AU2001270168A1 - Air and moisture vapor breathable biodegradable films and method of manufacture - Google Patents

Description

AIR AND MOISTURE VAPOR BREATHABLE BIODEGRADABLE FILMS AND METHOD OF MANUFACTURE

RELATED APPLICATIONS

This application is a continuation-in-part application of

Application Serial No. 09/480,374, filed January 10, 2000, which is, in

turn, a continuation-in-part application of Application Serial

No. 09/080,063, filed May 15, 1998, now U.S. Patent No. 6,013,1 51 ,

and Application Serial No. 09/395,627, filed on September 14, 1999.

All of the above applications are incorporated herein in their entireties by

reference.

FIELD OF THE INVENTION

The present invention relates to air and moisture vapor

breathable biodegradable plastic films and to processes for their

manufacture.

BACKGROUND OF THE INVENTION

Methods of making plastic film date back many years. For

example, more than thirty years ago U. S. Patent No. 3,484,835 (1968) 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. 4,376,147 (1983) discloses an embossed cross

direction (CD) and machine direction (MD) film. U. S. Patents

Nos. 5,202,173 (1993) and 5,296,184 (1994) teach an ultra-soft

thermoplastic film which was made by incrementally stretching the

embossed film and the formation of perforations 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 (MVT).

In 1976, 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). 1976, 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 141592 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.

U. S. Patents Nos. 3,137,746; 4,777,073; 4,814, 124; and 4,921 ,653

disclose the same processes described by the above-mentioned

publications involving the steps of first embossing a polyolefin film

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

product. Other patent publications have issued, including WO 98/23673,

which are directed to thermoplastic copolyester films having improved

moisture vapor transmission rates and are made by mixing a copolyester

resin and an inorganic filler.

Biodegradable and/or compostable products help preserve

environmental resources and prevent generation of additional waste.

Both manufacturers and consumers are aware of the finite amount of

space in landfills and other disposal sites and may affirmatively seek

biodegradable and/or compostable products over nonbiodegradable and/or

noncompostable products. The need for biodegradability and/or

compostability is particularly important in disposable, high use products

such as baby diapers, feminine hygiene products, hospital drapes, and the

like.

Thermoplastic films that are biodegradable and/or

compostable are known in the prior art. The above-mentioned U.S. Patent No. 5,407,979 discloses a biodegradable thermoplastic film

composed of three components: an alkanoyl polymer, destructured

starch, and an ethylene copolymer. The components can be extruded and

the film can be stretched to form a breathable film. U.S. Patent

No. 5,200,247 discloses a biodegradable thermoplastic film containing an

alkanoyl polymer/polyvinyl alcohol (PVA) blend. U.S. Patent

No. 5,196,247 discloses a compostable polymeric composite sheet and

method of making or composting.

Totally biodegradable and/or compostable soft cloth-like

composites are disclosed in U.S. Patent No. 5,851 ,937. The composites

are made by incrementally stretching one or more plies of totally

biodegradable and/or compostable nonwoven webs and plastic films to

provide a soft cloth-like feel.

There still remain drawbacks to the production of breathable

films and laminates which are liquid barriers. It is difficult to obtain a

liquid barrier film of sufficient strength while maintaining the properties

of biodegradability, air breathability and moisture vapor transmission.

SUMMARY OF THE INVENTION

This invention is directed to a biodegradable film which is

both air and moisture vapor breathable, and is a barrier to liquid. These

films have moisture vapor transmission rates (MVTRs) greater than about

1000 grams (gms) per m² per day and 100°F and 95% relative humidity (RH) according to ASTM E96E and air permeabilities greater than about

30 cc/cm²/min at 90 psi air pressure.

In the above-identified patent applications serial

nos. 09/080,063 and 09/480,374, incrementally stretched films were

disclosed having high MVTRs. These applications were directed to

improvements in incrementally stretched embossed and unembossed films

having MVTRs, preferably on the order of about 1200 to about

4500 gms/m²/per day. Breathable laminates of these films with

nonwoven substrates were also disclosed.

This invention is directed to further improvements in

biodegradable films and laminates which are both permeable to air and

moisture vapor. In a broad form of the invention, the biodegradable film

comprises a blend of a biodegradable thermoplastic polymer and a

mechanical pore forming agent such as inorganic fillers of calcium

carbonate, silica and zeolite. The pore forming agent in the film or

laminate is activated upon stretching, preferably incremental stretching,

to form a microporous film or laminate of a fibrous web and film. The

biodegradable polymers such as polycaprolactone (PCL) blended with

starch polymers or polyvinylalcohol (PVA) that may be film-formed are

suitable. Other biodegradable polymers include polylactides (PLA),

polyesters and copolyesters. The biodegradable films and laminates can be used for diaper

backsheets, sanitary napkins and pads, and other medical, packaging and

garment applications. The biodegradable film is especially suitable for

these and other similar applications because of its air breathability,

moisture vapor breathability and water impermeability. The benefits and

properties of the biodegradable film of this invention and its method of

manufacture 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 air

and moisture vapor breathable biodegradable film having an air

permeability of at least about 30 cc/cm²/min at 90 psi air pressure and a

MVTR greater than about 1000 gms per m² per day and 100°F and 95%

relative humidity (RH) according to ASTM E96E. It is the further

objective of this invention to produce an incrementally stretched

biodegradable thermoplastic film having these breathable properties of

regular gauge, uniform porosity and without breakage.

A. Biodegradable Film and Laminate Materials

The biodegradable film composition can be achieved by

formulating a biodegradable thermoplastic polymer with suitable additives

and pore forming fillers to provide an extrudate or film. The film may be

laminated with a nonwoven web. Calcium carbonate, barium sulfate, silica, and zeolite particles are the most common fillers. As developed

above, it is known to provide biodegradable films with different polymer

phases in the film so that when the film is stretched at ambient or room

temperature, microvoids are produced to provide breathability and

moisture vapor transmission. These methods are described in U.S.

Patents Nos. 5,200,247, and 5,407,979. In contrast, this invention is

directed to the use of inorganic fillers to provide high air permeabilities

and high MVTRs with liquid barrier properties in biodegradable films.

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 40% to about 75% by weight of a biodegradable polymer of

the type identified above, and (b) about 25% to about 60% by weight of

an inorganic filler particles, for example, calcium carbonate, zeolite, silica,

talc, barium sulfate, mica, and the like, then extruding said melt blended

composition with other additives into a nip of rollers to form a film at a

speed on the order of at least about 550 fpm to about 1200 fpm without

draw resonance, and applying an incremental stretching force to said film

at said speed along lines substantially and uniformly across the film and

throughout its depth to provide a biodegradable microporous film.

More particularly, in preferred form, the melt blended

composition consists essentially of about 60% to about 75% of a

polyester such as aliphatic-aromatic copolyesters which are described in

WO 98/23673 and that description is incorporated herein by reference. ln particular, these thermoplastic copolyesters may comprise at least one

aliphatic dicarboxylic acid, at least one aromatic dicarboxylic acid, and at

least one aliphatic diol having from 4 to about 12 carbon atoms.

Alternatively, the thermoplastic copolyester may comprise at least one

aromatic dicarboxylic acid, at least one aliphatic diol and a polyalkylene

ether. The aliphatic dicarboxylic acid is selected from the group

consisting of adipic acid, glutaric acid, cyciohexanoic acid, and mixtures

thereof; at least one of said aromatic dicarboxylic acids is selected from

the group consisting of terephthalic acid, isophthalic acid,

naphthalenedicarboxylic acid, and mixtures thereof; and at least one of

said aliphatic diols is selected from the group consisting of

1 ,4-butanediol, cyclohexanedimethanol, a polyalkylene ether compound

selected from the group consisting of poly(ethylene glycol),

poly(tetramethylene glycol) and poly(propylene glycol), and mixtures

thereof. The thermoplastic copolyester may comprise various

combinations of aromatic dicarboxylic acid, aliphatic diols, cyclicaliphatic

dicarboxylic acids, polyalkylene ethers, and the like, all described in the

WO 98/23673 publication as examples of copolyesters within the scope

of this invention.

Other polymers include ester-ether polyester (Hytrel and

Armtel); nylon-ether polyester (Pebax); polyethylene terephthalate (PET);

polyvinyl alcohol (PVA); polycaprolactone (PCL); starch; polylactide (PLA);

a blend of starch and PVA, PCL, or PLA; polyesters such as polyhydroxy(butyrate) (PHB), polyhydroxy(valerate) (PHV); and mixtures

thereof. Preferably, about 25-40% of calcium carbonate, silica, barium

sulfate, or zeolite, having an average particle size of about 1 to about

10 / is used.

The biodegradable nonwovens may be laminated to the films

and they include preferably melt-stable lactide polymers of the type

disclosed in U.S. Patent No. 5,539,081 , that is, polylactide nonwovens

(PLA). All the filaments of the nonwoven are made entirely of a polymer

or a mixture of polymers derived from lactic acid, that is L lactic acid,

D lactic acid, or a mixture of L and D lactic acids. Other nonwovens

which are biodegradable and/or compostable include cotton nonwovens,

cellulosic nonwovens, aliphatic-aromatic copolyesters, and their blends.

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. Embossed or flat

(non-embossed) films can be produced. 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 14, 1999, 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. 4,718,178 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 its depth to

provide the incrementally stretched embossed or fiat film having a high

MVTR and air permeability.

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 1000 gms/m²/day. It has

been found that flat film can be incrementally stretched more uniformly

than embossed film. The stretching process may be conducted at

ambient temperature, room temperature, or at an elevated temperature,

as understood in the art. As also understood in the art, "ambient" means

surrounding temperature or atmosphere which could be whatever process

conditions exist surrounding the film. As described above, laminates of

the microporous film may be obtained with nonwoven fibrous webs.

In a preferred form, the microporous laminate 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 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 0.100" 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.

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 0.019" clearance

for material on all sides. As with the diagonal intermeshing stretcher, this

CD intermeshing element configuration would have a 0.100" 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, 0.100"

pitch, 30 Diametral pitch, 14%° 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 0.120 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 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 FIGURES

FIG. 1 is a microphotograph of the film surface of

Example 1 A at 1000X.

FIG. 2 is a microphotograph of a cross-section of

Example 1 A film at 2000X.

FIG. 3 is a microphotograph of the film surface of

Example 1 B at 1000X in the unstretched area due to intermeshing.

FIG. 4 is a microphotograph of the film surface of

Example 1 B at 1000X in the stretched area due to intermeshing

stretching. FIG. 5 is a microphotograph of a cross-section of

Example 1 B film at 2000X through the stretched surface area.

Examples 1A and 1 B

A biodegradable copolyester of an aromatic-aliphatic type,

as fully described in the examples of WO 98/23673, is employed in these

examples. More specifically, a film having representative biodegradable

copolyesters described in the examples of this publication, containing

about 25% to about 40% zeolite or calcium carbonate, are extruded by

using a conventional slot die cast film extrusion technique which is well

known to a person of ordinary skill in the art. In particular, films having

thicknesses of about 2 mil (50 grams per square meter) are extruded at

melt temperatures on the order of about 425°F-475°F. A

microphotograph of such a film surface is shown in FIG. 1 , and a cross-

section is shown in FIG. 2. The film was tested and found not to be air

permeable, but had a MVTR (moisture vapor transmission rate) of 939

g/m²/day according to the ASTM E96E test method.

The film of Example 1 A, when incrementally stretched at a

temperature of about 72°F with CD engagement of 0.070 inch followed

with MD engagement of 0.050 inch, with apparatus described above,

became air breathable and had an increased moisture vapor transmission

rate. The MVTR increased from 939 g/m²/day (Example 1 A) to

2350 g/m²/day (Example 1 B). The air permeability of the film having originally zero permeability (Example 1 A), became 570 cc of air/cm²/min

under 90 psi air pressure (Example 1 B).

Microphotographs of the film surfaces and cross-sections of

Examples 1 A and 1 B did show the embedded inorganic particles (see

FIGS. 1 -5). The high MVTR and air-permeable biodegradable film of this

invention did have the pore formation around the inorganic particles upon

incremental stretching (see FIGs. 4 and 5). Yet, the unstretched area did

not show pore formation (see FIG 3). The cross-section of Example 1 B

film (see FIG. 5) clearly indicated that pores are connected to allow air

flow. In Example 1 A film (see FIG. 2, cross-section), there were no pore

connections to allow air to flow through.

The mechanical properties of Example 1 A film are as

follows:

The biodegradable film of Example 1 B is suitable for diaper

backsheets, sanitary napkins, and health care garment applications where

air flow (ventilation), high moisture vapor transmission, and liquid barrier

properties are needed for skin care and comfort while wearing.

Examples 2A-2H

In these Examples, copolyesters of the aromatic-aliphatic

type as employed in Example 1 A are extruded into a film in a similar

fashion. These films of Examples 2A-2H are CD and/or MD stretched at

room temperature to become air and moisture vapor breathable

biodegradable films, as indicated below.

Other biodegradable polymers such as the polylactides,

polycaprolactones, starch, polyvinylalcohols, polyesters, and copolyesters, can be processed with inorganic filler particles to provide

air and moisture breathable films in view of the above description.

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

to those of ordinary skill in the art.

WHAT IS CLAIMED IS:

Claims (21)

1 . An air and moisture breathable biodegradable thermoplastic

film comprising

a biodegradable thermoplastic polymer containing a

dispersed phase of inorganic filler particles,

said film having a liquid impermeable thickness with

stretched areas to provide microporosity in the film having a moisture

vapor transmission rate MVTR greater than about 1000 g/m²/day

according to ASTM E96E and air breathability of greater than about

30 cc/cm²/min at 90 psi air pressure.

2. The film of claim 1 wherein the biodegradable thermoplastic

polymer is selected from the group consisting of polycaprolactone, starch,

polyvinylalcohol, polylactide, polyester, and copolyester, and mixtures

thereof.

3. The film of claim 1 wherein said filler is selected from the

group consisting of calcium carbonate, silica, talc, barium sulfate, zeolite,

and mica, and mixtures thereof.

4. The film of claim 1 laminated to a biodegradable fibrous

web.

5. The film of claim 4 wherein the fibers of said fibrous web are

selected from the group consisting of a cellulosic polymer, polyester,

copolyester, a polymer of entirely L lactic acid, a polymer of entirely

D lactic acid, a copolymer of L lactic acid and D lactic acid and a blend of

polymers of L lactic acid and D lactic acid.

6. The film of claim 1 wherein the biodegradable thermoplastic

polymer is selected from the group consisting of polyvinyl alcohol (PVA),

polycaprolactone (PCL), polylactide (PLA), starch, a blend of starch and

PVA, PCL or PLA, polyhydroxy(butyrate) (PHB), polyhydroxy(valerate)

(PHV), and aliphatic-aromatic copolyesters, and mixtures thereof.

7. The film of claim 1 wherein the microporous film has a

thickness on the order of about 0.25 to about 10 mils.

8. The film of claim 1 wherein the microporous film has a

thickness on the order of about 0.25 to about 2 mils.

9. The film of claim 1 wherein the moisture vapor transmission

rate (MVTR) is about 2000 to about 4500 grams per m² per day

according to ASTM E96E and air permeability is about 200 to about

1600 cc/min/cm² at 90 psi air pressure.

10. The film of claim 1 wherein said inorganic filler is selected

from the group consisting of calcium carbonate, barium sulfate, mica,

talc, silica and zeolite.

1 1. A high speed method of making an air and moisture

breathable biodegradable thermoplastic film having liquid barrier properties

comprising

melt blending about 40% to about 75% by weight of a

biodegradable thermoplastic polymer and about 25% to about 60% by

weight of inorganic filler particles to form a biodegradable thermoplastic

polymer composition,

extruding a web of said molten thermoplastic composition

from a slot die through a cooling zone into a nip of rollers to form a film

having a thickness of about 0.25 to about 10 mils at a speed on the

order of at least about 550 fpm to about 1200 fpm without draw

resonance,

applying an incremental stretching force to said film at said

speeds along the lines substantially and uniformly across said film and

throughout its depth to provide a biodegradable microporous film with an

MVTR greater than about 1000 g/m²/day according to ASTM E96E, and

air breathability greater than about 30 cc/cm²/min at 90 psi air pressure.

12. The method of claim 1 1 wherein the MVTR is on the order

of about 2000 to about 4500 g/m²/day according to ASTM E96E and air

permeability is about 200 to about 1600 cc/min/cm² at 90 psi air

pressure.

13. The method of claim 1 1 comprising introducing a

biodegradable nonwoven fibrous web into said nip of rollers and

controlling the compressive force to bond the web to the film and

stretching to form a laminated biodegradable film.

14. The method of claim 1 1 wherein the biodegradable

thermoplastic polymer is selected from the group consisting of

polycaprolactone, starch, polyvinylaicohol, polylactide, polyester,

copolyester, and mixtures thereof.

1 5. The method of claim 1 1 said filler is selected from the group

consisting of calcium carbonate, silica, talc, barium sulfate, zeolite, and

mica, and mixtures thereof.

16. The method of claim 1 1 wherein the fibers of said fibrous

web are selected from the group consisting of a cellulosic polymer,

polyester, copolyester, a polymer of entirely L lactic acid, a polymer of

entirely D lactic acid, a copolymer of L lactic acid and D lactic acid and

a blend of polymers of L lactic acid and D lactic acid.

17. The method of claim 1 1 wherein the biodegradable

thermoplastic polymer is selected from the group consisting of polyvinyl

alcohol (PVA), polycaprolactone (PCL), polylactide (PLA), starch, a blend

of starch and PVA, PCL or PLA, polyhydroxy(butyrate) (PHB),

polyhydroxy(valerate) (PHV), and aliphatic-aromatic copolyesters, and

mixtures thereof.

18. The method of claim 1 1 wherein the microporous film has

a thickness on the order of about 0.25 to about 10 mils.

19. The method of claim 1 1 wherein the microporous film has

a thickness on the order of about 0.25 to about 2 mils.

20. The method of claim 1 1 wherein the moisture vapor

transmission rate (MVTR) is on the order of about 2000 to about

4500 grams per m² per day according to ASTM E96E.

21 . The method of claim 1 1 wherein said inorganic filler has an

average particle size of about 1 to about 10 microns and is selected from

the group consisting of calcium carbonate, barium sulfate, silica and

zeolite.