WO2000006377A1

WO2000006377A1 - Method and apparatus for pin-hole prevention in zone laminates

Info

Publication number: WO2000006377A1
Application number: PCT/US1999/011131
Authority: WO
Inventors: Thomas G. Mushaben
Original assignee: Clopay Plastic Products Company, Inc.
Priority date: 1998-07-29
Filing date: 1999-05-20
Publication date: 2000-02-10
Also published as: JP4027597B2; US6673297B2; US20020001692A1; MXPA01000733A; BR9911863B1; EP1124684B1; US20010053433A1; US20020089087A1; ATE227644T1; PL195919B1; DE69903970T2; RU2220854C2; US6475591B2; CA2334885A1; HU223625B1; NZ508840A; AR020630A1; KR20010072061A; PL345682A1; JP2002521240A

Abstract

The method and apparatus of the present invention prevents the formation of pin-holes during stretching of strip laminates in the cross-machine direction (CD). Pin-holes are prevented by creating slack areas (10a) along the length of the laminates (10) where the edges of the non-woven strips (14) meet with the polymer film (12), pressing the slack areas (10a) into the interdigital stretching rollers (26) without stretching the slack areas (10a), and stretching the remainder of the laminate (10) in a typical manner. The slack areas (10a) are formed prior to interdigitation by, for example, formation of a furrow, a fold or a corrugation.

Description

Method and Apparatus for Pin-Hole Prevention in Zone Laminates

Field of the Invention

The present invention relates to methods and devices for

preventing the formation of pinholes in the production of laminates of non-

woven webs and polymer film. In particular, these laminates have spaced

laminated strips of non-woven webs and film with areas of nonlaminated film

therebetween (herein referred to as "zone laminates").

Background of the Invention

Methods of making microporous film products have been known

for some time. For example, U. S. Patent 3,832,267, to Liu, teaches the

melt-embossing of a polyolefin film containing a dispersed amorphous

polymer phase prior to stretching or orientation to improve gas and moisture

vapor transmission of the film. According to the Liu '267 patent, a film of

crystalline polypropylene having a dispersed amorphous polypropylene phase

is embossed prior to biaxially drawing (stretching) to produce an oriented

imperforate film having greater permeability. The dispersed amorphous

phase serves to provide microvoids to enhance the permeability of the otherwise imperforate film to improve moisture vapor transmission (MVT).

The embossed film is preferably embossed and drawn sequentially.

Many other patents and publications disclose the phenomenon

of making microporous thermoplastic film products. For example, European

patent 141 ,592 discloses the use of a polyolefin, particularly ethylene vinyl

acetate (EVA) containing a dispersed polystyrene phase which, when

stretched, produces a voided film which improves the moisture vapor

permeability of the film. The EP '592 patent also discloses the sequential

steps of embossing the EVA film with thick and thin areas followed by

stretching to first provide a film having voids which, when further stretched,

produces a net-like product. U. S. Patents 4,596,738 and 4,452,845 also

disclose stretched thermoplastic films where the dispersed phase may be a

polyethylene filled with calcium carbonate to provide the microvoids upon

stretching. Later U. S. Patents 4,777,073; 4,921 ,653; and 4,814, 124

disclose the same processes described by the above-mentioned earlier

publications involving the steps of first embossing a polyolefin film

containing a filler and then stretching that film to provide a microporous

product.

United States Patents 4,705,812 and 4,705,813 disclose

microporous films having been produced from a blend of linear low density

polyethylene (LLDPE) and low density polyethylene (LDPE) with barium

sulfate as the inorganic filler having an average particle diameter of

0.1 -7 microns. It is also know to modify blends of LLDPE and LDPE with a

thermoplastic rubber such as KRATON. Other patents such as U. S. Patent 4,582,871 disclose the use of thermoplastic styrene block tripolymers in the

production of microporous films with other incompatible polymers such as

styrene. There are other general teachings in the art such as the disclosures

in U. S. Patents 4,921 ,652 and 4,472,328.

The stretching, as discussed above, results in the appearance

of stripes along the length of the web. These stripes are caused by the

difference in appearance between the highly stretched areas, occurring

between the digits on the interdigital rolls, and the areas at the digits which

are not as highly stretched. These methods result in stripes of highly

stretched, highly porous areas adjacent moderately stretched, but still

substantially porous, areas.

Relevant patents regarding extrusion lamination of unstretched

non-woven webs include U. S. Patent Nos. 2,714,571 ; 3,058,868;

4,522,203; 4,614,679; 4,692,368; 4,753,840 and 5,035,941 . The above

'863 and '368 patents disclose stretching extruded polymeric films prior to

laminating with unstretched non-woven fibrous webs at pressure roller nips.

The '203 and '941 patents are directed to co-extruding multiple polymeric

films with unstretched non-woven webs at pressure roller nips. The '840

patent discloses preforming non-woven polymeric fiber materials prior to

extrusion laminating with films to improve bonding between the non-woven

fibers and films. More specifically, the '840 patent discloses conventional

embossing techniques to form densified and undensified areas in non-woven

base plies prior to extrusion lamination to improve bonding between non-

woven fibrous webs and films due to the densified fiber areas. The '941 patent also teaches that unstretched non-woven webs that are extrusion

laminated to single-ply polymeric films are susceptible to pinholes caused by

fibers extending generally vertically from the plane of the fiber substrate and,

accordingly, this patent discloses using multiple co-extruded film plies to

prevent pinhole problems. Furthermore, methods for bonding loose non-

woven fibers to polymeric film are disclosed in U. S. Patent Nos. 3,622,422;

4,379, 197 and 4,725,473.

U.S. Patent Application Serial No. 08/547,059 (herein

incorporated by reference in its entirety), now abandoned, discloses a

process and apparatus to continuously perform web splitting, separating,

guiding and laminating steps in a single unit. A single wide web of a non-

woven is slit into a number of narrow webs which are separated by the use

of turning bars and steered into a laminator. More specifically, a web is

unrolled from a wide roll of non-woven material. The incoming web is slit

into narrow webs, the narrow webs move down line to turning bars which

are displaced one from the other by a desired web separation distance. The

spaced narrow webs are then guided into a nip of rollers for extrusion

lamination with a polymer film. A molten polymer is extruded into the nip at

a temperature above its softening point to form a polymeric film laminated

to the narrow webs. The compressive force between the webs and the

extrudate at the nip is controlled to bond one surface of the web to the film

to form the laminate. The resulting laminate includes spaced strips of non-

woven laminated to the polymer film with areas of nonlaminated film

between the strips. U.S. Patent Application Serial No. 08/722,286 (herein

incorporated by reference in its entirety), a Continuation-ln-Part of U.S.

Patent Application Serial No. 08/547,059, discloses a process and apparatus

to continuously perform lamination of a polymer to another material to which

it is laminated. The '286 application is directed to a process and apparatus

to continuously perform non-woven web splitting, folding, guiding and

laminating steps in a single unit. Depending on the spacing between folded

webs, each strip of polymer may include a loose flap on either side of the

laminate area which may be suitable for forming a barrier cuff in a diaper or

other hygiene product. The spacing between folded webs determines the

width of the loose polymer flap which is formed. Again, the resulting

laminate includes spaced strips of non-woven laminated to the polymer film

with areas of nonlaminated film between the strips. These laminates, having

spaced laminated strips of non-woven and film with areas of nonlaminated

film therebetween, are referred to as zone laminates. The resulting laminate

includes spaced strips of non-woven laminated to the polymer film with areas

of nonlaminated film between the strips.

Summary of the Invention

With the development of the above referenced zone laminates,

it has been discovered that pin-holes form at the boundary area between the

laminated and non-laminated areas when the zone laminate is made

microporous by stretching across the length of the strip. The method and

apparatus of the present invention prevents the formation of pin-holes during

such stretching of zone laminates. Pinholes are prevented by creating slack areas along the length of the web where the edges of the non-woven strips

meet with the polymer film, pressing the slack areas into interdigital

stretching rollers without stretching the slack areas, and stretching the

remainder of the web by interdigitation. The slack regions are formed prior

to interdigitation by, for example, formation of a furrow, a fold or a

corrugation.

In one embodiment, the present invention includes a first

interdigital roller and a second interdigital roller and at least one disc for

contacting a slack area in the laminate and pressing the slack area into the

first interdigital roller without stretching the slack area. In a preferred form,

the device includes at least one disc which interengages with spaced rollers

to create a slack area along the length of a laminate, the interengaged disc

and rollers being laterally adjustable to create the slack area in a

predetermined position on the width of the web.

These and other advantages and features, which characterize

the invention, are set forth in the claims. For a better understanding of the

invention, and of the advantages and objectives attained through its use,

reference should be made to the Drawings, and to the accompanying

descriptive matter, in which exemplary embodiments of the invention are

described.

Brief Description of the Drawings

FIG. 1 is a schematic perspective view showing an apparatus

for pinhole prevention in zone laminates in accordance with one embodiment

of the present invention. FIG. 2 is a cross-sectional view showing an apparatus for

pinhole prevention suitable for use in accordance with one embodiment of

the present invention.

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2

of spacer discs and a furrow disc suitable for creating a slack area in a

laminate in accordance with the present invention.

FIG. 3A is an enlarged plan view of the spacer discs and furrow

discs shown in FIG. 3.

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2

of the presser disc forcing the laminate into the grooves on the first

interdigital roller in accordance with one embodiment of the present

invention.

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 2

showing the intersection of the first and second interdigital rollers used for

stretching the laminate in the cross-machine direction.

FIG. 6 is a plan view of a progressive roll former suitable for use

in creating a slack area in the laminate in accordance with one embodiment

of the present invention.

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 6.

FIG. 8 is a schematic perspective view of a corrugator suitable

for creating a slack area in the non-woven laminate suitable for use in the

present invention.

FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 8. FIG. 10 is a graph showing the relationship between line speed

and screw RPM of an extruder for use with the present invention.

FIG. 1 1 is a graph demonstrating the relationship between

moisture vapor transmission properties and incremental stretching.

FIG. 1 2 is a graph showing the relationship between moisture

vapor transmission rate and finish roll temperature prior to CD intermeshing.

FIG. 1 3 is an enlarged schematic cross-sectional view of the

boundary area of the laminate after interdigital stretching.

Detailed Description

The method and apparatus of the present invention prevent the

formation of pin-holes at the boundary area of a zone laminate at the edges

of a non-woven strip during interdigital stretching. Pin-holes form at the

edge of the non-woven strip because the film and non-woven laminate is

substantially stronger than the adjacent unlaminated polymer film; therefore,

substantially all of the stretching occurs in the unlaminated film of the

boundary area. It has been discovered that this excessive stretching in the

boundary areas causes the formation of pin-holes.

In order to prevent pin-holing, the present invention provides for

the formation of a slack area 10a at the boundary areas of the laminate, that

is, where the edge of the non-woven strips 14 meet the polymer film 1 2 in

laminate 10, as shown in FIGS. 1 , 3A and 1 3. In order to create these slack

areas a number of spacer discs 1 8 which are slidably mounted on axle 1 6 are

positioned such that the gap between adjacent discs 1 8 align with the

boundary areas. Furrow discs 22 are slidably mounted on axle 20 so that each furrow disc 22 is received in the gap between adjacent spacer discs 1 8

at the boundary areas. A set of two spacer discs 1 8 and one furrow disc 22

interengage (as shown in FIGS. 3 and 3a) to create a slack area 1 0a along

the length of the laminate 1 0. The laminate 1 0, including slack area 1 0a,

travels to the first interdigital roller 26 where the slack area is forced into the

interdigital grooves 28 on roller 26 by presser disc 32. Presser disc 32

includes a presser area 34 which conforms to the cross section of

grooves 28. The presser discs 32 force slack area 10a into the grooves 28

on the first interdigital roller 26 and form taut 37 areas along the remaining

width of laminate 1 0. The taut areas 37 pass between first roller 26 and

second roller 38 and are stretched by interdigital grooves 28 and 40 to form

microporous laminate 50.

The microporous laminate may optionally be stretched along the

length of microporous laminate 50 to increase porosity. The lengthwise

stretching may be performed by any known method of forming micropores

such as interdigital rolling or differential speed stretching of the laminate 1 0

either before or after stretching in the cross-machine direction.

As can be seen in FIG. 2, spacer discs 1 8 are mounted upon

axle 1 6 by collar 1 8a and set screw 1 8b. Furrow discs 22 are mounted

upon axle 20 by collar 22a and set screw 22b. Axle 20 is mounted upon a

rotatable axle support 20a which pivots from a nonengaged position to an

engaged position (shown in FIG. 2). The capacity to move furrow discs 22

to a nonengaged position allows for simplified threading of laminate 1 0

between spacer discs 1 8 and furrow discs 22. When engaged, a furrow disc 22 is interengaged with a pair of spacer discs 1 8 to form a furrow

which creates slack area 1 0a at the boundary areas of laminate 1 0.

Interdigital roll 26 is rotatably mounted on axle 24 and presser discs 32 are

rotatably mounted on axle 30. Presser discs 32 are movable along the

length of axle 30 by collar 32a and set screw 32b. Presser discs 32 are

movable along axle 30 in a method similar to the movement of furrow

discs 22 along axle 20 as discussed above. The presser disc 32 includes a

presser area 34 around its periphery which is complimentary to the grooves

on roll 26. Presser area 34 presses the slack area 10a of laminate 10 into

the grooves 28 on roll 26 without stretching of the slack area 10a. The

width of the laminate 1 0, other than the slack areas 10a, are held taut

against the grooves of roller 26 so that the taut areas 37 are interdigitally

stretched between roller 26 and roller 38.

The intermeshing rollers 26,38 are capable of large engagement

depths which may stretch the laminate up to about 200% or more of the

original width to form the micropores. The equipment incorporates a

controller (not shown) for the shafts 24,36 of the two intermeshing

rollers 26,38 to control the degree of intermeshing and hence the amount of

stretching imparted to the laminate. The controller also keeps shafts 24,36

parallel when the top shaft is raised or lowered to assure that the teeth of

one intermeshing roller always fall between the teeth of the other

intermeshing roller to avoid potentially damaging physical contact between

intermeshing teeth. This parallel motion is assured by a rack and gear

arrangement (not shown) wherein a stationary gear rack is attached to each side frame in juxtaposition to vertically slidable members. A shaft traverses

side frames and operates a bearing in each of the vertically slidable members.

A gear resides on each end of the shaft and operates in engagement with the

racks to produce the desired parallel motion.

As shown in FIG. 3, the force of furrow discs 22 between

spacer discs 1 8 causes the formation of a furrow to form slack area 1 0a

between spacer discs 1 8. As shown in detail in FIG. 3A the slack area 1 0a

is preferably formed at the boundary areas of the zone laminate where the

edges of the non-woven 1 4 meet polymer film 1 2. The laminate 10,

including slack areas 1 0a, travels from spacer discs 1 8 and furrow discs 22

to the first interdigitating roller 26. As the first interdigitating roller 26

rotates about axle 24, slack area 10a is pressed into the grooves 28 of the

first interdigitating roller 26 by the complimentary structure 34 of presser

rollers 32, as shown in FIG. 4. Due to the creation of the slack area 10a, the

laminate 10 is pressed into grooves 28 to form taut areas 37 but without

stretching the web. The web then rotates about first interdigitating roller 26

to meet second interdigitating roller 38. Interdigitating roller 38 rotates

about axle 36 and grooves 40 intermesh with grooves 28 to stretch the taut

areas 37 of laminate 10 in the cross-machine direction, that is, substantially

no stretching occurs where the slack areas 10a have been pressed into the

grooves 28 on the first roller 26.

As can be seen in FIG. 3 the spacer discs 1 8 may be variously

positioned along axle 1 6 by use of clamping collars 1 8a and clamping

screws 18b. Each furrow disc 22 includes a clamping collar 22a with a set screw 22b to allow the furrow disc to be variably positioned along axle 20.

Similarly, presser discs 32 include clamping collar 32a and set screw 32b to

allow the presser discs 32 to be variably positioned along axle 30. This

adjustability allows for the processing of various widths of laminate without

the need for substantial time spent setting up the machinery.

As seen in FIGS. 4 and 5, presser disc 32 interengages with

grooves 28 on interdigital roll 26 by complimentary presser area 34 such as

circumferential grooves to interact with a cross directional interdigital

stretcher, a helical gear to interengage with a diagonal intermeshing

stretcher, or a deformable member which conforms to the surface of roll 26.

Presser roller 32 forces the slack area 1 0a of laminate 1 0 into the grooves

of roller 26 so that the taut areas 37 of laminate 10 are formed on either

side of the presser roller 32. These taut areas 37 are subsequently stretched

between interdigital rollers 26,38 to form the microporous zone laminated

sheet 50 having substantially unstretched portions along the length thereof.

FIG. 1 3 shows the stretched laminate 50 including micropores 1 2a in the

taut areas 37 of the polymer film 1 2 and the lack of micropores in the

boundary area.

Other methods of forming a slack area 10a are shown in

FIGS. 6-9. As shown in FIGS. 6 and 7 a progressive roll former 100 which

includes a series of increasingly overlapped rollers may be used to create

slack area 1 0a. The first set of rollers 102a, 1 04a, 1 06a deform the

laminate 10 to form a small slack area. The second set of rollers 1 02b,

1 04b, 106b have a larger overlap and thus form a larger slack area. The third set of rollers 1 02c, 1 04c, 106c are overlapped to form a slack area 10a

of the desired shape.

A corrugator 1 20, as seen in FIGS. 8 and 9 includes a first

support plate 1 22 having a female corrugator 1 24 and a second support

plate 1 26 which includes male corrugator section 1 28. The male 1 28 and

female 1 24 corrugator sections have an increasing cross-sectional area along

the length of the web and are nested to cause the laminate 1 0 to deform and

thus create slack area 1 0a.

The laminate of the present invention may be achieved with the

use of a wide variety of polymer films; however, in a preferred form the film

is manufactured by first melt blending a composition of:

(a) about 35% to about 45% by weight of a linear

low density polyethylene,

(b) about 3% to about 10% by weight of a low

density polyethylene,

(c) about 40% to about 50% by weight calcium

carbonate filler particles, and

(d) about 2% to about 6% by weight of a triblock

copolymer of styrene selected from the group consisting

of styrene-butadiene-styrene, styrene-isoprene-styrene,

and styrene-ethylene-butylene-styrene, and blends

thereof, extruding the melt blended composition into a nip of rollers with

an air knife to form a film at a speed on the order of at least about 550 fpm

to about 1 200 fpm without draw resonance, and

applying an incremental stretching force to the film along lines

substantially uniformly across the taut areas of the laminate and throughout

its depth to provide a microporous film.

More particularly, in a preferred form, the melt-blended

composition consists essentially of about 42% by weight LLDPE, about 4%

by weight LDPE, about 44% by weight calcium carbonate filler particles

having an average particle size of about 1 micron, and about 3% by weight

triblock polymer, especially styrene-butadiene-styrene. If desired, the

stiffness properties of the microporous film products may be controlled by

including high density polyethylene on the order of about 0-5% by weight

and including 0-4% by weight titanium dioxide. Typically, a processing aid

such as a fluorocarbon polymer in an amount of about 0.1 % to about 0.2%

by weight is added, as exemplified by 1 -propene, 1 , 1 ,2,3,3,3-hexafluoro

copolymer with 1 , 1 -difluoroethylene is included in the melt. The triblock

polymer may also be blended with oil, hydrocarbon, antioxidant and

stabilizer.

Both embossed and flat films may be produced according to the

principles of this invention. In the case of an embossed film, the nip of

rollers comprises a metal embossing roller and a rubber roller. The

compressive force between the rollers forms an embossed film of desired

thickness on the order of about 0.5 to about 10 mils. It has also been found that rollers which provide a polished chrome surface form a flat film.

Whether the film is an embossed film or a flat film, upon incremental

stretching at high speeds, microporous film products are produced having

high moisture vapor transmission rate (MVTR) within the acceptable range

of about 1000 to 4000 gms/m²/day. It has been found that flat film can be

incrementally stretched more uniformly than embossed film. The process

may be conducted at ambient or room temperature or at elevated

temperatures. As described above, laminates of the microporous film may

be obtained with non-woven fibrous webs.

The non-woven fibrous web may comprise fibers of

polyethylene, polypropylene, polyesters, rayon, cellulose, nylon, and blends

of such fibers. A number of definitions have been proposed for non-woven

fibrous webs. The fibers are usually staple fibers or continuous filaments.

The non-wovens are usually referred to as spunbond, carded, meltblown and

the like. The fibers or filaments may be bicomponent to facilitate bonding.

For example, a fiber having a sheath and core of different polymers such as

polyethylene (PE) and polypropylene (PP) may be used or mixtures of PE and

PP fibers may be used. As used herein "non-woven fibrous web" is used in

its generic sense to define a generally planar structure that is relatively flat,

flexible and porous, and is composed of staple fibers or continuous filaments.

For a detailed description of non-wovens, see "Nonwoven Fabric Primer and

Reference Sampler" by E. A. Vaughn, Association of the Non-woven Fabrics

Industry, 3d Edition ( 1 992). ln a preferred form, the microporous laminate employs a film

having a gauge or a thickness between about 0.25 and 1 0 mils and,

depending upon use, the film thickness will vary and, most preferably, in

disposable applications, is on the order of about 0.25 to 2 mils in thickness.

The non-woven fibrous webs of the laminated sheet normally have a weight

of about 5 gms/yd² to 75 gms/yd², preferably about 20 to about 40 gms/yd².

The composite or laminate can be incrementally stretched in the cross-

machine direction (CD) to form a CD stretched composite. Furthermore, CD

stretching may be followed by stretching in the machine direction (MD) to

form a composite which is stretched in both CD and MD directions. As

indicated above, the microporous film or laminate may be used in many

different applications such as baby diapers, baby training pants, catamenial

pads and garments, and the like where moisture vapor and air transmission

properties, as well as fluid barrier properties, are needed.

The laminate is then incrementally stretched in the cross-

machine direction (CD) or diagonally using the apparatus of the present

invention to form a stretched laminate having unstretched regions along the

length of the laminate. Furthermore, stretching according to the present

invention may be followed by stretching in the machine direction (MD).

A number of different stretchers and techniques may be

employed to stretch the film or laminate of a non-woven fibrous web and

microporous-formable film. These laminates of non-woven carded fibrous

webs of staple fibers or non-woven spun-bonded fibrous webs may be

stretched with the stretchers and techniques described as follows: The diagonal intermeshing stretcher consists of a pair of left

hand and right hand helical gear-like elements on parallel shafts. The shafts

are disposed between two machine side plates, the lower shaft being located

in fixed bearings and the upper shaft being located in bearings in vertically

slidable members. The slidable members are adjustable in the vertical

direction by wedge shaped elements operable by adjusting screws. Screwing

the wedges out or in will move the vertically slidable member respectively

down or up to further engage or disengage the gear-like teeth of the upper

intermeshing roll with the lower intermeshing roll. Micrometers mounted to

the side frames are operable to indicate the depth of engagement of the

teeth of the intermeshing roll.

Air cylinders are employed to hold the slidable members in their

lower engaged position firmly against the adjusting wedges to oppose the

upward force exerted by the material being stretched. These cylinders may

also be retracted to disengage the upper and lower intermeshing rolls from

each other for purposes of threading material through the intermeshing

equipment or in conjunction with a safety circuit which would open all the

machine nip points when activated.

A drive is typically utilized to drive the stationery intermeshing

roller. If the upper intermeshing roller is to be disengagable for purposes of

machine threading or safety, it is preferable to use an antibacklash gearing

arrangement between the upper and lower intermeshing rollers to assure that

upon reengagement the teeth of one intermeshing roller always falls between

the teeth of the other intermeshing roller and potentially damaging physical contact between addenda of intermeshing teeth is avoided. If the

intermeshing rollers are to remain in constant engagement, the upper

intermeshing roll typically need not be driven. Drive may be accomplished

by the driven intermeshing roller through the material being stretched.

The intermeshing rollers closely resemble fine pitch helical

gears. In the preferred embodiment, the rollers have 5.935" diameter, 45°

helix angle, a 0.1 00" normal pitch, 30 diametral pitch, 14¹/2° pressure angle,

and are basically a long addendum topped gear. This produces a narrow,

deep tooth profile which allows up to about 0.090" of intermeshing

engagement and about 0.005" clearance on the sides of the tooth for

material thickness. The teeth are not designed to transmit rotational torque

and do not contact metal-to-metal in normal intermeshing stretching

operation. With such a diagonal intermeshing stretcher, a presser disc 32

having the configuration of a helical gear would be used. The use of a

diagonal intermeshing stretcher provides for a stretching force having force

components in both the cross-machine direction and the machine direction

of the laminate.

The drive for the CD intermeshing stretcher typically operates

both upper and lower intermeshing rollers except in the case of intermeshing

stretching of materials with a relatively high coefficient of friction. The drive

need not be antibacklash, however, because a small amount of machine

direction misalignment or drive slippage will cause no problem.

The CD intermeshing elements are machined from solid material

but can best be described as an alternating stack of two different diameter disks. In the preferred embodiment, the intermeshing disks would be 6" in

diameter, 0.031 " thick, and have a full radius on their edge. The spacer

disks separating the intermeshing disks would be 5 V2 " in diameter and

0.069" in thickness. Two rolls of this configuration would be able to be

intermeshed up to 0.231 " leaving 0.01 9" clearance for material on all sides.

As with the diagonal intermeshing stretcher, this CD intermeshing element

configuration would have a 0.1 00" pitch.

The MD intermeshing stretching equipment is identical to the

diagonal intermeshing stretch except for the design of the intermeshing

rollers. The MD intermeshing rolls closely resemble fine pitch spur gears. In

the preferred embodiment, the rolls have a 5.933" diameter, 0.100" pitch,

30 Diametral pitch, 14¹/2⁰ pressure angle, and are basically a long addendum,

topped gear. A second pass was taken on these rolls with the gear hob

offset 0.010" to provide a narrowed tooth with more clearance. With about

0.090" of engagement, this configuration will have about 0.01 0" clearance

on the sides for material thickness.

The above described diagonal or CD intermeshing stretchers

may be employed with the pin-hole prevention apparatus of the present

invention to produce the incrementally stretched film or laminate of non-

woven fibrous web and microporous-formable film to form the microporous

film products of this invention. For example, the stretching operation may

be employed on an extrusion laminate of a non-woven fibrous web of staple

fibers or spun-bonded filaments and microporous-formable thermoplastic film.

In one of the unique aspects of this invention, a laminate of a non-woven fibrous web of spun-bonded filaments may be incrementally stretched to

provide a very soft fibrous finish to the laminate that looks like cloth. The

laminate of non-woven fibrous web and microporous-formable film is

incrementally stretched using, for instance, the CD and/or MD intermeshing

stretcher with one pass through the stretcher with a depth of roller

engagement at about 0.060 inch to 0.1 20 inch at speeds from about 550

fpm to 1200 fpm or faster. The results of such incremental or intermesh

stretching produces laminates that have excellent breatheability and liquid-

barrier properties, yet provide superior bond strengths and soft cloth-like

textures.

The microporous laminate typically employs a film having a

gauge or a thickness between about 0.25 and 10 mils and, depending upon

use, the film thickness will vary and, most preferably, in disposable

applications is the order of about 0.25 to 2 mils in thickness. The non-

woven fibrous webs of the laminated sheet normally have a weight of about

5 grams per square yard to 75 grams per square yard preferably about 20 to

about 40 grams per square yard.

The following^' examples illustrate the method of making

microporous film and laminates of this invention. In light of these examples

and this further detailed description, it is apparent to a person of ordinary

skill in the art that variations thereof may be made without departing from

the scope of this invention. EXAMPLES 1 -5

Blends of LLDPE and LDPE having the compositions reported in

the following TABLE 1 were extruded to form films and the films were then

incrementally stretched to provide microporous films.

TABLE 1

*Other components include 2.5% by weight of a styrene-butadiene-styrene (SBS) triblock polymer, Shell Kraton 2122X, which is an SBS < 50% by wt. -(- mineral oil < 30% by wt., EVA copolymer < 1 5% by wt., polystyrene < 10% by wt., hydrocarbon resin < 10% by wt., antioxidant/stabilizer < 1 % by wt., and hydrated amorphous silica < 1 % by wt.

Each of the formulations of 1 -5 were extruded into films

employing an extrusion apparatus. The formulations of Examples 1 -5 were

fed from an extruder through a slot die to form the extrudate into the nip of

a rubber roll and a metal roll. The incoming webs of non-woven material

were also introduced into the nip of the rolls. In Examples 1 -5, the

thermoplastic film was produced for subsequent incremental stretching to form the microporous film. As shown in TABLE 1 , over speeds of about

550 fpm to 1 200 fpm, a polyethylene film on the order of about 2 mils in

thickness was made which is taken off the roller. The compressive force at

the nip is controlled such that the film is made without pin-holing and

without draw resonance in the case of Examples 2-5. The melt temperatures

from the feed zone to the screw tip of extruders were maintained at about

400-430°F with die temperatures of approximately 450°F to extrude the

precursor film around 2 mils (45 g/m²).

As shown in TABLE 1 , over speeds of about 550 fpm to

1 200 fpm, a polyethylene film on the order of about 2 mils in thickness was

made which is taken off the roller. The air knife has a length of about 1 20"

and an opening of about 0.035"-0.060" and air is blown through the opening

and against the extrudate at about 5 cfm/inch to 25 cfm/inch. The

compressive force at the nip and the air knife are controlled such that the

film is made without pin-holing and without draw resonance in the case of

Examples 2-5. Where the LDPE was included in the composition at a level

of 1 .5% by weight, draw resonance was encountered at a line speed of

550 fpm. However, when the LDPE was included in the formulation at a

level of 3.7% by weight with the LLDPE at a level of 44.1-44.9% by weight,

film production was able to be achieved at high speeds greater than 550 fpm

up to 1 200 fpm without draw resonance. The melt temperatures from the

feed zone to the screw tip of the extruders were maintained at about

400-430° F with die temperatures of approximately 450° F to extrude the

precursor film around 2 mils (45 gms/m²). FIG. 1 0 is a graph demonstrating the line speeds for

Examples 1 -5 and the necessary screw speed. Example 1 , which contained

only 1 .5% by weight of LDPE, resulted in a poor film gauge control with

draw resonance even with the air knife. However, when the LDPE was

increased to about 3.7% by weight, excellent web stability was achieved

without draw resonance even when line speeds were increased to about

1 200 fpm.

FIG. 1 1 is a graph demonstrating the moisture vapor

transmission properties (MVTR) of both embossed and flat films resulting

from incrementally stretching the precursor films of Examples 2-5 under

different temperatures and stretch roller engagement conditions. The MVTRs

for the embossed film on the order of about 1 200-2400 gms/m²/day were

achieved, whereas MVTRs ^• for the flat film on the order of about

1 900-3200 gms/m²/day were achieved. FIG. 1 2 shows the impact of the

temperature of the CD preheat roller upon MVTR. The MVTR for the film

varied between about 2000-2900 gms/m²/day with the roller preheat

temperature between about 75-220 F. The embossed film was made with

a metal embossing roller having a rectangular engraving of CD and MD lines

with about 1 65-300 lines per inch. This pattern is disclosed, for example,

in U. S. Patent No. 4,376, 147 which is incorporated herein by reference.

This micro pattern provides a matte finish to the film but is undetectable to

the naked eye.

Those skilled in the art will recognize that the exemplary

embodiment illustrated in the drawings is not intended to limit the invention. Indeed, those skilled in the art will recognize that other alternative

embodiments may be used without departing from the scope of the

invention.

What is claimed is:

Claims

1 . A laminate of non-woven and polymeric film comprising: a polymeric film; and at least one non-woven strip having opposite edges, the strip

laminated to the film to form a laminated area along the length of the film and unlaminated film areas along the opposite edges, said opposite strip edges each defining a boundary area between the laminated area and the unlaminated area;

wherein the boundary areas are unstretched and the laminated area and the unlaminated area are interdigitally stretched.

2. The microporous laminate of claim 1 wherein boundary areas are substantially pinhole free.

3. The microporous laminate sheet of claim 1 wherein the

laminated area and the nonlaminated areas are microporous.

4. The microporous laminate sheet of claim 3 wherein the film and non-woven laminate areas and the nonlaminated polymer film laminate area are interdigitally stretched in the cross-machine direction.

5. The microporous laminate sheet of claim 3 wherein the polymer

film comprises: a polyolefin; and a pore initiator.

6. The microporous laminate sheet of claim 1 wherein the polymer film comprises a blend of linear low density polyethylene and low density polyethylene.

7. The microporous laminate sheet of claim 1 wherein the polymer

film comprises: about 35% to about 45% by weight of a linear low density

polyethylene, about 3% to about 1 0% by weight of a low density

polyethylene, about 40% to about 50% by weight calcium carbonate filler

particles, and about 2% to about 6% by weight of a rubber compound.

8. The microporous laminate sheet of claim 7 wherein said polymer film consists essentially of about 42% by weight linear low density

polyethylene, about 4% by weight low density polyethylene, about 44% calcium carbonate filler particles, and about 3% by weight triblock polymer.

9. The microporous laminate sheet of claim 7 wherein said polymer film further comprises about 0-5% by weight high density polyethylene, about 0-4% by weight titanium dioxide, and about 0.1 % to about 0.2% by

weight processing aid.

1 0. The microporous laminate sheet of claim 9 wherein said polymer film comprises about 4% by weight high density polyethylene, about 3% by weight titanium dioxide, and about 0.1 % by weight fluorocarbon polymer processing aid.

1 1 . The microporous laminate sheet of claim 10 wherein said fluorocarbon polymer processing aid is 1 -propene, 1 , 1 ,2,3,3, 3-hexafluoro copolymer with 1 , 1 -difluoroethylene.

1 2. The microporous laminate sheet of claim 7 wherein said rubber compound is a triblock copolymer of styrene selected from the group consisting of styrene-butadiene-styrene, styrene-isoprene-styrene, and styrene-ethylene-butylene-styrene.

1 3. The microporous laminate sheet of claim 1 2 wherein said triblock polymer is preblended with oil, hydrocarbon, antioxidant and stabilizer.

1 4. A microporous laminate sheet having improved breatheability and liquid barrier properties comprising: a polymer film barrier layer; at least one non-woven layer having opposite edges laminated to the polymer barrier layer forming a laminated area and a nonlaminated

area, having boundary areas at the edges of the non-woven; wherein the film and non-woven laminate areas and the nonlaminated polymer film laminate area are interdigitally stretched in the cross-machine direction and the boundary areas are unstretched in the cross-

machine direction.

1 5. The microporous laminate sheet of claim 14 wherein the

polymer film comprises: a polyolefin; and a particulate filler.

1 6. The microporous laminate sheet of claim 14 wherein the

polymer film comprises: about 35% to about 45% by weight of a linear low density

polyethylene, about 3% to about 10% by weight of a low density

polyethylene, about 40% to about 50% by weight calcium carbonate filler

particles, and about 2% to about 6% by weight of a rubber compound.

1 7. The microporous laminate sheet of claim 14 wherein the polymer film comprises: about 42% by weight linear low density polyethylene, about 4% by weight low density polyethylene, about 44% calcium carbonate filler particles, and about 3% by weight triblock polymer.

1 8. The microporous laminate sheet of claim 1 7 wherein the triblock polymer is a styrene-butadiene rubber.

1 9. A method of forming a polymeric film having differing degrees

of microporosity including the steps of: providing a film of a microporous formable polymer composition; and interdigitally stretching the film throughout it depth along a plurality of lines while controlling said film in a substantially unstretched condition adjacent said lines to reduce pinhole formation in the film.

20. The method of claim 1 9 wherein controlling the film in an unstretched condition is performed by creating slack areas along the length of the sheet prior to interdigital stretching.

21 . The method of claim 20 wherein the slack is created by passing a preselected area of the sheet between opposed rollers.

22. The method of claim 20 wherein the step of creating the slack areas is selected from the group consisting of folding, corrugating and overlapping a preselected area of the sheet.

23. The method of claim 1 9 wherein the interdigital stretching forms micropores in the film along the plurality of interdigitally stretched lines.

24. A device for preventing pin-holing during the creation of micropores in a laminate comprising: a first interdigital roller;

a second interdigital roller, intersecting the first interdigitating roller, the intersection of said first and second interdigital roller serving to interdigitally stretch a laminate of non-woven and microporous formable film across the width of the laminate except in the slack areas of the laminate to form micropores; and at least one disc for contacting a slack area in the laminate and pressing the slack area into the first interdigital roller without stretching the slack area.

25. The device of claim 24, further comprising:

at least one set of interengaging spaced rollers for creating a slack area along the length of a laminate.

26. A device for preventing pin-holing during the creation of micropores in a laminate comprising: a first interdigital roller; a second interdigital roller, intersecting the first interdigitating roller, the intersection of said first and second interdigital roller serving to interdigitally stretch a laminate stretch a laminate of non-woven and microporous formable film across the width of the laminate except in slack areas of the laminate; and

means for creating at least one slack area along the length of a laminate.

27. The device of claim 26 further comprising: means for forcing the slack area into the first interdigital roller.

28. The pin-hole prevention device of claim 27, wherein the means

for forcing a slack area into the first interdigital roller includes at least one rotatable disc for contacting the slack area of the laminate and pressing the slack area into the first interdigital roller without stretching the slack area.

29. The pin-hole prevention device of claim 26, wherein the means for creating a slack area along the length of a laminate is selected from the

group consisting of furrowers, corrugators, and progressive roll formers.

30. The pin-hole prevention device of claim 26, wherein the means ating a slack area along the length of a laminate are laterally adjustable te the slack area in a predetermined position on the width of the web.