contact with tap water spray at the tip of the opening 12. The fibers were then filtered, washed and dried. The product was pulp-like short fibers that could be used as a substitute for asbestos or as a binder. The thin filter cake of pulp-like short fibers was thermocompressed at about 260 ° C. to form a nonporous membrane.

[Examples 6-16]

The pulp-like fibrids used in these examples were prepared as follows. A 19% solution of poly (m-phenylene isophthalamide) in dimethylacetamide was diluted with dimethylsulfoxide to 16% solids. This solution was spun at 25 ° C. through a 0.004 inch (0.102 mm) single hole spinneret with an L / D ratio of 3. The spin cell was similar to that shown in FIG. 6 and measured the outlet of the opening 130 from the outlet 103 of the spinneret and had an air gap of 0.155 inches (3.94 mm). The outlet of the opening had a diameter of 0.062 inches (1.575 mm) and a length of 0.062 inches (1.575 mm). The pressure of spinning solution is 28.1kg / cm (400 psig) and the air pressure for the delicacy was 5,2 kg / cm (74 psig).

Discontinuous fibers exiting the spin cell were focused on the water bath in contact with the tap water jet at the tip of the opening 130. The fibers were then washed several times with water in a domestic blender to remove solvent (final dimethylacetamide concentration was 0, 16% with undetectable dimethylsulfoxide present). The obtained fiber was in the form of pulp fibrids.

This fibrid quality was evaluated by blending 0.04% by weight of solids in midstream with high speed in a home cooking blender for about 1 minute. The high quality fibrids were easily separated from the blend and stayed uniformly dispersed in the mole without clumping. This aqueous dispersion was used as a tissue-type thin handsheet (3-4 g / m ), Dehydrated and dried. The sheet was inspected for clumps of pulp. The sheet was found to be a pure, uniform sheet with little or no clumps, and the lack of clumps indicates high quality pulp-like fibrids. The clump may be an intertwined filament or may be a solid polymer free from fibrillation upon spinning.

Fibrid diameters measured using a scanning electron microscope were 1-20 micrometers with very few particulate defects. The average length of 0.47 mm for pulp-like fibrids was measured by the Kazani method. This pulp-like fibrid had 773 ml of freeness as measured on a Choppler Wrigler apparatus.

Prior to fabricating the sheet, add the required amount of wet-lap pad to a typical one quart household blend containing approximately three quarters of water and ensure that no mass or thread is present at medium speed. The pulp-like fibrids were opened by blending for 2 minutes.

A total of 2.8 g of ingredients is collectively 2.0 oz / yd Base weight, 8 × 8 inch sheet was used to make. Handsheets made of pulp were cast in a standard deck box. Pulp-like fibrids (supplied in the form of a thin slurry) were slowly mixed with 10 liters of water in a deckle box. Vacuum was applied to form the sheet on a removable wire screen. Further dehydration was achieved by lightly squeezing the sheet and wire screen between two layers of blotter paper using a Noble and Woods sheet press. The wire screen was peeled off, replaced with a fresh blotting sheet, the sheet sandwich was pressed again, the sheet was then removed, and dried between fresh blotting layers.

Pulp fibrids (P) alone or mixed with poly (m-phenylene isophthalamide) film fibrids (F) and / or poly (m-phenylene isophthalamide) staple flocs (5) Was used. Film-like fibrids were prepared according to the method described in US Pat. No. 3,756,908 to Gros (the contents of which are incorporated herein by reference), with an average length of 0.25 mm and a 330 ml shopli Had Glar Prinis Staple flocs were prepared according to the method disclosed in Alexander, US Pat. No. 3,133,138 (incorporated herein by reference), having a cut length of 6 mm and 2 denier / filament.

Pulp-like fibrids, film-like fibrids, and / or staple flocs were mixed with each other in a deckle box before vacuum was applied. The sample sheet was thermocompressed for 1 minute at a pressure of 1000 psi on a Farrel Watson-Stillman press Model No. 9175-MR. Sheets were tested for basis weight, dielectric strength, porosity, elongation at break, modulus and density. Sheet properties are reported in Table 3 below.

The advantages of fibrid addition on pulp are clearly demonstrated by the above data.

Example 13 with 50% by weight fibrid film and 50% staple floc is a representative composition of commercially available paper.

Comparing Examples 6 and 7 with Example 13, it can be seen that in Examples 6 and 7, the porosity was significantly increased to achieve good dielectric properties. In addition, it can be seen that the papers of Examples 6 and 7 have high elongation and low modulus when compared to those of Example 13.

High elongation and low modulus, ie high flexibility, are advantageous in certain applications where paper must be wound. However, since these papers have a high porosity, they can be saturated with resins or varnishes to make them harder. Therefore, this paper has better compliance. In addition, the degree of saturation by resin or varnish is well known in the art as a method of improving the mechanical and electrical properties. Example 9 describes a ter-blend of pulp-like fibrids, film-like fibrids, and flocs, with improved porosity and dielectric strength. This advantage can be obtained at 33% pulp fibrids, 33% fibrous fibrids and 33% floc. However, film-like fibrids tend to counteract the porosity benefits induced by pulp-like fibrids (see Examples 10, 14 and 16).

The porosity of the uncompressed sheet is a useful indicator of the porosity in the compressed sheet, especially when the porosity of the compressed sheet is very low (high porosity value, ie greater than 1800 seconds). Porosity experiments for this length of time may be inconvenient or impractical. Also, for sheets with high porosity (low porosity values, ie less than 0.1 second), porosity readings can be regulated by the actual ability to measure time in this respect.

Comparing Example 11 and Example 12, it can be seen that the porosity benefit can be obtained by replacing the filmy fibrids in the 25% filmy fibrids / 75% flocsite with 25% pulpy fibrids. Dielectric strengths above about 200 are commercially noteworthy, and for paper with high porosity, this value can be raised by saturating with resin and varnish.

Example 15 also shows the porosity advantage obtained when pulp-like fibrids are added.

Claims (22)

(1) an isotropic solution stream of polymer is extruded through the spinneret orifice into the chamber, (2) a pressurized gas is introduced into the chamber, and (3) the gas is directed in the chamber in the flow direction of the stream. And (4) feeding both the gas and the stream into the low pressure zone through the opening at a rate sufficient to attenuate the stream and fragment it into fibers, and (5) in the band A method of making subdenier fibers from an isotropic polymer solution, comprising contacting the fragmented stream with a solidifying fluid. The method of claim 1 wherein the polymer in solution is polyacrylonitrile. The method of claim 1 wherein the polymer in solution is poly (m-phenylene isophthalamide). The process of claim 1 wherein the polymer in solution is a copolymer of 3,4′-diaminodiphenyl ether and isophthaloyl-bis- (caprolactam). The method of claim 1 wherein the polymer in solution is a mixture of poly (m-phenylene isophthalamide) with a copolymer of 3,4′-diaminodiphenyl ether and isophthaloyl-bis- (caprolactam) How to be. The method of claim 1 wherein the low pressure zone is air at atmospheric pressure. The method of claim 1 wherein the gas in contact with the extrudate in the chamber is air. The method of claim 1 wherein the subdenier fibers are focused in the form of fibers, rovings or nonwoven mats. The method of claim 1 wherein the coagulating fluid is selected from the group consisting of water, dimethyl sulfoxide and dimethylacetamide. A product made by the method of claim 1. A product made by the method of claim 8. The method of claim 1 wherein the polymer solution contains about 12-19 weight percent poly (m-phenylene isophthalamide) and the gas is air having a pressure of about 6 kg / cm ² or more. The method of claim 12, wherein the polymer solution contains about 12 to 19 weight percent of poly (m-phenylene isophthalamide) in dimethylacetamide solvent. 13. The process of claim 12 wherein the polymer solution contains about 12 to 19 weight percent of poly (m-phenylene isophthalamide) in a mixed solvent of dimethylacetamide and dimethyl sulfoxide. Pulp-like fibrids prepared by the method of claim 12. About 0.1 to 50 micrometers in diameter, about 0.2 to 2 millimeters in length, about 100 to 2000 milliliters in freeness value, and 100% by weight of a poly (m-phenylene isophthalamide) porous sheet Pulp-like poly (m-phenylene isophthalamide) fibrids that can be formed. 18. The pulp poly (m-phenylene isophthalamide) fibrid of claim 16, wherein said sheet has a porosity of about 0.1 to 200 seconds per 100 cubic centimeters. The wet-laid sheet of claim 16, wherein the dielectric strength is about 300 volts or more per ounce per square yard and the porosity is about 0.1 to 200 seconds per 100 cubic centimeters. A wet laid sheet made from the fibrid of claim 16, wherein the dielectric strength is about 300 volts or more per ounce per square yard and porosity is about 0.1 to 2.0 seconds per 100 cubic centimeters. A wet laid sheet comprised of about 5 to 95 weight percent of the fibrid of claim 16, characterized in that the dielectric strength is about 300 volts or more per-1 ounce per square yard and porosity is about 0.1 to 200 seconds per 100 cubic centimeters. . A wet laid sheet made from about 5 to 95 weight percent of the fibrid of claim 16, characterized in that the dielectric strength is 300 volts or more per ounce per square yard and porosity is about 0.1 to 2.0 seconds per 100 cubic centimeters. A fibrid, poly (m-phenylene isophthalamide) film fibrid and poly (m-phenylene isophthalamide) staple composition of claim 16 having a dielectric strength of about 300 volts per ounce per square yard Or more, and having a porosity of about 0.1 to 200 seconds per 100 cubic centimeters.