WO2000030581A1

WO2000030581A1 - Disposable diaper having elastic side panels

Info

Publication number: WO2000030581A1
Application number: PCT/US1998/025171
Authority: WO
Inventors: Martin A. Allen; John T. Fetcko
Original assignee: Nordson Corporation
Priority date: 1998-11-24
Filing date: 1998-11-24
Publication date: 2000-06-02
Also published as: AU1702899A

Abstract

A form fitting diaper (10) comprises a backsheet (11) having a front section (12), a back section (13), and a crotch section (14), and has bonded thereto an absorbent layer (15). The diaper (10) further comprises a pair of elastic side panels (16, 17) bonded between the front and back sections (12, 13), of the backsheet (11) and define therewith a circumferentially continuous and elastic waist, and further defining leg openings (21, 22). The side panels (16, 17) having substantially unidirectional elasticity whereby the panels (16, 17) are elastic in the circumferential direction and substantially inelastic in the direction perpendicular thereto. The side panels (16, 17) being of composite construction comprising an elastomeric layer (34) with a unidirectionally elastic nonwoven layer (32 or 33) bonded thereto.

Description

DISPOSABLE DIAPER HAVING ELASTIC SIDE PANELS

This invention relates generally to form fitting diapers or

garments containing elastic panels. In one aspect, the invention relates to a

diaper containing an elastic panel of a composite comprising (a) an

elastomeric layer and (b) an elastic nonwoven web composed of nonelastic

fibers.

Modern diapers must possess many qualities: they must be

disposable, comfortable, form fitting, and have a pleasing appearance and

feel (e.g. hand). The form fitting requirement has led to the use of elastic

panels in diapers. Examples include elastic strips in the waist band and leg.

A recent use of elastic panels are side panels used in "pull-up" or "training"

diapers.

U.S. Patent 4,938,753 discloses a training diaper provided

with elastic side panels. The side panels comprise an elastomeric layer

flanked by nonelastic nonwovens.

An article entitled "Stretchable Fabric Technology Options",

Nonwovens World. Spring 1994 (pages 49-56), describes various elastic

fabrics for use in disposable products.

Thermoplastic elastomers have been used in many

applications, and while they possess the necessary elastic properties, they

have a rubbery or plastic appearance and/or hand. Nonwovens are widely

used in disposable products. These materials have a cloth-like appearance

and are comfortable, but are generally inelastic and therefore are not form

fitting. Efforts to combine nonwovens and elastomerics are disclosed

in U.S. Patent Nos. 4,720,415; 4,652,487; and 4,657,802. These patents

disclose processes wherein the elastomeric film is stretched and thermally

or adhesively bonded to an elastomeric web whereby, upon release of the

tension, the elastomeric web contracts and the inelastic web gathers or

ruffles between the bond areas.

Recent developments in "stretchable" nonwovens of the type

disclosed in U.S. Patent No. 5,244,482 exhibit some elasticity, but not

enough for many applications. Moreover, these fabrics do not exhibit

sufficient "elongation-at-break". This patent discloses that the stretchable

nonwoven web may be used in combination with other webs or substrates

such as webs from elastomeric polymers without specifying any end-use

products for these composites. U.S. Patent No. 5,244,482 also discloses

the heat stretching of composites (e.g. spunbond PP/meltdown

PP/spunbond PP) composed of inelastic fibers (PP) to impart unidirectional

elasticity thereto.

U.S. Patent No. 5,226,992 discloses a method for forming a

composite of an inelastic web and an elastic sheet. In this process an

inelastic web is stretched in one direction to cause the web to neck down in

the direction perpendicular to stretch. An elastomeric sheet is then bonded

to the fabric while it is in the necked position. Upon release of the tension

on the necked fabric, it assumes the dimensions of the elastomeric sheet.

Stretching the elastomeric sheet in the direction of necking (perpendicular to

the direction of stretch) permits the nonelastic fabric to stretch in that direction to its original size. It can be seen that the methods of U.S. Patent

No. 5,226,992 have certain disadvantages. The necked-down fabric with

an elastomeric sheet is difficult to manufacture because of the need to bond

the elastomeric sheet to the fabric under stressed or stretched conditions.

U.S. Patent No. 5,306,545 discloses a meltdown nonwoven

fabric formed by meltblowing an ethylene and olefin copolymer. The

density and crystallinity of the copolymer are controlled so as to optimize

the elasticity of the fabric. The resulting fabric exhibits elasticity in both

the lateral and vertical directions. The degree of elasticity is relatively small

(e.g. 10%) and the fabric exhibits some residual elongation when stretched.

The aforementioned U.S. Patent discloses that the copolymer may be used

in blends (such as with PP) for improved softness. The patent further

teaches that the elastic fabric may be layered with other fabrics to form

laminates, which may be useful in medical applications such as flexible

bandages.

SUMMARY OF THE INVENTION

The form-fitting diaper of the present invention comprises a

diaper backsheet having a front section and a back section, an absorbent

material positioned on an internal surface of the backsheet, and elastic side

panels interconnecting the front and back sections of the backsheet. Each

elastic side panel is a composite which includes dissimilar layers that are

bonded together. Briefly, each composite elastic side panel is a two-layer or

three-layer composite comprising:

(a) an elastomeric layer, preferably an elastomeric film; and

(b) at least one layer (in the two-layer composite) or two

layers (in the three-layer composite) of an elastic

nonwoven web bonded to the elastomeric layer.

Preferably, the composite comprises two layers of an elastic

nonwoven web bonded to opposite sides of the elastomeric layer. In both

embodiments the elastic nonwoven web is composed of nonelastic

thermoplastic fibers and possesses unidirectional elasticity.

The preferred three-layer side panel comprises a core

elastomeric layer bonded between two elastic nonwoven layers. The

composite possesses cloth-like appearance and hand and yet exhibits

unidirectional elasticity. These two properties make the composite ideal for

form-fitting diapers.

As discussed in more detail below, the elastic nonwoven useful

in the side panels is made by thermomechanically processing a normally

nonelastic nonwoven web to impart unidirectional elasticity thereto.

Although the elastic composite can be made by a variety of

processes, the preferred process involves the steps of:

(a) passing two of the layers under a hot melt dispenser to

apply an adhesive to one side thereof; and (b) bringing the coated two layers into contact with the

third layer in the nip of counterrotating pressure rolls

whereby they are pressure bonded together.

In a preferred embodiment, the elastomeric layer is made of a

thermoplastic elastomer (e.g., elastomeric film), and the nonwoven layers

are of meltblown polyolefin. The film imparts strong elasticity to the

composite, and the meltblown polyolefin imparts unidirectional elasticity as

well as a pleasing hand and appearance to the composite. In use, the inner

nonwoven polyolefin layer of the diaper side panels will be in contact with

the skin of the wearer. Because the meltblown polyolefin is porous, it

provides a good degree of breatheability for added comfort to the wearer.

When made in accordance with the process described herein,

the side panel composite will have elasticity in the cross-direction, but not

the machine direction. The unidirectional stretch of the composite is an

advantageous feature for the side panels in "pull up" diapers. The

composite is bonded to the front and back sections of the backsheet to

permit the joined sections to be stretched apart (circumferentially) during

fitting (e.g. pull up). The panels, however, are not stretchable in a direction

normal to the circumference of the diaper so that the wearer of the diaper

can pull the diaper up (without stretch) by gripping the side panels and

pulling vertically.

The three-layer composite is preferred over the two-layer

composite because the nonwoven layers are either in contact with the body

or exposed, giving the diaper comfort and a pleasing cloth-like appearance. However, in certain applications the two-layer composite will suffice. Both

the two-layer composite and the three-layer composite exhibit the

stretchability properties necessary for use in the diaper of the present

invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a form fitting diaper

constructed according to the present invention.

Figure 2 is a cross-section of the front panel of the diaper

shown in Figure 1 .

Figure 3 is a schematic illustrating the laminating apparatus for

forming an elastic composite useful in the diaper of the present invention.

Figure 4 is a longitudinal sectional view of an elastic composite

useful in the diaper of the present invention.

Figure 5 is a top plan view of the composite shown in Figure 4

illustrating its unidirectional elasticity.

Figure 6 is a stress/strain diagram illustrating the elasticity of

the composite used in the diapers of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to fully appreciate the present invention, it is

necessary to understand certain terms used in this specialized art.

Accordingly, terms used to characterize certain features of the present

invention are defined below. Definitions:

The term "elasticity" refers to material capable of recovering

its original shape partially (at least 40%) or completely after the deforming

force has been removed.

The term "elastic" means a material which exhibits elasticity

and includes elastomers and fabrics of inelastic fibers in which the fabric

has been processed to impart elasticity thereto.

The term "elastomers" means elastomeric polymers that have

the ability to be stretched to at least twice their original length and to

retract very rapidly to approximately their original length when released.

Elastomeric polymers include the synthetic thermosetting and thermoplastic

polymers which have properties similar to those of vulcanized rubber such

as styrene butadiene copolymer, polychloroprene (neoprene), nitrile rubber,

butyl rubber, polysulfide rubber, cis-i4-polyisoprene, polybutadiene,

ethylene-propylene terpolymers (EPDM), silicone rubber, polyurethane

rubber, polyamide elastomers, EVA and EMA elastomers, and the styrene

triblock copolymers.

The preferred elastomers for use in the present invention are

the styrene triblock copolymers such as styrene-butadiene-styrene block

copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and

styrene-hydrogenated butadiene-styrene block copolymer (SEBS).

The terms "fibers" and "filaments" as used herein are

interchangeable to mean a solid having an extremely high ratio of length to

diameter. Thermoplastic fibers and filaments are made by extruding the thermoplastic from a spinneret, typically by spunbond or meltblowing

processes. These processes are well known to those skilled in the art and

are described in U.S. Patent No. 5,244,482, the disclosure of which is

incorporated herein by reference.

The term "nonwovens" means fabrics made from

thermoplastic fibers mechanically positioned in a random manner to form a

layer or sheet, and include spunbond fabrics, meltblown fabrics, carded

fibers, and spunlaced. These fabrics are often referred to as nonwoven

webs. The fibers used in the nonwovens are microsized ranging from 0.5

to 50 microns depending on the intended use of the web.

The term "inelastic fibers" or nonelastic fibers" means fibers

which when stretched along their length do not exhibit elasticity.

The term "inelastic nonwoven web" or "nonelastic nonwoven

web" means that the nonwoven web does not exhibit elasticity.

The term "elastic recovery" means the percentage to which a

specimen recovers its original length measured immediately following a

given percent elongation. For example, a recovery of 90% indicates that

the material will be 10% longer following the application and removal of a

deforming force.

The term "draw ratio" refers to stretch (from original shape)

imposed on a material in a given direction. Form Fitting Diaper Construction:

As shown in Figures 1 and 2, a diaper 10 constructed

according to the present invention is in the form of a ready-to-wear body

garment comprises a backsheet 1 1 having a front section 1 2, a back

section 13, a crotch section 14 interconnecting sections 1 2 and 1 3, an

absorbent layer 1 5, and elastic side panels 1 6 and 1 7. Elastic side panels

1 6 and 17 are bonded to the lateral edges of front section 1 2 and back

section 13 as at 20a and 20b for panel 1 7, and 20c and 20d for panel 1 6.

The absorbent layer 1 5 may be bonded to the lateral edges of the front and

back sections of the backsheet 1 1 . As shown in Figure 2, nonwoven inner

layer 18 covers absorbent layer 1 5 and its outer periphery may have its

edges bonded or glued to the backsheet 1 1 as at 19 to completely encase

the absorbent layer 1 5. The absorbent layer 1 5 with its encasing

nonwoven layer 18 will traverse the front section 1 2, crotch section 14,

and back section 1 3 of the backsheet 1 1 . The outline 1 5a of the absorbent

layer 1 5 on the front section 1 2 can be seen in Figure 1 .

The elastic side panels 1 6 and 1 7 in combination with crotch

section 14 of the backsheet 1 1 define leg openings 21 and 22 as illustrated

in Figure 1 . Backsheet 1 1 may have an hourglass shape to better conform

to the body of the diaper wearer.

Optionally, the diaper may include front and back elastic bands

24 and 25 in the waist area and secured to the backsheet 1 1 ; and elastic

leg bands 27 and 28 secured to backsheet 1 1 and surrounding a lower

portion of each leg opening 21 and 22. The waist bands 24 and 25 in combination with upper edge portions 29 and 30 of side panels 16 and 17

define a circumferential diaper waist 26.

The backsheet, absorbent, and elastic bands may be

constructed according to techniques well known in the art and described at

length in the literature. For example, the backsheet may be made of a

polyolefin film such as polypropylene or may be a composite of a polyolefin

film and a nonwoven cover bonded thereto. The absorbent may be made of

cellulosic material with or without a gelling agent. The bands may be made

of elastic strips or elastomerics as described in the aforementioned U.S.

Patent Nos. 4,720,415 or 5,226,992.

The novelty of the form fitting diaper constructed according to

the present invention resides in the composition of the elastic side panels

16 and 17.

As shown in Figure 4, the composite 31 of the present

invention preferably comprises three layers 32, 33, and 34 bonded together

by adhesive layers 35 and 36 at the layer interfaces. As indicated above, in

some uses the composite may comprise only one of the nonwoven layers

32 or 33.

Layer 34 is an elastomer and layers 32 and 33 are stretchable

or elastic nonwovens made from nonelastic thermoplastic fibers.

Elastomeric layer 34 adds strength to the side panels which may be

stretched to a large degree when the diaper is put on or taken off. The

nonwoven layers 32 and 33 provide unidirectional elasticity, softness and

breatheability to the diaper for comfort. Elastomeric Layer:

The layer of elastomer 34 may be made from any elastomeric

web or sheet, but is preferably made from extruded film or meltblown web

consisting of thermoplastic elastomers.

The extrusion of elastomers to form film and meltblown fabrics

is well known in the industry. Thermoplastic elastomers (described above)

preferably include the styrene based block copolymers incorporating

butadiene or isoprene as the aliphatic chain segment, the Kraton^®

copolymers manufactured by Shell Chemical Company, polyether ester

family of elastomers used in the manufacture of elastic meltblown fabrics

marketed by Kimberly-Clark under the trademark Demique^®, and the

ethylene vinyl acetate and the ethylene methyl acrylate copolymers

developed by Exxon Chemical Company. The thermoplastic elastomers are

not limited to the polymers and copolymers described above, but may

include any sheet form or web form of elastomeric material that can be

bonded to the nonwoven web.

The elastomeric layer 34 itself may be a composite of one or

more layers and may include additives such as polyolefins.

Many of the elastomers mentioned above and others including

pressure sensitive elastomers are described in detail in U.S. Patent No.

5,226,992, the disclosure of which is incorporated herein by reference. Elastic Nonwoven Webs:

The elastic nonwoven web (layers 32 and 33) useable in the

present invention is made by a process known as "stretchable nonwovens"

which is described in detail in U.S. Patent No. 5,244,482 and referred to in

the Nonwovens World article cited above. This process imparts

unidirectional elasticity to nonwoven webs composed of nonelastic fibers or

filaments.

Although the nonwoven web may be made by a variety of

processes including meltblowing, spunbond, thermally bonded staple fibers,

spunlaced webs, and the like, the preferred nonwovens are meltblown and

spunbond webs. The most preferred nonwovens are meltblown webs.

As described in detail in U.S. Patent No. 5,244,482, the

disclosure of which is incorporated herein by reference, the elastic

nonwoven webs are made by stretching a nonwoven precursor web in one

direction under heated conditions to cause the nonelastic fibers of the web

to consolidate in the direction of stress. This causes a number of the fibers

in the web to align in the direction of stress and other fibers disposed

crosswise thereof to resist the alignment or consolidation. The process

temperature is slightly below the polymer melting point. Upon the release

of the stress and cooling of the web, the web exhibits good elasticity

transverse to the direction of applied stress or draw (stretch). The web

further exhibits substantially inelastic behavior in the direction of the draw.

The unidirectional elasticity is mechanical (spring-like) in nature as opposed

to being elastomeric. The controlled draw ratio under the thermal conditions ranges from about 1 .05 to 4.0 (e.g. 5% to 300%, with the

preferred being from 10% to 100%).

The important parameters of the precursor web and the

process conditions, along with the unique properties of the web produced

by the process, are described in detail below.

A nonelastomeric nonwoven precursor web is selected based

on its dimensions, and its hot processing tensile properties (i.e., elongation-

at-break). In general, the breaking draw ratio of the web during hot

processing should be less than about 4.0 and greater than about 1 .4

evaluated while hot drawing at a strain rate greater than 2500%/min and a

temperature greater than the softening point but at least 10°F less than the

polymer melting temperature. The breaking draw ratio is an important

indicator of precursor molecular orientation state for achieving sufficient

stresses for cross-direction (CD) fiber buckling and bending, whereby there

is a reduction of the pore size distribution of the web by the process

described in U.S. Patent No. 5,244,482. The room temperature elongation

strain-at-break should be between 2 and 40%, preferably between 5 and

20% percent, based on test method ASTM D 1 1 17.77 using the Instron

tensile testing machine.

Compressive stresses which buckle and bend CD fibers are

described mathematically by a sine function of the fiber tensile stress; and

the angles involved become smaller as the machine direction (MD) draw

ratio increases. Therefore, compressive stresses decrease sinusoidally with draw ratio. Elastomeric polymer webs cannot be used for the nonwoven

layers in the present invention.

The precursor nonwoven web may be made from many of the

thermoplastics capable of being meltblown, provided the polymer selected

develops filaments of sufficiently high tensile processing modulus to permit

the development of high lateral compression forces on the web. The

thermoplastic resins useable in the production of nonwovens includes the

nonelastomeric polyolefins including homo and copolymers of ethylene and

propylene such as polyethylene, polypropylene including high density

polyethylene, ethylene copolymers (including EVA and EMA copolymers

with high tensile moduli), nylon, polyamides, polyesters, polystyrene, poly-

4-methylenepentene-1 , polymethylmethacrylate, polytrifluorochloroethylene,

polyurethanes, polycarbonates, silicones, and polyphenylene sulfide.

The crystallinity of the precursor web preferably should be

sufficiently high to provide a room temperature breaking elongation less

than 40%. The precurser meltblown webs should break at a strain of less

than 40% in accordance with ASTM test method D 5035-90. The

crystallinity in the range of 30 to 70% is preferred. In general, the proper

high modulus and state of molecular orientation of the precursor is best

reflected by a maximum or breaking draw ratio of the web during post

treating of less than about 4.0.

In the post treatment process, the thickness of the web should

preferably be at least 2 mils and up to about 200 mils. The width of the

web, of course, can vary within wide limits, with 5 to 150 inches being pref erred. The average fiber diameter of the precursor meltblown web will

preferably range from 0.5 to 20 microns, with .5 to 10 microns being most

preferred in order to provide the proper range of processing tensile stiffness

for the web. The porosity of the precursor web will normally be in the

range of 50 to 95%. Calendered precursor webs approach 50%.

Other properties of the web, which while not critical, are

important and include a low occurrence of large shot or excessive ropiness.

Another important feature of the precursor web is that it

includes at least some fiber-to-fiber bonding which is typical in meltblown

webs. The bonding can be achieved by inherent fiber-to-fiber fusion, or by

point bonding, calendering, or by fiber entanglement. The properties of the

selected polymer can be controlled to a degree by controlling the conditions

of the meltblowing process. Some of these control variables are disclosed

under the experiments described in U.S. Patent 5,244,482.

As indicated above, the primary purpose of the process of the

present invention is to consolidate the web in the cross-direction to reduce

the average pore size and the pore size distribution in the web.

Consolidation of the web in the cross-direction is to be distinguished from

consolidation resulting from calendering since consolidation to reduce

thickness as in calendering flattens the fibers and closes flow channels,

thus decreasing the permeability of the web to a greater extent compared to

web draw consolidation.

The random nonwoven nature of low stretch meltblown webs

with the attendant thermal bonding and/or filament entanglement enable the development of MD stresses to reorient fibers and create sufficient

compressive stresses to laterally (CD) consolidate or squeeze them together

thus reducing the size of voids therebetween during uniaxial drawing. This

results in narrowing of the web width without disrupting the planar integrity

of the web and produces a product of unique properties. During the post-

drawing process, the modulus that is in effect while the filament segments

are being drawn depends on processing time-temperature effects.

Maximum consolidation in the CD is achieved at a trial and error modulus at

which the compressive stresses overcome to the largest extent the critical

buckling stresses for the population of CD segments in the web. The

following table gives preferred operating parameters for manufacturing the

elastic meltblown webs.

Broad Preferred Best

Range Range Mode

Draw Ratio 1 .05-4.00 1.10-2.00 1 .2-1 .80

Temperature 165-350 250-350 275-300

(°F) (PP)

Crystallinity 30-95 30-80 35-60

(%)

Thickness 2-200 2-100 3-20

(mils)

Avg. Fiber 0.5-50 .5-20 .5-10

Dia. (microns)

Strain rate, 10-500 20-200 30-60

(%/min)

Elastic 50-99 70-99 80-95

Recovery (%) As mentioned above, details of the processing conditions and

properties of the resulting web are found in the aforementioned U.S. Patent

No. 5,244,482. This process imparts unidirectional elasticity to a

nonwoven web of inelastic fibers. This elasticity is mechanical (spring-like)

in nature rather than rubberlike in nature. Thus the elastic nonwoven

retains its physical cloth-like appearance and feel.

Nonwoven layers 32 and 33 may consist of a mixture of

thermoplastics and may include additives such as absorbents,

superabsorbents, surfactants, and dyes to improve certain properties of the

nonwovens.

The elastic nonwoven web may itself consist of more than one

layer as demonstrated in the aforementioned U.S. Patent No. 5,244,482.

Method of Manufacture of the Elastic Composite:

As previously mentioned, the composite 31 useful as side

panels in the diaper illustrated in Figure 1 comprises two layers 32 and 34

or 33, or three layers 32, 33, and 34 which are bonded together by any

means including thermal bonding or by the application of chemical or

adhesive layers 35 and 36 (see Figure 4) at the interfaces. Other bonding

techniques such as ultrasonic welding, hydro-entanglement, and the like,

may also be used.

The thermal bonding can be achieved by techniques well

known in the art wherein the two or three layers 32, 33, and 34 are passed ed through the nip of counterrotating heated rollers with or without

embossments to thermally bond or fuse the layers together.

In accordance with one aspect of the present invention,

laminating the preferred three layers together to form the composite 31 may

be by a process schematically illustrated in Figure 3 and described below.

(The two-layer embodiment may be similarly laminated using only one

applicator.)

An elastomeric layer 34 is dispensed from a roll mounted on

spindle 38; an elastic nonwoven web 32 is dispensed from a roll mounted

on spindle 39; and a second elastic nonwoven web 33 is dispensed from a

roll mounted on spindle 40.

A hot melt adhesive applicator 41 is disposed over one surface

of web 32 and a hot melt adhesive applicator 42 is disposed over a top

surface of layer 33. Applicators 41 and 42 discharge an adhesive spray 43

and 44 onto their respective underlying surfaces 32 and 33.

The three layers 32, 33, and 34 are fed into nip 46 of

counterrotating rollers 47 and 48, with the elastomeric layer 34 being

sandwiched between the flanking elastic nonwoven layers 32 and 33. The

counterrotating rollers 47 and 48 compress the three layers 32, 33, and 34

together as they pass through the nip 46, and pressure bond them together

to form composite 31 .

Guide rollers 49 are used to tension and guide the respective

layers 32, 33, and 34 in the process. The composite 31 is wound on

spindle 50. The layers 32, 33, and 34 are pulled through the nip by driven

spindle 50 so that all three layers have the same line speed. Guide rollers

49 maintain very little tension on the layers to avoid stretching.

The rollers 47 and 48 may be smooth, embossed or coated,

and may be heated or unheated. The pressure at the nip 46 may vary

within a wide range, depending on the type of bonding. One of rollers 47

and 48 may be embossed as in a diamond pattern to create compressive

regions on the layers passing therethrough. The embossment normally will

comprise between 1 to 19% of the roll surface area.

The line speed of the layers through the nip will typically be 50

to 350 feet per minute, preferably 200 to 300 feet per minute.

The dispensers for dispensing the hot melt adhesive may be

commercial spray nozzle applicators, commercial bead applicators, or

commercial meltblown dispensers manufactured by J&M Laboratories, Inc.

All that is necessary is that the bonding means provide at least two

transversely spaced bond regions along the layers being bonded together.

Preferably, the bond regions are in the form of a meltblown or spray film of

adhesive material covering the mating surface to be bonded, producing a

three-layer composite which behaves as a single fabric.

Any of the commercial hot melt adhesives capable of bonding

the layers may be used. The preferred hot melt adhesives are the SIS and

SBS block copolymer based adhesives. These adhesives contain the block

copolymer, tackifier, and oil in various ratios, typically 80-85 wt%, 5-10

wt%, and 5-15 wt%, respectively. The dimensions and properties of the composite 31 , of course,

will vary within wide limits depending upon the materials used in each layer,

the bonding process, the amount of materials in each layer, additives, and

the intended application, etc. However, by way of example, the following

dimensions and properties are representative:

Avg.

Basis Fiber

Thickness Weight Diam.

(mils) (OzJyd²) (microns)

Broad Preferred

Range Ranαe

Thermoplastic Elastomer (layer 34):

Film 0.5-3.0 0.5-2.0 N/A N/A Elastic Nonwoven (layers 32 and/or 33):

Meltblown 3-20 0.5-2.0 .5-15 .5-10

Spunbond 3-20 0.5-2.0 15-50 20-30

The unidirectional elasticity of the composite 31 may be

described with reference to Figure 5 wherein composite 31 is illustrated as

having a length L and an unstretched normal width W. As has been

described above, composite 31 comprises nonwoven web layers 32 and 33

with elastomeric layer 34 bonded therebetween. The composite preferably

exhibits properties of a single fabric in stretching, contracting, and handling.

Elastic nonwoven webs 32 and 33 were each made by being drawn in the

direction illustrated by arrow 51 by the heat drawing process described above with reference to U.S. Patent No. 5,244,482, so that the webs each

exhibit unidirectional elasticity, or stretchability, in a direction at right angles

to arrow 51 . Arrow 51 , therefore, represents the machine direction (MD) of

the heat drawing process. Nonwoven webs 32 and 33, and thus composite

31 , will have unidirectional elasticity in the direction of arrow 52, and be

substantially inelastic in the cross direction (CD) represented by the

direction of arrow 51 . Thus in relation to the diaper illustrated in Figure 1 ,

arrow 52 would correspond to the circumferential direction of the diaper

waist, and arrow 51 would be perpendicular thereto. Elastomeric layer 34

exhibits elasticity in substantially all directions in the plane of Figure 5.

Also illustrated in Figure 5 is the situation where a force is

applied in a direction between arrows 51 and 52, as represented by arrow

53. This force will have a CD component parallel to arrow 52, and a MD

component in the direction of arrow 51 . Due to the unidirectional elastic

properties of composite 31 , the composite will stretch in the direction of

arrow 52 in proportion to the CD component only, and be substantially

inelastic to the MD component in the direction of arrow 51 .

The elastic composite 31 is stretchable in a direction indicated

by arrow 52 to about 400%, preferably 300%, and most preferably 200%,

of its original width with the elastic elongation indicated by arrow 54. The

recovery from the elongation should be to the composite's original width or

within 5% to 10% of the original width. For elongations of 100% (e.g. the

elongation 54 equals two times W) the recovery should be within 10% of the original width W, preferably within 5%, after several loading and

unloading cycles.

One of the defining characteristics of the composite 31

useable in the diaper of the present invention is that the elastic nonwoven

layers 32 and 33 permit the thermoplastic elastomer layer 34 to stretch in a

direction transverse to the length, indicated by arrow 52, but prevents the

elastomer from stretching in the MD, indicated by arrow 51 . This, of

course, assumes that the elastic nonwoven web had been made by heat

stretching in the MD. As described above, the unidirectional elasticity of

the composite 31 when used as side panels 1 6 and 17 facilitates the pull-

up of diaper 10 by providing elasticity in the circumferential waist direction

and inelasticity in the direction of the pull-up.

It will be appreciated that it is possible to use elastic

nonwoven layers 32 and 33 that have been drawn (under thermal

conditions) in the CD (arrow 52) whereby the elasticity of composite 31 is

in the MD (arrow 51 ).

A significant difference between the composite 31 and that

described in U.S. Patent No. 5,226,992 is that the nonwoven web, because

of its elastic properties, assists in the recovery of the composite to its

original or near its original unstretched dimension; whereas, the necked-

bonded material of U. S. Patent No. 5,226,992 does not itself possess

elasticity, but merely permits the web to be stretched in a direction parallel

to the direction of necking. Examples

A three layer composite 31 was made and tested. The

composite had the following layers:

layer 32 Stretchable polyester nonwoven (carded)

Thickness: 5 mil Basis Weight: 0.6 oz/yd² Average Fiber Size: 30 microns

layer 34: Elastomeric Film: Styrene triblock copolymer

Thickness: 1.0 mil

layer 33: Polypropylene Spunbond MFR: 35

Thickness: 4 mils Basis Weight: 0.6 oz/yd²

Average Fiber Size: 20 microns

Adhesive: Hot Melt Adhesive HM-1295 marketed by H. B. Fuller

Adhesive Amount: 5 Grams per square meter

The composite was made using an apparatus similar to Figure

3 wherein the counterrotating rollers 47 and 48 were smooth rollers. Layer

34 is elastic in the machine direction (direction of travel) of the apparatus of

Figure 3, while web layers 32 and 33 may be elastic or inelastic in the

machine direction depending on the unidirectional orientation of the layers

when they are manufactured, as has been discussed in relation to Figure 5.

For the web shown in Figure 5, layers 32 and 33 will be inelastic in the

machine direction (arrow 51 ) and elastic in the transverse direction (arrow

52). In either case, drive spindle 50 imparts very little tension on the layers

of the composite so there is minimal or no stretching. ln the test results described below, the thermoplastic

elastomer web 34 was fed sandwiched between the elastic nonwoven

webs 32 and 33 into the nip 46 of the counterrotating rollers operating at a

pressure of 50 pounds per linear inch and a temperature of approximately

72°F (ambient). The line speed was 300 feet per minute. Note that the

line speed of the composite exiting the nip was the same as the line speed

of the layers fed into the nip. The composite was 12 mils thick and 12

inches wide. Samples of the composite were cut from the roll stock and

tested. The tests are described as follows.

Stress/strain tests were carried out on samples of the

composite and the base elastomeric film (layer 34) alone. The stress vs.

strain data (Figure 6) reveal that the composite exhibits properties similar to

the base film up to strains of about 50%. At strains above 50%, the

composite behavior is different than that of the base film. The composite

has nearly linear behavior up to and beyond a strain of 250%, while the

base film alone begins to exhibit nonlinear behavior above 50%. Linear

stress/strain behavior is typical of springs and/or spring-like materials.

The above tests demonstrate that the composite 31 has

excellent elasticity closely tracking that of the elastomer at low strain

levels, remaining spring-like at higher strain levels, while composite 31 also

exhibits the hand and aesthetics of the nonwoven material. The composite

of the present invention can be tailored to meet a variety of needs which

would combine the barrier properties of film or other meltblown elastomeric,

and the protective covering and soft hand of the nonwoven fabrics. Fabrication of the Form Fitting Diaper:

The composite 31 is used as diaper side panels 16 and 17 (see

Figure 1 ) in the manner described above. The composite 31 is positioned to

be bonded to the front 12 and back 13 of the backsheet 1 1 so that

stretchability or elasticity is in a circumferential direction (indicated by arrow

56) of Figure 1 , but not in the vertical direction. This is important because

the wearer generally grips the side panels and pulls upwardly to properly

locate the diaper on the body. Elasticity in the vertical direction (as viewed

in Figure 1 ) of the side panels 16 and 17 would make it difficult to pull the

diaper up.

The side panels may be bonded directly to the backsheet 1 1 at

overlapped 20 edges, illustrated in Figure 2. Figure 2 illustrates bonding of

the composite 31 with the crotch section of backsheet 1 1 at overlaps 20.

A similar overlap bonding may be used to bond the composite to the front

12 and back 13 sections of the backsheet by overlapping the composite

with the lateral edges of the front and back sections as illustrated by 20a

and 20b for panel 17, and 20c and 20d for panel 16. Alternatively, a

nonwoven web or sheet may be bonded to the backsheet 1 1 and that web

or sheet bonded to the side panels along edge seams.

Optionally, side panels 16 and/or 17 may comprise a front

panel and a back panel which are joined along a seam intermediate the

backsheet front 12 and back 1 3. With reference to Figure 1 , side panel 17

comprises front panel 17a bonded to a lateral edge of backsheet front

section 12 at 20a, and back panel 17b bonded to backsheet back section 13 at 20b. Front panel 17a and back panel 17b are bonded together along

seam 57b intermediate front 12 and back 13. Seam 57b runs substantially

from waist 26 to leg opening 22. The seam may be formed using a variety

of well known bonding techniques such as adhesives or heated pressure

bonding. The combination side panel 17 comprising panels 17a and 17b

exhibits the unidirectional elasticity and fabric-like properties heretofore

discussed in detail. Side panel 16 may likewise be a combination of front

panel 16a and back panel 16b bonded to the backsheet at 20c and 20d,

and further bonded along seam 57a. Seams 57a and 57b may be bonded in

a fashion whereby the seams may be easily ripped apart to quickly remove

the diaper in the event the diaper is to be disposed of.

Although the present invention has been described with

specific reference to diapers, it is to be recognized that the invention can be

used in any garment with stretchability.

For example, the composite 31 may be used in the waist 26 of

the diaper 10 to impart stretchability thereto. Briefly, a strip of the

composite 31 will be stretched, and in the stretched condition bonded to

the diaper backsheet in the waist area at spaced locations along the

composite strip length. Upon release, the composite will contract with the

diaper backsheet forming ruffles along the composite strip.

Claims

WHAT IS CLAIMED IS:

1 . A form fitting diaper for a human body, which comprises:

(a) a backsheet having

(i) a front section having spaced apart lateral edges,

(ii) a back section having spaced apart lateral edges,

and

(iii) a crotch section interconnecting the front and

back sections;

(b) a nonwoven inner layer having its outer periphery

bonded to the backsheet;

(c) an absorbent layer positioned between the backsheet

and the nonwoven inner layer;

(d) a first side panel interconnecting one lateral edge of the

front of the backsheet section to one lateral edge of the back section of the

backsheet; and

(e) a second side panel interconnecting the other lateral

edge of the front section of the backsheet with the other lateral edge of the

back section of the backsheet, the side panels and the front and back

sections of the backsheet defining a circumferentially continuous waist

adapted to fit around the body, each side panel being composed of a

composite comprising

(i) a first layer of a stretchable, elastic nonwoven

composed of nonelastic fibers; (ii) a second layer of a stretchable elastic nonwoven

composed of nonelastic fibers, and

(iii) an elastomeric layer positioned between the first

and second layers and having one surface bonded to the first layer and a

second surface bonded to the second layer; whereby the composite is

stretchable without ruffles in any of the layers.

2. The form fitting diaper of Claim 1 wherein the first and second

layers of the elastic nonwovens exhibit elasticity in the circumferential

direction of the waist and are substantially nonelastic in a direction

perpendicular thereto.

3. The form fitting diaper of Claim 2 wherein the nonelastic fibers

of the first and second layers of the side panel nonwovens are spunbond or

meltblown fibers having a fiber diameter of between 0.5 and 50 microns.

4. The form fitting diaper of Claim 3 wherein the nonwovens are

meltblown fibers having an average fiber diameter of between 0.5 and 15

microns.

5. The form fitting diaper of Claim 1 wherein the layers of each

side panel are bonded together by a layer of hot melt adhesives so that the

composite behaves as a single fabric.

6. The form fitting diaper of Claim 1 wherein the elastomeric layer is a

film made of a thermoplastic elastomer.

7. The form fitting diaper of Claim 1 wherein the first and second

layers comprise thermoplastic fibers.

8. The form fitting diaper of Claim 7 wherein the nonwoven

layers comprise polyolefin fibers.

9. The form fitting diaper of Claim 8 wherein the polyolefins are

selected from the group consisting of homo and copolymers of propylene

and ethylene.

10. The form fitting diaper of Claim 1 wherein the first and second

nonwoven layers of the side panels are made of fibers of different compo¬

sitions, respectively.

1 1 . The form fitting diaper of Claim 1 wherein the first and second

nonwoven layers are of the same composition.

12. The form fitting diaper of Claim 1 wherein the composite

exhibits substantially unidirectional elasticity of at least 100% with at least

90% recovery.

3. The form fitting diaper of Claim 6 wherein the elastomeric film

a thermoplastic elastomer selected from the styrene triblock copolymers.