Method for preparing multiple component meltblown webs

Abstract

A process for forming multiple component meltblown webs in which a poor-spinning polymer is co-spun with a good-spinning polymer in a meltblowing process using high throughput and short die-to-collector distances.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method for preparing meltblown webs having improved uniformity and barrier properties at high polymer throughput and low die-to-collector distances. More specifically, the method involves meltblowing multiple component meltblown fibers wherein at least one of the components is a polymer that spins poorly at low die-to-collector distances and at least one of the components is a polymer that spins well at low die-to-collector distances.

[0003] 2. Description of Related Art

[0004] In a meltblowing process, a nonwoven web is generally formed by extruding molten polymer through a die and attenuating the extruded melt streams with a high-velocity gas stream to form meltblown fibers which are collected as a web. Die-to-collector distances (DCD) of at least about 12 inches are generally required to provide fiber forming, cooling and attenuation. However such distances often result in undesirable non-uniformities in the web. Attempts to reduce the DCD generally results in the formation of harsh stiff webs due to fusing and over-bonding of the meltblown fibers which often contain solid polymer globules commonly referred to as "shot". Certain polymers such as polyolefins are especially difficult to form into meltblown webs at high polymer throughputs and short die-to-collector distances. Lau, U.S. Pat. No. 4,526,733 describes a method for forming meltblown fibers and webs using an attenuating quench gas having a temperature at least 100.degree. F. (37.8.degree. C.) cooler than the molten polymer. The use of a relatively cool attenuating gas allows short die-to-collector distances to be used and provides meltblown webs having improved properties, but also requires the use of insulated or heated dies, or heating the polymers to higher than normal spinning temperatures to avoid freezing of the polymer inside the die tip.

[0005] In the production of meltblown webs, it is sometimes desirable to form meltblown fibers from more than one polymeric material where each material can have different physical properties and contribute different characteristics to the meltblown web. There is a need to provide a new method for forming uniform meltblown multiple component webs at high throughput.

BRIEF SUMMARY OF THE INVENTION

[0006] In one embodiment, the present invention is directed to a process for forming a multiple component meltblown web comprising the steps of melt blowing at least first and second molten polymers through a die comprising a plurality of spin orifices to form multiple component meltblown fibers, andcollecting the multiple component meltblown fibers as a multiple component meltblown web on a collector surface at a die-to-collector distance of less than 15.2 cm.

[0007] In a further embodiment, the present invention is directed to a process for forming a multiple component meltblown web comprising the steps of melt blowing at least first and second molten polymers through a die comprising a plurality of spin orifices to form multiple component meltblown fibers, and collecting the multiple component meltblown fibers on a collector surface at a die-to-collector distance of less than about 20.3 cm, wherein a formation ratio of less than about 30 cm.multidot.orifice.multidot.min/g is used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic cross-sectional view of a meltblowing die useful in practicing the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention is directed toward a method for forming multiple component meltblown webs having improved barrier and uniformity properties. The multiple component webs are formed at high polymer throughput in a meltblowing process using a short die-to-collector distance without requiring specially insulated dies or a relatively cool quench gas. The multiple component meltblown fibers comprise a first polymeric component which does not normally spin well at short die-to-collector distances, for example a polyolefin, and a second polymeric component which has good spinning properties at short die-to-collector distances, such as a polyester. Surprisingly, it has been found that high quality meltblown webs having good uniformity and barrier properties are formed from a poor-spinning polymer when it is combined with a good-spinning polymer to form a multiple component meltblown web using a short die-to-collector distance and high polymer throughput.

[0010] As used herein, the term "polymer" generally includes but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term "polymer" shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, atactic, and random symmetries.

[0011] The term "polyolefin" as used herein, is intended to mean any of a series of largely saturated open chain polymeric hydrocarbons composed only of carbon and hydrogen atoms. Typical polyolefins include polyethylene, polypropylene, polymethylpentene and various combinations of the ethylene, propylene, and methylpentene monomers.

[0012] The term "polyethylene" (PE) as used herein is intended to encompass not only homopolymers of ethylene, but also copolymers wherein at least 85% of the recurring units are ethylene units.

[0013] The term "polyester" as used herein is intended to embrace polymers wherein at least 85% of the recurring units are condensation products of dicarboxylic acids and dihydroxy alcohols with linkages created by formation of ester units. This includes aromatic, aliphatic, saturated, and unsaturated di-acids and di-alcohols. The term "polyester" as used herein also includes copolymers (such as block, graft, random and alternating copolymers), blends, and modifications thereof. An example of a polyester is poly(ethylene terephthalate) (PET) which is a condensation product of ethylene glycol and terephthalic acid.

[0014] The term "meltblown fibers" as used herein, means fibers which are formed by meltblowing, which comprises extruding a melt-processable polymer through a plurality of capillaries as molten streams into a high velocity gas (e.g. air) stream. The high velocity gas stream attenuates the streams of molten thermoplastic polymer material to reduce their diameter and form meltblown fibers having a diameter between about 0.5 and 10 microns. Meltblown fibers are generally discontinuous fibers but can also be continuous. Meltblown fibers carried by the high velocity gas stream are generally deposited on a collecting surface to form a meltblown web of randomly dispersed fibers.

[0015] The term "nonwoven fabric, sheet or web" as used herein means a structure of individual fibers, filaments, or threads that are positioned in a random manner to form a planar material without an identifiable pattern, as opposed to a knitted or woven fabric.

[0016] The term "multiple component fiber" as used herein refers to any fiber that is composed of at least two distinct polymers which have been spun together to form a single fiber. The term "fiber" as used herein refers to both discontinuous and continuous fibers. The at least two polymeric components are preferably arranged in distinct substantially constantly positioned zones across the cross-section of the multiple component fibers and may extend substantially continuously along the length of the fibers. Preferably the multiple component fibers are bicomponent fibers which are made from two distinct polymers. Multiple component fibers are distinguished from fibers which are extruded from a homogeneous melt blend of polymeric materials. However, any of the distinct polymers used to form the multiple component fibers disclosed herein may comprise a blend of polymeric materials. Multiple component fibers useful in practicing the current invention include sheath-core and side-by-side fibers. Preferably the multiple component fibers are bicomponent fibers in which the two distinct polymers are arranged in a side-by-side configuration.

[0017] The term "multiple component web" as used herein refers to a nonwoven web comprising multiple component fibers. The term "bicomponent web" as used herein refers to a nonwoven web comprising bicomponent fibers. The term "single component meltblown web" is used herein to refer to meltblown webs which are formed from a single polymer or a substantially homogeneous polymer blend as opposed to being formed from distinct zones of polymers arranged along the length of the fibers.

[0018] The term "poor-spinning polymer" as used herein refers to a polymer which forms poor quality single component meltblown webs using short die-to-collector distances at high polymer throughput. Poor quality meltblown webs are highly fused, stiff, rough feeling, with large fused fibers and usually contain significant amounts of "shot". Poor-spinning polymers generally have a specific heat of greater than about 1.6 kJ/kg/K and a glass transition temperature (T.sub.g) less than about 25.degree. C. Poor-spinning polymers may have a glass temperature of less than about 0.degree. C. Examples of poor-spinning polymers include polyolefins such as polyethylene (heat capacity=1.86 kJ/kg/K; T.sub.g=-130.degree. C.) and polypropylene (heat capacity=1.8 kJ/kg/K; T.sub.g=-10.degree. C.).

[0019] The term "good-spinning polymer" as used herein refers to a polymer which forms good quality single component meltblown webs at short die-to-collector distances and high polymer throughput. A meltblown web is generally considered to be a good quality web if it is characterized by low levels or the substantial absence of "shot", and being drapeable with a relatively soft hand as a result of the fibers not being over-fused, etc. Generally good-spinning polymers form webs at short DCD's (e.g. less than about 15.2 cm) and high throughput that have similar properties to webs formed at the same throughput at more conventional, higher DCD's (e.g. 30+ cm). Good-spinning polymers generally have a specific heat of less than about 1.6 kJ/kg/K and a glass transition temperature of greater than about 25.degree. C. Examples of good-spinning polymers include polyesters such as poly(ethylene terephthalate) (heat capacity=1.1 kJ/kg/K; T.sub.g=70.degree. C.), polyamides such as poly(.epsilon.-caprolactam) (nylon 6, heat capacity=1.4 kJ/kg/K; T.sub.g=50.degree. C.) and poly(hexamethylene adipamide) (nylon 66, heat capacity=1.59 kJ/kg/K; T.sub.g=40.degree. C.), and polystyrene (heat capacity=1.2 kJ/kg/K; T.sub.g=100.degree. C.).

[0020] FIG. 1 is a schematic lateral cross-sectional view of a conventional side-by-side bicomponent meltblowing die 10 useful in practicing the method of the present invention. Two different polymers, one of which is a poor-spinning polymer and the other of which is a good-spinning polymer, are melted in separate extruders (not shown) and metered separately by gear pumps (not shown) to conduits 12 and 14 which are divided from each other by a plate 16. The polymer components are fed to a line of spin orifices 18 and are combined just prior to exiting the spin orifice. Alternately, plate 16 can be removed and the bicomponent meltblown fibers can be made by extruding a the polymer components as a layered molten mass through a row of side-by-side orifices as described in Krueger et al. U.S. Pat. No. 6,057,256, which is hereby incorporated by reference. A post-coalescent die, as disclosed in copending provisional application No. 60/223,040, filed Aug. 4, 2000, now U.S. Ser. No. ______, incorporated herein by reference, in which the distinct polymeric components are extruded through separate extrusion orifices and are contacted and fused after exiting the capillaries to form multiple component meltblown fibers, can also be used. Other die configurations are also suitable, for example the die tip may be recessed with respect to the die face or may extend a short distance beyond the die face.

[0021] The polymer components are preferably fed to the spin orifices at a total polymer throughput per orifice of greater than about 0.5 g/orifice/min, more preferably greater than about 0.6 g/orifice/min. If a post-coalesecent spin configuration is used, the total polymer throughput "per orifice" is the combined polymer flows through the pairs or groups of orifices that form each extruded multiple component melt stream.

[0022] The skilled artisan will recognize that the configurations and shapes of the extrusion capillaries can be modified in numerous ways for various reasons. For example, by machining pie-slice shaped cross-sections in the die tip, the process is able to accommodate delivering more than two polymer components into the fibers to form fibers having a substantially circular cross-section with pie-shaped component cross-sections. Likewise, those skilled in the art will recognize that on a production scale, it can be necessary to use many extruder/die apparatuses ("spin blocks") in order to obtain full coverage of the collection surface so as to produce an acceptable nonwoven web or fabric.

[0023] As the polymer components exit the die through spin orifice 18 they form multiple component polymeric melt streams which are contacted by high velocity jets of attenuating gas exiting through channels 20. Preferably the attenuating gas is a heated gas having a temperature that is within about 30.degree. C., and more preferably within about 10.degree. C. of the temperature of the molten polymer components as they exit the spin capillaries. The attenuating gas is generally heated air, however other inert gases may be used. The extruded polymer melt streams are pneumatically drawn by the attenuating gas to form meltblown fibers having an average effective diameter of less than about 10 microns, and generally in the range of 0.5 to 10 microns. As used herein, the "effective diameter" of a fiber with an irregular cross section is equal to the diameter of a hypothetical round fiber having the same cross sectional area. The average effective diameter of the meltblown fibers is preferably between about 1 and 6 microns, and most preferably between about 2 and 4 microns. A plurality of gas-borne meltblown fiber streams, formed by attenuating a plurality of molten polymer streams extruded through the plurality of extrusion orifices in the meltblowing die, form a curtain of meltblown fibers extending across the width of moving collecting surface 22, such as a foraminous belt, screen, or scrim, located at a distance "h" below the meltblowing die. Distance "h" is the DCD, the distance between the die face and the collector surface. The DCD is preferably less than about 6 inches (15.2 cm), more preferably between about 3 to 5.5 inches (7.6 to 14.0 cm), and most preferably between about 4.5 to 5.5 inches (11.4 to 14.0 cm). Optionally, a relatively cool quench gas may impinge upon the curtain of fibers downstream of the attenuating gas jet.

[0024] Composite materials may be formed by collecting the meltblown fibers on a different sheet material such as another nonwoven layer, woven fabric, or foam, or bonding a previously formed meltblown web to such sheet materials or a polymer film. For example the meltblown fibers can be deposited between two spunbond nonwoven layers using methods known in the art to form a SMS (spunbond-meltblown-spunbond) fabric. The layers may be joined using methods known in the art such as by thermal, ultrasonic, and/or adhesive bonding. The meltblown layer and other sheet layer preferably each include polymeric components which are compatible so that the layers can be thermally bonded, such as by thermal point bonding. For example, in a preferred embodiment, the composite laminate comprises a meltblown web and spunbond web, each of which include at least one substantially similar or identical polymer. Alternatively, the layers of the composite sheet can be produced independently and later combined and bonded to form the composite sheet.

[0025] Collecting surface 22 may be fitted with one or more vacuum chambers located beneath the collecting surface on which the meltblown web is collected, the vacuum functioning to conduct the attenuating gas stream through the collecting surface and away from the fibers deposited thereon. At very short die-to-collector distances, it may be desirable to provide additional quenching means for cooling of the meltblown fibers such as providing a cooled air flow to the fibers as they exit the die, by spraying the fibers with a water mist as they are carried to the collector or by cooling the collector surface.

[0026] The web may be passed through a nip formed by a pair of rolls to press the meltblown fibers together, however this is optional since meltblown fibers generally form a cohesive meltblown web as they are deposited on the collecting surface. The multiple component meltblown web preferably has a basis weight between about 2 and 40 g/m.sup.2, more preferably between 5 and 30 g/m.sup.2, and most preferably between 10 and 35 g/m.sup.2. The meltblown webs are useful for forming spunbond-meltblown-spunbond fabrics having good barrier properties and useful in end uses such as medical gowns and drapes. Preferably the spunbond-meltblown-spunbond fabrics have a hydrostatic head greater than about 30 cm H.sub.2O, more preferably greater than about 60 cm H.sub.2O.

[0027] It has been found that multiple component fibers comprising both a poor-spinning polymer component and a good-spinning polymer component can be spun at high polymer throughput and short die-to-collector distances, for example less than about 6 inches (15.2 cm), to obtain multiple component meltblown webs having improved uniformity and barrier properties compared to similar webs formed at higher, more conventional die-to-collector distances. In addition, it has been found that good quality multiple component webs can be formed from a combination of poor-spinning polymer and good-spinning polymer under spinning conditions (low DCD and high throughput) that would normally result in unacceptable properties for single component meltblown webs made from the poor spinning polymer alone.

[0028] In a preferred embodiment of the current invention, the ratio of the die-to-collector distance (cm) divided by the total polymer throughput per orifice (g/orifice/min), referred to herein as the formation ratio, is less than about 30 cm.multidot.orifice.multidot.min/g- , preferably less than about 20 cm.multidot.orifice.multidot.min/g. In a preferred embodiment, the formation ratio is in the range of about 10 to 20 cm.multidot.orifice.multidot.min/g, most preferably in the range of about 14 to 18 cm.multidot.orifice.multidot.min/g. If a post-coalesecent spin configuration is used, the formation ratio is calculated using the combined flows through the pairs or groups of orifices that form each multiple component melt stream as the total polymer throughput "per orifice".

[0029] As polymer throughput is increased, it becomes increasingly difficult to form good quality meltblown webs at short die-to-collector distances from poor-spinning polymers. In a preferred embodiment of the current invention, good-quality multiple component meltblown webs comprising a poor-spinning polymeric component and a good-spinning polymeric component are formed using a die-to-collector distance less than about 8 inches (20.3 cm), preferably less than about 6 inches (15.2 cm) and a formation ratio less than about 30 cm.multidot.orifice.multidot- .min/g, preferably less than about 20 cm.multidot.orifice.multidot.min/g. Under these conditions of die-to-collector distance and formation ratio, it is not possible to form good-quality meltblown single component webs from the poor-spinning polymeric component alone.

[0030] One example of a combination of polymers for forming bicomponent meltblown webs according to the present process is polyethylene and poly(ethylene terephthalate), where polyethylene is the poor-spinning component and poly(ethylene terephthalate) is the good-spinning component. Preferably the polyethylene is a linear low density polyethylene having a melt index of at least 10 g/10 min (measured according to ASTM D-1238; 2.16 kg@190.degree. C.), an upper limit melting range of about 120.degree. to 140.degree. C., and a density in the range of 0.86 to 0.97 gram per cubic centimeter. Meltblown webs comprising bicomponent polyethylene/poly(ethylene terephthalate) meltblown fibers are especially useful in nonwoven fabrics for medical end uses since they are radiation sterilizable. The bicomponent polyethylene/poly(ethylene terephthalate) meltblown webs can be bonded to spunbond layers typically used in such end uses to provide composite laminates having a good balance of strength, softness, breathability, and barrier properties. According to a preferred embodiment of the invention, a low intrinsic viscosity polyester polymer and polyethylene are combined to make a meltblown bicomponent web in the meltblown web production apparatus. The low viscosity polyester preferably comprises poly(ethylene terephthalate) having an intrinsic viscosity of less than about 0.55 dl/g, preferably from about 0.17 to 0.49 dl/g, more preferably from about 0.20 to 0.45 dl/g, most preferably from about 0.22 to 0.35 dl/g (measured using ASTM D 2857, using 25 vol. % trifluoroacetic acid and 75 vol. % methylene chloride at 30.degree. C. in a capillary viscometer). Other preferred polymer combinations include polypropylene/poly(ethylene terephthalate), polypropylene/poly(hexamethylenediamine adipamide), and polyethylene/poly(hexamethylenediamine adipamide).

Test Methods

[0031] In the description above and in the examples that follow, the following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society for Testing and Materials, and AATCC refers to the American Association of Textile Chemists and Colorists.

[0032] Fiber Diameter was measured via optical microscopy and is reported as an average value in microns. For each meltblown sample the diameters of about 100 fibers were measured and averaged.

[0033] Basis Weight is a measure of the mass per unit area of a fabric or sheet and was measured using a custom-made instrument that uses beta-radiation to determine the mass over a circular area having a diameter of 0.4 inches (1.02 cm) [i.e. a sample area of 0.126 in.sup.2 (0.81 cm.sup.2)]. Methods using beta-radiation for measurement of basis weight are well known in the art. The instrument measured basis weight in a manner similar to commercially available on-line devices such as the Honeywell-Measurex Da Vinci Precision Measurement system. Measurements were taken across the width of a sheet, the sheet was indexed forward, another set of measurements were taken across the sheet width, etc. For the examples below, about 40 measurements were taken across the sheet width for about 100 different locations along the length of the sheet which corresponds to about 4000 data points per sample. Standard statistics were used to calculate the mean basis weight and variability in basis weight for each data set. The variability in basis weight is reported as the standard deviation (.sigma.) for a total of between about 3000 to 4000 individual basis weight measurements. This method has been found suitable for characterizing the variability of small non-uniformities in the sheet by making measurements on small sample areas. Other methods known in the art for measuring basis weight may also be used provided they are capable of accurately measuring the basis weight for sample areas of about 0.126 in.sup.2 (0.81 cm.sup.2).

[0034] Hydrostatic Head is a measure of the resistance of the sheet to penetration by liquid water under a static pressure. The test was conducted according to AATCC-127-1989, which is hereby incorporated by reference, and is reported in centimeters of water. Because meltblown webs generally have low strength, they may fail during the hydrostatic head measurement if they are unsupported. Therefore, the values reported herein are obtained from measurements made on spunbond-meltblown-spunbond (SMS) composite fabrics. SMS fabrics suitable for use in measuring the hydrostatic head are prepared by thermally point bonding a spunbond layer on each side of the meltblown web with about 10-30% bond area. Any spunbonded fabric is suitable so long as it has sufficient strength to survive the test method without failing.

[0035] The Specific Heat of a polymer is a fundamental physical property of the polymer that relates to the amount of heat per mass required to raise the temperature of the polymer one degree Kelvin at a constant pressure. Tabulated values for numerous materials can easily be found in technical publications. Specific heat is a function of the temperature at which it is measured. The specific heat values reported herein are measured at 25.degree. C.

[0036] The Glass Transition Temperature (T.sub.g) of a polymer is a fundamental physical property of the polymer and is a second order transition that relates to the temperature above which it is possible to soften and potentially crystallize the amorphous portion of the polymeric material. Glass transition temperatures can be measured by many techniques, such as by differential thermal analysis and differential scanning calorimetry. Since the measured value of T.sub.g is rate dependent, glass transition temperatures reported herein are measured using very slow rate methods or are obtained by extrapolating the data from faster, non-equilibrium techniques to zero rates. This is a fairly common practice, in order that the glass transition temperature can be considered as a characteristic only of the polymer and not of the measuring method. Tabulated values of T.sub.g for numerous materials can be readily found in technical publications.

EXAMPLES 1-3

[0037] A meltblown bicomponent web was made with a polyethylene component and a poly(ethylene terephthalate) component. The polyethylene component was made from linear low density polyethylene with a melt index of 135 g/10 minutes (measured according to ASTM D-1238, 2.16 kg@190.degree. C.) available from Equistar as GA594. The polyester component was made from poly(ethylene terephthalate) with a reported intrinsic viscosity of 0.53 dl/gm available from DuPont as Crystar.RTM. polyester (Merge 4449). The polyethylene polymer was heated to 260.degree. C. and the polyester polymer was heated to 305.degree. C. in separate extruders. The polyester was hydrolytically degraded in the melt system using approximately 1500 ppm moisture in the resin which results in an intrinsic viscosity of less than about 0.35 dl/g. The two polymers were separately extruded and metered to two independent polymer distributors. The planar melt streams exiting each distributor were independently filtered and then combined in a bicomponent meltblown die to provide a side-by-side filament cross section. The die was heated to 305.degree. C. and had 645 capillary openings arranged in a 54.6 cm line. The polymers were spun through the each capillary at a polymer throughput rate of 0.80 g/orifice/min. Attenuating air was heated to a temperature of 305.degree. C. and supplied at a pressure of 5.5 psi through two 1.5 mm wide air channels. The two air channels ran the length of the 54.6 cm line of capillary openings, with one channel on each side of the line of capillaries set back 1.5 mm from the capillary openings. A forced entrainment air flow of 1200 m/min at about 13.degree. C. was provided on both sides of the fibers through a duct that was 2 inches (5 cm) high and extended beyond the edges of the fiber zone. The polyethylene was supplied to the spin pack at a rate of 6.2 kg/hr and the polyester was supplied to the spin pack at a rate of 24.8 kg/hr to produce a bicomponent meltblown web that was 20 weight percent polyethylene and 80 weight percent polyester. In Example 1, the filaments were collected at a die to collector distance of 11.4 cm (4.5 in) on a moving forming screen to produce a meltblown web a basis weight of 18.8 g/m.sup.2 which was collected on a roll.

[0038] In Example 2, a meltblown sheet was formed according to the procedure of Example 1 except that the distance from the die tip exit to the collection belt was 14 cm (5.5 in).

[0039] In Example 3, a meltblown sheet was formed according to the procedure of Example 1 except that the distance from the die tip exit to the collection belt was 16.5 cm (6.5 in).

[0040] Composite SMS sheets for use in hydrostatic head measurements were fabricated by thermally bonding a layer of spunbond on each side of the melblown web. Each spunbond layer was a 20 g/m.sup.2 bicomponent web formed from 80 weight % polyester and 30 weight % polyethylene, where the polyethylene formed a concentric sheath around the polyester core. The spunbond fibers were about 1.3 dpf and were created with a direct, high speed beam spinning process. The composite SMS web was thermally bonded between an engraved oil-heated metal calender roll and a smooth oil heated metal calender roll. Both rolls had a diameter of 466 mm. The engraved roll had a chrome coated non-hardened steel surface with a diamond pattern having a point size of 0.466 mm.sup.2, a point depth of 0.86 mm, a point spacing of 1.2 mm, and a bond area of 14.6%.

[0041] It can be seen from the meltblown web properties reported in Table 1 below that as the DCD, and therefore the formation ratio decreases, all other process variables remaining constant, the variability of the basis weight of the sheet decreases. A lower Basis Weight variability results in better composite sheet barrier properties as is shown in the Hydrostatic Head values given in Table 1.

1TABLE 1 MELTBLOWN FABRIC PROPERTIES Formation Ratio Basis Basis Composite DCD (cm .multidot. orifice .multidot. Weight Weight .sigma. Hydrostatic Example (cm) min/g) (g/m.sup.2) (g/m.sup.2) Head (cm) 1 11.4 14.2 18.8 0.85 82.8 2 14.0 17.5 19.1 1.15 72.7 3 16.5 20.6 19.0 1.43 71.1

[0042] Attempts to meltblow a single component polyethylene web at the same conditions of throughput and DCD, and thus the same formation ratio, yielded fused fiber, shot, fly and a web that would stick and adhere to the collection belt such that it was not possible to collect samples. The web that was removed from the belt by scraping with a metal blade felt very rough and had clearly lost the properties characteristic of a fibrous meltblown web.

Claims

What is claimed is:

1. A process for forming a multiple component meltblown web comprising the steps of: melt blowing at least first and second molten polymers through a die comprising a plurality of spin orifices to form multiple component meltblown fibers; and collecting the multiple component meltblown fibers as a multiple component meltblown web on a collector surface at a die-to-collector distance of less than 15.2 cm.

2. The process according to claim 1 wherein the die-to-collector distance is between about 7.6 to 14 cm.

3. The process according to claim 2 wherein the die-to-collector distance is between about 11.4 to 14 cm.

4. The process according to claim 1 wherein the total polymer throughput is greater than about 0.5 g/orifice/min.

5. The process according to claim 4 wherein the total polymer throughput is greater than about 0.6 g/orifice/min.

6. The process according to claim 1 wherein the first polymer is a good-spinning polymer when meltblown to form a single component web at a die-to-collector distance of less than 15.2 cm and the second polymer is a poor-spinning polymer when meltblown to form a single component web at a die-to-collector distance of less than 15.2 cm.

7. The process according to claim 6 wherein the first polymer has a specific heat less than about 1.6 kJ/kg/.degree. K and a glass transition temperature greater than about 25.degree. C. and the second polymer has a specific heat of greater than about 1.6 kJ/kg/.degree. K and a glass transition temperature less than about 25.degree. C.

8. The process according to claim 7 wherein the first polymer is selected from the group consisting of poly(ethylene terephthalate), poly(hexamethylene adipamide), poly(.epsilon.-caprolactam), and polystyrene and the second polymer is a polyolefin.

9. The process according to claim 8 wherein the first polymer is poly(ethylene terephthalate) and the second polymer is polyethylene.

10. The process according to claim 8 wherein the first polymer is poly(ethylene terephthalate) and the second polymer is polypropylene.

11. The process according to claim 8 wherein the multiple component meltblown fibers are bicomponent fibers.

12. The process according to claim 11 wherein the first and second polymers are arranged in a side-by-side configuration.

13. A process for forming a multiple component meltblown web comprising the steps of: melt blowing at least first and second molten polymers through a die comprising a plurality of spin orifices to form multiple component meltblown fibers; and collecting the multiple component meltblown fibers on a collector surface at a die-to-collector distance of less than about 20.3 cm; wherein a formation ratio of less than about 30 cm.multidot.orifice.multidot.min/g is used.

14. The process according to claim 13 wherein the die-to-collector distance is less than about 15.2 cm.

15. The process according to claim 13 wherein the first polymer is a good-spinning polymer and the second polymer is a poor-spinning polymer when each polymer is meltblown separately to form single component webs using a die to collector distance of less than about 20.3 cm and a formation ratio of less than about 30 cm.multidot.orifice.multidot.min/g.

16. The process according to claim 14 wherein the first polymer is a good-spinning polymer and the second polymer is a poor-spinning polymer when each polymer is meltblown separately to form single component webs using a die-to-collector distance of less than about 15.2 cm and a formation ratio of less than about 30 cm.multidot.orifice.multidot.min/g.

17. The process according claim 13 wherein the first polymer has a specific heat less than about 1.6 kJ/kg/.degree. K and a glass transition temperature greater than about 25.degree. C. and the second polymer has a specific heat of greater than about 1.6 kJ/kg/.degree. K and a glass transition temperature less than about 25.degree. C.

18. The process according to claim 17 wherein the glass transition temperature of the second polymer is less than about 0.degree. C.

19. The process according to claim 13 wherein the formation ratio is less than about 20 cm.multidot.orifice.multidot.min/g.

20. The process according to claim 13 wherein the formation ratio is between about 14 and 18 cm.multidot.orifice.multidot.min/g.

21. The process according to either of claims 1 or 13 wherein the polymers are blown by a high velocity gas jet at a temperature within about 30.degree. C. of the temperature of the polymers as they exit the die.

22. The process according to claim 21 wherein the gas jet is heated to a temperature within about 10.degree. C. of the temperature of the polymers as they exit the die.

23. The process according to claim 13 wherein the first polymer is selected from the group consisting of polyamides, polyesters, and polystyrene and the second polymer is a polyolefin.

24. The process according to claim 23 wherein the first polymer is selected from the group consisting of poly(ethylene terephthalate), poly(hexamethylene adipamide), poly(.epsilon.-caprolactam), and polystyrene and the second polymer is selected from the group consisting of polyethylene and polypropylene.

25. The process according to claim 24 wherein the first polymer is poly(ethylene terephthalate) and the second polymer is polyethylene.

26. The process according to claim 24 wherein the first polymer is poly(ethylene terephthalate) and the second polymer is polypropylene.

27. The process according to claim 17 wherein the multiple component fibers are bicomponent fibers.

28. The process according to claim 27 wherein the first and second polymers are arranged in a side-by-side configuration.

29. The process according to either of claims 1 or 13 wherein the meltblown web has a basis weight of between about 2 and 40 g/m.sup.2 and a hydrostatic head of greater than about 30 cm H.sub.2O, the hydrostatic head being measured when the meltblown web is in a thermally point-bonded spunbond-meltblown-spunbond composite having a bonded area of between about 10 to 30 percent.