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 C. A. 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 alkanol 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.

In 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 10/1 ils 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 flat 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/yd, 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/° 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, 141/2'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 0.010" 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 microparous-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 1 OOOX.

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 1 A and 1B 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 1A, 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 gim2/day (Example-1B). 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 1B 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 :

Example A Example B Ratio of 1 B/1 A Total Basis Weight (GSM) 50 35 0. 7 Air flow cc/cm2/min at 90 psi 0 570 MVTR 939 2350 2.5 (g/m2/day) ASTM E96E MD ultimate tensile 1116 885 (grams/inch) CD ultimate tensile 756 661 (grams/inch) MD elongation at break (%) 707 494 CD elongation at break 539 436

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 1A 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. Example Intermeshing Air fiow Moisture Vapor Basis Stretch Transmission weight ration stretching (inches) cc/cm2/min Rate E96E (GSM) (before/after) CD MD 90 psi air gm2/day 1 A 0 0 0 939 50 0 (reference) 2A 0.040 0 50 1365 48 1. 05 2B 0.040 0.040 110 1665 45 1.11 2C 0.050 0 140 1665 45 1. 11 2D 0.050 0.050 280 2122 39 1.28 2E 0.060 0 200 1895 40 1. 25 2F 0.060 0.060 490 2350 33 1. 51 2G 0.070 0 310 2122 36 1. 39 2H 0.070 0.070 720 2652 29 1. 72 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 :