FIELD OF THE INVENTION

The present invention is directed to fibrous nonwoven webs made from fibers which are bonded together using relatively non-compressive bonding techniques such as through air bonding. The webs themselves include bonding fibers which have a uniform polymer composition along their length and width as opposed to such bonding fibers as bicomponent and biconstituent fibers which use different polymer compositions along either or both their length and width.

BACKGROUND OF THE INVENTION

Fibrous nonwoven webs are typically made from fibers which are laid down in a random fashion and then bonded to one another to increase the integrity of the overall web. There are a number of bonding techniques used to bond together all or a portion of the fibers. Powder bonding is one technique wherein a heat activatable adhesive in powder form is applied through all or a portion of the web. The web is then heated to activate the adhesive and bond the fibers together. In this method it is not the intent to heat the fibers sufficiently to cause the fibers themselves to bond to one another but only to activate the powdered adhesive. This is a commonly used technique with such fibers as polyester fibers which do not readily hear, soften and bond to one another with or without externally applied pressure.

Another bonding method is therπo-mechanical bonding. In this bonding method heat and pressure are used to bond the fibers of the nonwoven web together. One version of this method involves using a heat source to heat at least a portion of the fibers, typically to a temperature close to their melting or softening point, and then applying pressure to the web by some type of mechanical means as with a smooth or patterned bonding roll or rolls. Alternatively, the heating source may be incorporated into the bonding rolls so that the heating and compaction of the fibers is accomplished all in one step. Such thermo- mechanical bonding creates areas of high density and low loft due to the compaction and fusing of the fibers to one another in the areas of the bond sites. This bonding technique is often used for fibers such as polyolefin fibers or blends of polyolefin fibers and other fibers such as polyester fibers.

Yet another bonding technique is ultrasonic bonding wherein an ultrasonic horn and anvil assembly are used to pattern bond the fibers of the web together. This technique is similar to the above-described thermo- mechanical method in that it creates densified areas in the nonwoven web.

Still a further bonding technique is the through air bonding process wherein heated air is passed through the fibrous web at a sufficiently high temperature and for a sufficient amount of time to cause at least a portion of the fibers to soften or melt and bond to other fibers at all or at least a portion of the fiber cross-over points. If a very lofty web is desired, this process is carried out with little or no compaction of the web. As a result, a web is achieved which has a very open structure. This process generally involves the use of multicomponent or ulticonstituent fibers. These types of fibers include along at least a portion of either or both their length and

width a polymer composition which has a lower melting or softening point than the other portions of the fiber. In addition, this lower melting or softening point polymer will usually be one of the lowest if not the lowest melting/softening point polymers in the entire web matrix. Examples of such fibers include, for example, bicomponent and biconstituent fibers. These fibers are formed from multiple polymer compositions which are generally processed through separate extruders and combined to form a single fiber. Bicomponent fibers may have, for example, a lower melting sheath such as polyethylene and a higher melting core such as polypropylene or polyester. Another example of a bicomponent sheath/core fiber is a polyester/polyester fiber wherein the polymer composition of the sheath is different from the polymer composition of the core. When heated sufficiently, the lower melting sheath acts, in essence, like a glue to bond the fibers of the web together. Such bicomponent fibers are commonly used alone or in combination with other fibers when forming through air bonded fibrous webs.

Bicomponent fibers are very expensive when compared to the cost of other fibers such as single component fibers like polyester and polypropylene fibers. In fact, bicomponent fibers often cost as much as twice that of common staple fibers. As a result, when making through air bonded webs it is not uncommon to use as little bicomponent fiber as is possible in an effort to reduce cost. Despite this, the use of such fibers in single use disposable items such as diapers and other personal care absorbent products remains a costly endeavor.

Personal care absorbent products include such items as diapers, training pants, feminine hygiene products, incontinence devices, bandages, wipers and the like. A primary function of these products is absorbing and retaining fluids including body fluids such as blood, urine

and feces. As a result, these products will often require the use of fibrous nonwoven webs which are lofty and low density in nature to enable them to readily accept quick insults of fluids. To accomplish this, it is often necessary to use webs which include bicomponent fibers to maintain their lofty structure. Thermo-mechanically bonded webs are usually poor candidates for such uses since their structures have been compressed during the bonding process thereby reducing the available void volume for receiving fluids. Transfer layers, which are typically positioned between the body side liner and the absorbent core of personal care absorbent products, are but one example of such a material where a thermo-mechanically bonded web will not perform adequately. Consequently, there is a need for more cost effective materials to accommodate these applications.

SUMMARY OF THE INVENTION

The present invention is directed to lofty fibrous nonwoven webs which are made to conform to a specific set of properties and are constructed from support fibers and bonding fibers. The bonding fibers have a lower melting or softening temperature also collectively referred to as "bonding temperature" than the support fibers. The bonding fibers of the present invention are to be distinguished from multiconstituent and multicomponent fibers such as, for example, bicomponent fibers which have exposed exterior portions of their fiber surfaces which are comprised of different polymer compositions which have lower bonding temperatures than the other components comprising the fiber. The support fibers, as the name implies, give support and rigidity to the resultant nonwoven web. As a result of carefully controlling the selection of the fibers and the bonding conditions, it is possible to obtain fibrous nonwoven webs which are lofty in nature and designed with a specific set of properties.

While the present invention is described in connection with the use of staple fibers and a through air bonding process, such descriptions should not be construed as a limitation as to the type of fibers or bonding processes that can be used provided the resultant web exhibits the properties and characteristics described herein. For example, longer more continuous fibers such as spunbond fibers and/or mixtures of spunbond fibers and staple fibers are also considered to be within the scope of the present invention. In addition, while the materials of the present invention have been described in conjunction with their advantageous use in connection with personal care absorbent products, this should not be construed as a limitation on the possible end uses for the materials of the present invention. For example, the materials of the present invention may be suitable for other uses as in connection with the construction of all or a portion of health care and clean room related products such as sterilization wrap material, surgical gowns and drapes and other protective apparel such as caps, face masks, shoe coverings, coats and coveralls.

The fibrous nonwoven web of the present invention comprises a blend of bonding fibers and support fibers at least partially bonded together by the bonding fibers to form the web. The bonding fibers have a bonding temperature and define a length and a width. The polymer composition of the bonding fibers is processed through a single extruder and has a uniform polymer composition along both the length and the width of the fibers. The support fibers also have a bonding temperature but the bonding temperature of the bonding fibers is lower than the bonding temperature of the support fibers. The bonding fibers are present in the web in a weight percent, based upon the total weight of the web, of from about 40 to about 90 percent and the support fibers are present in the web in a weight percent, based upon the total weight of the web,

of from about 10 to about 60 percent. The resultant web has a density of between about 0.010 and about 0.060 grams per cubic centimeter and a machine direction tensile strength of at least about 1000 grams per 7.6 centimeters. In alternate embodiments the tensile strength can be at least about 2000 grams per 7.6 centimeters.

Further defining the web, the web can have a surface area per void volume of about 125 square centimeters per cubic centimeter or less while under a pressure of 68.9 pascals and more specifically a surface area per void volume of about 70 square centimeters per cubic centimeter or less while under a pressure of 68.9 pascals. Permeability of the web is measured in square microns and will be about 400 square microns or greater.

The polymer composition of the bonding and support fibers should be chosen such that the bonding fibers have a lower bonding temperature than the support fibers. Suitable fiber polymers include, but are not limited to, polyolefins and polyesters.

Formation of the fibrous nonwoven web involves mixing together appropriate weight percent quantities of bonding and support fibers and then heating the bonding and support fibers to the bonding temperature of the bonding fibers but below the bonding temperature of the support fibers for a sufficient amount of time to cause the bonding fibers to bond together and yield a fibrous nonwoven web with the prescribed properties set forth herein. Through air bonding is a particularly advantageous method for bringing about such bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a partial cut away top plan view of a personal care absorbent article, in this case a diaper,

which can employ the fibrous nonwoven webs according to the present invention.

Figure 2 is a graph which plots the weight percent of bonding fibers in the fibrous nonwoven webs of Examples 28 through 33 versus the bulk of the same webs.

Figure 3 is a graph which plots the weight percent of bonding fibers in the fibrous nonwoven webs of Examples 28 through 33 versus the density of the same webs.

Figure 4 is a graph which plots the weight percent of bonding fibers in the fibrous nonwoven webs of Examples 28 through 33 versus the surface area per void volume of the same webs.

Figure 5 is a graph which plots the weight percent of bonding fibers in the fibrous nonwoven webs of Examples 28 through 33 versus the machine direction tensile strength of the same webs.

Figure 6 is a graph which plots the weight percent of bonding fibers in the fibrous nonwoven webs of Examples 28 through 33 versus the permeability of the same webs.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to lofty fibrous nonwoven webs or fabrics which are designed to compete with and replace similar webs whose primary means of interfiber bonding are ulticonstituent fibers and multicomponent fibers. The lofty fibrous nonwoven webs according to the present invention are low density webs with densities ranging between about 0.010 and about 0.060 grams per cubic centimeter (g/cc) , having a surface area per void volume value of 125 square centimeters per cubic centimeter (cm /cm ) or less while under a pressure of 68.9 pascals and a permeability of about 400 square microns or greater. In more refined embodiments the surface area per void volume is less than or equal to 70 square centimeters per cubic centimeter while under a pressure of 68.9 pascals which translates into an even more lofty/open structure.

Having developed materials with these properties, the lofty fibrous nonwoven webs according to the present invention are suitable for a wide variety of uses. One such use is in conjunction with personal care absorbent articles.

Personal care absorbent articles are products and/or materials which are designed to absorb and retain body fluids such as blood, menses, urine and feces. Examples of such personal care absorbent articles include, but are not limited to, diapers, training pants, incontinence devices, feminine hygiene products, bandages and the like. Referring to Figure l of the drawings, a personal care absorbent article 10, such as a diaper, typically includes some type of top sheet or body side liner 12 which is liquid pervious and a bottom sheet or outercover 14 which is usually liquid impervious. Disposed between the top sheet 12 and the bottom sheet 14 is an absorbent core 16 whose function it is to absorb and retain fluids. Many personal care absorbent articles such as the diaper shown in Figure 1 often have to accept relatively large and quick insults of fluid such as urine. As a result, such products 10 can optionally include other layers such as a surge or separation layer 18 disposed between the top sheet 12 and the absorbent core 16. The separation layer 18 should generally be a relatively open structure which will quickly take in delivered fluids, temporarily retain the fluids and then give them up to the absorbent core 16 below for retention and storage. The materials of the present invention are particularly well-suited for use in this capacity and, therefore, may form all or a portion of such top sheets and/or separation layers.

When being used in such capaci ies as described above, the materials of the present invention should also have a certain minimum degree of integrity. Consequently, it is desirable that materials according to the present invention have a machine direction (MD) tensile strength of at least

about 1000 grams per 7.6 centimeters. In addition, in such applications the materials of the present invention should resist collapse and when compressed should spring back to a major portion of their uncompressed bulk or thickness. This property is called bulk recovery and the materials according to the present invention should generally have a bulk recovery of 60 percent or greater. The methods for calculating these properties are set forth below under the section entitled "Test Procedures."

As shown by the testing below, materials which meet these criteria are made from or include one or more types of bonding fibers and support fibers. The bonding fibers of the present invention can be staple fibers or more continuous type fibers such as spunbond fibers. The bonding fibers of the present invention are to be distinguished from multiconstituent and multicomponent fibers such as, for example, bicomponent and biconstituent fibers which have exposed exterior surfaces which are comprised entirely or at least partially of polymer compositions which have a lower bonding temperature and different polymer composition than the other components comprising the same fibers. This component which has the lower bonding temperature is used to bond the bicomponent/biconstituent fibers to themselves and, if possible to other fibers while the remaining components of the bicomponent/biconstituent fibers act to give rigidity to the fibers and the resultant web. The bonding fibers of the present invention define a length and a width with the polymer composition of the bonding fibers being uniform along both the length and the width of the fibers as is the case with, for example, polyolefin fibers such as polypropylene fibers. Unlike bicomponent and biconstituent fibers, the bonding fibers of the present invention do not have distinct regions of different polymer compositions such as is the case with sheath/core, side- by-side and islands-in-the-sea fibers which include a lower bonding temperature polymer as an exposed exterior surface

of the fibers. The bonding fibers of the present invention, such as polyolefin fibers, will have the same polymer composition throughout and a softening or melting temperature, collectively referred to as a "bonding temperature" which should be lower than the "bonding temperature" of the support fibers. As a result, it is desirable to select the support fibers, which also may be staple length or continuous, from polymers such as polyester which has a higher bonding temperature than a polyolefin such as polypropylene. As shown by the testing below, the relative proportion of bonding fibers and support fibers must be carefully chosen in order to yield a resultant web with the desired properties. Generally, a fibrous nonwoven web according to the present invention will contain from about 40 to about 90 weight percent bonding fibers based upon the total weight of the web and from about 10 to about 60 percent by weight support fibers based upon the total weight of the web.

The bonding fibers and staple fibers are blended together and then heated to a sufficiently high temperature and for a sufficient amount of time so that the bonding fibers at least partially bond to themselves at all or a portion of their crossover points to yield a resultant fibrous nonwoven web with the properties described herein.

One particularly well known and advantageous nonwoven web forming process suitable for use with the present invention is the bonded carded web forming process utilizing through- air bonding.

Bonded carded webs are made from staple fibers which are usually purchased in bales. The bales are placed in a picker which separates the fibers. Next, the fibers are sent through a combing or carding unit which further breaks apart and aligns the staple fibers in the machine direction so as to form a machine direction-oriented fibrous nonwoven web. Once the web has been formed, it is then bonded by

one or more of several bonding methods. One bonding method is powder bonding wherein a powdered adhesive is distributed through the web and then activated, usually by heating the web and adhesive. Another bonding method is pattern bonding wherein heated calender rolls or ultrasonic bonding equipment are used to bond the fibers together, usually in a localized bond pattern though the web can be bonded across its entire surface if so desired. The best method though for the present invention is through-air bonding. Through-air bonding uses a through-air bonder which does not unduly compress or collapse the structure during the bonding process. In through-air bonding, heated air is forced through the web to at least partially melt the bonding fibers and bond together the fibers at their crossover points. Typically the unbonded web is supported on a forming wire or drum. In addition a vacuum may be pulled through the web if so desired to further contain the fibrous web during the bonding process. The advantage of through air bonding over powder bonding is that an additional component, such as the powdered adhesive, is not needed which simplifies the process and reduces the overall cost of manufacture. As pointed out previously, pattern bonding is not suitable because it unduly compresses the fibers and resultant web.

When selecting the bonding conditions, the fibers of the, as yet, unbonded web should be heated to the bonding temperature of the bonding fibers but below the bonding temperature of the support fibers. To this end it should be appreciated that certain polymers are semi-crystalline in nature and, therefore, while still having a differential scanning calori etry (DSC) melting point, will also be sufficiently soft below this temperature so as to be able to bring about interfiber bonding between the crossover points of the bonding fibers. As a result, the "bonding temperature" will typically be a temperature obtained by the bonding fiber polymer, at least at its surface, that is

within the softening temperature range of the bonding polymer but less than or equal to the DSC melting point of the same polymer. More typically the bonding temperature will be between the DSC melting temperature of the bonding fiber and a temperature about 25°C less than the DSC melting temperature. The bonding temperature should also be at least about 25°C less than the lowest bonding temperature of the support fibers which should be regarded as their DSC melting points. Above the bonding temperature of the bonding fiber, the polymer will begin to flow and the bonding fiber will lose its fiber shape. Consequently, the bonding conditions should be designed so that this does not happen. This will be a function of the bonding air temperature, the air flow and the dwell time within the bonding unit. In selecting the bonding temperature, the conditions within the bonding unit (air temperature, hood pressure and dwell time) should be designed such that bonding is achieved between the bonding fibers while maintaining the integrity of the support fibers. To demonstrate the present invention, a number of sample materials were prepared some of which acted as controls. These sample materials as well as the test procedures used to evaluate them are set forth below.

TEST PROCEDURES

BASIS WEIGHT

The basis weight for each of the samples was determined in accordance with Federal Test Method 191A/5041. Sample sizes were 9 inches by 9 inches (22.9 centimeters by 22.9 centimeters) and a total of 8 samples were weighed and then averaged for each material. The values reported are for the average.

BULK fTHICKNESS) and BULK RECOVERY

Bulk which is a measure of thickness and bulk recovery were measured using an INSTRON or SINTECH tensile tester to

measure the resisting force as a material was compressed between a movable platen and a fixed base at a constant rate using a certain amount of force and subsequently releasing the force at the same rate. Preferably pressure, or force, and the platen pressure are recorded. If only force is recorded, pressure is calculated using the equation:

F x 10,000 cm ² /m ² p = reading A _p where:

^P r _eadi n _σ ⁼ P ^ressure reading from the SINTECH or INSTRON in pascals

F = force pushing back on the platen in pascals A = area of the platen in square centimeters (19.02 cm ² )

In performing the measurements, the base of the apparatus must be larger in size that the platen. Zero height between platen and base distance was set by bringing the platen down until it barely touched the base. The platen was then raised to the desired initial height from zero distance. The initial platen position must be greater than the initial thickness of the material so that the test starts out at zero pressure on the sample. The material can be the same size as the platen or larger.

A 4.92 centimeter diameter circular platen was used to compress materials against the fixed base at a rate of 5.00 mm/minute up to a maximum load of 13,790 pascals (2.0 psi) . The platen was then returned at the same rate to the initial starting position. The initial starting position for the platen was 13 millimeters from the base. Material samples were cut to 10.16 centimeter square shapes and tested in the center of the samples. Force and position data were recorded every 0.01 minutes or every 0.5 millimeters. Three samples were run for each material and

averaged. The values reported are for the averages. The same was also true for bulk recovery values.

Suitable equipment for this test could include: Compression Tester:

INSTRON model 6021 with compression test software and 1 kN load cell made by Instron of Bucks, England. Balance:

Mettler model PM4600 of Highstown, New Jersey To measure bulk or thickness, the following equation was used:

Bul (thickness) = x _Q - x where: x _Q = distance of initial platen position from the base in millimeters x - platen position from initial position in millimeters at a specific pressure, in this case 68.9 pascals Thus all bulk values reported were for samples while under a load or pressure of 68.9 pascals.

Percent Bulk Recovery in the dry state for the sample materials was calculated at 68.9 pascals (0.01 pounds per square inch) using the platen positions on the compression and recovery cycles when the pressure on the sample was 68.9 pascals. The formula used was as follows:

Recovered Bulk at 68.9 pascals

% Bulk Recovery = x 100

Initial Bulk at 68.9 pascals

DENSITY

The density of the materials was calculated by dividing the weight per unit area of a sample in grams per square meter (gsm) by the bulk of the sample in millimeters (mm) at 68.9 pascals and multiplying the result by 0.001 to convert the value to grams per cubic centimeter (g/cc) . A total of three samples were evaluated and averaged for the density values reported herein.

SURFACE AREA PER VOID VOLUME f5A/W)

Surface area per void volume was calculated by determining the fiber surface area in square centimeters per one gram of sample and dividing that by the void volume of the sample which is simply the inverse of density measured at 68.9 pascals. Surface area per void volume gives an indication of how much resistance liquid encounters as it passes through the web structure. SA/W can be thought of as being similar to the mesh size of a screen. A large SA/W means that the wires of the screen are closer together thus making the holes in the screen smaller. As the holes get smaller, it becomes more difficult for liquid to pass through the screen. For purposes of the present invention it is desirable to generate webs with low SA/W values so that liquid can pass through the web with relative ease. The data generated in conjunction with the Examples was based upon an average of three samples per Example.

The surface area of the fibers in a one gram sample of web material was calculated using the following equation: Surface Area (SA) per gram of web = 3363 x {(Fiber 1 Denier/Fiber 1 Density) ^0,5 x (1/Fiber 1 Denier) x Fiber 1 Weight % of Web} + 3363 x {(Fiber 2 Denier/Fiber 2 Density) ^0-5 x (1/Fiber 2 Denier) x Fiber 2 Weight % of Web}.

Surface Area per Void Volume (SA/W) was then calculated by dividing the SA by the W or, as stated above, mulriplying by the density of the web as follows:

SA/W = SA (cm ² /g) x Density of Web (g/cm ³ ) = SA/W in cm /cm ³ .

To illustrate the above calculations, the SA/W for Example 7 is set forth below.

The fibrous nonwoven web in Example 7 had the following properties:

Web Density = 0.022 g/cc Fiber 1 Diameter = 18.6 microns (μ) Fiber l Density = 0.9 g/cc Fiber 1 Weight % of Web = .70 Fiber 2 Diameter = 24.8 microns Fiber 2 Density = 1.38 g/cc Fiber 2 Weight % of Web = .30

SA = {3363 x (2.2/0.9) ⁰ ' ⁵ x (1/2.2) x .70} + {3363 x (6.0/1.38) ⁰ ' ⁵ X (1/6.0 X .30} = 2023.6 cm ² /g SA/W = SA x Density of Web = 2023.6 cm ² /g x 0.022 g/cm ³ = 44.6 cm ² /cm ³ .

MD TENSILE STRENGTH

The machine direction (MD) tensile strength of the sample materials was measured in accordance with ASTM D 5035-90 test method except that sample sizes were 7.6 centimeters by 15.2 centimeters with the machine direction of the sample running in a direction parallel to the longer dimension of the sample. A total of eight sample materials were tested and then averaged. The values reported are for the averages.

PERMEABILITY

Permeability (K) was calculated using the following equation:

K = 0.075 x R ² x (1-E) X (E/(l-E)) ² ' ⁵ where R = average fiber radius and E = web openness.

R was calculated as follows:

R = {(4 x (Weight % fiber 1)/ (Density of fiber 1) x (Specific surface area of the web) x 0.0001) + (4 x

(Weight % fiber 2) /(Density of fiber 2) x (Specific surface area of the web) x 0.0001) }/2.

The Specific Surface Area (SSA) of the web was calculated as follows:

SSA ={4 x (Weight % of fiber 1) /( (Micron diameter of fiber

1) x (Density of fiber 1) x 0.0001)} + {4 x (Weight % of fiber 2) /((Micron diameter of fiber 2) x (Density of fiber

2) x 0.0001) }. E was calculated as follows:

E = l-{(Web density) x (Weight % of fiber 1)/ (Density of fiber 1) - (Web density) x (Weight % of fiber 2) /(Density of fiber 2)}.

In all cases above, fiber 1 and fiber 2 are the support and bonding fibers respectively or vice versa. If more than two fibers are used, the equations can be expanded. This calculation assumes cylindrical fibers and that the web is at 100% saturation.

To demonstrate the use of the above equations, the permeability value was calculated for the web generated in

Example 7.

The fibrous nonwoven web in Example 7 had the following properties: Web Density = 0.022 g/cc

Fiber 1 Diameter = 18.6 microns (μ)

Fiber 1 Density = 0.9 g/cc

Fiber 1 Weight % of Web = .70

Fiber 2 Diameter = 24.8 microns Fiber 2 Density = 1.38 g/cc

Fiber 2 Weight % of Web = .30

Specific Surface Area (SSA) of the Web = {4 x .70/(18.6 x

0.9 X 0.0001)} + {4 x .30/(24.8 X 1.38 x 0.0001)} =

2023.27 cm ² /g R = {(4 X .70/(0.9 X 2023.27 X 0.0001) + (4 X .30/(1.38 X

2023.27 x 0.0001) }/2 = 9.8 microns

E = 1 - {(0.022 X .70/0.9) - (0.022 X .30/1.38)} = 0.9781

Therefore, the permeability (K) = 0.075 x 9.8 ² x (1 -

0.9781) X (0.9781/(1 - 0.9781) 2.5 = 2119 X

EXAMPLES

A total of 35 examples are set forth below. Examples 1 through 19 used non-bicomponent fibers. Examples 20 through 27 used bicomponent fibers and were generated as a point of comparison for the materials of the present invention. Based upon the results of Examples 1 through 27, a second set of examples were run to further define the present invention. Examples 28 through 35 used non- bicomponent fibers.

In Examples 1 through 19 through air bonded carded webs were made from varying weight percents of polypropylene (PP) staple fibers and polyester (PET) staple fibers. The polypropylene fibers were 38 millimeters long, 2.2 denier (18.6 micron diameter) Type 196 polypropylene staple fibers manufactured by Hercules Incorporated. The polymer for the polypropylene fibers had a density of 0.9 grams per cubic centimeter (g/cc) and a melting temperature of 162°C. The Type 196 polypropylene fiber has a uniform polymer composition along both its length and width. The fiber is believed to be oxidized on its exposed exterior surface so as to change the melt flow characteristics at that surface to facilitate bonding, nevertheless, the polypropylene composition is still consistent throughout the fiber. This fiber is extruded from a single polymer composition and then post-treated. This fiber is referred to by the manufacturer as a "skin/core" fiber but is distinguishable from, for example, a bicomponent fiber due to its uniform or consistent polymer composition. Such fiber technology may be taught by one or more of the following references each of which are incorporated herein by reference in their entirety: U.S. Patent No. 5,288,348 to Modrak; U.S. Patent No. 5,318,735 to Kozulla; European Patent Publication No. 0 445 536 A2 to Kozulla; and European Patent Publication No. 0 552 013 A2 to Gupta et al. The polyester fibers were 51 millimeter long, 6.0 denier (24.8 micron diameter) Type 295 polyester fibers manufactured by the Hoechst

- 13 -

Celanese Corporation. The polymer for the polyester fibers had a density of 1.38 grams per cubic centimeter and a melting temperature of 260°C. Both fibers were treated by the respective manufacturers to make the fibers more wettable. The two fibers were uniformly blended, carded and then through air bonded in the weight percents, based upon the total weight of the webs, and under the conditions set forth below with respect to each example.

EXAMPLE 1

In Example 1 a 49.2 gram per square meter (gs ) web was made from a uniformly mixed blend of 60 weight percent 2.2 denier polypropylene fibers and 40 weight percent 6.0 denier polyester fibers. Weight percents in this example and all other examples are based upon the total weight of the web. The web was bonded in a through air dryer at a line speed of 122 meters per minute at a temperature of 146°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 1.8 seconds. The resultant web had a bulk at 68.9 pascals of 1.88 millimeters (mm) , a bulk recovery of 87.8 percent, a density of 0.026 grams per cubic centimeter (g/cc) at 68.9 pascals, a surface area per void volume (SA/W) of 49.8 square centimeters per cubic centimeter (cm 2/cm3) at 68.9 pascals, a machine di.rection (MD) tensile strength of 3008 grams per 7.6 centimeters and a permeability of 1817 square microns (μ ) . The test results from Example 1 and all the examples are set forth in Table 1.

TABLE 1

ro O

Basis Bulk Bulk Density SA/W MD Permeability

Example Fibers Fiber

Ratio Weight Recovery Tensile

(%) (gsm) (mm) (%) (g/cc) (cm ² /cm ³ ) (g/76cm) (μ ² )

31 2 2PP/6 OPET 80/20 1 19 4 2 95 853 040 868 6435 745

32 2 2PP/6 0PET 90/10 110 9 2.36 88.2 .047 1066 6903 521

33 2 2PP 100/00 120 4 1.45 982 .083 198.5 8698 182

34 2 8PP/6 OPET 60/40 53 2 2.49 81.6 021 37.2 1214 2944

35 2.8PP/6.0PET 60/40 56 3 2.46 82.5 .023 38.9 1246 2650

EXAMPLE 2

In Example 2 a 97.3 gsm web was made from a uniformly mixed blend of 60 weight percent 2.2 denier polypropylene fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 147°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 4.166 mm, a bulk recovery of 88.4 percent, a density of 0.023 g/cc at 68.9 pascals, a surface area per void volume of 44.4 cm /cm at 68.9 pascals, an MD tensile strength of 4212 grams per 7.6 centimeters and a permeability of 2201 square microns.

EXAMPLE 3

In Example 3 a 100.7 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 146°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 3.785 mm, a bulk recovery of 85.2 percent, a density of 0.027 g/cc at 68.9 pascals, a surface area per void volume of 53.8 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 3912 grams per 7.6 centimeters and a permeability of 1539 square microns.

EXAMPLE 4

In Example 4 a 51.5 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 122 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time

within the dryer per unit area of web material was 1.8 seconds. The resultant web had a bulk at 68.9 pascals of 2.134 mm, a bulk recovery of 83.3 percent, a density of 0.024 g/cc at 68.9 pascals, a surface area per void volume of 48.8 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 3706 grams per 7.6 centimeters and a permeability of 1850 square microns.

EXAMPLE 5 In Example 5 a 95.0 gsm web was made from 100 weight percent 2.2 denier polypropylene fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 1.070 mm, a bulk recovery of 84.1 percent, a density of 0.089 g/cc at 68.9 pascals, a surface area per void volume of 212.2 cm ² /cm ³ at 68.9 pascals, a permeability of 161 square microns and an MD tensile strength of 2708 grams per 7.6 centimeters.

EXAMPLE 6

In Example 6 a 51.2 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 122 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 1.8 seconds. The resultant web had a bulk at 68.9 pascals of 3.175 mm, a bulk recovery of 82.4 percent, a density of 0.016 g/cc at 68.9 pascals, a surface area per void volume of 32.6 cm /cm ³ at 68.9 pascals, an MD tensile strength of 3346 grams per 7.6 centimeters and a permeability of 3469 square microns.

EXAMPLE 7

In Example 7 a 49.8 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 122 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 1.8 seconds. The resultant web had a bulk at 68.9 pascals of 2.261 mm, a bulk recovery of 86.5 percent, a density of 0.022 g/cc at 68.9 pascals, a surface area per void volume of 44.6 cm /cm ³ at 68.9 pascals, an MD tensile strength of 3248 grams per 7.6 centimeters and a permeability of 2119 square microns.

EXAMPLE 8

In Example 8 a 51.2 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 122 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 1.8 seconds. The resultant web had a bulk at 68.9 pascals of 1.422 mm, a bulk recovery of 85.7 percent, a density of 0.036 g/cc at 68.9 pascals, a surface area per void volume of 72.9 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 4785 grams per 7.6 centimeters and a permeability of 971 square microns.

EXAMPLE 9

In Example 9 a 67.8 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 99 meters per minute at a temperature of I46°c and at an air flow hood pressure of 498 pascals. The dwell time

within the dryer per unit area of web material was 2.2 seconds. The resultant web had a bulk at 68.9 pascals of 2.261 mm, a bulk recovery of 85.4 percent, a density of 0.030 g/cc at 68.9 pascals, a surface area per void volume of 60.7 cm 2/cm3 at 68.9 pascals, an MD tensile strength of 5190 grams per 7.6 centimeters and a permeability of 1304 square microns.

EXAMPLE 10 In Example 10 a 67.8 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 99 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 2.2 seconds. The resultant web had a bulk at 68.9 pascals of 2.921 mm, a bulk recovery of 86.1 percent, a density of 0.023 g/cc at 68.9 pascals, a surface area per void volume of 47.0 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 3970 grams per 7.6 centimeters and a permeability of 1977 square microns.

EXAMPLE 11 In Example 11 a 68.2 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 99 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 2.2 seconds. The resultant web had a bulk at 68.9 pascals of 3.150 mm, a bulk recovery of 81.4 percent, a density of 0.022 g/cc at 68.9 pascals, a surface area per void volume of 43.8 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 4104 grams per 7.6 centimeters and a permeability of 2119 square microns.

EXAMPLE 12

In Example 12 an 81.7 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 76 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 2.9 seconds. The resultant web had a bulk at 68.9 pascals of 3.962 mm, a bulk recovery of 81.4 percent, a density of 0.021 g/cc at 68.9 pascals, a surface area per void volume of 41.7 cm 2/cm3 at 68.9 pascals, an MD tensile strength of 4692 grams per 7.6 centimeters and a permeability of 2278 square microns.

EXAMPLE 13

In Example 13 an 86.8 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 53 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 4.l seconds. The resultant web had a bulk at 68.9 pascals of 3.480 mm, a bulk recovery of 89.0 percent, a density of 0.025 g/cc at 68.9 pascals, a surface area per void volume of 50.5 cm /cm ³ at 68.9 pascals, an MD tensile strength of 5291 grams per 7.6 centimeters and a permeability of 1736 square microns.

EXAMPLE 14

In Example 14 a 119.7 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 53 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time

within the dryer per unit area of web material was 4.1 seconds. The resultant web had a bulk at 68.9 pascals of 5.156 mm, a bulk recovery of 85.7 percent, a density of 0.023 g/cc at 68.9 pascals, a surface area per void volume of 47.0 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 4241 grams per 7.6 centimeters and a permeability of 1977 square microns.

EXAMPLE 15 In Example 15 a 125.1 gram per square meter (gsm) web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 53 meters per minute at a temperature of 146°C and at an air flow hood pressure of 498 pascals. The dwell time within the dryer per unit area of web material was 4.1 seconds. The resultant web had a bulk at 68.9 pascals of 5.207 mm, a bulk recovery of 84.4 percent, a density of 0.024 g/cc at 68.9 pascals, a surface area per void volume of 48.6 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 4601 grams per 7.6 centimeters and a permeability of 1850 square microns.

EXAMPLE 16 In Example 16 a 28.8 gram per square meter (gsm) web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 145 meters per minute at a temperature of 144.8°C and at an air flow hood pressure of 298 pascals. The dwell time within the dryer per unit area of web material was 1.6 seconds. The resultant web had a bulk at 68.9 pascals of 1.73 mm, a bulk recovery of 82.3 percent, a density of 0.017 g/cc at 68.9 pascals, a surface area per void volume of 33.7 cm /cm ³ at 68.9 pascals, an MD tensile strength of 1393 grams per 7.6 centimeters and a permeability of 3159 square microns.

EXAMPLE 17

In Example 17 a 35.3 gram per square meter (gsm) web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 145 meters per minute at a temperature of 145°C and at an air flow hood pressure of 298 pascals. The dwell time within the dryer per unit area of web material was 1.6 seconds. The resultant web had a bulk at 68.9 pascals of 1.88 mm, a bulk recovery of 79.7 percent, a density of 0.019 g/cc at 68.9 pascals, a surface area per voi •d volume of 38.0 cm2/cm3 at 68.9 pascals, an MD tensile strength of 1653 grams per 7.6 centimeters and a permeability of 2660 square microns.

EXAMPLE 18

In Example 18 a 40.7 gram per square meter (gsm) web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 145 meters per minute at a temperature of 145°C and at an air flow hood pressure of 298 pascals. The dwell time within the dryer per unit area of web material was 1.6 seconds. The resultant web had a bulk at 68.9 pascals of 2.21 mm, a bulk recovery of 83.9 percent, a density of 0.018 g/cc at 68.9 pascals, a surface area per void volume of 37.3 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 1802 grams per 7.6 centimeters and a permeability of 2893 square microns.

EXAMPLE 19

In Example 19 a 41.7 gram per square meter (gsm) web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 145 meters per minute at a temperature of 145. °C and at an air flow hood pressure of

298 pascals. The dwell time within the dryer per unit area of web material was 1.6 seconds. The resultant web had a bulk at 68.9 pascals of 1.93 mm, a bulk recovery of 82.9 percent, a density of 0.022 g/cc at 68.9 pascals, a surface area per void volume of 43.7 cm 2/cm3 at 68.9 pascals, an MD tensile strength of 2158 grams per 7.6 centimeters and a permeability of 2119 square microns.

COMPARATIVE EXAMPLES In examples 20 through 27 a series of comparative examples were prepared and tested. In each of the comparative examples, the 2.2 denier polypropylene fibers were replaced with a concentric sheath/core bicomponent fiber as the bonding or lower melting point fiber. The bicomponent fibers used included 1.7 denier (17 micron diameter) and a 3.0 denier (21 micron diameter) ESC polyethylene (PE) sheath/polypropylene (PP) core bicomponent staple fibers manufactured by the Chisso Corporation of Osaka, Japan. The 1.7 denier and 3.0 denier fibers both had a length of 38 millimeters and an average density of 0.925 grams per cubic centimeter. Both fibers were treated by the manufacturer with a surfactant to make them more wettable. The polyester (PET) fiber was the same as that used in Examples 1 through 19. The carding and bonding equipment used were also the same as that for the previous examples.

EXAMPLE 20

In Example 20 a 46.5 gsm web was made from a uniformly mixed blend of 60 weight percent 3.0 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 137 meters per minute at a temperature of 130°C and at an air flow hood pressure of 423 pascals. The dwell time within the dryer per unit area of web material was 1.6 seconds. The resultant web had a bulk at 68.9 pascals of 3.023 mm, a bulk recovery of 78.1

percent, a density of 0.015 g/cc at 68.9 pascals, a surface area per void volume of 25.8 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 3883 grams per 7.6 centimeters and a permeability of 5418 square microns.

EXAMPLE 21

In Example 21 a 121.1 gsm web was made from a uniformly mixed blend of 60 weight percent 3.0 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 130°C and at an air flow hood pressure of

448 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 7.620 mm, a bulk recovery of 84.7 percent, a density of 0.016 g/cc at 68.9 pascals, a surface area per void volume of 26.7 cm ² /c at 68.9 pascals, an MD tensile strength of 9086 grams per 7.6 centimeters and a permeability of 4906 square microns.

EXAMPLE 22

In Example 22 a 121.4 gsm web was made from a uniformly mixed blend of 60 weight percent 3.0 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 130°C and at an air flow hood pressure of

448 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 4.623 mm, a bulk recovery of 83.5 percent, a density of 0.026 g/cc at 68.9 pascals, a surface area per void volume of 44.1 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 13009 grams per 7.6 centimeters and a permeability of 2312 square microns.

EXAMPLE 23

In Example 23 a 150.2 gsm web was made from a uniformly mixed blend of 60 weight percent 3.0 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 53 meters per minute at a temperature of 130°C and at an air flow hood pressure of 448 pascals. The dwell time within the dryer per unit area of web material was 4.1 seconds. The resultant web had a bulk at 68.9 pascals of 4.166 mm, a bulk recovery of 87.2 percent, a density of 0.036 g/cc at 68.9 pascals, a surface area per voi •d volume of 60.5 cm2/cm3 at 68.9 pascals, an MD tensile strength of 13094 grams per 7.6 centimeters and a permeability of 1385 square microns.

EXAMPLE 24

In Example 24 a 151.2 gsm web was made from a uniformly mixed blend of 60 weight percent 3.0 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 53 meters per minute at a temperature of 130°C and at an air flow hood pressure of 448 pascals. The dwell time within the dryer per unit area of web material was 4.1 seconds. The resultant web had a bulk at 68.9 pascals of 7.010 mm, a bulk recovery of 81.9 percent, a density of 0.022 g/cc at 68.9 pascals, a surface area per void volume of 36.2 cm /cm ³ at 68.9 pascals, an MD tensile strength of 6668 grams per 7.6 centimeters and a permeability of 3000 square microns.

EXAMPLE 25

In Example 25 a 42.7 gsm web was made from a uniformly mixed blend of 60 weight percent 3.0 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 137 meters per minute at a temperature of 130°C and at an air flow hood pressure of

423 pascals. The dwell time within the dryer per unit area of web material was 1.6 seconds. The resultant web had a bulk at 68.9 pascals of 2.972 mm, a bulk recovery of 76.9 percent, a density of 0.014 g/cc at 68.9 pascals, a surface area per void volume of 24.1 cm 2/cm3 at 68.9 pascals, an MD tensile strength of 3612 grams per 7.6 centimeters and a permeability of 6023 square microns.

EXAMPLE 26 In Example 26 a 122.8 gsm web was made from a uniformly mixed blend of 60 weight percent 1.7 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 53 meters per minute at a temperature of 131°C and at an air flow hood pressure of 324 pascals. The dwell time within the dryer per unit area of web material was 4.1 seconds. The resultant web had a bulk at 68.9 pascals of 4.801 mm, a bulk recovery of 82.5 percent, a density of 0.026 g/cc at 68.9 pascals, a surface area per void volume of 53.1 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 16,212 grams per 7.6 centimeters and a permeability of 1511 square microns.

EXAMPLE 27

In Example 27 a 119.0 gsm web was made from a uniformly mixed blend of 60 weight percent 1.7 denier polyethylene sheath/polypropylene core fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 53 meters per minute at a temperature of 131°C and at an air flow hood pressure of 324 pascals. The dwell time within the dryer per unit area of web material was 4.1 seconds. The resultant web had a bulk at 68.9 pascals of 3.175 mm, a bulk recovery of 88.8 percent, a density of 0.037 g/cc at 68.9 pascals, a surface area per void volume of 77.8 cm /cm at 68.9 pascals, an MD

tensile strength of 20,308 grams per 7.6 centimeters and a permeability of 867 square microns.

ADDITIONAL EXAMPLES When comparing data from Example 5 (100% polypropylene fibers) to Examples 1 through 4 and to Examples 6 through 19 (blends of polypropylene and polyester fibers) some trends were seen where bulk, density, surface area per void volume, machine direction tensile strength, and permeability were dependent upon the polypropylene fiber content in the web. As the polypropylene fiber content was increased, the bulk decreased, the density increased, the surface area per void volume increased, the MD tensile strength increased and the permeability decreased. To further demonstrate such a dependency, additional examples were made where bonding conditions and basis weights were held essentially constant while the polypropylene bonding fiber content was changed from 40% to 80%, 90% and 100% of the total web composition.

EXAMPLE 28

In Example 28 a 128.9 gsm web was made from a uniformly mixed blend of 40 weight percent 2.2 denier polypropylene fibers and 60 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 147°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 7.54 mm, a bulk recovery of 77.8 percent, a density of 0.017 g/cc at 68.9 pascals, a surface area per void volume of 28.3 cm 2/cm3 at 68.9 pascals, an MD tensile strength of 2899 grams per 7.6 centimeters and a permeability of 4450 square microns.

EXAMPLE 2 9

Example 29 was the same fiber composition as the material as in Example 2 and was included again to provide a transition point from the 40% polypropylene content to the 100% polypropylene content. In this example a 97.3 gsm web was made from a uniformly mixed blend of 60 weight percent 2.2 denier polypropylene fibers and 40 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 147°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 4.166 mm, a bulk recovery of 88.4 percent, a density of 0.023 g/cc at 68.9 pascals, a surface area per void volume of 44.4 cm /cm ³ at 68.9 pascals, an MD tensile strength of 4212 grams per 7.6 centimeters and a permeability of 2201 square microns.

EXAMPLE 30 Example 30 had the same fiber composition as the material in Example 3 and was included to provide a transition point from the 40% polypropylene content to the 100% polypropylene content. In this example a 100.7 gsm web was made from a uniformly mixed blend of 70 weight percent 2.2 denier polypropylene fibers and 30 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 147°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 3.785 mm, a bulk recovery of 85.2 percent, a density of 0.027 g/cc at 68.9 pascals, a surface area per void volume of 53.8 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 3912 grams per 7.6 centimeters and a permeability of 1539 square microns.

EXAMPLE 3 1

In Example 31 a 119.4 gsm web was made from a uniformly mixed blend of 80 weight percent 2.2 denier polypropylene fibers and 20 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 147°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 2.95 mm, a bulk recovery of 85.3 percent, a density of 0.040 g/cc at 68.9 pascals, a surface area per void volume of 86.8 cm ² /cm at 68.9 pascals, an MD tensile strength of 6435 grams per 7.6 centimeters and a permeability of 745 square microns.

EXAMPLE 32

In Example 32 a 110.9 gsm web was made from a uniformly mixed blend of 90 weight percent 2.2 denier polypropylene fibers and 10 weight percent 6.0 denier polyester fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 147°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was. 3.6 seconds. The resultant web had a bulk at 68.9 pascals of 2.36 mm, a bulk recovery of 88.2 percent, a density of

0.047 g/cc at 68.9 pascals, a surface area per void volume of 106.6 cm /cm ³ at 68.9 pascals, an MD tensile strength of 6903 grams per 7.6 centimeters and a permeability of 521 square microns.

EXAMPLE 33

In Example 33 a 120.4 gsm web was made from 100 weight percent 2.2 denier polypropylene fibers. The web was bonded in a through air dryer at a line speed of 61 meters per minute at a temperature of 147°C and at an air flow hood pressure of 622 pascals. The dwell time within the dryer per unit area of web material was 3.6 seconds. The

resultant web had a bulk at 63.9 pascals of 1.45 mm, a bulk recovery of 98.2 percent, a density of 0.083 g/cc at 68.9 pascals, a surface area per void volume of 198.5 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 8698 grams per 7.6 centimeters and a permeability of 182 square microns.

EXAMPLE 34

In Example 34 a 53.2 gsm web was made from a uniformly mixed blend of 60 weight percent 2.8 denier (21.0 micron diameter) by 38 millimeter long Type-182 Red 516 polypropylene staple fibers from Hercules Incorporated and 40 weight percent 6.0 denier polyester fibers. The polyester fibers were the same as the polyester fibers used in the other examples. The polypropylene staple fibers had a uniform polymer composition along both their length and width but had not been oxidized on their exterior surfaces as with the polypropylene fibers in the previous examples thus demonstrating that the phenomenon of the present invention is not specific to a single polyolefin fiber. The web was bonded in a through air dryer at a line speed of 15 meters per minute at a temperature of 150 degrees Celsius and at an air flow hood pressure of 199 pascals. The dwell time within the dryer per unit area of web material was 2.4 seconds. The resultant web had a bulk at 68.9 pascals of 2.49 mm, a bulk recovery of 81.6 percent, a density of 0.021 g/cc at 68.9 pascals, a surface area per void volume of 37.2 cm ² /cm ³ at 68.9 pascals, an MD tensile strength of 1214 grams per 7.6 centimeters and a permeability of 2944 square microns.

EXAMPLE 35

In Example 35 a 56.3 gsm web was made from a uniformly mixed blend of 60 weight percent 2.8 denier (21.0 micron diameter) by 38 millimeter long Type-182 Blue 206 polypropylene staple fibers from Hercules Incorporated and 40 weight percent 6.0 denier polyester fibers. The polyester fibers were the same as the polyester fibers used

in the other examples. The polypropylene staple fibers had a uniform polymer composition along both their length and width but had not been oxidized on their exterior surfaces as with the polypropylene fibers in the previous examples thus demonstrating that the phenomenon of the present invention is not specific to a single polyolefin fiber. The web was bonded in a through air dryer at a line speed of 15 meters per minute at a temperature of 150 degrees Celsius and at an air flow hood pressure of 199 pascals. The dwell time within the dryer per unit area of web material was 2.4 seconds. The resultant web had a bulk at 68.9 pascals of 2.46 mm, a bulk recovery of 82.5 percent, a density of 0.023 g/cc at 68.9 pascals, a surface area per void volume of 38.9 cm /cm at 68.9 pascals, an MD tensile strength of 1246 grams per 7.6 centimeters and a permeability of 2650 square microns.

COMPARISONS

When physical property values from Examples 28 through 33 were plotted in Figures 2 through 6, it can be seen that as the weight percent of polypropylene fiber increased, the bulk of the web decreased. See Figure 2. The decrease in bulk was a direct result of the reduction in the amount of support fibers in the web which, in these examples, were the polyester fibers. The bulk of the web directly affects other physical property values such as density, surface area per void volume and permeability.

Referring to Figure 3, it can be seen that as the proportions of polypropylene bonding fibers increased, density also increased. For uses such as those outlined herein, it has been determined that density values below about 0.010 g/cc yield a web which is too open and fails to control liquids. At densities above about 0.060 g/cc the resultant web is too dense which in turn retards liquid intake and permeability. In Figure 4, Surface Area per Void Volume is plotted relative to the amount of bonding

fiber. Here again to ensure adequate liquid intake and permeability, the SA/W should be less than about 125 cm ² /c and more desirably less than 70 cm ² /cm ³ . As a result, webs with bonding fiber contents approaching 100 percent will not meet this criterion.

Figure 5 shows MD tensile strength as a function of bonding fiber content. ith the target 120 gsm webs of Examples 28 through 33, it was possible to achieve MD tensile strengths in excess of 2000 g/7.6 cm. In addition, as shown by Example 16, even with basis weights in the range of 28 gsm it was possible to achieve MD tensile values in excess of 1000 g/7.6 cm.

The effect of bonding fiber content on permeability is shown in Figure 6 of the drawings. For purposes of the present invention, permeabilities in excess of about 400 square microns are desired. Here again it can be seen that webs with 100 percent bonding fibers will not meet this criterion. To obtain a lofty fibrous nonwoven web that conforms to the specific set of properties of the present invention, it is therefore necessary to control the amount of bonding fibers present in the web to a weight percent level of from about 40 to about 90 percent of the total weight of fibers in the web.

Thus, when evaluating the above data, when the weight percent of the bonding fibers went above 90 weight percent, the surface area per void volume necessary for the present invention became too high, greater than 125 square centimeters per cubic centimeter. In addition, at bonding fiber weight percents above 90 percent the density was too high, greater than about 0.060 grams per cubic centimeter. Conversely, when the weight percent of the bonding fibers went too low, below about 40 percent, then the strength of the resultant web was not high enough for the needs of the present invention. Thus it can be seen that the amount of

bonding fibers critically affects the properties of the web according to the present invention at either end of the weight percent spectrum. Too much bonding fiber creates a material that is too dense, especially for such applications as outlined above including personal care absorbent articles. Too little bonding fiber and the web material becomes too weak.

Another interesting point to note is the ability of the fibrous nonwoven webs of the present invention to yield properties in the same range as that of bicomponent- containing fibrous nonwoven webs. Comparing, for example, the data from Example 6 with that of Example 20, it can be seen that two similar basis weight webs can be formed which both exhibit good physical properties. The web according to the present invention (Example 6) had a basis weight of

51.2 gsm compared to a basis weight of 46.5 gsm for the bicomponent web of Example 20. Bulk, bulk recovery, density and SA/W values were all quite similar with the only real degree in variability being in the permeability values. Thus it can be seen that cost effective webs can be made which will compete with the more expensive bicomponent-containing webs.

Having thus described the invention in detail, it should be apparent that various modifications and changes can be made to the process and materials of the present invention without departing from the spirit and scope of the following claims.