Patent Application
20150322603
This invention relates to a process for forming a non-woven web.
Meltblown fibers can be manufactured with very fine diameters, in the range of 1-10 microns, which is very advantageous in forming various kinds of non-woven fabrics. However, meltblown fibers are relatively weak in strength. To the contrary, spunbond fibers can be manufactured to be very strong but have a much larger diameter, in the range of 15-50 microns. Fabrics formed from spunbond are less opaque and tend to exhibit a rough surface since the fiber diameters are quite large. In addition, spinning of thermoplastic resins through a multi-row spinnerette, according to the spinning technology taught in U.S. Pat. No. 5,476,616, is quite challenging because of the fast solidification of the outer rows and/or columns of filaments. Due to this fast solidification in the outer rows and/or columns, the filaments tend to be larger and/or form rope defects with adjacent inner rows and/or columns of filaments.
The problem, up to now, is that no one has been able to find a way to extrude small fibers, having a diameter matching those of meltblown fibers, yet having the strength of spunbond fibers.
Now, a process for forming a non-woven web has been invented which solves this problem.
Briefly, this invention relates to an apparatus and a process for forming a non-woven web, and the web itself. The apparatus for producing a non-woven web includes a die block having an inlet for receiving a molten material which communicates with a cavity. The die block also has a gas passage through which pressurized gas can be introduced. The gas passage has an inside diameter. An insert is positioned in the gas passage and has an inside diameter and an outside diameter. A major portion of the outside diameter is smaller than the inside diameter of the gas passage to form an air chamber therebetween. The apparatus also includes a spinnerette secured to the die block which has a gas chamber isolated from the cavity. The spinnerette also has a gas passageway which connects the gas chamber to the gas passage. A plurality of nozzles and a plurality of stationary pins are secured to the spinnerette. The plurality of nozzles and the plurality of stationary pins are grouped into an array of a plurality of rows and a plurality of columns, having a periphery. Each of the plurality of nozzles is connected to the cavity. The apparatus further includes a gas distribution plate secured to the spinnerette which has a plurality of first, second and third openings formed therethrough. Each of the first openings surrounds one of the nozzles, each of the second openings surrounds one of the stationary pins, and each of the third openings is located adjacent to the first and second openings. The apparatus also includes an exterior member secured to the gas distribution plate. The exterior member has a plurality of first and second enlarged openings formed therethrough. Each of the first enlarged openings surrounds one of the nozzles and each of the second enlarged openings surrounds one of the stationary pins. The array of nozzles and stationary pins has at least one row and at least one column, which are located adjacent to the periphery, being made up of the second enlarged openings. The pressurized gas exits through both the first and second enlarged openings at a predetermined velocity. The molten material is extruded into filaments and each of the filaments is shrouded by the pressurized gas to be solidified and attenuated into fibers. In addition, the periphery around all of the extruded filaments/fibers is shrouded by another pressurized gas curtain to isolate them from the surrounding ambient air, essentially a dual shroud system. Lastly, the apparatus includes a moving surface located downstream of the exterior member onto which the fibers are collected into a non-woven web.
The process for forming a non-woven web includes the steps of forming a molten polymer and directing the molten polymer through a die block. The die block has a cavity and an inlet connected to the cavity which conveys a molten material therethrough. The die block also has a gas passage formed therethrough for conveying pressurized gas. The gas passage has an inside diameter. An insert is positioned in the gas passage. The insert has an inside diameter and an outside diameter. A major portion of the outside diameter is smaller than the inside diameter of the gas passage to form an air chamber therebetween. A spinnerette body is secured to the die block. The spinnerette body has a gas chamber and a gas passageway connecting the gas chamber to the gas passage. The spinnerette body has a plurality of nozzles and a plurality of stationary pins secured thereto which are grouped into an array of a plurality of rows and a plurality of columns. The array has a periphery. A gas distribution plate is secured to the spinnerette body. The gas distribution plate has a plurality of first, second and third openings formed therethrough. Each of the first openings surrounds one of the nozzles, each of the second openings surrounds one of the stationary pins, and each of the third openings is located adjacent to the first and second openings. An exterior member is secured to the gas distribution plate. The exterior member has a plurality of first and second enlarged openings formed therethrough. Each of the first enlarged openings surrounds one of the nozzles and each of the second enlarged openings surrounds one of the stationary pins. The array of nozzles and stationary pins has at least one row and at least one column of the second enlarged openings which are located adjacent to the periphery. The extruded filament exiting each of the nozzles is shrouded by the pressurized gas to be solidified and attenuated into fibers. In addition, the periphery around all of the extruded filaments/fibers is shrouded by pressurized gas exiting each of said second enlarged openings to isolate them from the surrounding ambient air, essentially a dual shroud system. Lastly, the fibers are collected on a moving surface to form a non-woven web.
The nonwoven web of this invention has a plurality of fibers formed from a molten polymer with an average fiber diameter ranging from between about 0.5 microns to about 50 microns, a basis weight of at least about 0.5 grams per square meter (gsm), and a tensile strength, measured in a machine direction, which ranges from between about 10 gram force per grams per square meter per centimeter width of the non-woven web (gf/gsm/cm) to about 50 gf/gsm/cm width of the non-woven web.
The general object of this invention is to provide an apparatus for forming a non-woven web. A more specific object of this invention is to provide a process for forming a non-woven web and the web itself.
Another object of this invention is to provide a non-woven web which has fine fibers, each having a diameter similar to the diameter of a conventional meltblown fiber, and having a comparable strength to spunbond fabrics.
A further object of this invention is to provide a non-woven web with fine fibers having a diameter ranging from between about 0.5 microns to about 50 microns, a basis weight of at least about 0.5 gsm, and a tensile strength of from between about 10 gf/gsm/cm width of the non-woven web to about 50 gf/gsm/cm width of the non-woven web.
Still another object of this invention is to provide a die block where the incoming pressurized gas passages are thermally insulated from the remainder of the die block which allows for the use of gas having a colder temperature.
Still further, an object of this invention is to provide a process having a dual shroud system whereby each extruded filament is shrouded by pressurized gas as it is crystallized and attenuated into a fiber and all of the filaments/fibers are shrouded by pressurized gas to isolate them from the surrounding ambient air.
Other objects and advantages of the present invention will become more apparent to those skilled in the art in view of the following description and the accompanying drawings.
Definitions
Non-woven is defined as a sheet, web or batt of natural and/or man-made fibers or filaments (excluding paper) that have not been converted into yarns, and that are bonded to each other by mechanical, hydro-mechanical, thermal or chemical means.
Spunmelt is a process where fibers are spun from molten polymer through a plurality of nozzles in a die head connected to one or more extruders. The spunmelt process may include meltblowing, spunbonding and the present inventive process, which we call spunblowing.
Meltblown is a process for producing very fine fibers having a diameter of less than about 10 microns, where a plurality of molten polymer streams are attenuated using a hot, high speed gas stream once the filaments emerge from the nozzles. The attenuated fibers are then collected on a flat belt or dual drum collector. A typical meltblowing die has around 35 nozzles per inch and a single row of spinnerettes. The typical meltblowing die uses two inclined air jets for attenuating the filaments.
Spunbond is a process for producing strong fibrous nonwoven webs directly from thermoplastics polymers by attenuating the spun filaments using cold, high speed air while quenching the fibers near the spinnerette face. Individual fibers are then laid down randomly on a collection belt and conveyed to a bonder to give the web added strength and integrity. Fiber size is usually below 250 μm and the average fiber size is in the range of from between about 10 microns to about 50 microns. The fibers are very strong compared to meltblown fibers because of the molecular chain alignment that is achieved during the attenuation of the crystallized (solidified) filaments. A typical spunbond die has multiple rows of polymer holes and the polymer melt flow rate is usually below about 500 grams/10 minutes.
The present invention is a hybrid process between a conventional meltblown process and a conventional spunbond process. The present invention bridges the gap between these two processes. The present invention uses a multi-row spinnerette similar to the spinnerette used in spunbonding except the nozzles and stationary pins are arranged in a unique fashion to allow parallel gas jets surrounding the spun filaments in order to attenuate and solidify them. In the present invention, each of the extruded filaments is shrouded by pressurized gas and its temperature can be colder or hotter than the polymer melt. In addition, the periphery around all of the filaments is surrounded by a curtain of pressurized gas, essentially a dual shroud system.
An alternative embodiment of the present invention uses an aspirator to attenuate the molten filaments into fibers. The aspirator uses high velocity gas (air) that is directed essentially parallel to the flow direction of the filaments, instead of being directed at a steep incline angle thereto. The combination of these features produce fibers having small or fine diameters, similar to conventional meltblown fibers, yet much stronger fibers, similar to conventional spunbond fibers. The apparatus of the present invention is very flexible and versatile in that it can accommodate both meltblown and spunbond polymer resins, which may have a melt flow rate of from between about 4 grams per 10 minutes (g/10 min.) to about 6,000 g/10 min., according to the American Standard Testing Method (ASTM) D 1238, at 210° C. and 2.16 kg.
Referring to
The polymer resin 14 can vary in composition. The polymer resin can be a thermoplastic. The polymer resin 14 can be selected from the group consisting of: polyolefins, polyesters, polyethylene terephthalates, polybutylene terephthalates, polycyclohexylene dimethylene terephthalates, polytrimethylene terephthalates, polymethyl methacrylates, polyamides, nylons, polyacrylics, polystyrenes, polyvinyls, polytetrafluoroethylenes, ultrahigh molecular weight polyethylenes, very high molecular weight polyethylenes, high molecular weight polyethylenes, polyether ether ketones, non-fibrous plasticized celluloses, polyethylenes, polypropylenes, polybutylenes, polymethylpentenes, low-density polyethylenes, linear low-density polyethylenes, high-density polyethylenes, polystyrenes, acrylonitrile-butadiene-styrenes, styrene-acrylonitriles, styrene tri-block and styrene tetra block copolymers, styrene-butadienes, styrene-maleic anhydrides, ethylene vinyl acetates, ethylene vinyl alcohols, polyvinyl chlorides, cellulose acetates, cellulose acetate butyrates, plasticized cellulosics, cellulose propionates, ethyl cellulose, natural fibers, any derivative thereof, any polymer blend thereof, any copolymer thereof or any combination thereof. In addition, the polymer resin 14 can be selected from biodegradable thermoplastics derived from natural resources, such as polylactic acid, poly-3-hydroxybutyrate, polyhydroxyalkanoates, or any blend, copolymer, polymer solutions or combination thereof. Those skilled in the chemical arts may know of other polymers that can also be used to form the non-woven web 12. It should be understood that the non-woven 12 of this invention is not limited to just those polymers identified above.
The non-woven web 12 can be formed from a homopolymer. The non-woven web 12 can be formed from polypropylene. Alternatively, the non-woven web 12 can be formed from two or more polymers. The non-woven web 12 can contain bicomponent fibers wherein the fibers have a sheath-core configuration with the core formed from one polymer and the surrounding sheath formed from a second polymer. Still another option is to produce the non-woven web 12 from bicomponent fibers where the fibers have a side-by-side configuration. Those skilled in the polymer arts will be aware of various fiber designs incorporating two or more polymers.
It should be understood that the non-woven web 12 can include an additive which can be applied before or after the fibers are collected. Such additives can include, but are not limited to: a superabsorbent, absorbent particulates, polymers, nano-particles, abrasive particulates, active particles, active compounds, ion exchange resins, zeolites, softening agents, plasticizers, ceramic particle pigments, dyes, flavorants, aromas, controlled release vesicles, binders, adhesives, tackifiers, surface modification agents, lubricating agents, emulsifiers, vitamins, peroxides, antimicrobials, deodorizers, flame retardants, anti-foaming agents, anti-static agents, biocides, antifungals, degradation agents, stabilizing agents, conductivity modifying agents, or any combination thereof.
Referring to
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It should be understood that in
Each of the pair of gas passages 32, 32 can vary in diameter, length and configuration. Each of the pair of gas passages 32, 32 can be linear, curved, angled, or have some other unique configuration. It has been found that by positioning a hollow insert 34 in each of the pair of gas passages 32, 32, that one can better control the temperature of the incoming gas. By “gas” it is meant the state of matter distinguished from the solid and liquid states by relatively low density and viscosity and the spontaneous tendency to become distributed uniformly throughout any container; a substance in the gaseous state. In the apparatus 10, a pressurized gas, most likely air, is introduced into the die block 26 and spinnerette body 52. By “air” it is meant a colorless, odorless, gaseous mixture, mainly nitrogen (approximately 78%) and oxygen (approximately 21%) with lesser amounts of other gases.
The insert 34 can be a ceramic insert. By “ceramic” it is meant any of various hard, brittle, heat and corrosion-resistant materials made by shaping and then firing a nonmetallic mineral, such as clay, at a high temperature. Alternatively, the insert 34 can be constructed of various other heat resistant materials. Still another option is to coat the insert 34 with a heat resistant coating, such as a ceramic coating. One could also coat the insert 34 with some other material which has good thermal insulation properties.
As best shown in
Each insert 34 has a first end 36 and a second end 38. The first end 36 is spaced apart from the second end 38. The first end 36 is aligned with an exterior surface 42 of the die block 26 and the second end 38 is aligned with an inner surface 40 of the die block 26. The first end 36 contains an outwardly protruding flange 44 and the second end 38 also contains an outwardly protruding flange 46. By “flange it is meant a protruding rim, edge, rib or collar, as on a pipe shaft, used to strengthen an object, hold it in place or attach it to another object. The structural shape of the flanges, 44 and 46 create a physical chamber 48 in a bore hole 50, which is machined into the die block 26, and in which each insert 34 is fitted. Each of the pair of inserts 34, 34 is fitted into one of the pair of bore holes, 50, 50. The chambers 48, 48 are located between the inside diameter d of each bore hole 50 and the outside diameter d2 of each of the pair of inserts 34, 34. Each chamber 48 extends longitudinally along a portion of the insert 34 between the two flanges, 44 and 46. Desirably, each chamber 48 will extend along a major portion of the outside diameter d2 of each of the pair of inserts 34, 34. Each chamber 48 can be filled with a gas, such as air. Each chamber 48 functions as a thermal insulator that limits heat transfer from the hot, die block 26 to the pressurized gas passing through the inside diameter d1 of each of the pair of inserts 34, 34. Because of this, no cold spots will develop in the die block 26. In addition, the hot die block 26 will not heat up the incoming pressurized gas that is being routed to the spinnerette body 52. The combination of the pair of inserts 34, 34 and the adjacent chambers 48, 48, enable the operator to direct the pressurized gas (air) through the die block 26 without affecting the temperature of either the die block 26 or the incoming pressurized gas (air) significantly. Because of this, much colder pressurized gas (air) can be utilized in this inventive process. This colder pressurized gas (air) can enhance fiber crystallization (solidification of the extruded filaments into fibers) and increase the fiber tensile properties.
Still referring to
The presence of the chambers 48, 48, in combination with the material from which the inserts 34,34 are made of, or coated with, will assure one that the pressurized gas (air) that is routed through the inserts 34, 34 will not be heated a substantial amount due to the temperature of the die block 26. In other words, the inserts 34, 34, in combination with the chambers 48, 48 function provide thermal insulation and limit heat transfer.
It should be understood that the inside diameter d of each of the bore holes 50, 50 can also be coated with a ceramic coating to provide another layer of heat insulation, if desired.
A die block 26 is constructed out of a mass of metal or steel which is a good conductor of heat. The heavy mass of the die block 26 also causes it to retain any heat that is conveyed to it. The temperature of the die block 26 is elevated above ambient temperature due to the molten material 22 (polymer) flowing through the die block 26 and due to heating cartages (not shown) that prevent the polymer melt from being solidified by the cold ambient air or the process air. By “ambient temperature” it is meant the surrounding temperature, such as room temperature. The melt temperature of the various molten material 22 (polymer) does vary but usually exceeds 100° C. For many polymers, the melt temperature can be as high as 200° C., 250° C., 300° C., 350° C., 400° C., or even higher. By thermally insulating the incoming pressurized gas (air) from the elevated temperature in the die block 26, one can better control the entire process and produce extruded filaments and fibers that are very precise in composition, diameter and strength.
Referring again to
It should be understood that the gas chamber 54 is separate and distinct from the cavity 30 formed in the die block 26. In other words, the gas chamber 54 is isolated from the cavity 30. By “isolate” it is meant to set apart or cut off from others, to render free of external influences; insulate. This means that the molten material 22 is not in contact with the pressurized gas (air) while it is in the cavity 30.
It should be understood that the spinnerette body 52 could be coated with a ceramic coating, if desired.
The apparatus 10 further includes a plurality of nozzles 58. By “nozzle” it is meant a projecting part with an opening, as at the end of a hose, for regulating and directing the flow of a fluid or molten material. Each of the nozzles 58 is secured to the spinnerette body 52. Each of the nozzles 58 is spaced apart from an adjacent nozzle 58. In the spinnerette body 52, the number of nozzles 58 can vary. A spinnerette body 52 can contain from as few as ten nozzles 58 to several thousand nozzles 58. For a commercial size line, the number of nozzles 58 in the spinnerette body 52 can range from between about 1,000 to about 10,000. Desirably, the spinnerette body 52 will have at least about 1,500 nozzles. More desirably, the spinnerette body 52 will have at least about 2,000 nozzles. Even more desirably, the spinnerette body 52 will have at least about 2,500 nozzles. Most desirably, the spinnerette body 52 will have 3,000 or more nozzles.
The size of the nozzles 58 can vary. The size of the nozzles 58 can range from between about 50 microns to about 1,000 microns. More desirably, the size of the nozzles 58 can range from between about 150 microns to about 700 microns. More desirably, the size of the nozzles 58 can range from between about 20 microns to about 600 microns. Nozzles of various size can be used but generally all of the nozzles have the same size.
Referring to
It should be understood that the nozzles 58 can be of any geometrical shape, although a circular shape is favored.
Each of the nozzles 58, in the form of a hollow, cylindrical tube 60, has an inside diameter d3 and an outside diameter d4. The inside diameter d3 can range from between about 0.125 millimeters (mm) to about 1.25 mm. The outside diameter d4 of each nozzle 58 should be at least about 0.5 mm. Desirably, the outside diameter d4 of each nozzle 58 can range from between about 0.5 mm to about 2.5 mm.
The molten material 22 (polymer) is extruded through the inside diameter d3 of each nozzle 58. The back pressure on the molten material 22 (polymer), present in each of the hollow, cylindrical tubes 60, should be equal to or exceed about 5 bar. By “bar” it is meant a unit of pressure equal to one million (106) dynes per square centimeter. Desirably, the back pressure on the molten material 22 (polymer), present in each of the hollow, cylindrical tubes 60, can range from between about 20 bar to about 200 bar depending on the polymer properties and the operating conditions. More desirably, the back pressure on the molten material 22 (polymer), present in each of the hollow, cylindrical tubes 60, can range from between about 25 bar to about 150 bar. Even more desirably, the back pressure on the molten material 22 (polymer), present in each of the hollow, cylindrical tubes 60, can range from between about 30 bar to about 100 bar.
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Typically, the number of columns 66 will range from about 50 to about 500. Desirably, the number of columns 66 will range from about 60 to about 450. More desirably, the number of columns 66 will range from about 100 to about 300. Even more desirably, the number of columns 66 will range from about 150 to about 250. Most desirably, the number of columns 66 will be greater than 200.
The spinnerette body 52 will have a nozzle density ranging from between about 30 nozzles per centimeter to about 200 nozzles per centimeter. Desirably, the nozzle density will be over 50 nozzles per centimeter. More desirably, the nozzle density will be over 75 nozzles per centimeter. Even more desirably, the nozzle density will be over 100 nozzles per centimeter. Most desirably, fine nozzle density will be over 150 nozzles per centimeter.
The polymer throughput through each nozzle 58 is stated in “gram per hole per minute” (ghm). The polymer throughput through each nozzle 58 can range from between about 0.01 ghm to about 4 ghm.
The finished diameter of each of the extruded and attenuated fibers is below about 50 microns. The average fiber diameter is from between about 0.5 microns to about 50 microns, with a standard deviation above 0.5 microns. Desirably, the average fiber diameter is from between about 1 micron to about 50 microns, with a standard deviation above 0.5 microns. More desirably, the average fiber diameter is from between about 1 micron to about 30 microns, with a standard deviation above 0.5 microns. Even more desirably, the average fiber size is from between about 1 micron to about 20 microns, with a standard deviation above 0.5 microns. Most desirably, the average fiber size is from between about 1 micron to about 10 microns, with a standard deviation above 0.5 microns.
The periphery 68 is indicated by a line extending around the outside of the plurality of nozzles 58 and the plurality of stationary pins 62. The rows 64 are shown as being long lines extending horizontally in the apparatus 10 while the columns 66 are shorter in length and are aligned perpendicular to the rows 64. By “perpendicular” it is meant intersecting at or forming a right angle (90 degrees). Although the rows 64 and the columns 66 are shown as being aligned perpendicular to each other, one can certainly use different angular alignments, if desired. The rows 64 and the columns 66 are also depicted as being arranged in parallel rows 64 and parallel columns 66. By “parallel” it is meant being an equal distance apart everywhere. However, one could stagger the rows 64 and/or the columns 66, if desired. The number of rows 64 can vary as can the number of columns 66.
In
As mentioned above, the total number of nozzles 58 and stationary pins 62 that can be secured to the spinnerette body 52 can vary. The larger the size of the spinnerette body 52, the more nozzles 58 and stationary pins 62 that it can support. For a typical commercial spinnerette body 52, it will have several rows 64 and many more columns 66. The number of rows 64 can vary but generally will range from about 4 to about 20. The number of columns 66 can also vary but generally will range from about 50 to about 500. Desirably, a commercial size spinnerette body 52 will have about 8 to about 16 rows and from between about 100 to about 300 columns. For example, a spinnerette body 52 containing a total of 2,496 combined nozzles 58 and stationary pins 62 could have twelve rows 64 and two hundred and eight columns 66.
Referring now to
The plurality of first, second and third openings, 72, 74 and 76 respectively, are all shown as being circular openings having a predetermined diameter. This assumes that each of the plurality of nozzles 58 and each of the plurality of stationary pins 62 have a circular outside diameter. The geometrical shape of the third openings 76 do not have to be circular, if desired. However, it is much more cost effective to form a circular hole than some other shape and therefore, from a practical point of view, the third openings 76 will also most likely have a circular outside diameter.
Each of the plurality of first openings 72 are sized and configured to match or be slightly larger than the outside diameter d4 of the plurality of nozzles 58. A tight, snug or press fit can be utilized to retain the plurality of nozzles 58 in a set arrangement. Each of the plurality of second openings 74 are sized and configured to match or be slightly larger than the outside diameter d5 of the plurality of stationary pins 62. Again, a tight, snug or press fit can be utilized to retain the plurality of stationary pins 62 in a set arrangement. Each of the plurality of third openings 76 are sized and configured to allow an appropriate amount of pressurized gas (air) to pass through them. The amount of pressurized gas (air) that is needed can be calculated based upon a number of factors, such as the composition of the molten material 22 (polymer) that is being extruded, the number of nozzles 58 and stationary pins 62 that are present, the inside diameter d3 of each of the nozzles 58, the flow rate of the molten material 22 (polymer) passing through each of the nozzles 58, the velocity of the pressurized gas (air) passing through the gas distribution plate 70, etc. By “velocity” it is meant the rapidity or speed of motion, swiftness. Those skilled in the art can easily calculate the amount of pressurized gas (air) that is needed, its velocity and a temperature which is advantageous to running the apparatus 10 at a maximum speed.
Still referring to
One will also notice that in
Likewise, one can clearly see that each of the third openings 76 is smaller than the outside diameters of either the first openings 72 or the second openings 74. However, if one wished to size the outside diameter of each of the third openings 76 to be larger than or match the outside diameter d4 and d5 of each of the first and second openings, 72 and 74 respectively, this could easily be accomplished, especially if small polymer nozzles 58 are being used One drawback with making the third openings 76 larger is that the rows 64 and columns 66 would then have to be spaced farther apart. This would limit the total number of nozzles 58 and stationary pins 62 that could be secured to the spinnerette body 52.
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It should be understood that the gas distribution plate 70 could be coated with a ceramic coating, if desired.
Referring now to
It should be understood that the exterior member 78 could be coated with a ceramic coating, if desired.
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The pair of cover strips 88, 88 also functions to redistribute the clamping force exerted on the exterior member 78 and the gas distribution plate 70 to secure them to the spinnerette body 52. The pair of cover strips 88, 88 also function to protect the nozzles 58 from the entrained air in the room that may be drawn in from the sides and which could have a cooling effect on the outer rows.
Referring now to
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The temperature of the pressurized gas (air) used in shrouding and attenuating the filaments 86 at or near the nozzles 58 can be at a lower temperature, the same temperature, or at a higher temperature, than the melt temperature of the passing filaments 86. Desirably, the temperature of the pressurized gas (air) used in shrouding and attenuating the filaments 86 at or near the nozzles 58 is at a temperature ranging from between about 0° C. to about 250° C. colder or hotter than the melt temperature of the filaments 86. More desirably, the temperature of the pressurized gas (air) used in shrouding and attenuating the filaments 86 at or near the nozzles 58 is at a temperature ranging from between about 0° C. to about 200° C. colder or hotter than the melt temperature of the filaments 86. Even more desirably, the temperature of the pressurized gas (air) used in shrouding and attenuating the filaments 86 at or near the nozzles 58 is at a temperature ranging from between about 0° C. to about 150° C. colder or hotter than the melt temperature of the filaments 86. Most desirably, the temperature of the pressurized gas (air) used in shrouding and attenuating the filaments 86 at or near the nozzles 58 is at a temperature ranging from between about 0° C. to about 100° C. colder or hotter than the melt temperature of the filaments 86.
The pressurized gas (air) emitted through the multiple second openings 82 will form pressurized gas (air) streams which will limit or prevent the plurality of filaments 86 from being contacted by the surrounding ambient air. Desirably, this pressurized gas (air) can form an envelope, shroud or curtain around the entire circumference or periphery 84 of the total number of filaments 86. The velocity and pressure at which the filaments 86 exit the plurality of nozzles 58 can be varied to suit one's equipment and to form fibers 98, see
Referring now to
The aspirator 100 functions as a second stage to attenuate the filaments 86 so that they acquire similar strength properties to fibers formed using conventional spunbond technology.
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The moving surface 104 can be operated at room temperature, especially when the forming wire 106 or conveyor belt is constructed from polyethylene terephthalate (PET) material. However, when the moving surface 104 is constructed from metal or steel wire, or is covered with metal belts, it can be heated slightly to impose specific textures or patterns that may enhance the characteristics of the non-woven web 12.
The moving surface 104 can move at varying speeds that can influence the composition, density, integrity, etc. of the finished non-woven web 12. For example, as the speed of the moving surface 104 is increased, the loft or thickness of the non-woven web 12 will decrease.
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Downstream of the vacuum chamber 110 is a bonder 112. The bonder 112 can vary in design. The bonder 112 can be a mechanical bonder, a hydro-mechanical bonder, a thermal bonder, a chemical bonder, etc. The bonder 112 is optional but for most non-woven webs 12 formed from very thin, randomly oriented fibers, the bonding step will provide added strength and integrity. When the bonder 112 is utilized, it will enhance the integrity of the non-woven web 12 by forming spot bonds, point bonds, zone bonds, etc.
It should be understood that the non-woven web 12 can be subjected to other mechanical or chemical treatment, if desired. For example, the non-woven web 12 could be hydroentangled, be perforated, be cut, be slit, be punched, be stamped, be embossed, be printed, be coated, etc. After the bonder 112, if no other treatments are desired, the non-woven web 12 can be wound up on a supply roll 114. A cutter 116 can be used to cut, divide, sever or slit the non-woven web 12 at an appropriate length and/or width.
Referring again to
The process for forming a non-woven web 12 will be explained with reference to
A gas distribution plate 70 is secured to the spinnerette body 52. The gas distribution plate 70 has a plurality of first, second and third openings, 72, 74 and 76 respectively, formed therethrough. Each of the first openings 72 accommodates one of the nozzles 58, each of the second openings 74 accommodates one of the stationary pins 62, and each of the third openings 76 is located adjacent to the first and second openings, 72 and 74 respectively.
An exterior member 78 secured to the gas distribution plate 70, away from the spinnerette body 52. The exterior member 78 has a plurality of first and second enlarged openings, 80 and 82 respectively, formed therethrough. Each of the first enlarged openings 80 surrounds one of the nozzles 58 and each of the second enlarged openings 82 surrounds one of the stationary pins 62. The array of nozzles 68 and stationary pins 62 has at least one row 64 and at least one column 66, which are located adjacent to the periphery 68, being made up of the second enlarged openings 82.
The process also includes directing pressurized gas (air) through the plurality of first, second and third openings, 72, 74 and 76 respectively, formed in the gas distribution plate 70. The molten material 22 (polymer) is extruded through each of the nozzles 58 to form multiple filaments 86. At least a portion of each of the multiple filaments 86 is then shrouded by the pressurized gas (air) emitted through the first enlarged openings 80, formed in the exterior member 78, at a predetermined velocity. The pressurized gas (air) exiting the second enlarged openings 82, formed in the exterior member 78, is used to isolate all of the filaments 86 from surrounding ambient air.
Upon being extruded out the terminal end 96 of each of the nozzles 58, the filaments 86 start to solidify and are attenuated by the exiting pressurized gas (air) into fibers 98. An optional, second stage of attenuation can be accomplished using an aspirator 100, see
The fibers 98 are collected on a moving surface 104 to form a non-woven web 12. The moving surface 104 can be a forming wire 106, a conveyor belt, a rotating drum, a drum collector, a dual drum collector, etc.
The process can also include the step of subjecting the non-woven web 12, while it is positioned on the moving surface 104, to a vacuum so as to remove process gas and ambient air, as well as limiting the fibers 98 from flying around and thereby enhances web uniformity. The vacuum can be supplied by a vacuum chamber 110 located adjacent to the moving surface 104. Desirably, the vacuum chamber 110 is situated below the moving surface 104.
The process can further include the step of bonding the non-woven web 12. The bonder 112 can be located downstream of the vacuum chamber 110 or downstream of the location where the fibers 98 contact the moving surface 104. The bonder 112 functions to bond individual spots, zones, lines, areas, etc. of the non-woven web 12 so as to increase the integrity of the non-woven web 12. A cutter 116 can be positioned downstream of the bonder 112. The cutter 116 serves to cut, sever, slit or separate one section of the non-woven web 12 from an adjacent section. The cutter 116 can be any kind or type of cutting mechanism known to those skilled in the art.
Lastly, the process can include rolling up the finished non-woven web 12 onto a supply roll 114 such that it can be shipped to a manufacturing site or location where the non-woven web 12 can be utilized. The non-woven web 12 can be used in a variety of products and for numerous applications. Fine diameter fibers having good strength properties are especially desired for use in various kinds of absorbent products, such as diapers, feminine napkins, panty liners, training pants, incontinent garments, etc. Fine diameter fibers having good strength properties can also be used in acoustic insulation, thermal insulation, wipes, etc. The fibers 98 can further be used in a variety of products.
The non-woven web 12, produced on the apparatus 10 described above, contains a plurality of fibers 98 formed from a molten material 22 (polymer). Desirably, the molten material 22 (polymer) is a homopolymer. More desirably, the molten material 22 (polymer) is polypropylene. Optionally, the non-woven web 12 could be formed from two or more different polymer resins. Furthermore, the non-woven web 12 could contain bicomponent fibers.
The non-woven web 12 has an average fiber diameter which ranges from between about 0.5 microns to about 50 microns. Desirably, the average fiber diameter ranges from between about 1 micron to about 30 microns. More desirably, the average fiber diameter ranges from between about 1 micron to about 20 microns. Even more desirably, the average fiber diameter ranges from between about 1 micron to about 15 microns. Most desirably, the average fiber diameter ranges from between about 1 micron to about 10 microns. The standard deviation for the average fibber diameter should be above 0.5 microns.
The non-woven web 12 has a basis weight of at least about 0.5 grams per square meter (gsm). Desirably, the non-woven web 12 has a basis weight of at least about 1 gsm. More desirably, non-woven web 12 has a basis weight of at least about 20 gsm. Even more desirably, non-woven web 12 has a basis weight of at least about 50 gsm. Most desirably, the non-woven web 12 has a basis weight above 100 gsm.
The non-woven web 12 has a tensile strength, measured in a machine direction (MD), which ranges from between about 10 grams force per grams per square meter per centimeter (gf/gsm/cm) width of the non-woven web to about 100 gf/gsm/cm width of the non-woven web. Desirably, the non-woven web 12 has a tensile strength, measured in a machine direction (MD), which ranges from between about 12 gf/gsm/cm width of the non-woven web to about 80 gf/gsm/cm width of the non-woven web. More desirably, the non-woven web 12 has a tensile strength, measured in a machine direction (MD), which ranges from between about 13 gf/gsm/cm width of the non-woven web to about 70 gf/gsm/cm width of the non-woven web. Even more desirably, the non-woven web 12 has a tensile strength, measured in a machine direction (MD), which ranges from between about 14 gf/gsm/cm width of the non-woven web to about 60 gf/gsm/cm width of the non-woven web. Most desirably, the non-woven web 12 has a tensile strength, measured in a machine direction (MD), which ranges from between about 15 gf/gsm/cm width of the non-woven web to about 50 gf/gsm/cm width of the non-woven web.
The fibers 98 forming the non-woven web 12 are randomly arranged.
The fibers 98 forming the non-woven web 12 can be bonded to increase the integrity of the non-woven web 12. The fibers 98 can be bonded using various techniques. For example, the fibers 98 can be mechanically bonded, hydro-mechanically bonded, thermally bonded, chemically bonded, etc. Spot bonding, zone bonding, as well as other bonding techniques known to those skilled in the art can be used.
The following experiments were performed and show the unique characteristics of the non-woven web 12 manufactured using the above described apparatus 10 and process.
1. Inventive Non-Woven Web
The following nonwoven samples were produced using a pilot line that had two 25″ dies with multi-row spinnerettes 52, 52 secured thereto, manufactured by Biax-FiberFilm Corporation having an office at N992 Quality Drive, Suite B, Greenville, Wis. 54942-8635. Each spinnerette 52, 52 had a total of 4,150 nozzles, each having an inside diameter d3 of 0.305 mm. Each nozzle 58 was surrounded by a first enlarged opening 80 formed in the exterior member 78 where pressurized gas (air) was allowed to exit. The inside diameter d6 of each of the first enlarged openings 80 was 1.4 mm. By comparison, a typical commercial spinnerette, manufactured by Biax-FiberFilm Corporation, can have from between about 6,000 to about 11,000 nozzles per meter. Conventional meltblown material 22 (polymer) was obtained from different vendors and the processing condition and system parameters are disclosed in Table 1.
2. Process Conditions
Several nonwovens webs were made using the above described pilot line.
Three different kinds of polymer resins were used. The first polymer resin was ExxonMobil polypropylene (PP) resin marketed under the trade name Achieve 6936G1. ExxonMobil Chemical has an office at 13501 Katy Freeway, Houston, Tex. 77079-1398. Achieve 6936G1 has a melt flow rate of 1,550 grams/10 minute (g/10 min.), according to American Standard Testing Method (ASTM) D 1238, at 210° C. and 2.16 kilograms (kg). The second polymer resin was ExxonMobil polypropylene—PP3155, PP1355 has a melt flow rate of 35 g/10 min., according to ASTM D 1238, at 210° C. and 2.16 kg. The third polymer resin was Metocene MF650W marketed by LyondellBasell. LyondellBasell has an office at LyondellBasell Tower, Suite 700, 1221 McKinney Street, Houston, Tex. 77010, Metocene MF650W has a melt flow rate of 500 g/10 min. according to ASTM D 1238, at 210° C. and 2.16 kg. The process conditions of the different samples are disclosed in Table 1.
3. Characterization Methods
3.1 Basis Weight
Basis weight is defined as the mass per unit area and can be measured in grams per meter squared (g/m2) or ounces per square yard (osy). A basis weight test was performed according the INDA standard IST 130.1 which is equivalent to the ASTM standard ASTM D3776. INDA is an abbreviation for: “Association of the Non-Woven Fabrics Industry”. Ten (10) different samples were die-cut from different locations in the non-woven web and each sample had an individual area equal to 100 square centimeters (cm2). The weight of each sample was measured using a sensitive balance within ±0.1% of weight on the balance. The basis weight, in grams/meter2 (g/m2) was measured by multiplying the average weight by a hundred (100).
3.2 Fiber Diameter Measurements
To examine the fiber morphology and the fiber diameter distribution of the manufactured nonwoven webs, samples were sputter coated with a 10 nanometer (nm) thin layer of gold and analyzed with a scanning electron microscope, model SEM, Phenom G2, manufactured by Phenom World BV having an office at Dillenburgstraat 9E, 9652 AM Eindhoven, The Netherlands. Images were taken at 500× and 1,500× magnification under 5 kilovolts (kV) of an accelerating voltage for the electron beams. Fiber diameters were measured using Image J software. “Image J” is a public domain, Java-based image processing program developed at the National Institute of Health and can be downloaded from http://imagej.nih.gov/ij/. For each sample, at least 100 individual fiber diameters were measured.
3.3 Fabric Tensile Strength
The breaking force is defined as the maximum force applied to a nonwoven web carried to failure or rupture. For ductile material like nonwoven webs, they experience a maximum force before rupturing. The tensile strength was measured according to the ASTM standard D 5035-90 which is the same as INDA Standard IST 110.4 (95). To measure the strength of the non-woven web, six (6) specimen strips from each non-woven web were cutout at different locations across the non-woven web and each one had a dimension of 25.4 millimeters (mm)×152.4 mm (1″ by 6″). Each strip was clamped between the jaws of the tensile testing machine which was a Thwing Albert Tensile Tester. The clamps pulled the strip at a constant rate of extension of 10 inch/minute. The average breaking force and the average extension percentage at the breaking force was recorded for each non-woven web in the form of gram force per basis weight per width of non-woven web (gf/gsm/cm).
3.4 Air Permeability Measurement
Air permeability of non-woven fabrics is the measured airflow through an area of the fabric at a specific pressure drop. Using the Akustron Air Permeability Tester, the air permeability was measured for the fiber mats under a pressure drop equal to 125 Pa. Ten measurements for each mat were recorded and the average values are reported herein. This method of measuring air permeability is equivalent to the Frazier air permeability testing method or the ASTM D737 test method.
In this example, we were looking at the effect of spinning technology on web properties. Three (3) different non-woven webs were made using the same polymer resin. All three (3) had the same basis weight but each was spun using a different spinnerette design and different processing conditions. As shown in Table 2, sample S-1 was produced using a Biax multi-row spinnerette design that did not have air insulation inserts 34 or an air shrouding curtain (second enlarged openings 82) surrounding the periphery 84 of the first enlarged openings 80. Sample S-2 was produced using a conventional meltblown process which had only one line of nozzles along with inclined air jets. Sample S-3 was produced using the inventive process.
The sample S-3 achieved almost double the machine direction (MD) tensile strength as compared to sample S-1 or sample S-2. Also, one will notice that the fiber diameter of sample S-3 was slightly larger than the fiber diameter of the conventional meltblown sample S-2. The primary reason for this difference in diameter is that when using the inventive process, the colder air temperature in the annular channels is directed essentially parallel to the direction of flow of the filaments 86 in a multi-row fashion. In addition, by attenuating the fibers 98 using colder gas (air) one can increase fiber crystallinity and align the molecular chains inside the solidified fibers 98. This feature facilitates attenuation of the filaments into strong, fine fibers 98. In a conventional meltblown process, the attenuating air is introduced at a steep or inclined angle, using hot air jets.
Referring now to
It should be understood that the fibers 98 in the non-woven web 12 can have a Standard Deviation of from between about 0.9 microns to about 5 microns. Desirably, the fibers 98 in the non-woven web 12 have a Standard Deviation of from between about 0.92 microns to about 3 microns. More desirably, the fibers 98 in the non-woven web 12 have a Standard Deviation of from between about 0.95 microns to about 1.5 microns.
In this second example, we were comparing a sample produced by the inventive process S-5 to a sample produced by a conventional meltblown process S-4, and to sample produced by a conventional spunbond process S-6. Three (3) samples were made and each had the same basis weight. As shown in Table 3, the properties of sample S-5 were about half-way between the properties of the meltblown web S-4 and the spunbond web S-6. Table 3 also shows that the air permeability of the sample S-5 (using our inventive process) falls almost half-way between the conventional meltblown sample S-4 and the conventional spunbond sample S-6. This proves that our new technology is capable of producing non-woven webs that have fine fiber diameters, comparable to meltblown fibers, yet strong as compared to spunbond fibers.
Referring to
From the above two examples, it is clear that a non-woven web 12 made using our inventive apparatus and process is unique and has properties that are about half-way between the properties exhibited by a non-woven web made using a conventional meltblown process or a non-woven web made using a conventional spunbond process.
Furthermore, the apparatus 10 of this invention is flexible and versatile enough to use a wide variety of polymeric resins to produce a wide range of non-woven webs. The apparatus 10 can be operated using meltblown grade resins and well as spunbond grade resins.
While the invention has been described in conjunction with several specific embodiments, it is to be understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.
