HK1018293B - Process and apparatus for making spun-bonded web - Google Patents

Description

Method and apparatus for making spun-bonded fiber net

Background

Spunbond nonwoven webs are an important commercial and industrial product. Such products, which typically have a textile feel and appearance, are used as components of disposable diapers or to form medical garments, home furnishings, filter media, carpet backing, soft backing for fabrics, linoleum, geotex (r), and the like.

According to the prior art, molten melt processable thermoplastic polymeric materials are extruded through a spinneret to form a plurality of fibrous strands, then drawn to increase strength, passed through a cooling zone to solidify and be collected on a support to form a web, and finally bonded to form a spunbond web. The extruded molten strand is drawn and attenuated by passing it through a pneumatic delivery nozzle or by wrapping it around driven draw rolls, an apparatus using draw rolls and air flow for drawing is disclosed in U.S. Pat. No. 5,5439364. The equipment conventionally used for spunbond nonwoven products in the past has the disadvantages of relatively high manufacturing costs, multiple spinning locations, large air volumes, and/or variations in fiber denier when used to form nonwoven products at high speeds when economy principles are considered.

It is an object of the present invention to provide an improved method of forming a spunbond nonwoven web.

It is another object of the present invention to provide a method of forming a spunbond web that can form a generally uniform product at high speeds with a satisfactory balance of properties.

It is another object of the present invention to provide a method of forming a spunbond web that is easy for the operator to handle and produces high quality nonwoven products without the presence of detrimental entangling rolls.

It is another object of the present invention to provide an improved method of forming a spunbond web wherein the filaments are automatically laid down and require only a few operators.

It is a further object of the present invention to provide an improved technique which is flexible with respect to the chemical composition of the melt processable thermoplastic polymer material as the starting material.

It is another object of the present invention to provide a process which can produce a substantially uniform, lightweight spunbond product with good control of fiber denier at reliable, relatively high spinning speeds.

It is another object of the present invention to provide an improved method of forming a spunbond web that reduces capital costs as well as operating costs.

It is a further object of the present invention to provide a method of forming a spunbond web wherein the operating costs are reduced in view of the air flow requirements as compared to the use of air delivery nozzles to accomplish fiber attenuation as in the prior art.

It is a further object of the present invention to provide an improved apparatus for producing a spunbond web.

These and other objects, as well as the scope, nature and use of the invention, will become apparent to those skilled in the art of nonwovens from the following description and appended claims.

Summary of The Invention

Known methods of forming spunbond webs are to extrude molten processable polymeric material from a plurality of orifices to form a multifilament tow, which is then drawn to increase its strength, solidified by a cooling zone, and collected on a support to form a web and bonded to form a spunbond web; the improvement wherein the multifilament tow is passed lengthwise between a cooling zone and a support while being wrapped around at least two driven spaced apart draw rolls covered by a jacket in the region where the multifilament tow is in contact therewith, the jacket having an inlet end and an outlet end, whereby the multifilament tow is introduced from the inlet end of the jacket and the tension created by the spaced apart driven draw rolls is applied to the multifilament tow for drawing the same in the vicinity of the spinneret orifice and further tension is applied to the multifilament tow by pneumatic delivery nozzles located at the outlet end of the jacket, which facilitates contacting the multifilament tow with the driven spaced apart draw rolls and discharging the multifilament tow lengthwise from the outlet end of the jacket to the support.

An apparatus for producing a spunbond web is provided comprising:

(a) a plurality of melt orifices configured to form a melt when extruding molten thermoplastic polymer material

Forming a multi-filament tow which is formed by a plurality of filaments,

(b) a cooling zone for solidifying the melt-extruded thermoplastic polymer multifilament tow

The chemical combination is carried out by dissolving,

(c) at least two driven drafts spaced apart from each other downstream of the cooling zone

The roller is covered by a cover in the contact area with the thermoplastic polymer multifilament tow

The casing having an inlet end and an outlet end, thereby to thermoplastically bond the casing to the body

The polymer multifilament tow is introduced and acted on the thermoplastic polymer multifilament by the drawing roller

The pulling force on the bundle completes the drawing of the multifilament tow adjacent the spinneret,

(d) a pneumatic delivery nozzle at the outlet end of the housing for the thermoplastic polymer

The multifilament tow is in good contact with spaced apart drawing rolls and further can be drawn

The thermoplastic polymer multifilament tow is discharged from the outlet end of the housing in the longitudinal direction

And then the mixture is discharged out of the furnace,

(e) a support member located below the pneumatic conveying nozzle and spaced apart from the pneumatic conveying nozzle

To receive and lay down a thermoplastic polymer multifilament tow into a net, and

(f) a bonding device capable of bonding the thermoplastic polymer multifilament tows after the formation of the fiber web

Forming a spunbond web.

Description of the drawings

FIG. 1 is a schematic view of an apparatus of the present invention that can be used to practice the improved process of the present invention for making spunbond webs. FIG. 2 is a cross-sectional view of a detail showing the edge (polymeric edges) feature of a polymer located where the mantle is adjacent to the draw roll to form a substantially continuous channel.

Description of the preferred embodiments

The starting material for producing the spunbond web is a melt processable thermoplastic polymer material that can be melt extruded to form continuous filaments, suitable materials include polyolefins such as polypropylene and polyesters. Isotactic polypropylene is a preferred form of polypropylene. A particularly preferred isotactic polypropylene has a melt flow rate of about 4 to 50 grams per 10 minutes according to ASTM D-1238, a Standard of the American society for testing and materials. Polyesters are typically diols formed from the reaction of an aromatic dicarboxylic acid (e.g., terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, etc.) and an alkylene glycol (e.g., ethylene glycol, propylene glycol, etc.). In a preferred embodiment, the polyester is primary polyethylene terephthalate. A particularly preferred polyethylene terephthalate heading material has an intrinsic viscosity (I.V.) of about 0.64 to about 0.69 (e.g., 0.685) g/dl, a glass transition temperature of about 75 to about 80 ℃, and a melting point of about 260 ℃. This intrinsic viscosity can be determined by dissolving 0.1g of polyethylene terephthalate in 25ml of a solution comprising a 1: 1 weight mixture of trifluoroacetic acid and methylene chloride while measuring at 25 ℃ using a number 50 Cannon-Fenske viscometer. Other copolymeric regrind in polymer families other than polyethylene terephthalate may optionally be present in smaller concentrations. Also, some minor concentration of polyethylene isophthalate fibers may optionally be included in the polyester tow, so that the resulting web can be thermally bonded more quickly. Other exemplary thermoplastic polymer materials also include polyamides (e.g., nylon 6 and nylon-6, 6), polyethylenes (e.g., high density polyethylene), polyurethanes, and the like. The present technology also allows for the use of recycled and/or scrap melt processable thermoplastic polymer materials (e.g., recycled polyethylene terephthalate) as it is convenient for the user.

When the starting thermoplastic polymer material is a polyester (e.g. polyethylene terephthalate), it is recommended that the same polymer granules are subjected to a pre-treatment of shaking heat in a temperature range above the glass transition temperature and below the melting point for a sufficient time to exclude moisture and modify the physical characteristics of the particle surfaces so that they do not substantially stick to each other. This pre-treatment can order or crystallize the surface of the granular starter material and thus have better flowability and transport in a controlled manner when it is fed into the melt extrusion device. If the polyester particles are not subjected to such a pretreatment, aggregation of the particles occurs. Such pre-treatment is not required for starter materials such as isotactic polypropylene due to their lack of such aggregative properties. The starting material of polyethylene terephthalate preferably has a moisture content of not more than 25ppm prior to extrusion.

The melt processable thermoplastic polymeric material is heated above its melting point (e.g., typically about 20 to 60 ℃ above the melting point) and extruded from a plurality of melt spinning orifices (i.e., a multi-orifice spinneret). Typically, the polymeric material is heated to melt as it passes through the heated extruder and is filtered as it passes through a spinneret assembly located within the spinneret, and is finally extruded from the spinneret orifice at a rate controlled by a metering pump. An important problem is that any solid particles must be removed from the molten thermoplastic polymer in order to avoid clogging the spinneret orifices. The size of the orifices can be selected so that the desired denier is achieved by drawing and stretching the individual fibers in the resulting multifilament tow before they are fully consolidated. Generally suitable orifice diameters range from 0.254 to 0.762mm (10-30 mils). The cross-sectional shape of the holes may be circular or other shapes such as trilobal, octalobal, star, dumbbell, etc. The typical fill pressure for polyethylene terephthalate is about 8268 to 41340KPa (1200 to 6000 psi)²) The packing pressure typically used for isotactic polypropylene is 6890 and 31005KPa (1000 and 4500 psi). Typical polymer ejection rates are typically in the range of 0.4 to 2.0 grams/minute/hole when polyethylene terephthalate is used as the starter material, and in the case of isotactic polypropylene as the starter materialTypical polymer ejection rates are typically 0.2 to 1.5 g/min/hole when dosed. There are many different options for the number and arrangement of orifices, which correspond to the number of continuous filaments in the final multifilament fibrous material. For example, typically the number of orifices will be in the range of about 200-²(10-100/inch)²) The frequency of (c). In a preferred embodiment, the orifices are arranged in a straight line (i.e., a straight line spinneret). For example, such linear spinnerets may have a width of about 0.1 to 4.0 meters (3.9 to 157.5 inches) or more, with the width being selected based on the width of the spunbond nonwoven web to be formed, or an arrangement of multiple spinning positions may be used.

Below the spinneret orifice, a cooling zone is provided in which the melt-extruded thermoplastic polymer multifilament strands complete their solidification process. The molten multifilament tow is passed lengthwise through a cooling zone provided with a low velocity high volume air stream, preferably cooled here in a generally uniform manner without the presence of undesirable disturbances. In the cooling zone, the molten multifilament strand is converted from the molten state to a semi-cured density and from the semi-cured density to a fully cured density. The multifilament strand is subjected to a greater drawing and orientation of the polymer molecules just below the spinneret orifices before being uncured. The air flow provided in the cooling zone is preferably circulated to produce more efficient heat transfer. In a preferred embodiment of the process, the temperature of the gas stream in the cooling zone is about 10 to 60 deg.C (e.g., 10 to 50 deg.C), and preferably 10 to 30 deg.C (e.g., room temperature or below). The chemical composition of the gas stream is not critical to the operation of the process so long as the gas stream is provided so as not to unduly react with the molten processable thermoplastic polymer material. In a particularly preferred embodiment of the process, the atmosphere of the cooling zone has a relative humidity of about 50%. The gas stream entering the cooling zone is preferably in cross-flow form and blown substantially continuously onto the tow from one or both sides of the tow. Other forms of cooling flow may also be used. The standard length of the cooling zone is typically 0.5 to 2.0 meters (19.7 to 78.7 inches). The cooling zone may be enclosed and provided with means for controllably venting the air stream entering the zone or may simply be partially or fully open to the surrounding atmosphere.

The cured multifilament yarn is wrapped around at least two spaced apart driven draw rolls and the rolls are covered by a cover in the area where the multifilament yarn is wrapped. If desired, one or more pairs of spaced drafting rollers may be arranged in rows and similarly enclosed under the same continuous housing. The angle of wrap of the multifilament tow around the draw roll is typically about 90 to 270 degrees and preferably in the range of 180 and 230 degrees. The housing is spaced apart from the drawing roller and forms a continuous channel through which the filament bundle can pass freely. The draw-off rollers apply a pulling force to the tow to draw it adjacent the spinneret orifice before it is fully solidified in the cooling zone. At the outlet end of the housing, a pneumatic delivery nozzle is provided which facilitates contact of the multifilament tow with the spaced drawing rollers and discharges the multifilament tow from the outlet end of the housing along its length onto a support for collection as will be described below.

The driven draw rolls used in accordance with the present invention have a length greater than the width of the spunbond multifilament web being processed and may be cast or machined from aluminum or other durable material. The surface of the drawing roller is preferably smooth. The standard diameter range of the draft rollers is typically about 10-60cm (3.9-23.6 inches), and in a preferred embodiment the diameter of the draft rollers is about 15-35cm (5.9-13.8 inches). It will be apparent to those skilled in the fiber art that the diameter of the draw rolls and the wrapping angle of the tow will primarily determine the spacing relationship of the draw rolls. The surface speed of the driven draw rolls during the process of the present invention is typically in the range of about 1000-.

The driven drawing roller applies a pulling force to the multifilament tow to make it undergo a large drawing in the upstream region before the complete solidification of the individual fibers is completed.

The housing or enclosure surrounding the draft rollers is a key feature of the present invention. The housing is spaced from the surface of the draw roll by a distance sufficient to provide a continuous unobstructed enclosed channel containing the multifilament tow wound onto the draw roll and containing a continuous flow of air from the inlet end to the outlet end. In a preferred embodiment, the inner surface of the closure cover is no more than about 2.5cm (1 inch) and no less than 0.6cm (0.24 inch) from the drafting rollers. A pneumatic delivery nozzle is communicated with the outlet end of the housing so that gas such as air is introduced from the inlet end of the housing and smoothly flows over the surface of the drawing roller around which the multifilament tow is wound and is discharged downward by the pneumatic delivery nozzle. The housing delimiting the continuous channel forms a shield for the drawing roller and can be made of any durable material, for example a polymer material or a metal material. In a preferred embodiment, at least a portion of the housing is made of a transparent and strong polymer material, such as polycarbonate-linked material, which allows the strand to be viewed from the outside. If the housing is too far from the drawing roller, the air flow velocity in the housing will become too low to improve the contact between the multifilament tow and the driven drawing roller.

The best result is that the limited gas flow area created in the enclosure is a smooth and substantially unobstructed area or area where gas is dissipated along the length of the enclosure from the inlet end to the outlet end of the enclosure. This prevents any significant interruption or loss of airflow at the mid-position of the enclosure when practicing the invention. When the air flow in the housing is continuous and not disturbed, the air flow will cause the contact between the driven drawing roller and the multifilament tow to be strengthened, thereby overcoming or greatly reducing the slippage of the multifilament tow wound around the drawing roller. In a preferred embodiment of the invention, the housing comprises an edge or extension of polymeric material (i.e. an aerodynamic deflector plate) which can be positioned close to the drafting roller and over the full length of the roller, adjacent only to the location where: the multifilament tow exits the draw rolls and is engaged with a second draw roll before the position. This allows the edges to be substantially completely coated on the draw roll, preferably the edges are capable of breaking down into fine powder when in contact with the draw roll. The edges of the polymer preferably have relatively high melting points and are adjacent to the draw rolls when leaving a very small opening of about 0.1-0.08mm (0.5-3 mils). Typical polymer materials suitable for forming the polymeric edge include polyimide, polyamide, polyester, polytetrafluoroethylene, etc., and graphite may be selectively added as a filler, maintaining uniform air flow in the housing and eliminating undesirable twining of the multifilament tow. Thus, the possibility of the tow stopping due to the entangling roll is greatly reduced and the throughput of a continuous uniform spunbond web can be improved.

A pneumatic delivery nozzle at the outlet end of the housing provides a continuous downward flow of air at the outlet end of the housing, the air flow generated by the nozzle being substantially parallel to the direction of movement of the tow as it passes through the opening of the nozzle. A continuous flow of gas through the casing is generated by the above-mentioned nozzles by suction from a gas source, whereby the gas flow is introduced into the inlet end of the casing and flows along the entire length of the casing. The air flow entering the inlet end of the housing will merge with the air flow introduced by the pneumatic delivery nozzle. The downward air flow directed by the nozzle impinges on the tow and creates a further sufficient pulling force to help maintain uniform contact with the rollers and substantially no slippage. The air flow introduced by the pneumatic delivery nozzle is at a velocity greater than the surface velocity of the driven draft rollers to produce a desired draw force. By means of the air flow generated in the housing, the pneumatic delivery nozzle will facilitate good contact of the filament bundle with the drawing rollers, so that a uniform drawing of the filaments in the final nonwoven product is achieved. The pneumatic delivery nozzle provides tension to the filament bundle to facilitate good contact of the filament bundle with the draw roll, thereby eliminating slippage between the multifilament filament bundle and the draw roll during the entire process and achieving a uniform filament denier premium product. The pneumatic delivery nozzle is not capable of producing any significant drafting or stretching of the filaments, and the rotation of the drafting rollers initially produces a drafting force. The pneumatic delivery nozzle can advance the multifilament tow as it passes through it while creating a sufficient tension to hold the tow on the draw roll without substantial slippage.

The moving tow may optionally be electrostatically charged if desired using a high voltage, low current power supply of the known art to assist in laying the fibers on a support (described in detail below).

A support member is positioned below and at a distance from the pneumatic delivery nozzle for receiving the multifilament tow and laying the tow into a fibrous web. The support is preferably a continuously movable and highly air permeable rotating belt, such as is commonly used in the production of spunbonded nonwoven fabrics, wherein a partial vacuum is applied to the underside of the belt to assist in laying the multifilament strands on the support to form the web. The vacuum provided below is preferably balanced to some extent by the air generated by the pneumatic delivery nozzle. The basis weight of the resulting web can be adjusted at will by varying the speed of the rotational movement of the belt on which the web is collected. The support is positioned below the pneumatic delivery nozzle at a sufficient distance to ensure that the multifilament tow is free to bend or curl to some extent as it slowly moves forward before being placed on the support in a substantially random manner.

The multifilament tow is then passed from the collecting support to a bonding device where adjacent fibers are bonded to one another to form a spunbond web. Compaction is typically performed using mechanical means prior to bonding using existing nonwoven processing techniques. The bonded portion of the multifilament product is typically passed through a heated high pressure nip roll assembly and heated to a softening or melting temperature so that the heated adjacent fibers are permanently bonded or fused together at the crossover points. Such pattern bonding (i.e., point bonding) using a roll press or bonding (i.e., area bonding) across the entire surface of the web can be accomplished according to known techniques. This bonding is preferably achieved by thermal bonding under simultaneous heat and pressure. In a particularly preferred embodiment, the resulting web is bonded at spaced apart locations and simultaneously bonded using a desired selected pattern. Typical bonding pressures range from about 17.9 to 89.4kg/cm (100 pounds/inch) and the bonding area is typically about 10% to 30% of the surface on which such patterned bonding is performed. The rollers may be heated by circulating oil or induction heating, etc. U.S. patent No. 5298097 discloses a suitable thermal bonding process for reference.

Spunbond webs of the present invention typically have continuous filament deniers of about 1.1-22dTex (1-20 denier). The fiber fineness of the polyethylene terephthalate is preferably about 0.55 to 8.8dTex (0.5 to 8 deniers), more preferably 1.6 to 5.5dTex (1.5 to 5 deniers). The fiber fineness of the isotactic polypropylene is preferably about 1.1-11dTex (1-10 denier), more preferably about 2.2-4.4dTex (2-4 denier). Typically, spunbond webs made using the process of the present invention have a tenacity of about 2.2 to 3.4dN/dTex (2.0 to 3.1 g/denier) for the polyethylene terephthalate fibers and 13.2 to 17.7dN/dTex (1.5 to 2 g/denier) for the isotactic polypropylene fibers. The relatively uniform nonwoven web has a basis weight of about 13.6 to about 271.7 grams/meter²(0.4-8.0 oz/yd)²). In a preferred embodiment, the basis weight is about 13.6 to about 67.9 grams/meter²(0.4-2.0 oz/yd)²). At a distance of 232cm²(36 inches)²) The nonwoven product produced according to the process of the present invention has a coefficient of variation per unit weight of the web of at least as low as 4%.

The technique according to the invention allows the rapid formation of highly uniform spunbonded nonwoven webs without great safety investment and cumbersome operating requirements. And it can use waste and/or recycled thermoplastic polymer material as starting material from an economic point of view. The automatic heading function of the technique ensures that the heading operation of the worker is minimized, thereby maximizing the productivity of the factory.

An embodiment of the invention is described below with reference to fig. 1 and 2, however, it is to be understood that the invention is not limited to the details of the embodiment described.

In various embodiments, the thermoplastic polymer material is a sheet material that is fed into a heated MPM single screw extruder (not shown) and then a heated transfer tube in a molten state is fed into a Zenith pump (not shown) at 11.68 cm above the pump²Per revolution (0.71 inch)³Rpm) to the spin/spinneret assembly 1. The extruder control pressure was maintained at about 3445KPa (500 lbs/inch)²). The thermoplastic polymeric material in the molten state is passed through a spin/spinneret assembly 1, the assembly 1 including a filter medium for forming a molten thermoplastic polymeric multifilament tow 2. The resulting multifilament tow was then cooled while passing through a cooling zone 4 of 0.91m (36 inches) length, where the air temperature was about 13 ℃ and the air was contacted from one side approximately perpendicularly to the tow in an undisturbed manner, the air stream being supplied through a duct 6 at a flow rate of 35.9 cm/sec (110 ft/min).

The lower portion of the tow 8 is then introduced into the inlet end 10 of the housing 12, which housing 12 encloses the draw rolls 14 and 16 in the area where the tow is wrapped. The diameter of the draft rollers 14 and 16 was 19.4cm (7.6 inches). The wrap angle of the tow with each draw roll was about 210 degrees. The inner surface of the housing 12 is spaced about 2.5cm (1 inch) from the surface of the draft rollers 14, 16. As shown in fig. 1, the polymeric extensions or edges 18, 20 and 22 are provided to form a substantially complete passageway from the inlet end 10 to the outlet end 24 of the housing 12. Fig. 2 shows a detail of this extension or edge, wherein the replaceable polymer edge 26 is mounted within a support 28 of the housing 12, and the polymer edge or extension 18 shown in fig. 1 corresponds to the replaceable polymer edge 26 with the support 28 shown in fig. 2. Any contact of the polymer edge 26 with the draw roll 14 will cause the edge to break down into a powder form without causing any significant damage to the draw roll, the tow exiting the first draw roll 14 being designated 30 in fig. 2, the draw rolls 16 and 14 shown in fig. 1 drawing the tow 2 before it has fully solidified.

At the outlet end 24 of the housing 12, a pneumatic delivery nozzle 32 is provided, the air being delivered downwardly from a delivery duct 34 substantially parallel to the direction of movement of the tow. The air pressure in the nozzle was 186KPa (27 pounds per inch)²) And the loss amount is about 4.2 meters³Per minute (150 feet)³In terms of minutes). The pneumatic delivery nozzle 32 generates an air velocity greater than the surface velocity of the draw rolls 14 and 16. The pneumatic delivery nozzle 32 creates further tension on the tow and causes additional air to be drawn into the housing 12 at the inlet end 10, thereby creating an air flow over the length of the housing 12, so that the tow is uniformly wound around the draft rollers 14 and 16 without slippage, and a uniform draft is achieved. In addition, pneumatic delivery nozzle 32 will discharge tow 36 from outlet end 24 of housing 12 onto support 38, which is a movable, air permeable, continuous belt.

As the tow 36 exits the pneumatic delivery nozzle 32, the individual continuous filaments therein are generally crimped in a random manner because no more powerful pulling force is exerted thereon, the speed of the tow is reduced and its forward movement is slowed. The tow is then collected in a substantially random manner on a support 38, such support or lay-up tape 38 being a commercial product known under the trade name Electrotech-20 from Albany international of Portland, Tennessee. The support 38 is disposed below and at a distance from the air delivery nozzle 32.

The resulting web 40 on support 38 then passes through a press roll 42 and patterned bonding roll 44. The patterned bonding roll 44 is pressed into an engraved diamond pattern on the surface of the web and heated to soften the thermoplastic polymer material. As the web passes through press roll 42 and patterned bonding roll 44, the area of the web surface that is bonded is approximately more than 20% of the entire surface. The resulting spunbond web is then collected by winding at 46. Specific examples will be described in detail below.

Example 1

The thermoplastic polymer material used was a commercial polyethylene terephthalate with an intrinsic viscosity of 0.685 g/dl. The determination of the intrinsic viscosity will be described below. The sheet-like polymer material is first subjected to a pre-treatment for crystallization at a temperature of about 174 c and dried with a drying gas at about 149 c. The pressure of the spin pack used was 13780KPa (2000 lbs/inch)²) 384 holes are evenly spaced in the region of the spinneret plate having a width of 15.2cm (6 inches). The capillary openings of the spinneret were trilobal in shape with a slot 0.38mm (0.015 inch) long, 0.13mm (0.005 inch) wide and 0.18mm (0.007 inch) deep. Molten polyethylene terephthalate fed at a rate of 1.2 g/min/hole was extruded at a temperature of 307 ℃.

The driven draft rollers 14 and 16 rotate at a surface speed of about 2743 meters/minute (3000 yards/minute). The product had a fiber denier of about 4.5dTex (4.1 denier) and a tenacity of about 20.3dN/dTex (2.3 g/denier). The speed of movement of the laying belt 38 is variable, so that the resulting spunbonded web can have a basis weight of 13.6 to 135.8 g/m²(0.4-4.0 oz/yd)²) May be varied within the range of (1). At a distance of 232cm²(36 inches)²) Sample of (2) was tested, and the unit weight was 105.3g/m²(3.1 oz/yd²) The coefficient of variation per unit weight of the spunbond product was only 4%.

Example 2

The thermoplastic polymer used was a commercial isotactic polypropylene having a melt flow rate of 40 grams per 10 minutes as determined by ASTM D-1238. The polymeric material is in the form of a sheet and is melt extruded. The spin pack pressure used was 9646KPa (1400 lbs/inch)²). The holes were arranged at 240 evenly spaced intervals in the region of the spinneret plate having a width of 30.5cm (12 inches). The spinneret capillary holes were circular with a diameter of 0.038cm (0.015 inch) and a gap length of 0.152cm (0.060 inch). The molten isotactic polypropylene fed at a rate of 0.6 g/min/hole was extruded at a temperature of 227 ℃.

Is driven to draftThe rolls 14 and 16 were rotated at a surface speed of about 1826 meters/minute (200 yards/minute). The product had a fiber denier of about 3.3dTex (3.0 denier) and a tenacity of about 15.9dN/dTex (1.8 g/denier). The speed of movement of the lay-up belt 38 can be varied to provide a spunbond web having a basis weight of 0.4-2.0 oz/yd²(13.6-67.9 g/m)²) May be varied within the range of (1). At a distance of 232cm²(36 inches)²) Sample (2) having a basis weight of 44.1 g/m²(1.3 oz/yd)²) The coefficient of variation per unit weight of the spunbond product was only 3.3%.

While the preferred embodiment has been described, it will be understood that various modifications and changes will occur to those skilled in the art, and such modifications and changes are not to be considered as beyond the purview of the claims.

Claims (20)

1. A process for producing a spunbond web wherein a molten melt processable thermoplastic polymer material is extruded through a plurality of orifices to form multifilament strands which are drawn to increase their strength, then passed through a cooling zone to solidify, and collected on a support to form a web and bonded to form a spunbond web; the improvement wherein said multifilament tow is transported along its length between a cooling zone and a support while the tow is wrapped around at least two spaced apart driven draft rollers, a housing covering the draft rollers in the area around which the tow is wrapped around the draft rollers, the housing having an inlet end and an outlet end, such that the inlet end of the housing receives the multifilament tow and applies a pulling force to the multifilament tow by the action of said spaced apart driven draft rollers, thereby causing the multifilament tow to be drawn adjacent the spinneret orifice, and the multifilament tow is subjected to another pulling force by a pneumatic delivery nozzle at the outlet end of the housing to assist in contacting the multifilament tow with said spaced apart driven draft rollers and discharging the tow from the outlet end of the housing onto the support along its length.

2. A process according to claim 1, characterized in that said melt processable thermoplastic polymer material is predominantly polyethylene terephthalate.

3. A method according to claim 1, characterized in that said melt processable thermoplastic polymer material is polypropylene.

4. The process of claim 1 wherein said melt processable polymeric material is extruded through a plurality of orifices in the form of linear orifices.

5. The method of claim 1 wherein said cooling zone is a cross-cooling zone.

6. The method of claim 1 wherein said at least two spaced apart draw rolls rotate at a surface speed of about 1000 and 5000 meters/minute.

7. The process of claim 1 wherein said multifilament tow passing through said pneumatic conveying nozzle is collected on the surface of a continuous belt located at a distance from the pneumatic conveying nozzle.

8. The method of claim 1 wherein the filaments of said multifilament tow collected on the support member have a denier of about 1.1 to 22 dTex.

9. The method of claim 1 wherein said multifilament tow is formed primarily of polyethylene terephthalate and the filaments have a denier of about 0.55 to 8.8dTex as collected on a support.

10. The method of claim 1 wherein said multifilament tow is comprised of isotactic polypropylene and the individual filaments have a denier of about 1.1 to 11dTex as collected on a support.

11. The method of claim 1 wherein said web collected on said support is pattern bonded as it is formed into a spunbond web.

12. The method of claim 1 wherein said web collected on said support is surface bonded as it is formed into a spunbond web.

13. The method of claim 1 wherein said spunbond web has a basis weight of about 13.6 to about 271.7 grams/meter²。

14. An apparatus for making a spunbond web comprising:

(a) a plurality of melt orifices which form a composite when the molten thermoplastic polymer material is extruded

The combination of the silk and the silk,

(b) a cooling zone for solidifying the melt-extruded thermoplastic polymer multifilament tow

The chemical combination is carried out by dissolving,

(c) at least two spaced-apart drawing rollers downstream of the cooling zone, comprising a housing

The area of the thermoplastic polymer multifilament tow in contact with the drawing roller is wrapped around the drawing roller

A roller, the housing having an inlet end and an outlet end, whereby the housing can be connected

Of multifilament strands containing thermoplastic polymer and drawing rollers for thermoplastic polymer

The multifilament tow is pulled near the spinneret orifice by applying a pulling force to the multifilament tow

The stretching out of the bag body is carried out,

(d) a pneumatic delivery nozzle at the outlet end of the housing for assisting in thermoplastic polymerization

Contact between the multifilament bundle and spaced drawing rollers and enabling thermoplastic formation

The polymeric multifilament tow exits the housing at an outlet end along its length,

(e) a support member located below and at a distance from the air delivery nozzle

It can receive the multifilament tow of the thermoplastic polymer and facilitate laying into fibers

A net, and

(f) bonding means for bonding multifilament yarns of thermoplastic polymer after formation of the web

And bundled to form a spunbond web.

15. The apparatus of claim 14, wherein said plurality of melt orifices are arranged in a linear pattern.

16. The apparatus of claim 14 wherein said cooling zone (b) is capable of providing cross-cooling wherein cool air impinges upon the melt extruded multifilament strands of thermoplastic polymer.

17. The apparatus of claim 14 wherein said housing (c) includes a polymeric edge disposed adjacent said draw roll to form a substantially complete enclosure in the region of the draw roll around which the thermoplastic polymer multifilament material is wound and which disintegrates into powder when contacted by the draw roll.

18. Apparatus according to claim 14, wherein said support (e) is a continuous belt.

19. The apparatus of claim 14 wherein said bonding means (f) is an autoclave nip assembly capable of forming a pattern bonded spunbond web.

20. The apparatus of claim 14 wherein said bonding means (f) is an autoclave nip assembly capable of forming a surface-bonded spunbond web.