CA1288914C - Process for preparing non-woven webs - Google Patents
Process for preparing non-woven websInfo
- Publication number
- CA1288914C CA1288914C CA000535543A CA535543A CA1288914C CA 1288914 C CA1288914 C CA 1288914C CA 000535543 A CA000535543 A CA 000535543A CA 535543 A CA535543 A CA 535543A CA 1288914 C CA1288914 C CA 1288914C
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- die
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- gas
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- Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for producing a non-woven web of thermoplastic polymer fibers comprises extruding a thermoplastic polymer through a series of die openings while passing a stream of hot gas from both sides of the die openings to impinge and attenuate the molten extruded resin fibers, wherein the gas is passed through a plurality of flow distribution holes and through a flow deflector to intermix gas jets discharging from the holes.
A process for producing a non-woven web of thermoplastic polymer fibers comprises extruding a thermoplastic polymer through a series of die openings while passing a stream of hot gas from both sides of the die openings to impinge and attenuate the molten extruded resin fibers, wherein the gas is passed through a plurality of flow distribution holes and through a flow deflector to intermix gas jets discharging from the holes.
Description
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FI~LD OF THE INVE~TIOH
T~1s lnvention re1~tes to the melt Dlowing of car~on fi~ers ~nd tnermop1asttc fiDers, ana more particuldrly to an ~mprove~ melt Dlowlng die and 1ts support and use for controlled ~ot gas stream attenuat10n of fine carDon f~Ders and thermoplastic fi~ers.
BACKGRO _ OF ~HE lNVENTlON
Car~on ana graphite fiDers dre currently manufactured by extruding molten caroonaceous materials tnrough fine extrusion holes, ~nd spun into f1ne threads or filaments. Tne filaments are suDsequently staDtlized, i.e. renderea infusiDle tnrougn a heat treatment in an oxidi~ing atmosphere and tnen heat treated in ~n inert atmosphere to convert them into carDon or grapnite fiDers.
Similarly, tnermoplastic fiDers are manufactured in mats, roving, and otner forms by extruding molten thermoplastic througn fine extruston holes and blowing the extrudate witn an air supply. Many prob1ems nave been found with respect to shaping and controll1ng the ~ir supply as well as w~th controlling the temperature of the molten thermopldstic resin ana the air.
Spinning of the carbon or grapnite fi~ers involves using an oxygen ~ich ~air) not gas to araw t~e filaments from an extrusion die to produce fiDers of very small diameter, as low as a~out 2 microns.
Tne oxygen penetrates tne molten fiDers and ts entrapped as the 25 ~iDers cool. ~ne presence of oxygen within tne indiv1dual fibers assists in stabiliz1ng tne ftbers in the suDsequent steps of the process. Melted fiDer precursor pitch ~s supplied from a sutta~le tan~, fed unaer pressure through a die by operation of a suitable pump. Jne molten p~tc~ is expressed t~rougn die open1ngs as a ser1es of vert1cal laterall~ spaced holes witn1n a melt-~low aie into the oxygen rich stream. rhe compressea atr tmp1nges throug~ obl~que slots ~gainst tne extruae~ p1tcn materlal to form a plur~llty of flne ~Itch flbers. The tle tlp I~ of trI~noul~r crosa-xect~on, havln~ downwardly, InwartIy, and opposItely dirccted ~lopIn~
35 w411~ flttcd Into a trlangular ~hAped openln~ deflned by oppo~ed air plates or air lips formin~ the attenuating air passages. The melted pitch passes throush the die openings and upon discharge therefrom, is contacted by the high velocity hot gas streams which pass through the oblique slots angled to intersect ~ust below the die openings. The air 5 streams attenuate the molten pitch fibers and draw them down to a diameter significantly smaller than the diameter of the multiple die openings within the die tip.
Problems have been encountered in maintaining the pitch at proper uniform temperature along the length of the die relative to the hundreds 10 of extrusion holes within the die tip. The utilization of the air streams for fiber attenuating purposes has in some cases materially adversely affected the maintenance of a uniform and set temperature and the extrusion of the pitch under pressure through multiple orifices created by the fine holes within the die head and opening to the apex of the die 15 tip nose. The presence of the air streams have tended to cause build up of the pitch at the tip of the melt blowing die, interfering with the attenuating air stream.
Attempts have been made to improve melt blowing dies to facilitate the fiber or filament drawing process. U.S. patent 3,825,380 is directed 20 to a die having a special nose configuration of triangular cross-section and particularly suitable for melt blowing of very fine fibers with the design of the melt blowing die eliminating dead spaces on the edge of the junction of two sides of the triangle of the die tip nose where the orifices open at the apex end of the melt blowing die.
U.S. patent 4,285,655, which is directed to a coat hanger die, employs a formula wherein the radius of the manifold at its inlt is selected in consideration of the flow characteristics of the resin melt to provide a low melt velocity at the inlet for the melt led under pressure to the plurality of extrusion orifices remote from that inlet.
U.S. patent 4,295,809 provides a mechanism for shifting the air lips relative to the triangular cross-sectional die tip nose for controlling the flow of heated gas blown out through air slots on either side of the die nose. AaJustments are made via appropriate spacers of the set Dack of the lower face of the air lips relative to tne point of intersection 35 of tne o~lique surfaces of tne aie tip, as wel 1 as the gaps between the air lips ana the aie tip itself tnrough which the dual air streams pass for intersection downstream of tne srnall diameter holes througn which the melt is expressedO
~ 2~339~4 -Wnile these patents represent some atternpts at improving the operation of the melt Dlowing die and tne creation of uniform me1t Dlown filaments WithOut plugglng or stoppage of the melt Dlowing die producing the same, pro~1ems persist within the industry, particularly where tne melt material nas a relatively hign softening temperature.
It is, tnerefore, a primary oDject of the present invention to provide an improved meIt Dlowing die, particularly useful in spinning hign softening temperature car~onaceous material fibers and their suDsequent conversion to carDon or grapnite fiDers of Detter uniformity and at lower cost; in wnich the attenuating air streams have lmproved controlld~ility; tne presence of tne attenuating air streams aoes not adversely affect tne creation of and maintenance of tne proper temperature of tne pitcn me1t during the extrusion of the same, the air flow streams are thermally isolated from the body of the die; the die nas exce11ent heat staDility and control, and wherein the components may De mecnanically assem~led and disassembled witn ease wnile allowing certain elements to De readily removed without tne necessity of aismantling tne complete assemDly of the melt blowing die itself.
It is desiraDle to provide an improved process for forming nonwoven tnermoplastic weD materials of controlled uniforlnity or nonuniformity as desired Dy tne operator.
BRIEF ~ESCRIPTION UF THE DRAWINGS
Figure 1 is a top plan view of an air manifold frame and melt ~lowing die assemDly torming a preferrea embodiment of the present invention.
Figure 2 is a vertical, transverse sectional view of tne melt blowing die of Figure 1 ta~en aDout lines 2-2.
Figure 3 is a transverse, vertical sectional view of the melt blowing aie of Figure 1 ta~en about line 3-3.
Figure 4 is a longitudinal vertical sectional view of the melt ~lowing die at the vertical interface of the die body halves.
Figure 5 is a side eJevational view, partially broken away, of the melt blowing die showing the connections and adjustment between the die body halves and the components of the air deflector assembly and the air plates thereof.
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DESCRIPTION OE THE PREFERRED EMBODIMENT
Referring initially to Figure 1, there is illustrated an air manifold frame and melt b~owing die assembly, indicated generally at 10, comprising two main components, an air manifold frame indicated generally at 12 and an improved melt blowing die 14 for pitch spinning 5 of fine filaments of high softening temperature carbonaceous material and permitting subsequent change to carbon or graphite form.
The melt blowing die 14 fixedly supports to either side thereof, air manifolds 16. The melt blowing die 14 is fixedly 25 mounted to the frame 12 by mounting blocks 18 integral with diametrically opposed frame lo members 19, at the center of the frame 12, with the melt blowing die 14 bolted or screwed at its ends to blocks 18, integral with frame 12.
As shown in Figure 1, the melt blowing die 14 is formed principally by a machined metal die body, indicated generally at 2Q, comprised of two, mirror image die body halves 22 in side-to-side abutment.
15 Rectangular, parallelepiped air chambers 24 are screwed or bolted to the outside sides of the die body halves 22. The ~unction of the die body 20 is to express molten pitch through a series of aligned closely spaced very small extrusion holes within the die tip of the melt blowing die 14, with the extrusions being attenuated by an inert gas stream such as air 20 ~mpinging on the extruded material as it leaves the tip of the melt blowing die. The filament forming expressed material is drawn outwardly and away from the small diameter extrusion holes within the die tip by the air streams impinging on the material from opposite sides thereof.
P. compressed inert gas such as air is fed to the interior of the air 25 manifolds 16 from sDurces, indicated by arrows at 2B, via hose or pipe fittings 30 at one end of each cylindrical air manifold 16. The opposite ends of the air manifolds are closed off by end caps 32. The compressed air interiorly of the air manifold is bled from the interior thereof through tube couplings, indicated generally at 26, opening at 3 one end 26a to opposite ends of the air chambers 24 . The tube couplings 26 include a corrugated tube central section 26b joining rigid hollow metal tubes to each end to permit fluidtight connections to be maintained in spite of some axial expansion or contraction thereof as a result of temperature change. The opposite ends 26c of the tube 3 5 couplings mount to the ends of the air chambers 24 and open to the interior thereof. The air chambers 24 are of the same length as die body 20.
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Diametrically opposed mounting flanges 34 fixedly mount the ends of the die body 20 to blocks 18, via screws 35. The blocks 18, integral with the frame 12 locate the melt blowing die 14 in position for use while permitting its easy removal for maintenance or rep]acement. Further, 5 tube couplings 26 facilitate the separation of the integrated air chambers 24 from the air manifolds 16 during such maintenance or replacement.
As will be appreciated hereinafter, the machined metal die body halves 22 include a series of longitudinally spaced, vertical ho]es or bores 38 within which are positioned cartridge halves 22 to maintain the 10 pitch passing therethrough molten to insure the carbonaceous filaments are extruded from the die tip extrusion holes. Additionally, as seen in Figure 1, a larger diameter circular cylindrical vertical pitch inlet passage or hole 42 is formed Dn centerline 44 of the die body 20 defined by the mating sidewalls of the die ~ody halves 22. Passage or hole 42 15 receives the pressurized molten pitch from a pitch supply line (not shown), as may be better appreciated from view~ng Figures 2 and 4.
Referring next to Figure 2, this enlarged transverse vertical sectional view shows the make up of the melt ~lowing die 14 and its major components. In addition to the melt blowing die body 20 comprised 20 of body halves 22 and the air chambers indicated generally at 24, mounted respectively to the exterior side faces 48 of the die body halves 22, the melt blowing die 14 includes a die tip indicated generally at 50 mounted to and integrated with the die body halves 22 and spanning the centerline 44 of the die body 20, a pair of air. deflector assemblies 25 indicated ~enerally at 52 and a pair of air plates 58- The air def]ector assemblies are comprised of two basic m~ch~ned metal blocks or bodies; a male air deflector block 54 and a female air deflector block 56.
The die body halves 22 are of generally rectangular parallelepiped form, each having a vertical interior side face 60 opposite exterior side 30 face 48, a top face 62, and bottom face 64. The side faces are at right angles to the top and bottom faces. A large L-shaped recess or groove 66 is formed within the bottom face 64 defining a narrow groove bottom wall 6B, laterally opposed grDove vertical sidewalls 70 and 72, and a stepped horizontal wall 74. In turn, wall 74 IS recessed at 78 to define 35 a shoulder 80. As such, the bottom of the body halves have laterally spaced vertical projections running longitudinally the full length of the die head as at 76 and 79 respectively to the outside and inside of the die body halves 22. Within each of grooves 66 are mounted the male and female air deflector blocks 54, 56, as well as air plates 58 to respective 4() sides of die tip 50.
Referrin~ next to Figure 4, it may be seen that the die body ha]ves 22 are maintained In flush abutment at opposed side faces 60 of members 22 via a number of coupling bolts or screws 82 having threaded ends within tapped holes 84. ~t is noted that the coupling bolts or screws 82 5 are located to the right and left and outside of a coat hanger cavity, indicated generally at 86. Cavity 86 ls defined by coat hanger type mirror image coat hanger recesses 88 of coat hanger configuration with vertical, pitch inlet passage 42 opening to that cavity.
It is important to keep in mind that the pitch producing ultimately 10 the fine micron ~ized diameter carbon or graphite filaments is a high softening polnt pitoh, requiring it to be initially brought to a temperature in the range of 400 to 800 F., to melt the pitch and then such melting temperature must be maintained when distributing the molten pitch after passage through vertical pitch inlet passage 42 into 15 and through cavity 88, for extrusion into filaments via the tens or hundreds of fine longitudinally spaced vertical extrusion ori`fices or holes 90 within die tip S0, Figure 4.
To maximize the number of filaments being blown drawn and therefore the number of die extrusion orifices or holes 90, the coat 20 hanger type die 20 has the disadvantage that residence time of the pitch ls quite long, deterioration of the molten pitch due to heat is promoted, and extrusion of uniform filaments is difficult and is aggravated by the difficulty in temperature control due to the large mass of the metal die bodies 22 required to resist the high pressure of the molten pitch 25 extruded through the small diameter holes 90. Coat hanger type dies facilitate this process. The inlet passage 42 diverts the molten pitch through a split coat hanger manifold 92 whose manifold sections 92a taper off to vertical manifold side ends 92b, such that the residence time distribution of the pitch is relatively uniform over the complete length of 30 the die body bearing the extrusion orifices or holes 90.
As may be seen in Figure 2, the inlet passage 42 merges with the manifold 92 and, in turn, the manifold 92 feeds a downwardly tapering coat hanger cavity 86 whose lateral sidewalls 94 move closer to each other as the pitch travels towards the lower portion of the coat hanger 35 cav~ty 86. As the molter. pitch is forced downwardly through the coat hanger cavity 86 and between converging, sidewalls 94 of that cavity, the pitch reaches a maximum restriction along line 96 within the cavity 86, at which line, the cavity sidewalls 94 diverge obliquely away from each other as at 94a, Figure 2. The oblique sidewalls 94a of the coat hanger cavity 86 define a downwardly enlarging oavity portion 86a within the projections 79 of the two die body halves 22.
The melt blowing die 14 is made up of a series of machined metal block components, all of which run the full length of the assembly 5 including the die body halves 22 and die tip 50. The machined metal blocks may be of stainless steel.
Spanning across and having a lateral width equal to the total width of the center projections 79 of the die body halves 22, is die tip 50, which is formed of a rectangular cross-section base portion 100 having 10 an upper surface 102, right angle sides 104 and a bottom surface 106.
Projecting downwardly from the center of base portion 100 and integral therewith is a triangular-shaped die tip nGse 108. The extrusion holes 90 are drilled through the center of the die tip 50 and open at the apex of the triangular die tip nose 108 of that member. A rectangular 15 cross-section aroove 112 is machined within the upper surface 102 of the die tip extending beyond the ends of the coat hanger cavity 86 and somewhat beyond the line of extrusion holes 90. Mounted within the rectangular cross-section groove 112 and filling the same is a similarly sized and configured screen pack 114. The screen pack 114 is a 20 conventional filter type medium such as 150 mesh stainless steel screen whose function is to shear the molten pitch li~uid to reduce the viscosity of the f]uid entering the small diameter extrusion holes 90 within the die tip 50. The screen pack 114 faces the widest portion of the triangular cross-section shaped portion 86a of the coat hanger cavity 86 and spans 25 the same to facilitate the passage of the pitch me]t through the screen pack 114 and it subse~uent passage through the fine diameter extrusion holes 90.
The upper face 102 of the die tip base 100 includes recesses 116 to opposite sides thereof forming steps, permitting the stepped portion of 30 the base 100 to fit within the recesses 79 of the die body halves 22.
One of the important aspects of the present invention is the manner in which the components of the melt blowing die are detachably mounted to each other to facilitate maintenance and repair while creating a melt blowing extrusion die capable of producing under high pressure, fine 35 blown spun filaments of high softening ~emperature mesophase carbonaceous pitch. The step mounting of the die tip 50 across the interface 44 between die body halves 22 and to the lower end of those blocks is achieved through the utilization of a number of counting screws 120, Figure 3. A series of longitudinally spaced, aligned tapped holes 40 122 are formed within the interior projections 79 of both die body halves ~1~2~
22 at recesses 78. Further, base 100 of the die tip 50 includes a series of longitudinally spaced, dri]led holes 124 to opposite sldes of the line of extrusion holes 90, with holes 124 counterbored at 126 so as to receive the heads 120a of the mounting screws 120. Heads 120a are therefore 5 recessed within the bottDm face 106 of the die tip 50.
The Inert gas, such as air, under pressure for attenuating the extruded pitch material as it exits the extrusion holes 90, tends to offset the requi~ement for sustained uniform high temperature of the die body halves 22 throuSlh which the extrusion melt passes. The present 10 ~nvention utilizes die body halves 22 which are considerably wider, thus providin~ more mass to the melt blowing die than those conventionally employed ln the art. Further, conventionally, electric cartridge heaters of the Calrod type are borne by the die body to maintain the pitch at or above melt temperature as it passes under pressure through the coat I 5 hanger cavity 86 for uniform distribution to the aligned longitudinally spaced extrusion holes 90 within the die tip 50 By increasing the lateral thickness of the die body halves 22, greater spacing of such cartridge heaters from the feed entry point or pitch inlet passage 42 and the coat hanger cavity 86 which are on the centerline 44 of the die body 20 20, is achieved. The die body halves 22, eherefore, function as massive heat sinks to insure maintenance of the desired above melt temperature for the pitch material passing under pressure to the extrusion holes 90 of the die tip.
As a further aspect of the present invention, the die body halves 25 22 carry a series of longitudinally spaced vertical cartridge heater insertion holes 38, Fi~ures 2 and 4, which receive the cartridge heaters of rod form as at 132. The heaters are electrically energized from an electrical power source (not shown) via electrical leads 134, ~igure 2.
The vertical insertion holes 38 which extend downwardly from the top or 30 upper face 62 of the body halves 22, extend almost the full vertical distance through the body halves 22 to the L-shaped grooves 66, but terminate short of the groove bottom wall 68. The insertion holes 38, however, open to that groove bottom wall via smaller diameter holes 135 which are counterbored and tapped at 138. The tapped counterbore 13B
35 in each instance receives a removable threaded plug 14~. The plugs 140 at the bottom of the die body halves 22 facilitate the removal of any cartridge heaters 132 which may have swelled and become lodged as a result of use of the apparatus. Consequently, the machine tolerance o~
the insertion holes 38 is decreased allowing better contact and heat 40 transfer between the cartridge heaters 132 and the die body 20. Under such conditions, by removal of the air deflector system bodies or blocks 54, 56, and the air plates 58, one or more plugs 140 may be removed, permitting insertion of a plunger or push rod (n ~t shown) sized smaller than the djameter oI the hole 136. This permits the end of the push rod 5 to push on the bottom of the inserted cartridge heater 132 and force it axially upward and out of insertion hole 38.
A principal aspect of the present invention involves the careful control of the attenuating air streams for the extruded filaments as the molten p~tch leaves the extrusion holes 90 and the preventi~n of adverse 10 effects on the temperature control of that material as it passes under pressure from the inlet passage 42 through the coat hanger cavity 86 and through the die body extrusion holes 90. The supply of heated air is effected through the dual air chambers 24 mounted to respective sides of die body 20. Again, the air chambers 24 are formed of machined 15 steel or other heat conductive metal components . The air chambers include upper and lower machined bodies as at 142 and 144, respectively, Figure 2. The upper body 142 is of inverted l~-shaped cross-section including a base or top wall 146 and inner and outer sidewalls 148 and 150, respectively. The open end of the Ushaped body 20 142 is closed off by the lower body 144 which is of modified rectangular block form. Body 144 includes an upper surface or face 152, a bottom face 154, and inner and outer faces 156 and 158, respectively. The upper face 152 carries recesses at its edges as at 160 and 162 which receive the outboard ends of the sidewalls 148, 150, respectively of the 25 upper body 146.
The air chambers 24 are closed at its ends by end walls 164, and shown in Figure 2, each end wall 164 has a circular hole or opening 166 which functions as an air inlet and is sealably connected to one end 26c of transfer tube 26 for feeding air under pressure from a respective air mani~o~d 16. The upper and lower bodies 142 and 144 of air chamber 24 are screw mounted to the outside of the die body blocks or halves 22 by mounting screws 170 passing through holes 169, 171 respectively within bodies 142, 144 and have threaded ends received within tapped holes 168 of die body halves 22.
Important to the present invention and functioning to effectively thermally iso]ate the attenuatin~ air from the die body 20, the sidewall 148 of each air chamber 24 is provided with a shallow groove or recess 176 over nearly its full length, and mostly from top to bottom forming a dead air space 178 between the air chamber 24 and die body 20. This space significantly lnhibits heat loss from the die body 20 to the air chambers as result of the attenuating air flow from inert air sources 28 The lower body 144 of the eir chamber 24 has a relatively deep V-shaped groove 180 within upper face 152, at the center thereof, and a 5 number of horizontally spaced air distribution holes 182 are drilled inwardly from the inner face 156 of body 144, which open to the V-groove 180. The large num~er of holes 182 may be seen in Figure 5.
Similar sized air distribution holes 184 of like number, are formed within the die body halves 22 from the side face 48 inwardly, being aligned 10 with and opening to the L-shaped grooves 66 near the bottom of those grooves, Figure 2. The air distribution holes 184 pass through the outer projection 76 of die body half 22.
The present invention involves the utilization of a novel air deflector assembly 54 defined by the male and female air deflector blocks 15 or bodies 56, 54, respectively, fitted within the narrowed bottom portion 66a of groove 66. The male air deflector block 54 is of inverted L-shape cross-section including a base portion 190 and a right angle leg portion 192, The base portion 190 has its width equal to the lateral width of the narrowed bottom portion 66a of the L-shaped groove 66 and leg 20 portion 192 is of a vertical height equal to the depth of the narrow portion 66a of groove 66. The air deflector blocks are of elongated form running the full longitudinal length of the melt blowing die 20 and are of stainless steel or other metal. The male air deflector block 54 further includes a right angle strip projection 194 which extends from base 25 portion 190 parallel to leg portion 192 and being laterally spaced therefrom. Pro~ection 194 extends across and beyond the air distribution holes 184 within the die body half 22. Further, in the manner of the air chamber interior sidewall 148, the base portion 190 of the male air deflector block 54 includes, almost across the full width of the same, a 30 shallow recess or groove 196 which forms a dead space 198 between it and the die body half 22 functioning to thermally isolate the base portion 190 of the male air deflector block 54 immediately facing the die body half 22 from die body 20. Leg 192 of male air deflector bloc}~ 54 is provided with a shallow recess 202 defining with groove sidewall 72 and 35 wide face 104 of die tip 50, a dead air space 204 for thermal isolation of block 54.
The female air deflector block 56 is of generally rectangular cross-sectional configuration and of a width less than the lateral w~dth of the narrow portion 66a of groove 66 bearing that member. Block 66 is comprised of a top face 2û6, a bottom face 208, an exterior side face 210 and an interior side face 212. The top face 2~6 is provided wjth a generally rectangular cross-sectional recess or groove 214 which extends the full length of body ~6 and within which projects the end of strip 5 projection 194. The groove 204 is considerably wider than the thickness of strip projection 192. The lateral width of the grooved 214, the depth of the same, the height of the strip projection 194, that is, its extent of its projection from base portion lS0 of the male air deflector block 54 insures substantial spacing therebetween for the flow of the attenuating 10 air stream through a tortuous air passage, as seen by the arrows, Figure 2, defined by the confronting surfaces of blocks 54, 56. Side 212 of block 56 is recessed over a major portion of its vertical height as at 212a immediately facing the leg portion 192 of the male air deflector block 54 to form a further downstream portion of the air passage for the 15 air deflector assembly .
The corners or edges of the bodies or blocks 54, 56 along the air path defined by facing surfaces are rounded to smooth out the flow of air, although the purpose of configuring the facing surfaces of the spaced bodies or blocks 54, 56 i5 to effect a significant amount of 20 turbulence of the air stream as it passes through the passage defined by the blocks to prevent stratification of the attenuating air stream and significant heat loss to the air stream from the die body 20 and deterioration of the filament forming process.
The male air deflector bloclc 54 of each of the air deflector 25 assemblies }s fixedly mounted and iJJunovable, while the same is not true for the female air deflector block 56 of each assembly 52. Referring to Figure 3, tapped holes 216 within the tie body halves 22 receive the threaded ends of mounting screws 218 whose heads 218a project within tapered holes 220 within the base portion 190 of the male air deflector 30 block 54 at longitudinally spaced positions matching the longitudinally cpaced tapped holes 216 for receiving the mounting screws 218.
Insofar as the female air deflector blocks 56 are concerned, these blocks are maintained in vertically adjusted but locked position within grooves 66 via a series of locking screws 224, Figure 2, which project 35 through oval vertically elongated holes or slots 226 within the exterior pro)ection 76 at the bottom of each male die body half 22. Tapped holes 228 are formed within the female air deflector blocks 56 which receive the threaded ends of the locking screws 224.
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The female air def]ector blocks 56 are vertlcally raised and lowered In a stepped adjustment process which is effected through the utilization of at least two series of oblique spaced, smooth bore alignment h~les 230 within the die body halves 22 and specifically horizontaliy drilled within 5 the exterior projection 76 of die body 22. Further, each female air deflector block 56 includes at least two cooperating series of horizontally aligned and horizontally spaced alignment holes 232 sized identical to alignment holes 230 of the die body halves 22 and within which when given holes 230 and 232 are aligned, is projectable, a dowel pin 234, 10 Figures 3 and S, at such coincident hole location.
While the dowel pins 234 function to step raise or lower ~he female air deflector blocks 56, the purpose of such adjustment is not to modify the size of air passage defined by the male and female deflector blocks, but rather to control the amount of tip pr~trusiDn sr recession of air 15 plates 58, above or below the apex of nose 108 of the die tip S0. In that respect, the air plates 5~ are mounted flush to the bottom face 208 of the female air deflector blocks 56 and are raised and lowered with blocks 56. Additionally, the air plates 58 are horizontally adjustably positioned relative to the die tip 50 so as to vary the air gaps G
20 between the air plates and the die tip nose 108 adjacent the open end of the extrusion holes 90 within the die tip. The overall slze of the air plates 58 are increased relative to the known prior art structures, both to accommodate the mass increase of the die body 20 and to prevent distortion of the air plates along their. Iength at the high proeess 25 temperatures (600-650O F. ) required in the extrusion of high sof$ening temperature mesophase pitch. Each air plate 58 is of generally paralle]epiped or rectangular block form havin~ an upper or top face 240, a bottom facle 242, an exterior side face 244 and an oblique interior side face 246. The oblique angle of the interior side face 246 matches 30 the oblique angle of the side faces 110 of nose 108 of the die tip S0 and is complementary thereto. The vertical height of air plates 58 is somewhat smaller than the vertical height of the triangular cross-section nose 108 of die tip 50 to define part of the attenuating air passage by spacing top face 240 of the air plate from bottom face 106 of the die tip 35 base 100, in each instance.
Further, the lateral width of the air plate 58 is less than the distance between the die body half projection 76 and the oblique sidewall 110 of the die tip nose 108. As shown by arrow 248, Figure 2, lateral shifting of the air plates are permitted. That movement is guided by 40 the presence of a recess 250 within the upper face 240 of each air .2 ~3~3~3 de~lect~r pla~e 58 with contact ~ccurrin~ ~etween the lower or bottom face 208 of each female air deflector ~l~ck 56 and the recess 250 of the corresponding male air de~lector plate 58.
The physical mounting of the male air deflector plates 58 to the female air deflector blocks 56 is achieved in the manner seen in Flgure 3. Horizontally elongated oval slots or holes 252 are formed vnthin the air plates 58, in an aligned row extending from one end of the air plate to the other, through which project the threaded ends of mounting screws 254. The threaded ends are received within tapped vertical holes 256 within male air deflector blocks 56 formed as a series in like number and aligned with the h~les 252 within the air plates 58. The heads 254b of the locking screws 254 engage the bottom face 242 of the air plates to the side ~ the el~ngated h~les or slo~s 2i2. The screws 254 pern~t when backed off, sliding contact between the air plates and the female air de~ector blocks 56 allowing a lateral shift in posi~on of the air plates 58 on the female air deflector blocks 56. Screws 254 are then tightened down. Further, the air plates can be vertically raised and lowered to permit the air plates to project forwardly of or back of the nose 108 of die tip SO. Recession of the tips of air plates rearwardly of the plane of die nose 109 is technically termed "set back~' of the air slot edge 245 wnere tne oDlique siae face 2q6 of eacn air plate 58 meets tne bottom face 242 of tne same.
Furtner, the air gaps G exist between tne oDlique faces 110 of tne die tip nose 108 and siae faces 246 of tne air plates 5B are readily adjustabie by means of a plurality of jack screws 260. A
series of jack screws 260 extend along the full lengtn of tne melt Dlowing die 14. The jack screws 260 are mounted witnin vertically elongatea oval noles or slots 262, Figure 2, formed witnln the exterior projection 76 of each die Dody nalf 22. In the illustrated emDodiment, tne s1Ots 262 are aligned witn slots 226 receiving locking screws 224 for tne female air deflectors Dloc~s 56. Tne jack screws 260 nave neaded enas at 260a and tnreaded stems or enas 260 receivea witnin tapped noles 264 witnin tne air plates 25B at longitùdinal1y spaced positions corresponain~ to the slots 262 and screws 260 carriea tnereby~ Further, a collar 266 is provided to each of tne jack screws 260 sucn that the Jack screws 260 are captured between collars 266 and heads 206a. Upon rotation of the jacK screws 260, tnere is a lateral shifting of tne air plates 58 towards and away from the triangular snaped nose 108 of the die tip 50 ~s snown ~y double neaded arrow 261, Figure 2, and thus effect d change in aimension of tne air gap ~ formed therebetween to respective siae of tne extruaed filamentary pitcn materia1. The presence of the oval snaped slots 226 and 262 within the die body halves 22 permits vertical raising and lowering of tne air plates 58 and thus change in set Dac~ of tnese air plates relative to the die nose 10~ wnere tne extrusion noles 90 open at the apex of tne triangular cross-section nose 108 of the die.
~he entire description and ad~antages given herein for tne die IO Dody applies as well to tnermoplastic materials in the same fashion as for pitcn or farDonaceous materials. Wnile tne flow rates and temperatures for the process using molten tnermoplastics may be dif~erent ~rom the process usin~ car~onacea~s materials, the description of the operation of tne die applies to thermoplastics~
Thermoplastic materials suitaDle for the process of tne invention include polyolefins including homopolymers~ copo)ymers, terpolymers, etc. Suitable materials include polyesters sucn as poly(metnylmetnacrylate) and poly(etnylene terepntnate). Also suita~le are polyamides such as poly(nexametnylene adipamide), poly~omega-caproamlae), and poly(nexametnylene se~acamideJ. Also suitable are polyvinyls sucn as polystyrene. Otner polymers may also De usea. sucn as polytrifluorocnloroetnylene. Tne polyolefins are preferred. Tnese include homopolymers and copolymers of tne families of polypropylenes, polyetny1enes, and otner, nigner polyolefins. The polyetnylenes include LDPE, HDPE, LLDPE, and very low density polyethylene.
U.S. Patent No. 4,078,124 to Prentice discloses various tnermoplastic weDS, their cnaracteristics, and tneir production.
It snould De apparent from the aDove description that the melt Dlowing die and air manifold frame for supporting same is particularly ~seful in tne me1t blowing of high softening temperature mesopnase pitcn. In tne past, using conventional melt blowin~ dies, the production was cnaracterized Dy generally poor quality, snot-fillea mats, and Dy snort run times terminatea Dy die plugging and excessive die pressures. Furtner, as the pitch softening pints increase Deyona aDout 500F, furtner complications arise from the increased~tendency towards mesophase creation witn tne attendant unaesiraD~e effects on tne sta~ility of die oper~tion and fiDer in homogeneity dna quality. Wnen feedstocks containing high concentrations of mesophase are employed in melt blowing, the high viscosity and increased coking tendency of these 5 feedstocks require a melt blowing die manufactured in accordance with the present Invention. The melt blowing die of the present invention yields improved control and more uniform fiber diameters, permitting a significant increase in air flow rates as, for example, 80 SCFM versus 60 and air temperatures of 6100 F to 6200 F, in order to maintain the same lO average diameter. In operation, the temperature at the extrusion die tip may range from 5700 to 585o F. Improved operation has been achieved utilizing a die tip having twenty holes to the inch with the extrusion holes being of 0~12 inches diameter and with the die tip set forward by 0 . 01l inches relative to the air plates to each side thereof . The 15 mounting frame facilitates the removal of the die as a unit and quick disconnection between the air charnbers and the air manifolds feeding the same along respective ~ides of the elongated die. With the die body widened relative to conventional die bodies, the invention moves the cartridge heaters outwardly from the coat hanger slot or cavity and with 20 the increased mass of metal for the die body halves, more effective and uniform heating of the extrusion liquid from inlet passage 42 through the coat hanger cavity and the extrusion orifices 90 is achieved. Further, this allows the cartridge heater bores 38 to be in line with the grooves 66 bearing air deflector assemblies 52. This permits bores to be drilled 25 completely through the die body halves, permits the use of threaded plugs within counterbores on the lower surface of the die body halves at the grooves 66 to close off the bores by being threaded within the counterbores. Thus, if necessary, and upon removal solely of the air plates and male and female air deflector bodies, access may be had 30 through the threaded plugs to the bores bearing the cartridge heaters for facilitating by rod insertion therein, forced removal of the cartridge heaters. As a result, the cartridge heater bores, in turn, can be sized very close to the diameter of the cartridge heater, ~rrespective of the fact that the cartridge heaters tend to swell in their middles. Thus, 35 cartridge heaters, even if wedged due to expansion problems, can be driven out axially from one end or the other of the die body halves.
The good surface contact between the cartridge heaters and the die halves at the bores renders heating of the coat han~er slot or cavity pitch liquid under conditions of high thermal transfer efficiency, with lose control of pitch melt temperature assured.
The present invention advantageously employs grooving of the sidewall of the air chambers in facing abu~nent with the exterior face of the die body halves with the shallow yrooves functionin~ to create with 5 the die body a dead air space for thermal isolation of the air chamoers relative to the die body halves. Such shallow recesses and the dead air spaces defined thereby may be filled with suitable thermal insulation material to increase the thermal isolation between the die body and the air chamber. Such material may constitute a high temperature graphite 10 composition. The same is true for the dead air spaces 198 and 204 defined by shallow recesses within the base 190 and leg 192 of the male air deflector block 54 facing respectively bottom face or wall 68 of slot 66 and sidewall 7~ of that groove within the die body halves 22 receiving the same. These arrangements minimize heat loss from the die body 15 halves to the attenuating air stream passiny throush the tortuous passage defined by the spaced, opposing male and female air deflection bodies or blocks 54, 56.
Advantageously, air plates ~8 are shiftable transversely towards and away from the triangular cross-section shaped die tip nose 108 to 20 vary the air gaps G to respective sides of the die tip nose where the extrusion holes 90 open to the attenuating air streams directed against the extruded material at the point of extrusion and from opposite sides thereof. Further, the air plates may be step adjusted rearwardly or forwardly of the die tip nose, being preferably positioned slightly 25 rearwardly of the die tip nose to prevent interference to the air streams by buildup of the ejected liquid on the facing tips of the air plates.
The mounting of the air plates to the fema~e air deflector block permits lateral shifting of the air plates relatlve to the blocks supporting the same, whi]e facilitating the step adjustment vertically of the air plates 30 for set-back adjustment, all achieved in a simple but expeditious manner, utilizing appropriate locking screws, elongated slots and alignment pins selectively positioned commonly within smooth bore holes within the die body halves and the female air deflector block 56. The configurations provided to the confronting surfaces of the male and female air deflector 35 blocks for the flir deflector assembly provides tortuous paths for imparting turbulence to the attenuating air streams prior to discharge via dual gàps G against the extruded material where it leaves the extrusion holes 90 at the die tip nose 108. The turbulence set up during air movement from the air chambers through the attenuation 40 discharge gaps G may be best ~een by reference to Fiçlure 2 and the arrows showin~ that air ~ow.
While the Inven~on has been par~cularly shown and descrl~ed with reference to a preferred en~bod~nent thereof, it will be understood by those skil~ed in the art that various chan~es ~n form and details may ~e ma~e therei~ without depar~ng from the spirit and scope of the inven~on.
According to the inventiYe process and referring to the drawings, thermoplastic polymer such as polypropylene is processed in an extruder (not shown), for example, and forced through the extruder into the die 14 at inlet passage or ho1e 42 (Figures 7, 2, and 4) for delivery into the coat hanger cavity ~6 and subsequent melt-blowing as described herein for the processing of carbonaceous fibers.
The thermoplastic polymer is forced out the row of extrusion orifices or small diameter holes 90 into the gas stream which attenuates the polymer into fibers which are collected on a moving collection device (not shown) such as a drum to form a continouus mat.
The characteristics and quality of non-woven thermoplastic polymer mats or other non-woven shapes produced by melt-blowing may vary considerably depending on process conditions and the control thereDf. That is product properties and characterists such as tensile strength and tear resistance are greatly affected by air flow rate, polymer flow rate, air temperature, and polymer temperature.
These process conditions are particularly important across the length or profile of the extruding fibers and the air knife. Some production efforts have in the past been abandoned because of inability to control the air flow consistency along the length of the air knife.
A broad range of process conditions may be used according to the process of the invention depending upon thermoplastic material chosen and the type of web~product properties needed. Any operating temperature of the thermoplastic material is acceptable so long as the material is extruded from the die so as to form a nonwoven product. An acceptable range of temperature for the thermoplastic material in the die, and consequently the approximate temperature of the die head arovnd the material, is 350 - 900F. A preferred range is 400 - 750F. For polypropylene, a highly preferred range is 400 -650F.
Any operating temperature of the air in the air knife is acceptable so long as it per~its production of useable non-woYen B~
product. An acceptable range is 350-9OGCF.
The flow rates of thermoplastic and air may vary greatly depending on the thermoplastic material extruded, the distance of the extrusion head from the take-up device, and the temperatures employed. An acceptable range of the ratio of pounds of air to pounds of polymer is about 20-500, more commonly 30-100 for polypropylene. Typical polymer flow rates vary from about 0.3-1.5 grams/hole/minute, preferably about 0.5-1Ø
In a preferred process of the invention, the die body is heated by seven groups of cartridge heaters, each group individually and independently controllable to permit variation of weight profile along the length of the die for various resins and varying throughput.
The heating zone may extend beyond the resin feed zone (coat hanger section) to eliminate the effect of heat loss from the ends of the die assembly.
Uniformity of air velocity along the length of the die is essential to provide a uniform weight web. The design of the air chambers assures uniform the transformation of the air flow from two ~preferably) large diameter inlet ports to a plurality of small diameter holes from each of which air emits at uniform velocity over the full length cf the die. If desired inserts (not shown) in the air inlet pipes in the Air Chambers 24 can be modified to provide a specific uniform or non-uniform distribution of exit velocity from the small holes within Pipe 26. For uniform distribution and mixing of gas, the insert has a bell curve profile whereby the flow space at the midpoint of Pipe 26 is very small, e.g. 1/8 inch from the wall of Pipe 26 and tapering to nearly the fu17 flow space at the ends of Pipe 26. The gas preferably exits from a slit at the top of Pipe 26, mixes in the upper corners of Chamber 164, mixes again in the bottom 3~ portion below Pipe 26, and is then accelerated into the air passages in the die body.
Extension of the die tip and air knives well beyond 4 inchee of the active d;e tip length results in elimination of eddy currents that would adverse1y affect the ~uality of the web at the edges.
Adjustment features of the assembly which prDvide independent, precise, and reproducible variation of the width of the air gap and stickout or setback of the die tip relative to the air knives, permit selection or optimum values of air gap and setback for any given resin. The optimization may target quality of web or economy of product~on or both.
Thermal isolation of the resin and the airflow passages from each other affords the possibility of running the die with resin and air 5 te~peratures dt considerably different levels in some cases preferably more than 100F different, a feature which greatly enhances the ability to produce high quality web and optimize the production process. This is particularly useful but not limited to polyolefins, polyamides and polyesters. It also provides the capability to tailor make the web to yield specific properties.
EXAMPLE
Using the apparatus described above with ~ 20 inch die assembly, d non-woven web of very uniform characteristics of size, shape, and quality was produced from Exxon #3145 High Melt Flow polypropylene resin. Two runs were made: the first dt 300C resin temperature and 300~C air temperature, the second at 285C resin temperature and 285~C air temperature. The air volume was 400 cfm. Each run lasted two hours. In each case, a water spray was applied to the attenuating f;bers after emission and before take-up.
The resin was fed to ConAir hoppers and extruded to the die from a David Standard 2 1/2 inch extruder using a Nichols Zenith Metering Pump. The air was supplied to the die by an Ingersoll Rand compressor and an Armstrong air heater. A microprocessor was used to control flow and record all functions. For each run, four 20 inch wide webs of 10, 20, 30, and 50 grams/m2 were taken up on a drum receiver. Since the procèssor was set to maintain a uniform airflow velocity profile along the air knife, each 20 inch web was of uniform size, fiber distribution and weight distribution over the full width. This was accomplished because the design of the die permits continuous operation of the air flow with less than 10~ variation in velocity over the length of the air knife and virtually no air temperature or resin temperature variation. The webs had soft hand getting firmer with decreasing temperature.
FI~LD OF THE INVE~TIOH
T~1s lnvention re1~tes to the melt Dlowing of car~on fi~ers ~nd tnermop1asttc fiDers, ana more particuldrly to an ~mprove~ melt Dlowlng die and 1ts support and use for controlled ~ot gas stream attenuat10n of fine carDon f~Ders and thermoplastic fi~ers.
BACKGRO _ OF ~HE lNVENTlON
Car~on ana graphite fiDers dre currently manufactured by extruding molten caroonaceous materials tnrough fine extrusion holes, ~nd spun into f1ne threads or filaments. Tne filaments are suDsequently staDtlized, i.e. renderea infusiDle tnrougn a heat treatment in an oxidi~ing atmosphere and tnen heat treated in ~n inert atmosphere to convert them into carDon or grapnite fiDers.
Similarly, tnermoplastic fiDers are manufactured in mats, roving, and otner forms by extruding molten thermoplastic througn fine extruston holes and blowing the extrudate witn an air supply. Many prob1ems nave been found with respect to shaping and controll1ng the ~ir supply as well as w~th controlling the temperature of the molten thermopldstic resin ana the air.
Spinning of the carbon or grapnite fi~ers involves using an oxygen ~ich ~air) not gas to araw t~e filaments from an extrusion die to produce fiDers of very small diameter, as low as a~out 2 microns.
Tne oxygen penetrates tne molten fiDers and ts entrapped as the 25 ~iDers cool. ~ne presence of oxygen within tne indiv1dual fibers assists in stabiliz1ng tne ftbers in the suDsequent steps of the process. Melted fiDer precursor pitch ~s supplied from a sutta~le tan~, fed unaer pressure through a die by operation of a suitable pump. Jne molten p~tc~ is expressed t~rougn die open1ngs as a ser1es of vert1cal laterall~ spaced holes witn1n a melt-~low aie into the oxygen rich stream. rhe compressea atr tmp1nges throug~ obl~que slots ~gainst tne extruae~ p1tcn materlal to form a plur~llty of flne ~Itch flbers. The tle tlp I~ of trI~noul~r crosa-xect~on, havln~ downwardly, InwartIy, and opposItely dirccted ~lopIn~
35 w411~ flttcd Into a trlangular ~hAped openln~ deflned by oppo~ed air plates or air lips formin~ the attenuating air passages. The melted pitch passes throush the die openings and upon discharge therefrom, is contacted by the high velocity hot gas streams which pass through the oblique slots angled to intersect ~ust below the die openings. The air 5 streams attenuate the molten pitch fibers and draw them down to a diameter significantly smaller than the diameter of the multiple die openings within the die tip.
Problems have been encountered in maintaining the pitch at proper uniform temperature along the length of the die relative to the hundreds 10 of extrusion holes within the die tip. The utilization of the air streams for fiber attenuating purposes has in some cases materially adversely affected the maintenance of a uniform and set temperature and the extrusion of the pitch under pressure through multiple orifices created by the fine holes within the die head and opening to the apex of the die 15 tip nose. The presence of the air streams have tended to cause build up of the pitch at the tip of the melt blowing die, interfering with the attenuating air stream.
Attempts have been made to improve melt blowing dies to facilitate the fiber or filament drawing process. U.S. patent 3,825,380 is directed 20 to a die having a special nose configuration of triangular cross-section and particularly suitable for melt blowing of very fine fibers with the design of the melt blowing die eliminating dead spaces on the edge of the junction of two sides of the triangle of the die tip nose where the orifices open at the apex end of the melt blowing die.
U.S. patent 4,285,655, which is directed to a coat hanger die, employs a formula wherein the radius of the manifold at its inlt is selected in consideration of the flow characteristics of the resin melt to provide a low melt velocity at the inlet for the melt led under pressure to the plurality of extrusion orifices remote from that inlet.
U.S. patent 4,295,809 provides a mechanism for shifting the air lips relative to the triangular cross-sectional die tip nose for controlling the flow of heated gas blown out through air slots on either side of the die nose. AaJustments are made via appropriate spacers of the set Dack of the lower face of the air lips relative to tne point of intersection 35 of tne o~lique surfaces of tne aie tip, as wel 1 as the gaps between the air lips ana the aie tip itself tnrough which the dual air streams pass for intersection downstream of tne srnall diameter holes througn which the melt is expressedO
~ 2~339~4 -Wnile these patents represent some atternpts at improving the operation of the melt Dlowing die and tne creation of uniform me1t Dlown filaments WithOut plugglng or stoppage of the melt Dlowing die producing the same, pro~1ems persist within the industry, particularly where tne melt material nas a relatively hign softening temperature.
It is, tnerefore, a primary oDject of the present invention to provide an improved meIt Dlowing die, particularly useful in spinning hign softening temperature car~onaceous material fibers and their suDsequent conversion to carDon or grapnite fiDers of Detter uniformity and at lower cost; in wnich the attenuating air streams have lmproved controlld~ility; tne presence of tne attenuating air streams aoes not adversely affect tne creation of and maintenance of tne proper temperature of tne pitcn me1t during the extrusion of the same, the air flow streams are thermally isolated from the body of the die; the die nas exce11ent heat staDility and control, and wherein the components may De mecnanically assem~led and disassembled witn ease wnile allowing certain elements to De readily removed without tne necessity of aismantling tne complete assemDly of the melt blowing die itself.
It is desiraDle to provide an improved process for forming nonwoven tnermoplastic weD materials of controlled uniforlnity or nonuniformity as desired Dy tne operator.
BRIEF ~ESCRIPTION UF THE DRAWINGS
Figure 1 is a top plan view of an air manifold frame and melt ~lowing die assemDly torming a preferrea embodiment of the present invention.
Figure 2 is a vertical, transverse sectional view of tne melt blowing die of Figure 1 ta~en aDout lines 2-2.
Figure 3 is a transverse, vertical sectional view of the melt blowing aie of Figure 1 ta~en about line 3-3.
Figure 4 is a longitudinal vertical sectional view of the melt ~lowing die at the vertical interface of the die body halves.
Figure 5 is a side eJevational view, partially broken away, of the melt blowing die showing the connections and adjustment between the die body halves and the components of the air deflector assembly and the air plates thereof.
:
8~
DESCRIPTION OE THE PREFERRED EMBODIMENT
Referring initially to Figure 1, there is illustrated an air manifold frame and melt b~owing die assembly, indicated generally at 10, comprising two main components, an air manifold frame indicated generally at 12 and an improved melt blowing die 14 for pitch spinning 5 of fine filaments of high softening temperature carbonaceous material and permitting subsequent change to carbon or graphite form.
The melt blowing die 14 fixedly supports to either side thereof, air manifolds 16. The melt blowing die 14 is fixedly 25 mounted to the frame 12 by mounting blocks 18 integral with diametrically opposed frame lo members 19, at the center of the frame 12, with the melt blowing die 14 bolted or screwed at its ends to blocks 18, integral with frame 12.
As shown in Figure 1, the melt blowing die 14 is formed principally by a machined metal die body, indicated generally at 2Q, comprised of two, mirror image die body halves 22 in side-to-side abutment.
15 Rectangular, parallelepiped air chambers 24 are screwed or bolted to the outside sides of the die body halves 22. The ~unction of the die body 20 is to express molten pitch through a series of aligned closely spaced very small extrusion holes within the die tip of the melt blowing die 14, with the extrusions being attenuated by an inert gas stream such as air 20 ~mpinging on the extruded material as it leaves the tip of the melt blowing die. The filament forming expressed material is drawn outwardly and away from the small diameter extrusion holes within the die tip by the air streams impinging on the material from opposite sides thereof.
P. compressed inert gas such as air is fed to the interior of the air 25 manifolds 16 from sDurces, indicated by arrows at 2B, via hose or pipe fittings 30 at one end of each cylindrical air manifold 16. The opposite ends of the air manifolds are closed off by end caps 32. The compressed air interiorly of the air manifold is bled from the interior thereof through tube couplings, indicated generally at 26, opening at 3 one end 26a to opposite ends of the air chambers 24 . The tube couplings 26 include a corrugated tube central section 26b joining rigid hollow metal tubes to each end to permit fluidtight connections to be maintained in spite of some axial expansion or contraction thereof as a result of temperature change. The opposite ends 26c of the tube 3 5 couplings mount to the ends of the air chambers 24 and open to the interior thereof. The air chambers 24 are of the same length as die body 20.
~ ~28~
Diametrically opposed mounting flanges 34 fixedly mount the ends of the die body 20 to blocks 18, via screws 35. The blocks 18, integral with the frame 12 locate the melt blowing die 14 in position for use while permitting its easy removal for maintenance or rep]acement. Further, 5 tube couplings 26 facilitate the separation of the integrated air chambers 24 from the air manifolds 16 during such maintenance or replacement.
As will be appreciated hereinafter, the machined metal die body halves 22 include a series of longitudinally spaced, vertical ho]es or bores 38 within which are positioned cartridge halves 22 to maintain the 10 pitch passing therethrough molten to insure the carbonaceous filaments are extruded from the die tip extrusion holes. Additionally, as seen in Figure 1, a larger diameter circular cylindrical vertical pitch inlet passage or hole 42 is formed Dn centerline 44 of the die body 20 defined by the mating sidewalls of the die ~ody halves 22. Passage or hole 42 15 receives the pressurized molten pitch from a pitch supply line (not shown), as may be better appreciated from view~ng Figures 2 and 4.
Referring next to Figure 2, this enlarged transverse vertical sectional view shows the make up of the melt ~lowing die 14 and its major components. In addition to the melt blowing die body 20 comprised 20 of body halves 22 and the air chambers indicated generally at 24, mounted respectively to the exterior side faces 48 of the die body halves 22, the melt blowing die 14 includes a die tip indicated generally at 50 mounted to and integrated with the die body halves 22 and spanning the centerline 44 of the die body 20, a pair of air. deflector assemblies 25 indicated ~enerally at 52 and a pair of air plates 58- The air def]ector assemblies are comprised of two basic m~ch~ned metal blocks or bodies; a male air deflector block 54 and a female air deflector block 56.
The die body halves 22 are of generally rectangular parallelepiped form, each having a vertical interior side face 60 opposite exterior side 30 face 48, a top face 62, and bottom face 64. The side faces are at right angles to the top and bottom faces. A large L-shaped recess or groove 66 is formed within the bottom face 64 defining a narrow groove bottom wall 6B, laterally opposed grDove vertical sidewalls 70 and 72, and a stepped horizontal wall 74. In turn, wall 74 IS recessed at 78 to define 35 a shoulder 80. As such, the bottom of the body halves have laterally spaced vertical projections running longitudinally the full length of the die head as at 76 and 79 respectively to the outside and inside of the die body halves 22. Within each of grooves 66 are mounted the male and female air deflector blocks 54, 56, as well as air plates 58 to respective 4() sides of die tip 50.
Referrin~ next to Figure 4, it may be seen that the die body ha]ves 22 are maintained In flush abutment at opposed side faces 60 of members 22 via a number of coupling bolts or screws 82 having threaded ends within tapped holes 84. ~t is noted that the coupling bolts or screws 82 5 are located to the right and left and outside of a coat hanger cavity, indicated generally at 86. Cavity 86 ls defined by coat hanger type mirror image coat hanger recesses 88 of coat hanger configuration with vertical, pitch inlet passage 42 opening to that cavity.
It is important to keep in mind that the pitch producing ultimately 10 the fine micron ~ized diameter carbon or graphite filaments is a high softening polnt pitoh, requiring it to be initially brought to a temperature in the range of 400 to 800 F., to melt the pitch and then such melting temperature must be maintained when distributing the molten pitch after passage through vertical pitch inlet passage 42 into 15 and through cavity 88, for extrusion into filaments via the tens or hundreds of fine longitudinally spaced vertical extrusion ori`fices or holes 90 within die tip S0, Figure 4.
To maximize the number of filaments being blown drawn and therefore the number of die extrusion orifices or holes 90, the coat 20 hanger type die 20 has the disadvantage that residence time of the pitch ls quite long, deterioration of the molten pitch due to heat is promoted, and extrusion of uniform filaments is difficult and is aggravated by the difficulty in temperature control due to the large mass of the metal die bodies 22 required to resist the high pressure of the molten pitch 25 extruded through the small diameter holes 90. Coat hanger type dies facilitate this process. The inlet passage 42 diverts the molten pitch through a split coat hanger manifold 92 whose manifold sections 92a taper off to vertical manifold side ends 92b, such that the residence time distribution of the pitch is relatively uniform over the complete length of 30 the die body bearing the extrusion orifices or holes 90.
As may be seen in Figure 2, the inlet passage 42 merges with the manifold 92 and, in turn, the manifold 92 feeds a downwardly tapering coat hanger cavity 86 whose lateral sidewalls 94 move closer to each other as the pitch travels towards the lower portion of the coat hanger 35 cav~ty 86. As the molter. pitch is forced downwardly through the coat hanger cavity 86 and between converging, sidewalls 94 of that cavity, the pitch reaches a maximum restriction along line 96 within the cavity 86, at which line, the cavity sidewalls 94 diverge obliquely away from each other as at 94a, Figure 2. The oblique sidewalls 94a of the coat hanger cavity 86 define a downwardly enlarging oavity portion 86a within the projections 79 of the two die body halves 22.
The melt blowing die 14 is made up of a series of machined metal block components, all of which run the full length of the assembly 5 including the die body halves 22 and die tip 50. The machined metal blocks may be of stainless steel.
Spanning across and having a lateral width equal to the total width of the center projections 79 of the die body halves 22, is die tip 50, which is formed of a rectangular cross-section base portion 100 having 10 an upper surface 102, right angle sides 104 and a bottom surface 106.
Projecting downwardly from the center of base portion 100 and integral therewith is a triangular-shaped die tip nGse 108. The extrusion holes 90 are drilled through the center of the die tip 50 and open at the apex of the triangular die tip nose 108 of that member. A rectangular 15 cross-section aroove 112 is machined within the upper surface 102 of the die tip extending beyond the ends of the coat hanger cavity 86 and somewhat beyond the line of extrusion holes 90. Mounted within the rectangular cross-section groove 112 and filling the same is a similarly sized and configured screen pack 114. The screen pack 114 is a 20 conventional filter type medium such as 150 mesh stainless steel screen whose function is to shear the molten pitch li~uid to reduce the viscosity of the f]uid entering the small diameter extrusion holes 90 within the die tip 50. The screen pack 114 faces the widest portion of the triangular cross-section shaped portion 86a of the coat hanger cavity 86 and spans 25 the same to facilitate the passage of the pitch me]t through the screen pack 114 and it subse~uent passage through the fine diameter extrusion holes 90.
The upper face 102 of the die tip base 100 includes recesses 116 to opposite sides thereof forming steps, permitting the stepped portion of 30 the base 100 to fit within the recesses 79 of the die body halves 22.
One of the important aspects of the present invention is the manner in which the components of the melt blowing die are detachably mounted to each other to facilitate maintenance and repair while creating a melt blowing extrusion die capable of producing under high pressure, fine 35 blown spun filaments of high softening ~emperature mesophase carbonaceous pitch. The step mounting of the die tip 50 across the interface 44 between die body halves 22 and to the lower end of those blocks is achieved through the utilization of a number of counting screws 120, Figure 3. A series of longitudinally spaced, aligned tapped holes 40 122 are formed within the interior projections 79 of both die body halves ~1~2~
22 at recesses 78. Further, base 100 of the die tip 50 includes a series of longitudinally spaced, dri]led holes 124 to opposite sldes of the line of extrusion holes 90, with holes 124 counterbored at 126 so as to receive the heads 120a of the mounting screws 120. Heads 120a are therefore 5 recessed within the bottDm face 106 of the die tip 50.
The Inert gas, such as air, under pressure for attenuating the extruded pitch material as it exits the extrusion holes 90, tends to offset the requi~ement for sustained uniform high temperature of the die body halves 22 throuSlh which the extrusion melt passes. The present 10 ~nvention utilizes die body halves 22 which are considerably wider, thus providin~ more mass to the melt blowing die than those conventionally employed ln the art. Further, conventionally, electric cartridge heaters of the Calrod type are borne by the die body to maintain the pitch at or above melt temperature as it passes under pressure through the coat I 5 hanger cavity 86 for uniform distribution to the aligned longitudinally spaced extrusion holes 90 within the die tip 50 By increasing the lateral thickness of the die body halves 22, greater spacing of such cartridge heaters from the feed entry point or pitch inlet passage 42 and the coat hanger cavity 86 which are on the centerline 44 of the die body 20 20, is achieved. The die body halves 22, eherefore, function as massive heat sinks to insure maintenance of the desired above melt temperature for the pitch material passing under pressure to the extrusion holes 90 of the die tip.
As a further aspect of the present invention, the die body halves 25 22 carry a series of longitudinally spaced vertical cartridge heater insertion holes 38, Fi~ures 2 and 4, which receive the cartridge heaters of rod form as at 132. The heaters are electrically energized from an electrical power source (not shown) via electrical leads 134, ~igure 2.
The vertical insertion holes 38 which extend downwardly from the top or 30 upper face 62 of the body halves 22, extend almost the full vertical distance through the body halves 22 to the L-shaped grooves 66, but terminate short of the groove bottom wall 68. The insertion holes 38, however, open to that groove bottom wall via smaller diameter holes 135 which are counterbored and tapped at 138. The tapped counterbore 13B
35 in each instance receives a removable threaded plug 14~. The plugs 140 at the bottom of the die body halves 22 facilitate the removal of any cartridge heaters 132 which may have swelled and become lodged as a result of use of the apparatus. Consequently, the machine tolerance o~
the insertion holes 38 is decreased allowing better contact and heat 40 transfer between the cartridge heaters 132 and the die body 20. Under such conditions, by removal of the air deflector system bodies or blocks 54, 56, and the air plates 58, one or more plugs 140 may be removed, permitting insertion of a plunger or push rod (n ~t shown) sized smaller than the djameter oI the hole 136. This permits the end of the push rod 5 to push on the bottom of the inserted cartridge heater 132 and force it axially upward and out of insertion hole 38.
A principal aspect of the present invention involves the careful control of the attenuating air streams for the extruded filaments as the molten p~tch leaves the extrusion holes 90 and the preventi~n of adverse 10 effects on the temperature control of that material as it passes under pressure from the inlet passage 42 through the coat hanger cavity 86 and through the die body extrusion holes 90. The supply of heated air is effected through the dual air chambers 24 mounted to respective sides of die body 20. Again, the air chambers 24 are formed of machined 15 steel or other heat conductive metal components . The air chambers include upper and lower machined bodies as at 142 and 144, respectively, Figure 2. The upper body 142 is of inverted l~-shaped cross-section including a base or top wall 146 and inner and outer sidewalls 148 and 150, respectively. The open end of the Ushaped body 20 142 is closed off by the lower body 144 which is of modified rectangular block form. Body 144 includes an upper surface or face 152, a bottom face 154, and inner and outer faces 156 and 158, respectively. The upper face 152 carries recesses at its edges as at 160 and 162 which receive the outboard ends of the sidewalls 148, 150, respectively of the 25 upper body 146.
The air chambers 24 are closed at its ends by end walls 164, and shown in Figure 2, each end wall 164 has a circular hole or opening 166 which functions as an air inlet and is sealably connected to one end 26c of transfer tube 26 for feeding air under pressure from a respective air mani~o~d 16. The upper and lower bodies 142 and 144 of air chamber 24 are screw mounted to the outside of the die body blocks or halves 22 by mounting screws 170 passing through holes 169, 171 respectively within bodies 142, 144 and have threaded ends received within tapped holes 168 of die body halves 22.
Important to the present invention and functioning to effectively thermally iso]ate the attenuatin~ air from the die body 20, the sidewall 148 of each air chamber 24 is provided with a shallow groove or recess 176 over nearly its full length, and mostly from top to bottom forming a dead air space 178 between the air chamber 24 and die body 20. This space significantly lnhibits heat loss from the die body 20 to the air chambers as result of the attenuating air flow from inert air sources 28 The lower body 144 of the eir chamber 24 has a relatively deep V-shaped groove 180 within upper face 152, at the center thereof, and a 5 number of horizontally spaced air distribution holes 182 are drilled inwardly from the inner face 156 of body 144, which open to the V-groove 180. The large num~er of holes 182 may be seen in Figure 5.
Similar sized air distribution holes 184 of like number, are formed within the die body halves 22 from the side face 48 inwardly, being aligned 10 with and opening to the L-shaped grooves 66 near the bottom of those grooves, Figure 2. The air distribution holes 184 pass through the outer projection 76 of die body half 22.
The present invention involves the utilization of a novel air deflector assembly 54 defined by the male and female air deflector blocks 15 or bodies 56, 54, respectively, fitted within the narrowed bottom portion 66a of groove 66. The male air deflector block 54 is of inverted L-shape cross-section including a base portion 190 and a right angle leg portion 192, The base portion 190 has its width equal to the lateral width of the narrowed bottom portion 66a of the L-shaped groove 66 and leg 20 portion 192 is of a vertical height equal to the depth of the narrow portion 66a of groove 66. The air deflector blocks are of elongated form running the full longitudinal length of the melt blowing die 20 and are of stainless steel or other metal. The male air deflector block 54 further includes a right angle strip projection 194 which extends from base 25 portion 190 parallel to leg portion 192 and being laterally spaced therefrom. Pro~ection 194 extends across and beyond the air distribution holes 184 within the die body half 22. Further, in the manner of the air chamber interior sidewall 148, the base portion 190 of the male air deflector block 54 includes, almost across the full width of the same, a 30 shallow recess or groove 196 which forms a dead space 198 between it and the die body half 22 functioning to thermally isolate the base portion 190 of the male air deflector block 54 immediately facing the die body half 22 from die body 20. Leg 192 of male air deflector bloc}~ 54 is provided with a shallow recess 202 defining with groove sidewall 72 and 35 wide face 104 of die tip 50, a dead air space 204 for thermal isolation of block 54.
The female air deflector block 56 is of generally rectangular cross-sectional configuration and of a width less than the lateral w~dth of the narrow portion 66a of groove 66 bearing that member. Block 66 is comprised of a top face 2û6, a bottom face 208, an exterior side face 210 and an interior side face 212. The top face 2~6 is provided wjth a generally rectangular cross-sectional recess or groove 214 which extends the full length of body ~6 and within which projects the end of strip 5 projection 194. The groove 204 is considerably wider than the thickness of strip projection 192. The lateral width of the grooved 214, the depth of the same, the height of the strip projection 194, that is, its extent of its projection from base portion lS0 of the male air deflector block 54 insures substantial spacing therebetween for the flow of the attenuating 10 air stream through a tortuous air passage, as seen by the arrows, Figure 2, defined by the confronting surfaces of blocks 54, 56. Side 212 of block 56 is recessed over a major portion of its vertical height as at 212a immediately facing the leg portion 192 of the male air deflector block 54 to form a further downstream portion of the air passage for the 15 air deflector assembly .
The corners or edges of the bodies or blocks 54, 56 along the air path defined by facing surfaces are rounded to smooth out the flow of air, although the purpose of configuring the facing surfaces of the spaced bodies or blocks 54, 56 i5 to effect a significant amount of 20 turbulence of the air stream as it passes through the passage defined by the blocks to prevent stratification of the attenuating air stream and significant heat loss to the air stream from the die body 20 and deterioration of the filament forming process.
The male air deflector bloclc 54 of each of the air deflector 25 assemblies }s fixedly mounted and iJJunovable, while the same is not true for the female air deflector block 56 of each assembly 52. Referring to Figure 3, tapped holes 216 within the tie body halves 22 receive the threaded ends of mounting screws 218 whose heads 218a project within tapered holes 220 within the base portion 190 of the male air deflector 30 block 54 at longitudinally spaced positions matching the longitudinally cpaced tapped holes 216 for receiving the mounting screws 218.
Insofar as the female air deflector blocks 56 are concerned, these blocks are maintained in vertically adjusted but locked position within grooves 66 via a series of locking screws 224, Figure 2, which project 35 through oval vertically elongated holes or slots 226 within the exterior pro)ection 76 at the bottom of each male die body half 22. Tapped holes 228 are formed within the female air deflector blocks 56 which receive the threaded ends of the locking screws 224.
~ 2~3~39~1.4L
The female air def]ector blocks 56 are vertlcally raised and lowered In a stepped adjustment process which is effected through the utilization of at least two series of oblique spaced, smooth bore alignment h~les 230 within the die body halves 22 and specifically horizontaliy drilled within 5 the exterior projection 76 of die body 22. Further, each female air deflector block 56 includes at least two cooperating series of horizontally aligned and horizontally spaced alignment holes 232 sized identical to alignment holes 230 of the die body halves 22 and within which when given holes 230 and 232 are aligned, is projectable, a dowel pin 234, 10 Figures 3 and S, at such coincident hole location.
While the dowel pins 234 function to step raise or lower ~he female air deflector blocks 56, the purpose of such adjustment is not to modify the size of air passage defined by the male and female deflector blocks, but rather to control the amount of tip pr~trusiDn sr recession of air 15 plates 58, above or below the apex of nose 108 of the die tip S0. In that respect, the air plates 5~ are mounted flush to the bottom face 208 of the female air deflector blocks 56 and are raised and lowered with blocks 56. Additionally, the air plates 58 are horizontally adjustably positioned relative to the die tip 50 so as to vary the air gaps G
20 between the air plates and the die tip nose 108 adjacent the open end of the extrusion holes 90 within the die tip. The overall slze of the air plates 58 are increased relative to the known prior art structures, both to accommodate the mass increase of the die body 20 and to prevent distortion of the air plates along their. Iength at the high proeess 25 temperatures (600-650O F. ) required in the extrusion of high sof$ening temperature mesophase pitch. Each air plate 58 is of generally paralle]epiped or rectangular block form havin~ an upper or top face 240, a bottom facle 242, an exterior side face 244 and an oblique interior side face 246. The oblique angle of the interior side face 246 matches 30 the oblique angle of the side faces 110 of nose 108 of the die tip S0 and is complementary thereto. The vertical height of air plates 58 is somewhat smaller than the vertical height of the triangular cross-section nose 108 of die tip 50 to define part of the attenuating air passage by spacing top face 240 of the air plate from bottom face 106 of the die tip 35 base 100, in each instance.
Further, the lateral width of the air plate 58 is less than the distance between the die body half projection 76 and the oblique sidewall 110 of the die tip nose 108. As shown by arrow 248, Figure 2, lateral shifting of the air plates are permitted. That movement is guided by 40 the presence of a recess 250 within the upper face 240 of each air .2 ~3~3~3 de~lect~r pla~e 58 with contact ~ccurrin~ ~etween the lower or bottom face 208 of each female air deflector ~l~ck 56 and the recess 250 of the corresponding male air de~lector plate 58.
The physical mounting of the male air deflector plates 58 to the female air deflector blocks 56 is achieved in the manner seen in Flgure 3. Horizontally elongated oval slots or holes 252 are formed vnthin the air plates 58, in an aligned row extending from one end of the air plate to the other, through which project the threaded ends of mounting screws 254. The threaded ends are received within tapped vertical holes 256 within male air deflector blocks 56 formed as a series in like number and aligned with the h~les 252 within the air plates 58. The heads 254b of the locking screws 254 engage the bottom face 242 of the air plates to the side ~ the el~ngated h~les or slo~s 2i2. The screws 254 pern~t when backed off, sliding contact between the air plates and the female air de~ector blocks 56 allowing a lateral shift in posi~on of the air plates 58 on the female air deflector blocks 56. Screws 254 are then tightened down. Further, the air plates can be vertically raised and lowered to permit the air plates to project forwardly of or back of the nose 108 of die tip SO. Recession of the tips of air plates rearwardly of the plane of die nose 109 is technically termed "set back~' of the air slot edge 245 wnere tne oDlique siae face 2q6 of eacn air plate 58 meets tne bottom face 242 of tne same.
Furtner, the air gaps G exist between tne oDlique faces 110 of tne die tip nose 108 and siae faces 246 of tne air plates 5B are readily adjustabie by means of a plurality of jack screws 260. A
series of jack screws 260 extend along the full lengtn of tne melt Dlowing die 14. The jack screws 260 are mounted witnin vertically elongatea oval noles or slots 262, Figure 2, formed witnln the exterior projection 76 of each die Dody nalf 22. In the illustrated emDodiment, tne s1Ots 262 are aligned witn slots 226 receiving locking screws 224 for tne female air deflectors Dloc~s 56. Tne jack screws 260 nave neaded enas at 260a and tnreaded stems or enas 260 receivea witnin tapped noles 264 witnin tne air plates 25B at longitùdinal1y spaced positions corresponain~ to the slots 262 and screws 260 carriea tnereby~ Further, a collar 266 is provided to each of tne jack screws 260 sucn that the Jack screws 260 are captured between collars 266 and heads 206a. Upon rotation of the jacK screws 260, tnere is a lateral shifting of tne air plates 58 towards and away from the triangular snaped nose 108 of the die tip 50 ~s snown ~y double neaded arrow 261, Figure 2, and thus effect d change in aimension of tne air gap ~ formed therebetween to respective siae of tne extruaed filamentary pitcn materia1. The presence of the oval snaped slots 226 and 262 within the die body halves 22 permits vertical raising and lowering of tne air plates 58 and thus change in set Dac~ of tnese air plates relative to the die nose 10~ wnere tne extrusion noles 90 open at the apex of tne triangular cross-section nose 108 of the die.
~he entire description and ad~antages given herein for tne die IO Dody applies as well to tnermoplastic materials in the same fashion as for pitcn or farDonaceous materials. Wnile tne flow rates and temperatures for the process using molten tnermoplastics may be dif~erent ~rom the process usin~ car~onacea~s materials, the description of the operation of tne die applies to thermoplastics~
Thermoplastic materials suitaDle for the process of tne invention include polyolefins including homopolymers~ copo)ymers, terpolymers, etc. Suitable materials include polyesters sucn as poly(metnylmetnacrylate) and poly(etnylene terepntnate). Also suita~le are polyamides such as poly(nexametnylene adipamide), poly~omega-caproamlae), and poly(nexametnylene se~acamideJ. Also suitable are polyvinyls sucn as polystyrene. Otner polymers may also De usea. sucn as polytrifluorocnloroetnylene. Tne polyolefins are preferred. Tnese include homopolymers and copolymers of tne families of polypropylenes, polyetny1enes, and otner, nigner polyolefins. The polyetnylenes include LDPE, HDPE, LLDPE, and very low density polyethylene.
U.S. Patent No. 4,078,124 to Prentice discloses various tnermoplastic weDS, their cnaracteristics, and tneir production.
It snould De apparent from the aDove description that the melt Dlowing die and air manifold frame for supporting same is particularly ~seful in tne me1t blowing of high softening temperature mesopnase pitcn. In tne past, using conventional melt blowin~ dies, the production was cnaracterized Dy generally poor quality, snot-fillea mats, and Dy snort run times terminatea Dy die plugging and excessive die pressures. Furtner, as the pitch softening pints increase Deyona aDout 500F, furtner complications arise from the increased~tendency towards mesophase creation witn tne attendant unaesiraD~e effects on tne sta~ility of die oper~tion and fiDer in homogeneity dna quality. Wnen feedstocks containing high concentrations of mesophase are employed in melt blowing, the high viscosity and increased coking tendency of these 5 feedstocks require a melt blowing die manufactured in accordance with the present Invention. The melt blowing die of the present invention yields improved control and more uniform fiber diameters, permitting a significant increase in air flow rates as, for example, 80 SCFM versus 60 and air temperatures of 6100 F to 6200 F, in order to maintain the same lO average diameter. In operation, the temperature at the extrusion die tip may range from 5700 to 585o F. Improved operation has been achieved utilizing a die tip having twenty holes to the inch with the extrusion holes being of 0~12 inches diameter and with the die tip set forward by 0 . 01l inches relative to the air plates to each side thereof . The 15 mounting frame facilitates the removal of the die as a unit and quick disconnection between the air charnbers and the air manifolds feeding the same along respective ~ides of the elongated die. With the die body widened relative to conventional die bodies, the invention moves the cartridge heaters outwardly from the coat hanger slot or cavity and with 20 the increased mass of metal for the die body halves, more effective and uniform heating of the extrusion liquid from inlet passage 42 through the coat hanger cavity and the extrusion orifices 90 is achieved. Further, this allows the cartridge heater bores 38 to be in line with the grooves 66 bearing air deflector assemblies 52. This permits bores to be drilled 25 completely through the die body halves, permits the use of threaded plugs within counterbores on the lower surface of the die body halves at the grooves 66 to close off the bores by being threaded within the counterbores. Thus, if necessary, and upon removal solely of the air plates and male and female air deflector bodies, access may be had 30 through the threaded plugs to the bores bearing the cartridge heaters for facilitating by rod insertion therein, forced removal of the cartridge heaters. As a result, the cartridge heater bores, in turn, can be sized very close to the diameter of the cartridge heater, ~rrespective of the fact that the cartridge heaters tend to swell in their middles. Thus, 35 cartridge heaters, even if wedged due to expansion problems, can be driven out axially from one end or the other of the die body halves.
The good surface contact between the cartridge heaters and the die halves at the bores renders heating of the coat han~er slot or cavity pitch liquid under conditions of high thermal transfer efficiency, with lose control of pitch melt temperature assured.
The present invention advantageously employs grooving of the sidewall of the air chambers in facing abu~nent with the exterior face of the die body halves with the shallow yrooves functionin~ to create with 5 the die body a dead air space for thermal isolation of the air chamoers relative to the die body halves. Such shallow recesses and the dead air spaces defined thereby may be filled with suitable thermal insulation material to increase the thermal isolation between the die body and the air chamber. Such material may constitute a high temperature graphite 10 composition. The same is true for the dead air spaces 198 and 204 defined by shallow recesses within the base 190 and leg 192 of the male air deflector block 54 facing respectively bottom face or wall 68 of slot 66 and sidewall 7~ of that groove within the die body halves 22 receiving the same. These arrangements minimize heat loss from the die body 15 halves to the attenuating air stream passiny throush the tortuous passage defined by the spaced, opposing male and female air deflection bodies or blocks 54, 56.
Advantageously, air plates ~8 are shiftable transversely towards and away from the triangular cross-section shaped die tip nose 108 to 20 vary the air gaps G to respective sides of the die tip nose where the extrusion holes 90 open to the attenuating air streams directed against the extruded material at the point of extrusion and from opposite sides thereof. Further, the air plates may be step adjusted rearwardly or forwardly of the die tip nose, being preferably positioned slightly 25 rearwardly of the die tip nose to prevent interference to the air streams by buildup of the ejected liquid on the facing tips of the air plates.
The mounting of the air plates to the fema~e air deflector block permits lateral shifting of the air plates relatlve to the blocks supporting the same, whi]e facilitating the step adjustment vertically of the air plates 30 for set-back adjustment, all achieved in a simple but expeditious manner, utilizing appropriate locking screws, elongated slots and alignment pins selectively positioned commonly within smooth bore holes within the die body halves and the female air deflector block 56. The configurations provided to the confronting surfaces of the male and female air deflector 35 blocks for the flir deflector assembly provides tortuous paths for imparting turbulence to the attenuating air streams prior to discharge via dual gàps G against the extruded material where it leaves the extrusion holes 90 at the die tip nose 108. The turbulence set up during air movement from the air chambers through the attenuation 40 discharge gaps G may be best ~een by reference to Fiçlure 2 and the arrows showin~ that air ~ow.
While the Inven~on has been par~cularly shown and descrl~ed with reference to a preferred en~bod~nent thereof, it will be understood by those skil~ed in the art that various chan~es ~n form and details may ~e ma~e therei~ without depar~ng from the spirit and scope of the inven~on.
According to the inventiYe process and referring to the drawings, thermoplastic polymer such as polypropylene is processed in an extruder (not shown), for example, and forced through the extruder into the die 14 at inlet passage or ho1e 42 (Figures 7, 2, and 4) for delivery into the coat hanger cavity ~6 and subsequent melt-blowing as described herein for the processing of carbonaceous fibers.
The thermoplastic polymer is forced out the row of extrusion orifices or small diameter holes 90 into the gas stream which attenuates the polymer into fibers which are collected on a moving collection device (not shown) such as a drum to form a continouus mat.
The characteristics and quality of non-woven thermoplastic polymer mats or other non-woven shapes produced by melt-blowing may vary considerably depending on process conditions and the control thereDf. That is product properties and characterists such as tensile strength and tear resistance are greatly affected by air flow rate, polymer flow rate, air temperature, and polymer temperature.
These process conditions are particularly important across the length or profile of the extruding fibers and the air knife. Some production efforts have in the past been abandoned because of inability to control the air flow consistency along the length of the air knife.
A broad range of process conditions may be used according to the process of the invention depending upon thermoplastic material chosen and the type of web~product properties needed. Any operating temperature of the thermoplastic material is acceptable so long as the material is extruded from the die so as to form a nonwoven product. An acceptable range of temperature for the thermoplastic material in the die, and consequently the approximate temperature of the die head arovnd the material, is 350 - 900F. A preferred range is 400 - 750F. For polypropylene, a highly preferred range is 400 -650F.
Any operating temperature of the air in the air knife is acceptable so long as it per~its production of useable non-woYen B~
product. An acceptable range is 350-9OGCF.
The flow rates of thermoplastic and air may vary greatly depending on the thermoplastic material extruded, the distance of the extrusion head from the take-up device, and the temperatures employed. An acceptable range of the ratio of pounds of air to pounds of polymer is about 20-500, more commonly 30-100 for polypropylene. Typical polymer flow rates vary from about 0.3-1.5 grams/hole/minute, preferably about 0.5-1Ø
In a preferred process of the invention, the die body is heated by seven groups of cartridge heaters, each group individually and independently controllable to permit variation of weight profile along the length of the die for various resins and varying throughput.
The heating zone may extend beyond the resin feed zone (coat hanger section) to eliminate the effect of heat loss from the ends of the die assembly.
Uniformity of air velocity along the length of the die is essential to provide a uniform weight web. The design of the air chambers assures uniform the transformation of the air flow from two ~preferably) large diameter inlet ports to a plurality of small diameter holes from each of which air emits at uniform velocity over the full length cf the die. If desired inserts (not shown) in the air inlet pipes in the Air Chambers 24 can be modified to provide a specific uniform or non-uniform distribution of exit velocity from the small holes within Pipe 26. For uniform distribution and mixing of gas, the insert has a bell curve profile whereby the flow space at the midpoint of Pipe 26 is very small, e.g. 1/8 inch from the wall of Pipe 26 and tapering to nearly the fu17 flow space at the ends of Pipe 26. The gas preferably exits from a slit at the top of Pipe 26, mixes in the upper corners of Chamber 164, mixes again in the bottom 3~ portion below Pipe 26, and is then accelerated into the air passages in the die body.
Extension of the die tip and air knives well beyond 4 inchee of the active d;e tip length results in elimination of eddy currents that would adverse1y affect the ~uality of the web at the edges.
Adjustment features of the assembly which prDvide independent, precise, and reproducible variation of the width of the air gap and stickout or setback of the die tip relative to the air knives, permit selection or optimum values of air gap and setback for any given resin. The optimization may target quality of web or economy of product~on or both.
Thermal isolation of the resin and the airflow passages from each other affords the possibility of running the die with resin and air 5 te~peratures dt considerably different levels in some cases preferably more than 100F different, a feature which greatly enhances the ability to produce high quality web and optimize the production process. This is particularly useful but not limited to polyolefins, polyamides and polyesters. It also provides the capability to tailor make the web to yield specific properties.
EXAMPLE
Using the apparatus described above with ~ 20 inch die assembly, d non-woven web of very uniform characteristics of size, shape, and quality was produced from Exxon #3145 High Melt Flow polypropylene resin. Two runs were made: the first dt 300C resin temperature and 300~C air temperature, the second at 285C resin temperature and 285~C air temperature. The air volume was 400 cfm. Each run lasted two hours. In each case, a water spray was applied to the attenuating f;bers after emission and before take-up.
The resin was fed to ConAir hoppers and extruded to the die from a David Standard 2 1/2 inch extruder using a Nichols Zenith Metering Pump. The air was supplied to the die by an Ingersoll Rand compressor and an Armstrong air heater. A microprocessor was used to control flow and record all functions. For each run, four 20 inch wide webs of 10, 20, 30, and 50 grams/m2 were taken up on a drum receiver. Since the procèssor was set to maintain a uniform airflow velocity profile along the air knife, each 20 inch web was of uniform size, fiber distribution and weight distribution over the full width. This was accomplished because the design of the die permits continuous operation of the air flow with less than 10~ variation in velocity over the length of the air knife and virtually no air temperature or resin temperature variation. The webs had soft hand getting firmer with decreasing temperature.
Claims (8)
1. A process for producing a non-woven web of thermoplastic polymer fibers comprising:
(a) extruding thermoplastic polymer through a row of die openings in a triangular cross-sectional die head of a die body:
(b) discharging gas along the entire length of the die onto each side of the molten resin as it is extruded to attenuate the molten resin as fibers in a plane away from said die openings, said gas having a substantially uniform velocity along the length of the die wherein said gas for each side is passed sequentially through a pipe discharging through a slit or plurality of holes into an air chamber designed to provide uniform velocity gas along the length of the air chamber, from the air chamber through a plurality of flow distribution holes in the die body, the gas discharging from the flow distribution holes into a longitudinal groove in the die body as a plurality of streams said groove having gas deflector assembly to intermix the streams of gas discharging from the flow distribution holes and form said gas of substantially uniform velocity along the length of the die; and (c) collecting the attenuated fibers on a receiver in the path of said plain to form said nonwoven web.
(a) extruding thermoplastic polymer through a row of die openings in a triangular cross-sectional die head of a die body:
(b) discharging gas along the entire length of the die onto each side of the molten resin as it is extruded to attenuate the molten resin as fibers in a plane away from said die openings, said gas having a substantially uniform velocity along the length of the die wherein said gas for each side is passed sequentially through a pipe discharging through a slit or plurality of holes into an air chamber designed to provide uniform velocity gas along the length of the air chamber, from the air chamber through a plurality of flow distribution holes in the die body, the gas discharging from the flow distribution holes into a longitudinal groove in the die body as a plurality of streams said groove having gas deflector assembly to intermix the streams of gas discharging from the flow distribution holes and form said gas of substantially uniform velocity along the length of the die; and (c) collecting the attenuated fibers on a receiver in the path of said plain to form said nonwoven web.
2. The process of claim 1 wherein the gas is substantially isolated from said die body whereby said gas temperature and said molten resin temperature are independently controlled.
3. The process of claim 1 wherein said thermoplastic polymer is a polyolefin.
4. The process of claim 3 wherein said polyolefin is polypropylene.
5. The process of claim 4 wherein said polypropylene is emitted from said die head at about 500°-650°F.
6. The process of claim 5 wherein the gas is air emitted from the gas slots at 500°-650°F.
7. The process of claim 1 further comprising thermally isolating said stream of gas in said die body from the flow of thermoplastic polymer in said die body by providing dead air spaces along most of the path of said longitudinal groove, said dead air spaces being between said groove and most of the portion of said die body which contacts said thermoplastic polymer.
8. The process of claim 7 wherein the temperature of said polymer in said die body and the temperature of said gas in said longitudinal groove differ by at least 100°F.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US85672786A | 1986-04-26 | 1986-04-26 | |
| US856,727 | 1986-04-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1288914C true CA1288914C (en) | 1991-09-17 |
Family
ID=25324365
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000535543A Expired - Lifetime CA1288914C (en) | 1986-04-26 | 1987-04-24 | Process for preparing non-woven webs |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1288914C (en) |
-
1987
- 1987-04-24 CA CA000535543A patent/CA1288914C/en not_active Expired - Lifetime
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