WO2001051546A1

WO2001051546A1 - INCREMENTALLY STRETCHED NON-EMBOSSED FILMS HAVING HIGH MOISTURE VAPOR TRANSMISSION RATES (MVTRs)

Info

Publication number: WO2001051546A1
Application number: PCT/US2000/013853
Authority: WO
Inventors: Pai-Chuan Wu; Leopoldo V. Cancio
Original assignee: Clopay Plastic Products Company, Inc.
Priority date: 2000-01-10
Filing date: 2000-05-19
Publication date: 2001-07-19
Also published as: US20030005999A1; US6656581B2; AR025302A1; AU2000251467A1

Abstract

An incrementally stretched non-embossed film having a high vapor transmision rate (MVTR) comprising a thermoplastic polymer containing a dispersed phase of particles selected from the group consisting of an inorganic filler and an organic material. These non-embossed film products are permeable to moisture vapor and act as barriers to liquid. The microporous products have high moisture vapor transmission rates (MVTRs) on the order of about 2000 to about 4500 gms/m2/day according to ASTM E96E.

Description

INCREMENTALLY STRETCHED NON-EMBOSSED FILMS HAVING HIGH MOISTURE VAPOR TRANSMISSION RATES (MVTRs)

RELATED APPLICATION

This application is a continuation-in-part application of

Application Serial No. 09/080,063, filed May 1 5, 1 998, now U. S. Patent

No. 6,01 3, 1 51 , and Application Serial No. 09/395,627, filed

September 1 4, 1 999, which are incorporated herein in their entireties by

reference.

BACKGROUND OF THE INVENTION

Methods of making plastic film and nonwoven laminates date

back many years. For example, more than thirty years ago U. S. Patent

No. 3,484,835 (1 968) issued to Trounstine, et al., and it is directed to

embossed plastic film having desirable handling characteristics and

fabricating useful articles such as diapers. Since that time, many patents

have issued in the field. U. S. Patent No. 5,202, 1 73 issued on April 1 3,

1 993, for an ultra-soft thermoplastic film which was made by

incrementally stretching the embossed film to achieve breathability. The film may include fillers. Polymer films of polycaprolactone (PCL) and

starch polymer or polyvinyl alcohol (PVOH) upon incremental stretching

also produce breathable products, as disclosed in U. S. Patents

Nos. 5,200,247 and 5,407,979. More recently, U. S. Patent

No. 5,865,926 issued for a method of making a cloth-like microporous

laminate of a nonwoven fibrous web and thermoplastic film having air and

moisture vapor permeabilities with liquid-barrier properties.

Methods of making microporous film products have also been

known for some time. For example, U. S. Patent No. 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 first 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 rates (MVTRs) . The embossed

film is preferably embossed and drawn sequentially.

In 1 976, Schwarz published a paper which described polymer

blends and compositions to produce microporous substrates (Eckhard CA.

Schwartz (Biax-Fiberfilm), "New Fibrillated Film Structures, Manufacture

and Uses", Pap. Synth. Conf. (TAPPI). 1 976, pages 33-39). According to this paper, a film of two or more incompatible polymers, where one

polymer forms a continuous phase and a second polymer forms a

discontinuous phase, upon being stretched will phase separate thereby

leading to voids in the polymer matrix and increasing the porosity of the

film. The continuous film matrix of a crystallizable polymer may also be

filled with inorganic filler such as clay, titanium dioxide, calcium

carbonate, etc., to provide microporosity in the stretched polymeric

substrate.

Many other patents and publications disclose the

phenomenon of making microporous thermoplastic film products. For

example, European patent 1 41 592 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. This 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

Nos. 4,452,845 and 4,596,738 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

Nos. 4,777,073; 4,81 4, 1 24; and 4,921 ,653 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.

With reference to U. S. Patents Nos. 4,705,81 2 and

4,705,81 3, microporous films have 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 known to modify blends of LLDPE

and LDPE with a thermoplastic rubber such as Kraton. Other patents,

such as U. S. Patent No. 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

Nos. 4,472,328 and 4,921 ,652.

Relevant patents regarding extrusion lamination of

unstretched nonwoven webs include U. S. Patent Nos. 2,71 4,571 ;

3,058,868; 4,522,203; 4,61 4,679; 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 nonwoven

fibrous webs at pressure roller nips. The '203 and '941 patents are

directed to co-extruding multiple polymeric films with unstretched

nonwoven webs at pressure roller nips. The '840 patent discloses

preforming nonwoven polymeric fiber materials prior to extrusion

laminating with films to improve bonding between the nonwoven fibers and films. More specifically, the '840 patent discloses conventional

embossing techniques to form densified and undensified areas in

nonwoven base plies prior to extrusion lamination to improve bonding

between nonwoven fibrous webs and films by means of the densified fiber

areas. The '941 patent also teaches that unstretched nonwoven 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 nonwoven fibers to polymeric film are disclosed in U. S.

Patents Nos. 3,622,422; 4,379, 1 97 and 4,725,473.

It has also been known to stretch nonwoven fibrous webs

using intermeshing rollers to reduce basis weight and examples of patents

in this area are U. S. Patents Nos. 4, 1 53,664 and 4,51 7,71 4. The '664

patent discloses a method of incremental cross direction (CD) or machine

direction (MD) stretching nonwoven fibrous webs using a pair of

interdigitating rollers to strengthen and soften nonwoven webs. The '664

patent also discloses an alternative embodiment wherein the nonwoven

fibrous web is laminated to the thermoplastic film prior to intermesh

stretching.

Efforts have also been made to make breathable non-woven

composite barrier fabrics which are impervious to liquids, but which are

permeable to water vapor. United States Patent No. 5,409,761 is an example of a fabrication process from the patent art. According to this

'761 patent, a nonwoven composite fabric is made by ultrasonically

bonding a microporous thermoplastic film to a layer of nonwoven fibrous

thermoplastic material. These methods and other methods of making

breathable laminates of nonwoven and thermoplastic materials tend to

involve expensive manufacturing techniques and/or expensive raw

materials.

United States Patent 5,865,926 discloses a method of

making a microporous laminate of a nonwoven web and thermoplastic film

which is conducted on high-speed production machinery on the order of

about 200-500 fpm. Breathable composites were made having MVTRs

up to about 1 700 gms/m²/day at 1 00°F and 90% relative humidity (RH) .

Notwithstanding the extensive development of the art for

making breathable microporous films and laminates to provide air and

moisture vapor permeabilities with liquid-barrier properties, further

improvements are needed. In particular, improvements are desired for

producing microporous film products and laminates on high-speed

production machinery. It would be very desirable to produce microporous

film products without undesirable pin holes and without draw resonance.

In the past, attempts to increase production speeds have resulted in film

breakage or film products with inconsistent properties. SUMMARY OF THE INVENTION

This invention is direct to incrementally stretched non-

embossed films having high MVTRs greater than about 2000 gms/m²/day

at 1 00°F and 95% relative humidity (RH) according to ASTM E96E.

These non-embossed (flat) microporous films are permeable to air and

water vapor, but are barriers to liquid.

In the above-identified Patent Application Serial No.

09/080,063, incrementally stretched non-embossed films were disclosed

having high MVTRs. It was reported in that application that MVTRs for

embossed film on the order of about 1 200-1 400 gms/m²/day were

achieved, whereas MVTRs for flat or unembossed film on the order of

about 1 900-3200 gms/m²/day were achieved. This invention is directed

to further improvements of incrementally stretched non-embossed films

having high MVTRs, preferably on the order of about 2000 to about 4500

gms/m²/day . Breathable laminates of the microporous flat film with

nonwoven substrates are also produced at high speeds according to the

method of this invention.

In a broad form of the invention, the high MVTR film

comprises a blend of a thermoplastic polymer and a mechanical pore-

forming agent such as an inorganic filler (CaCO₃) . The pore-forming agent

in the film or laminate is activated upon incremental stretching to form a

microporous film or laminate of a fibrous web and film. While any one of

a number of thermoplastic polymers or blends may be employed along with pore-forming agents of inorganic or organic materials, there are

certain preferred compositions or modes of practice as described herein.

In one form of the invention, the microporous flat film is

made by melt-blending a composition comprising

(a) about 30% to about 45% by weight of a linear

low density polyethylene,

(b) about 1 % to about 1 0% by weight of a low

density polyethylene,

(c) about 40% to about 60% by weight calcium

carbonate filler particles, and, optionally,

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

copolymer of styrene sejected from the group

consisting of styrene-butadiene-styrene, styrene-

isoprene-styrene, and styrene-ethylene-butylene-

styrene, and blends thereof.

The melt-blended composition is extruded, preferably through a slot die,

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.

Speeds of at least about 750 fpm to about 1 200 fpm, or greater, have

been achieved without draw resonance. The use of the air knife to assist

in the elimination of draw resonance is known, for example, by reference

to U . S. Patent No. 4,626,574. Thereafter, an incremental stretching

force is applied to the film at the high speeds along lines substantially uniformally across the film and throughout its depth to provide a

microporous film. Thus, this invention provides a high speed method of

making microporous films and laminates with nonwoven substrates of

uniform gauge. The problem of draw resonance which has heretofore

resulted in irregular gauge or thickness in the film products is avoided,

even though line speeds of about 750-1 200 fpm are achieved.

The blend of LLDPE and LDPE within the approximate ranges

of components enables the production of film without breakage and pin

holes when balanced with the prescribed amount of calcium carbonate.

In particular, the LLDPE is present in an amount of about 35% to about

45% by weight in order to provide a sufficient amount of matrix to carry

the calcium carbonate filler particles thereby enabling the film to be

handled and stretched without pin holing and breakage. The LDPE in an

amount of about 3% to about 1 0% by weight also contributes to the

production of film without pin holing and enables the high speed

production without draw resonance. The polymeric matrix is balanced

with an amount of about 40% to about 55% by weight of calcium

carbonate particles having an average particle diameter of preferably about

1 micron to achieve sufficient MVTR in greater than 2000 gms/m²/day, or

in the range of about 2000-4500, or more, gms/m²/day. Furthermore, the

melt-blended composition may include a triblock polymer in an amount of

about 0% to about 6% by weight to facilitate stretching in high-speed

production without breakage. Other components such as about 5% by weight high density polyethylene (HDPE) and about 1 % by weight

antioxidants/processing aids are used. An incremental stretching force is

applied inline to the formed film under ambient conditions or at an

elevated temperature at speeds of at least about 550 fpm to about

1 200 fpm, or more, along lines substantially uniformly across the film and

throughout it depth to provide a microporous film.

The method of this invention also involves lamination of the

microporous-formable thermoplastic film to a nonwoven fibrous web

during extrusion. The extrusion lamination is conducted at the same high

speeds where a nonwoven fibrous web is introduced into the nip of rollers

along with the microporous-formable thermoplastic extrudate. The

compressive force between the fibrous web and the extrudate is

controlled to bond one surface of the web to the film and form a laminate.

The laminate is then incrementally stretched along lines substantially

uniformly across the laminate and throughout its depth in one direction to

render the film microporous. The laminate may be stretched in both the

cross direction and the machine direction to provide breathable cloth-like

liquid barriers capable of transmitting moisture vapor and air.

Other benefits, advantages and objectives of this invention

will be further understood with reference to the following detailed

description. DETAILED DESCRIPTION OF THE INVENTION

It is the primary objective of this invention to produce an

incrementally stretched non-embossed film having a high MVTR greater

than about 2000 gms/m²/day to about 4500 gms/m²/day at about

95% relative humidity (RH) at 1 00°F (according to ASTM E96E). It is the

further objective to produce such a microporous film and laminated

products thereof with nonwoven fibrous webs on high-speed production

machinery. It is the further objective of the method to produce such

microporous film products of regular gauge, uniform porosity and without

breakage.

A. Materials for the Method

The thermoplastic polymer for the film preferably is of the

polyolefin type and may be any of the class of thermoplastic polyolefin

polymers or copolymers that are processable into a film or for direct

lamination by melt extrusion onto the fibrous web. A number of

thermoplastic copolymers suitable in the practice of the invention are of

the normally-solid oxyalkanoyl polymers or dialkanoyl polymers

represented by poly(caprolactone) blended with polyvinylalcohol or starch

polymers that may be film-formed. The olefin based polymers include the

most common ethylene or propylene based polymers such as

polyethylene, polypropylene, and copolymers such as ethylene

vinylacetate (EVA), ethylene methyl acrylate (EMA) and ethylene acrylic

acid (EAA), or blends of such polyolefins. Other examples of polymers suitable for use as films include elastomeric polymers. Suitable

elastomeric polymers may also be biodegradable or environmentally

degradable. Suitable elastomeric polymers for the film include

poly(ethylene-butene), poly(ethylene-hexene), poly(ethylene-octene),

poly(ethylene-propylene), poly(styrene-butadiene-styrene), polyfstyrene-

isoprene-styrene), poly(styrene-ethylene-butylene-styrene), poly (ester-

ether), poly(ether-amide), poly(ethylene-vinylacetate), polyfethylene-

methylacrylate), poly(ethylene-acrylic acid), poly(ethylene butylacrylate),

polyurethane, poly(ethylene-propylene-diene), ethylene-propylene rubber.

This new class of rubber-like polymers may also be employed and they are

generally referred to herein as metallocene polymers or polyolefins

produced from single-cite catalysts. The most preferred catalysts are

known in the art as metallocene catalysts whereby ethylene, propylene,

styrene and other olefins may be polymerized with butene, hexene,

octene, etc., to provide elastomers suitable for use in accordance with the

principles of this invention, such as poly(ethylene-butene), poly(ethylene-

hexene), poly(ethylene-octene), poly(ethylene-propylene), and/or polyolefin

terpolymers thereof.

The microporous-formable film composition can be achieved

by formulating a thermoplastic polymer with suitable additives and pore-

forming fillers to provide an extrudate or film for lamination with the

nonwoven web. Calcium carbonate and barium sulfate particles are the

most common fillers. Microporous-formable compositions of polyolefins, inorganic or organic pore-forming fillers and other additives to make

microporous sheet materials are known. This method may be done in line

and provides economies in manufacturing and/or materials over known

methods of making laminates. In addition, as developed above,

microporous-formable polymer compositions may be obtained from blends

of polymers such as a blend of an alkanoyl polymer and polyvinyl alcohol

as described in U. S. Patent No. 5,200,247. In addition, blends of an

alkanoyl polymer, destructured starch and an ethylene copolymer may be

used as the microporous-formable polymer composition as described in U.

S. Patent No. 5,407,979. With these polymer blends, it is unnecessary

to use pore-forming fillers to provide microporosity upon incremental

stretching. Rather, the different polymer phases in the film themselves,

when the film is stretched at ambient or room temperature, produce

microvoids.

As developed above, these and other objectives are achieved

in a preferred form of the invention by first melt blending a composition

of

(a) about 30% to about 45% by weight of a linear

low density polyethylene,

(b) about 1 % to about 1 0% by weight of a low

density polyethylene,

(c) about 40% to about 60% by weight calcium

carbonate filler particles, and, optionally, (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 said melt blended composition into a nip of rollers

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 said film at said

speed along lines substantially uniformly across said film 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,

optionally, 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, processing aid such as a flurocarbon 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.

The triblock polymer may also be blended with oil, hydrocarbon, antioxidant and stabilizer. Antioxidants include tetrakis (methylene(3,5-di-

tert-butyl-4-hydroxyhydrocinnamate))methane (trade name is

Irganox 1 01 0), and tris(2,4-di-tert-butylphenyl)phosphite (trade name is

Irgafos 1 68) at a total of 500-4000 ppm (parts per million).

In the above method, the melt-blended composition is slot-die

extruded as a web through a cooling zone provided by an air knife, then

into a nip of rollers to form a film at high speeds. Use of the air knife, as

developed above, assists in the elimination of draw resonance, as is

known, for example, by reference to U. S. Patent No. 4,626,574. In

addition, as described in pending U. S. Application Serial No. 09/395,627,

filed September 1 4, 1 999, which is incorporated herein in its entirety by

reference. Devices for directing a stream of cooling gas to flow in the

cooling zone substantially parallel to the web surface are used. For

example, devices as shown in U. S. Patents Nos. 4,71 8, 1 78 and

4,779,355 may be used and the entire disclosures of these patents are

also incorporated herein by reference. After cooling, an incremental

stretching force is applied to the film or the laminate at high speeds along

lines substantially uniformly across the film and throughout it depth to

provide the incrementally stretched flat film having a high MVTR.

The flat films are produced according to the principles of this

invention upon extrusion of a web into a nip of rollers which provide a

polished chrome surface to form a flat film. The flat film, upon

incremental stretching, at high speeds, produces microporous film products having a high MVTR of greater than 2000 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 flat microporous film may be obtained with nonwoven fibrous

webs.

The nonwoven 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

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

filaments. The nonwovens 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

"nonwoven 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

nonwovens, see "Nonwoven Fabric Primer and Reference Sampler" by

E. A. Vaughn, Association of the Nonwoven Fabrics Industry, 3d Edition

(1 992).

In 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 the order of about 0.25 to 2 mils in thickness.

The nonwoven 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 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.

B. Stretchers for the Microporous Film and Laminates

A number of different stretchers and techniques may be

employed to stretch the film or laminate of a nonwoven fibrous web and

microporous-formable film. These laminates of nonwoven carded fibrous

webs of staple fibers or nonwoven spun-bonded fibrous webs may be

stretched with the stretchers and techniques described as follows:

1 . Diagonal Intermeshing Stretcher

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 means is typically utilized to drive the stationery

intermeshing roll. If the upper intermeshing roll is to be disengageable for

purposes of machine threading or safety, it is preferable to use an

antibacklash gearing arrangement between the upper and lower

intermeshing rolls to assure that upon reengagement the teeth of one

intermeshing roll always fall between the teeth of the other intermeshing

roll and potentially damaging physical contact between addenda of

intermeshing teeth is avoided. If the intermeshing rolls are to remain in constant engagement, the upper intermeshing roll typically need not be

driven. Drive may be accomplished by the driven intermeshing roll

through the material being stretched.

The intermeshing rolls closely resemble fine pitch helical

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

helix angle, a 0.1 00" normal pitch, 30 diametral pitch, 1 4¹/₂° 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.

2. Cross Direction Intermeshing Stretcher

The CD intermeshing stretching equipment is identical to the

diagonal intermeshing stretcher with differences in the design of the

intermeshing rolls and other minor areas noted below. Since the CD

intermeshing elements are capable of large engagement depths, it is

important that the equipment incorporate a means of causing the shafts

of the two intermeshing rolls to remain parallel when the top shaft is

raising or lowering. This is necessary to assure that the teeth of one

intermeshing roll always fall between the teeth of the other intermeshing

roll and potentially damaging physical contact between intermeshing teeth

is avoided. This parallel motion is assured by a rack and gear arrangement wherein a stationary gear rack is attached to each side frame in

juxtaposition to the vertically slidable members. A shaft traverses the side

frames and operates in a bearing in each of the vertically slidable

members. A gear resides on each end of this shaft and operates in

engagement with the racks to produce the desired parallel motion.

The drive for the CD intermeshing stretcher must operate

both upper and lower intermeshing rolls 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 reason for this will become evident with a description of the CD

intermeshing elements. _

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 1 /2"

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. 3. Machine Direction Intermeshing Stretcher

The MD intermeshing stretching equipment is identical to the

diagonal intermeshing stretch except for the design of the intermeshing

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

In the preferred embodiment, the rolls have a 5.933" diameter, 0.1 00"

pitch, 30 Diametral pitch, 1 4¹/_° pressure angle, and are basically a long

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

gear hob offset 0.01 0" 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.

4. Incremental Stretching Technique

The above described diagonal, CD or MD intermeshing

stretchers may be employed to produce the incrementally stretched film

or laminate of nonwoven 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

nonwoven 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 nonwoven 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 nonwoven

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 1 200 fpm or

faster. The results of such incremental or intermesh stretching produces

laminates that have excellent breathability and liquid-barrier properties, yet

provide superior bond strengths and soft cloth-like textures.

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.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further understood with reference to the

drawings in which:

FIG. 1 is a schematic of an inline extrusion lamination and

incremental stretching apparatus for making the microporous laminate of

this invention.

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

Fig. 1 illustrating the intermeshing rollers in diagrammatic form.

FIG. 3 is a graph demonstrating the line speeds for

Examples 1 -5.

FIG . 4 is a graph demonstrating the moisture vapor

transmission properties of both embossed and flat microporous films. FIG . 5 is a graph demonstrating the moisture vapor

transmission rate can be adjusted by heating the precursor film.

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 21 22X, which is an SBS < 50% by wt. -i- 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 as shown diagramatically in FIG. 1 . As

shown, the apparatus may be employed for film extrusion with and without lamination. In the case of film extrusion, the formulations of

Examples 1 -5 were fed from an extruder 1 through slot die 2 to form the

extrudate 6 into the nip of a rubber roll 5 and a metal roll 4 with an air

knife 3. Where extrusion lamination is practiced, there is an incoming web

of fibrous material 9 from roller 13 which is also introduced into the nip

of the rubber roll 5 and metal roll 4. 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 6 on the order of about 2 mils in

thickness was made which is taken off at roller 7. The air knife 3 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 6 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 extruders A and B 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. 3 is a graph demonstrating the line speeds for

Examples 1 -5. 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 3. 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. This is shown

diagramatically in FIG. 3.

FIG . 4 is a graph demonstrating the moisture vapor

transmission properties 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. As

shown schematically in FIG. 1 , where the incoming film 1 2 at ambient

temperature was passed through temperature controlled rollers 20 and 21

before CD and MD incremental stretching rollers (10 and 1 1 , and 10' and

1 1 '), the temperatures and the depths of engagements can be controlled.

Remarkably, the MVTR of the flat film exceeded the MVTR of the

embossed film as shown in FIG. 4. In brief, 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. Unexpectedly, as also shown in FIG. 5, the MVTR of the

microporous film can also be controlled by the web temperature during the stretching. Fig. 5 shows the film when heated to different temperatures

before CD stretching can result in different MVTRs. The data reported in

FIG. 5 was for a CD rollers engagement dept of 0.065" and MD rollers

engagement depth of 0.040" where the temperature of roller 21 was

maintained at ambient. 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, 1 47 which is incorporated herein by reference.

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

to the naked eye.

EXAMPLE 6

Other blends of LLDPE, LDPE and HDPE having the

compositions reported in the following TABLE 2 were extruded to form

flat films and the films were then incrementally stretched to provide

microporous films having high MVTRs greater than about 2000

gms/m²/day, for example from about 2000 to 4500 gms/m²/day.

TABLE 2

The formulation of TABLE 2 was extruded into films

employing an extrusion apparatus similar to that as shown diagramatically

in FIG. 1 . As shown, the apparatus may be employed for film extrusion

with and without lamination. In the case of film extrusion, the formulation

of EXAMPLE 6 is fed from an extruder 1 through slot die 2 to form the

extrudate 6 into the nip of a rubber roll 5 and a metal roll 4. The metal

roll is a polished chrome roll. Instead of the air knife, two air cooling

devices (ACD), ACD No. 1 and ACD No. 2 are used, but they are not

shown on the drawing. Again, where extrusion lamination is practiced,

there is an incoming web of fibrous material 9 from roller 13 which is also

introduced into the nip of the rubber roll 5 and metal roll 4. In EXAMPLE 6, the thermoplastic film is produced for subsequent

incremental stretching to form the microporous film. As shown in

TABLE 2, a polyethylene film 6 on the order of about 1 .2 mils in thickness

is made at a speed of about 900 fpm, which is taken off at roller 7. The

ACDs have dimensions approximating the web width with a sufficient

manifold sized to deliver the cooling air. As stated above, these ACDs are

described in more detail in the above mentioned 4,71 8, 1 78 and

4,779,355 patents. The air velocity blown through the nozzle of ACD

No. 1 and against the extrudate 6 is about 4000 fpm at the exit of the

nozzle, and air volume is 68 cfm per foot. The air velocity of ACD No. 2

is about 6800 fpm at the exit of the nozzle, and the air volume is 1 1 3 cfm

per foot. The ACD No. 1 is located about 3.7 inches (95 mm) from the

die and about 1 inch (25 mm) from the web 6. The ACD No. 2 is located

on the opposite side of the web 6 about 1 1 .2 inches (2.85 mm) from the

die and about 0.6 inches ( 1 5 mm) from the web. The nip of the rubber

roll 5 and metal roll 4 is located about 29 inches (736 mm) from the die.

The compressive force at the nip and the ACDs are controlled such that

the film is made without pin holing and without draw resonance. The

melt temperatures from the slot die feed zone to the screw tip of

extruders A and B (not shown) were maintained to provide an extrudate

temperature of about 243°C with cooling gas from the ACDs No. 1 and

No. 2 decreasing the web temperatures to 21 1 °C-1 81 °C before entering

the nip. In this EXAMPLE 6, with reference to FIG. 1 , where the incoming film 1 2 at ambient temperature is passed through temperature controlled

rollers 20 and 21 before CD and MD incremental stretching rollers (10 and

1 1 , and 10' and 1 1 '), the temperatures and the depths of engagements

can be controlled. In brief, moisture vapor transmission rates (MVTRs) for

the flat film on the order of about 2000-4500 gms/m²/day are achieved.

The MVTR of the microporous film can also be controlled by the web

temperature during the stretching. When the film is heated to different

temperatures before CD stretching, different MVTRs can result.

As reported in Patent Application Serial No. 09/395,627,

filed September 1 4, 1 999, it has been found that ACDs which provide a

substantially parallel cooling air flow with vortices over the web surface

efficiently cool the web. Surprisingly, web draw resonance which one

may normally encounter in prior techniques has been eliminated or

controlled at high speeds of about 500-1 200 fpm of the web.

Furthermore, as also reported in that application, when laminates of film

and nonwoven are made, the bond strengths are very effectively achieved

at targets which have not been possible with other known methods of

cooling while at the same time maintaining film gauge controls, even at

web high speeds.

In view of the above detailed description, it will be

understood that variations will occur in employing the principles of this

invention depending upon materials and conditions, as will be understood

by those of ordinary skill in the art.

WHAT IS CLAIMED IS:

Claims

1 . An incrementally stretched non-embossed film having

a high moisture vapor transmission rate (MVTR) comprising

a thermoplastic polymer containing a dispersed phase of

particles selected from the group consisting of an inorganic filler and an

organic material,

said film having a flat surface and a thickness with

incrementally stretched areas to provide microporosity in the film having

a high MVTR greater than about 2000 gms/m²/day according to ASTM

E96E.

2. The film of claim 1 wherein the MVTR is on the order

of about 2000 to about 4500 gms/m²/day according to ASTM E96E.

3. The film of claim 1 wherein the thermoplastic

composition is a polymer selected from the group consisting of

polyethylene, polypropylene, and copolymers thereof.

4. The film of claim 1 wherein said thermoplastic

composition is an elastomeric polymer.

5. The film of claim 4 wherein said elastomeric polymer

is selected from the group consisting of poly(ethylene-butene),

poly(ethylene-hexene), poly(ethylene-octene), poly(ethylene-propylene),

poly (styrene-butadiene-styrene) , poly (sty rene-isoprene-styrene) ,

poly(styrene-ethylene-butylene-styrene), poly (ester-ether), poly (ether-

amide), poly(ethylene-vinylacetate), poly(ethylene-methylacrylate),

poly(ethylene-acrylic acid), poly(ethylene butylacrylate), polyurethane,

poly(ethylene-propylene-diene), and ethylene-propylene rubber.

6. The film of claim 1 wherein said inorganic filler is

selected from the group consisting of calcium carbonate and barium

sulfate.

7. The film of claim 1 laminated to a fibrous web.

8. The film of claim 7 wherein the fibers of said fibrous

web are selected from the group consisting of polypropylene,

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

co-extrusions of two or more of such fibers.

9. The film of claim 7 wherein the fibrous web has a

weight from about 5 to about 70 gms/yd² and the microporous film has

a thickness on the order of about 0.25 to about 1 0 mils.

1 0. The film of claim 1 wherein said film has a thickness

on the order of about 0.25 to about 1 0 mils.

1 1 . The film of claim 1 wherein the film composition

comprises

(a) about 30% to about 45% by weight of a linear

low density polyethylene,

(b) about 1 % to about 1 0% by weight of a low

density polyethylene, and

(c) about 40% to about 60% by weight of calcium

carbonate filler particles.

1 2. The film of claim 1 1 wherein the composition further

contains high density polyethylene and titanium dioxide.

1 3. An incrementally stretched non-embossed film having

a high moisture vapor transmission rate (MVTR) produced by a process

comprising the steps of

melt blending a thermoplastic polymer and filler particles to

form a microporous-formable thermoplastic polymer composition,

cast extruding a flat precursor film of the composition, and

incrementally stretching the flat precursor film to impart

microporosity in the film having a high MVTR greater than about 2000

gms/m²/day.

1 4. The film of claim 1 3 wherein the thermoplastic

composition is a polymer selected from the group consisting of

polyethylene, polypropylene, and copolymers thereof.

1 5. The film of claim 1 3, wherein said thermoplastic

composition is an elastomeric polymer.

1 6. The film of claim 1 3 wherein said elastomeric polymer

is selected from the group consisting of poly(ethylene-butene),

poly(ethylene-hexene), poly(ethylene-octene), poly(ethylene-propylene),

poly (styrene-butadiene-styrene) , poly(styrene-isoprene-styrene) ,

poly(styrene-ethylene-butylene-styrene), poly(ester-ether), poly(ether-

amide), poly(ethylene-vinylacetate), poly(ethylene-methylacrylate),

poly(ethylene-acrylic acid), poly(ethylene butylacrylate), polyurethane,

poly(ethylene-propylene-diene), and ethylene-propylene rubber.

1 7. The film of claim 1 3 wherein said inorganic filler is

selected from the group consisting of calcium carbonate and barium

sulfate.

1 8. The film of claim 1 3 laminated to a fibrous web.

1 9. The film of claim 1 8 wherein the fibers of said fibrous

web are selected from the gbroup consisting of polypropylene,

polyethylene, polyesters, cellulose, rayon, nylon, and blends or co-

extrusions of two or more of such fibers.

20. The film of claim 1 8 wherein the fibrous web has a

weight from about 5 to about 70 gms/yd² and the microporous film has

a thickness on the order of about 0.25 to about 1 0 mils.

21 . The film of claim 1 3 wherein said film has a thickness

on the order of about 0.25 to about 1 0 mils.

22. The film of claim 1 3 wherein the film composition

comprises

(a) about 30% to about 45% by weight of a linear

low density polyethylene,

(b) about 1 % to about 1 0% by weight of a low

density polyethylene, and

(c) about 40% to about 60% by weight of calcium

carbonate filler particles.

23. The film of claim 22 wherein the composition further

contains high density polyethylene and titanium dioxide.