Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
  • D01D5/00—Formation of filaments, threads, or the like
  • D01D5/11—Flash-spinning

Definitions

• the present invention generally relates to collecting highly oriented flash-spun continuous backwindable fibers from a spinneret in the form of a rod-shaped batt, commonly referred to as a log.
• the solvent which is discharged from the spinneret with the polymer fiber, flash evaporates and expands into the conduit compressing the fiber into the log, pushing the log forward in the conduit, and escaping through the gas release ports in the periphery of the conduit.
• the spinneret does not include a tunnel at the exit thereof.
• a tunnel has a significant effect on fiber tenacity.
• U.S. Patent 4,352,650 discusses the optimization of tunnel configuration for increasing fiber tenacity from about 4.2 gpd to about 5.2 gpd, wherein fiber tenacity is described as being increased by as much as 1.3 to 1.7 times by using an appropriately sized tunnel at the exit of the spinneret. Accordingly, it would be very desirable to use a tunnel and obtain higher tenacity fiber for the rod-shaped batts.
• a further shortcoming of prior art logmaking methods is that quite frequently, fibers momentarily exit the gas release ports located along the fiber collection tube with the expanding gas. This condition damages the continuity of the plexifilamentary structure of the flash-spun fibers resulting in more frequent filament breaks during backwinding of the flash-spun fibers making up the log. Moreover, fibers exiting the gas release ports leave continuous marks in the form of heavy axial ribs on the surface of the resulting log. These axial ribs change the resistance of log motion through the collection tube in an unpredictable manner. Due to this condition, logs produced are not consistent in quality.
• a further problem of prior art logmaking arrangements is the mechanical gate at the collection tube exit for initiating the logmaking process.
• the gate quite frequently catches fibers during start-up which results in start-up failures and adds to the cost of production.
• the nozzle section has a diverging internal contour wherein it has a diverging half angle of less than or equal to about 20 degrees and the collection tube is arranged to discharge the gases through the periphery and collect the fibers in a rod-shaped batt in the central passage thereof.
• the objects of the invention are also achieved by the provision of an apparatus for collecting continuous fibers moving with a stream of relatively high speed gases therein into a collection tube.
• the fibers are formed into a rod-shaped batt in the central passage thereof and a constriction device is connected to the outlet of the collection tube for constricting the central passage to control the rate at which the rod-shaped bat moves therethrough.
• Figure 1 is a longitudinal cross sectional view of a logmaking apparatus which would be typical of the prior art
• Figure 2 is a longitudinal cross sectional view similar to Figure 1 except of the preferred embodiment of the improved logmaking apparatus according to the present invention
• Figure 3 is an enlarged longitudinal cross sectional view of the nozzle section of the apparatus of the present invention
• Figure 4 is a transverse cross sectional view of the improved log making apparatus taken along line 3-3 in Figure 2;
• FIG. 5 is a fragmentary perspective view of the end of the discharge section with parts removed to reveal particular features of the invention.
• the apparatus 50 generally comprises a tubular collection chamber 55 including a plurality of gas release ports 57. Fiber is delivered from a spinneret 41 through a broadly diverging conically shaped transition portion 42 into the collection chamber 55. Fiber collection is initiated by a mechanical gate 61 which swings down to block the exit of the collection chamber 55. Once the fiber batt has formed, the gate 61 is opened to allow the batt to move out the exit of the collection tube 55. In practice, the formation of the batt is faster than the rate at which the mechanical gate 61 can be opened for satisfactory initiation of the batt.
• Movement of the batt out of the tube 55 is slowed by a series of rubber gaskets 65 sized slightly smaller than the interior of the collection tube 55. However, depending on the size and smoothness of the log, the log may move at various rates from the collection tube 55.
• a preferred embodiment of the apparatus for making flash-spun continuous backwindable fiber is generally indicated by the number 100.
• the apparatus 100 is attached to the exit tunnel 92 at the spinneret 91 of a conventional flash-spinning device 90.
• the apparatus 100 generally comprises three portions: (1) a nozzle section, generally indicated by the number 120; (2) a collection section, generally indicated by the number 150; and (3) a discharge section, generally indicated by the number 180.
• the three sections 120, 150 and 180 are connected preferably coaxially end to end such that the fiber is spun at the spinneret 91, passes through the tunnel 92 and into the apparatus 100, through the nozzle section 120, through the collection section 150, and finally through the discharge section 180.
• the nozzle section 120 comprises a generally open ended tube 121 having open interior 122 and oriented generally coaxial with the tunnel 92.
• the nozzle portion 120 is provided with suitable flanges 125 and 126 at the ends thereof for attachment to the flash-spinning device 90 and the collection section 150, respectively.
• the open interior 120 has a generally circular cross section along its length through the nozzle portion 120 and the interior 122 is larger at the exit end 132 than it is at the inlet end 131.
• the nozzle section preferably has a length of at least 1.5 times its diameter at the inlet end thereof and an internal contour that preferably diverges from the inlet to the outlet. As will be described below, the diverging contour is not necessarily continuous or always diverging, but preferably does not include any portions with reducing diameter.
• the open interior 122 includes a particular geometry which has two stages 135 and 140.
• the first stage 135 is generally cylindrical and extends for about 0.5 to 10 times the diameter thereof.
• the diameter of the first stage 135 is preferably larger than the diameter of the tunnel 92 such that the fiber leaving the tunnel 92 "sees" a step change in the diameter of the passageway from the spinneret 91 into the nozzle portion 120.
• a step change is preferably a 90° step as illustrated in the drawing.
• the step may comprise a short portion that has a shape extending perhaps 45° relative to axis of the apparatus 100.
• the step change is preferably considered by comparing the cross sectional areas of the straight cylindrical first stage 135 to the tunnel exit. It has been found that the cross sectional area of the first stage 135 should be at least 1.05X, but not more than 3X, of the tunnel exit cross sectional area. It is preferred that the step increase in cross sectional area is 1.1 X to 1.8X the tunnel exit cross sectional area.
• the step increase between the tunnel 92 and the first stage 135 of the nozzle section 120 provides at least two advantages. First, it does not hinder the expansion of the jet exiting the tunnel.
• the straight cylindrical first stage 135 of the two stage nozzle section 120 conducts the jet of solvent vapor exiting the tunnel 92 to the second stage 140 of the two stage nozzle section 120 without disturbing the directionality and stability of the jet's axial motion.
• the length of the straight cylindrical first stage 135 is approximately 0.5X to 10X the exit diameter of the tunnel 92, and preferably X to 4X the exit diameter of tunnel 92.
• the second stage 140 of the two stage nozzle section 120 comprises a diverging conical shape extending from the generally cylindrical first stage 135 to the exit end 132 of the nozzle section 120.
• the diverging angle ⁇ of the second stage 140 has been found to be suitable between one to about 20 degrees with respect to the axis or centerline of the apparatus 100 (also referred to as the half angle) but is preferably in the range of 4 to 12 degrees.
• the exit cross sectional area of the diverging second stage 140 (at the exit end 132) is at least 0. IX the cross sectional area of the collection section 150 down stream but not larger than the cross sectional area of the collection section 150.
• the preferred cross sectional area at the exit of the diverging section is 0.2X to 0.75X of the cross sectional area of the collection section 150.
• the angle of the diverging second stage 140 is such that, if the diverging second stage 140 were projected toward the tunnel 92, it would have approximately the same dimension as the exit of the tunnel 92 at the exit of the tunnel.
• the diverging second stage 140 in the preferred embodiment, is arranged so that an extension of the conical shape would intersect the tunnel exit with a cross sectional area that substantially corresponds to the cross sectional area of the tunnel exit.
• the nozzle section 120 permits the continuation and completion of the flashing of the solvent while allowing for gradual deceleration of the jet. Under such an arrangement, it has been found that the turbulent forces are not as pronounced and the fiber may be formed into an acceptable log.
• the collection section 150 is a generally cylindrical tube 151 having a plurality of gas release ports 152 in the peripheral wall thereof. The ports 152 are suitably spaced and sized to permit the solvent vapor to exit while substantially preventing the fiber from exiting therethrough.
• the collection section 150 includes a wire mesh screen 155 lining the interior of the cylindrical bore so as to prevent fiber from easily exiting the interior of the tube 151.
• the solvent vapor is permitted to exit through the ports 152 at substantially the same rate as in the prior art, but the fibers are less able to pass out therethrough because of the effective reduction in the size of the ports 152.
• the screen used is 10 mesh to 200 mesh, preferably 35 mesh to 100 mesh. Details about screens of specific mesh are given in Chemical Engineers' Handbook by R.H. Perry and CH. Chilton, 5th Edition, Table 21- 12.
• the screen 155 provides enough open area for gases to escape without any unacceptable pressure drop and at the same time prevents fibers from exiting through the openings in the screen 155 along with gases.
• the screen is made of a Teflon impregnated nickel to provide a tough and low friction surface for the log moving through the collection section 150.
• the discharge section 180 is comprised of a tubular section 181 having a generally imperforate elastomeric bladder 185 arranged to line the interior of the tubular section 181.
• the terminal edges of the tubular shaped bladder 185 are suitably sealed to the tubular section 181 so that the annular space 188 between the bladder 185 and the tubular section 181 may receive and hold air or other fluid through nipple 189 to change the dimension of the bladder 185 within the tubular section 181.
• the bladder 185 constricts the passage or essentially changes the interior dimension of the discharge section 180.
• a network or matrix of grooves 191 are cut into the inner surface of the tubular section 181 so that fluid may move toward the nipple 189 even while the bladder 185 is pressed fully against the inner surface of the tubular section 181.
• Log formation is initiated by collapsing the bladder by an impulse of high pressure air through nipple 189. Once the "log" formation is initiated, the bladder is allowed to quickly return to its initial dimension by releasing the air pressure. The resistance to "log” motion through the bladder is thereafter controlled by inflating the bladder to desired level during the process thus controlling the rate at which the log exits the collection section 150.
• the gas pressure in the collection section 150 depends in some part on the size and number of ports 152 through which the solvent vapor may exit therefrom. The number of the ports 152 which are open depends on where the end of the log is in the collection section 150.
• the pressure (or back pressure) will be much higher than if the end of the log is closer to the discharge section 180. Accordingly, by controlling the rate at which the logs are permitted to exit from the collection section 150 essentially provides control of the back pressure in the collection section 150.
• the back pressure has a significant effect on fiber quality and it is preferred to control the back pressure to desired level during the process to maintain the quality of the fiber. If the back pressure is too low, the "logs" produced are too soft to handle. If the back pressure is too high, flash spun fibers are not well fibrillated and also the process is more prone to fail due to fibers being blown out through the gas release ports on the collection tube.
• the present invention provides a significant improvement over prior art arrangements in that the industry will now be enabled to produce backwindable fiber having higher tenacity and strength.
• Backwindable fiber logs can now be made using a tunnel of the type that has long been known to provide greater tensile strength.
• the apparatus 100 of the invention is to be substituted for prior fiber receiving and log forming arrangements.
• the apparatus for spinning the fiber strand is essentially the same as described in prior art patents.
• the spinneret includes a tunnel at the exit thereof to enhance the acceleration of the flashing solvent vapors and provide enhanced tensile strength for the spun fibers.
• the fiber strand passes from the tunnel and into the nozzle section 120 where the lateral expansion continues in a diverging, continuously expanding arrangement gradually slowing the expanding jet of solvent vapor.
• the collection section 150 includes the ports 152 which permit the solvent vapor to escape from the collection section.
• the fiber strand is collected into the log with sufficient force to form a stable and suitable log. Portions of the fiber which move to the periphery of the collection conduit are retained therein by the mesh screen while the mesh screen does not substantially create excessive back pressure in the nozzle and tunnel.
• the log then slowly moves out of the conduit and into the discharge section.
• the bladder is arranged to control the discharge of the log based on the physical qualities of the log and the fiber therein, and on the rate at which the fiber is being delivered into the apparatus.
• a solution of 12%, by weight, of high density polyethylene (HDPE — melt index 0.75; stress exponent 1.45; rheology number 46; specific density 0.957; number average molecular weight 28000 and weight average molecular weight 135000) was prepared in Freon-11 solvent at 180° C and 1500 psi. Solution pressure was then dropped to 930 psi to create two phase solution prior to flash spinning. Spinneret size was 0.047 in. and there was no tunnel at the spinneret exit. The spinneret was connected to the collection tube via a 120 degree flared opening (60 degree half angle) at the spinneret exit as shown in Figure 1. The collection tube ID was 1.5 in. and was 10 in. long. Gas release ports were 0.125 in.
• HDPE high density polyethylene
• Example 1 except an appropriately sized tunnel was used at the spinneret exit.
• the tunnel exit diameter was 0.423 and was 0.27 in. long.
• Tunnel diverging angle with respect to the center axis was 10 degrees.
• Example 5 Due to the latter problem, the continuity of the plexifilamentary structure of flash spun fibers was damaged similar to Example 1. However, unlike Example 1, the web produced during this test was very well fibrillated and strong (5.1 gpd). Also, there were no defects, such as heavy and poorly fibrillated regions. Example 5
• Example 6 The solution supply and equipment set-up were same as in Example 4 except 100 mesh standard screen was used inside the collection tube as shown in Figure 2. With the use of the screen, problems associated with the fibers projecting out of the gas release ports as in Example 4 were eliminated. However, the fiber was very poorly fibrillated. In order to improve fibers fibrillation, 30 mesh size screen was tried and was found have to have excessively large openings to retain the fibers. A screen size of 50 mesh was found to be optimum for this test. It retained fibers inside the collection tube at the same time screen opening size was large enough for the gases to escape without excessive pressure drop. The flash spun fibers were strong and the plexifilamentary structure was very well fibrillated similar to Example 4. At the same time, the backwindability of fibers from the logs produced during this test was extremely good and continuity of plexifilamentary structure of flash spun fibers was very good as well. Example 6
• the solution supply and equipment set-up were the same as in Example 5 except an inflatable bladder was used instead of the rubber gaskets and the mechanical gate at the exit of fiber collection tube.
• the rubber bladder was made up of neoprene rubber.
• the thickness of bladder wall was 0.050 in. having durometer of about 70.
• the inside of the metal cylinder supporting the inflatable bladder was provided with a network of grooves 191 to facilitate the escape of the air through the air supply entrance hole. Air supply pressure was 45 psig.
• Example 6 The solution supply and equipment set-up were the same as in Example 6 except the preferred two stage nozzle was replaced by single stage diverging nozzle at the tunnel exit. This nozzle did not have straight cylindrical section at the entrance and had only a conical diverging section. However, there was a step increase in cross section area at the tunnel exit due to nozzle entrance diameter 0.51 in. as compared to tunnel exit diameter 0.423 in. The diverging angle of the nozzle was 4 degrees with respect to center axis and exit diameter was 1.0 in. as in Example 6. During the test, the process was not as stable as Example 6
• Example 7 The solution supply and equipment set-up were the same as in Example 7 except that the nozzle at the tunnel exit had neither a straight section (like Example 7) nor a step increase in cross sectional area at the tunnel exit (unlike Example 7).
• the entrance diameter of the nozzle was 0.450" as compared to tunnel exit diameter 0.423".
• the diverging angle was 4 degrees (half angle) and exit diameter was 1.0 in. similar to Example 7.
• Example 9 Example 9
• the solution supply and equipment set-up were the same as in Example 6 except that the collection tube had gas release ports 9 degrees apart in each row instead of 18 degrees apart.
• the screen size was 50 mesh.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Textile Engineering (AREA)
• Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)

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Citations (4)

• 1995
  • 1995-08-01 KR KR1019970700831A patent/KR100343091B1/ko not_active IP Right Cessation
  • 1995-08-01 WO PCT/US1995/009796 patent/WO1996005339A1/en active IP Right Grant
  • 1995-08-01 CA CA002196759A patent/CA2196759A1/en not_active Abandoned
  • 1995-08-01 DE DE69506264T patent/DE69506264T2/de not_active Expired - Fee Related
  • 1995-08-01 ES ES95929363T patent/ES2126309T3/es not_active Expired - Lifetime
  • 1995-08-01 EP EP95929363A patent/EP0775220B1/en not_active Expired - Lifetime
  • 1995-08-01 JP JP8507401A patent/JPH10503813A/ja not_active Ceased

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