WO2001051548A2 - Antibacterial microporous film and method of making - Google Patents

Abstract

Antibacterial unembossed and microembossed film products permeable to moisture vapor and which act as barriers to bacteria and liquid are made by a high speed method. The antibacterial microembossed microporous films have impact strengths greater than 150 grams according to ASTM D-1709 and high moisture vapor transmission rates (MVTRs) on the order of about 1000 to about 4500 gms/m2/day according to ASTM E96E.

Description

ANT1BACTERIAL MICROPOROUS FILM AMD METHOD OF MAKING

RELATED APPLICATIONS

This application is a continuation-in-part application of

Application Serial No. 09/480,374, filed January 1 0, 2000, which is,

in turn, 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 on September 1 4, 1 999. All

of the above applications are incorporated herein in their entireties by

reference.

FIELD OF THE INVENTION

This invention relates to antibacterial microporous films and

a high speed method of making them.

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 ( 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. 4,376, 147 (1 983) discloses an embossed cross direction

(CD) and machine direction (MD) film. U. S. Patents Nos. 5,202, 1 73

(1 993) and 5,296,1 84 (1 994) 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

mfcrovoids to enhance the permeability of the otherwise imperforate film to improve moisture vapor transmission (MVT). The embossed film is

preferably embossed with at least about 4 and not more than about

600 bosses per square inch and drawn sequentially. The 4 to 600 bosses

per square inch is equivalent to about 2 to 25 embossed lines per inch.

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. Svnth. 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. U. S. Patents

Nos. 3, 1 37,746; 4,777,073; 4,81 4, 1 24; 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. In the case of the

'746 patent, the embossing is up to 300 bosses per square inch which is

equivalent to about 1 7 embossed lines per inch. The '073 patent does

not teach the geometry of the embossing. The ' 1 24 and '653 patents

teach embossing to improve tear strength.

U. S. Patent No. 4,308,303 discloses a bacterial barrier of

a microporous film having a pore size not greater than about 0.2 micron

which is prepared by stretching a film containing filler with two sets of 4-

roll godets which operate at different speeds. U . S. Patents

Nos. 4,344,999; 4,353,945 and 4,71 3,068 are further examples of

patents disclosing stretching of polyolefin and filler precursers to provide

microporosities less than about 0.2 micron.

Notwithstanding the extensive development of the art for

making plastic films and breathable microporous films 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 having antibacterial properties and

other desirable properties.

SUMMARY OF THE INVENTION

This invention is directed to antibacterial microporous

thermoplastic films and a method for making them. The product can be

made on high-speed production machinery at speeds of at least about 550

fpm, preferably about 700-1 200 fpm.

In the above-identified patent applications, incrementally

stretched unembossed and microembossed thin films were disclosed

having high MVTRs, i.e., greater than 1 000 gms/m²/day, preferably about

2000 to 4500 gms/m²/day (ASTM E96E). This invention is directed to

further improvements of incrementally stretched unembossed and

mircoembossed thin films having antibacterial properties. These films also

have high MVTRs and high impact strength. Antibacterial microporous

strip or patch laminates of nonwoven webs with the microporous film are

also produced at high speeds according to this invention.

This invention provides an antibacterial microporous film

having a high moisture vapor transmission rate (MVTR) comprising a

thermoplastic polymer film containing a dispersed phase of particles

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

material. An antibacterial agent may also be added to the composition to

achieve additional protection against bacteria. The film has a thickness of about 0.0008 to about 0.002 inch with incrementally stretched areas in

the film to provide microporosity in the film with an MVTR greater than

about 1 000 gms/m²/day according to ASTM E96E. The film microporosity

has a pore size distribution wherein the largest pore size is about 0.22

micron as determined by PMI capillary flow porometry. Preferably, the

smallest pore size is about 0.05 micron and about 80% of the pores range

from about 0.05 to about 0.08 micron.

It has been found that an incrementally stretched

microporous thin thermoplastic film having a microembossed rectangular

engraving of intersecting cross direction (CD) and machine direction (MD)

iines of about 1 65 to 300 lines per inch in both directions provides a

higher impact strength than a non-embossed film. Impact strengths

greater than about 1 50 grams are achieved (ASTM D1 709) . The thin film

has a thickness of about 0.0008 to about 0.002 inch and an engraving

depth of about 0.0008 to about 0.002 inch. In a preferred rectangular

embossed film, about 250 lines per inch are embossed in both the

width (CD) and length (MD) of the film.

Antibacterial strip or patch laminates of nonwoven webs and

the incrementally stretched microembossed film are also provided where

only a portion of the film is laminated to the nonwoven web. In the case

of these laminates, the film-only portion is provided with improved impact

strength and the resulting laminate has an overall improved impact and

tear strength. The method of this invention involves extrusion of a

microporous-formable thermoplastic film into a CD and MD embossing

roller nip where the roller is engraved with a rectangular pattern of CD and

MD lines of about 1 65-300 per inch in both directions. The microporous-

formable thermoplastic composition of the film may comprise 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 is then

activated upon incremental stretching to form a microporous film. This

unique method not only provides economies in manufacturing breathable

laminates, but also enables their production on high-speed machinery on

the order of about 700-1 200 fpm.

The method involves melting a microporous-formable

thermoplastic composition and slot-die extruding a web of that

composition through a cooling zone into a nip of embossing rollers to form

a film at a speed preferably greater than about 700 feet per minute (fpm).

A stream of cooling gas (air) is directed at the film during its drawdown

into a film. The air flow through the cooling zone is substantially parallel

to the surface of the web to cool the web and form a film without draw

resonance.

In the preferred form of the method, the effectiveness of the

cooling gas is enhanced by creating a plurality of vortices of the gas as

the stream moves through the zone to cool the web. The vortices

enhance the effectiveness of the cooiing gas by mixing the cooling gas and making the flow of the cooling gas turbulent in the cooling zone. A

cooling device is used to create the vortices and make the gas stream

move in different directions parallel to the movement of the web.

Alternatively, the gas stream moves primarily in the same direction as the

web movement or in a direction opposite to the movement of the web.

Alternatively, where it is desired to achieve impact strength

of the microporous film in a strip laminate with a nonwoven, a strip of

nonwoven fibrous web is introduced into the nip of embossing rollers with

the extruded film and the lamination temperature is controlled by the

cooling gas to control target bond levels at high speeds of extrusion

lamination. For example, target bond levels between the plastic film and

the nonwoven web are achieved at speeds in excess of about 700 fpm

even up to about 1 200 fpm, or more. Target bond levels of, for example,

1 00 gms/cm (about 250 grams/inch) between the film and nonwoven are

achieved at line speeds on the order of 900 fpm for commercial purposes.

The compressive force between the web and the film at the nip is

controlled to bond the surface of the web to form a laminated sheet.

Furthermore, even at high line speeds the film gauge is controlled without

draw resonance. For example, a fixed film basis weight of about

40 grams per square meter (gsm) is achieved at 900 fpm. Thus, the

method of cooling eliminates draw resonance which otherwise may

normally be encountered under such conditions. According to the invention, breathable microembossed films

and laminates which are permeable to air and water vapor, but are a

barrier to bacteria and liquid, are produced. These breathable products are

made from a microporous-formable thermoplastic composition comprising

a thermoplastic polymer and filler particles. Antibacterial agents may

optionally be included. Upon slot-die extrusion and microembossing of

such composition, followed by applying a stretching force to the film at

high speeds along lines substantially and uniformly across the film and

throughout its depth, a microembossed microporous film having improved

impact strength is formed. Strip and patch breathable laminates are made

when a nonwoven fibrous web is laminated to a portion of the

microembossed film during the extrusion. The effectiveness of the cooling

gas is enhanced by creating a plurality of vortices of the gas as the stream

moves through the cooling zone to cool the web during extrusion

lamination. Thereafter, preferably an incremental stretching force is

applied to the microembossed film or the laminate at high speeds

substantially and uniformly across the film and throughout its depth to

provide a microporous laminate of film and nonwoven. Tentering may also

be used to stretch the laminate.

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 a primary objective of this invention to produce

antibacterial thin microporous films with improved properties, such as

impact strength, on high-speed production machinery. It is the further

objective of the method to produce antibacterial breathable strip and patch

laminated products of regular gauge without draw resonance. It is another

objective to produce such laminates having satisfactory bond strengths

while maintaining the appearance of a fabric or cloth having suitable

moisture vapor transmission rates and air permeability while maintaining

antibacterial and liquid-barrier properties.

The antibacterial properties are achieved by incrementally

stretching an extruded film containing filler particles to provide a pore size

distribution wherein the largest pore size is about 0.22 micron to prevent

the passage of bacteria. Preferably, the smallest pore size is about 0.05

micron and about 80% of the pores range from about 0.05 to about 0.08

micron.

The high speed method of making either an antibacterial film

or a strip (patch) laminate of a nonwoven fibrous web with the film

comprises melt blending a thermoplastic polymer and filler particles to

form a thermoplastic polymer composition. A web of the molten

thermoplastic composition is extruded from a slot die through a cooling

zone into a nip of rollers to form a film at a speed preferably greater than

about 700 fpm, and introducing strips of a nonwoven fibrous web into said nip of rollers and controlling the temperature and compressive force

between the web and the film at the nip to bond the surfaces of the web

strips to the film and to form a laminated sheet having a bond strength

between the film and the web of about 1 00 to about 600 grams/inch

when measured at about room temperature. Preferably, bond strengths

are about 200 grams/inch to about 500 grams/inch to facilitate

incremental stretching at about 700-1 200 fpm to provide a microporous

laminate. The incremental stretching force is applied across the laminated

sheet to provide a cloth-like microporous laminate having a web to film

bond strength of about 1 00 to about 200 grams/inch.

In a preferred mode, the high speed method of making an

antibacterial microporous thermoplastic film involves melt blending a

composition comprising

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

density polyethylene (LLDPE) ,

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

polyethylene (LDPE),

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

carbonate filler particles of about 0.1 to 1 micron, and

optionally

(d) an antibacterial agent in an effective amount of about

0.3 to about 1 percent by weight. The melt-blended composition is slot-die extruded as a web

through a cooling zone into a nip of a metal engraved embossing roller and

rubber roller. The embossing roller has a rectangular engraved pattern of

about 1 65 to 300, preferably about 250, lines per inch to provide a CD

and MD embossed film of 250 lines per inch in both directions. The film

thickness is generally about 0.0008 to 0.002 inch with an embossed

depth of about 0.0008 to 0.002 inch. Most preferably, the film thickness

is about 0.001 inch with the 250 lines per inch rectangular embossed

pattern and an embossed depth of about 0.001 to 0.001 5 inch. Upon

incrementally stretching this microembossed film, a microporous film is

produced having an unexpectedly higher impact strength when compared

to a non-embossed film. The embossed film is made at speeds on the

order of about 550 to about 1 200 fpm without draw resonance. A device

for directing a stream of cooling gas to flow in the cooling zone

substantially parallel to the web surface is shown, for example, in U. S.

Patents Nos. 4,71 8,1 78 and 4,779,355. The entire disclosure of these

patents is incorporated herein by reference as examples of devices which

may be employed to provide enhanced effectiveness of the cooling gas by

creating a plurality of vortices of the gas as the stream moves through the

cooling zone to cool the web. Thereafter, an incremental stretching force

is applied to the microembossed film at high speeds along lines

substantially and uniformly across the film and throughout its depth to

provide a microembossed microporous film. The blend of LLDPE and LDPE within the above approximate

ranges of components enables the production of microporous film at high

speed when balanced with the prescribed amount of calcium carbonate.

In particular, the LLDPE is present in an amount of about 30% 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 1 % 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 60% by weight of calcium

carbonate particles having an average particle diameter of preferably about

1 micron to achieve a sufficient moisture vapor transmission rate (MVTR)

in the range of about 1000 gms/m²/day to 4500 gms/m²/day as measured

by using the ASTM E96E method. 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

may be applied in line to the formed film under ambient conditions or at

an elevated temperature at speeds greater than about 700 fpm along iines 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 strip or patch of nonwoven

fibrous web during extrusion. The extrusion lamination is conducted at

the same high speeds where a nonwoven fibrous web is introduced into

the embossing 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 strip or patch laminate. The laminate is then incrementally

stretched along lines substantially uniformly across the laminate and

throughout its depth in one direction to render the microembossed 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.

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), poly(styrene-

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

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

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. Antibacterial agents suitable for use are 2-alkyl-1 ,2-

benzisothiazolin-3-ones (hereinafter BIT) such as 2-(n-hexyl)-BIT,

2-(2-ethylbutyl)-BIT, 2-(2-ethylhexyl)-BIT, 2-octylisothiazolin-3-one,

oxy-bis-1 0, 1 0-phenoxarsine, trichloromethylmercaptophthalimide; ureas

such as 2-(3,4-dichlorophenyl)- 1 , 1 -dimethylurea and

2-(4-isopropylphenyl)-1 , 1 -dimethylurea; 4-alkylsuiphonyl halogenated

pyridines such as 2,3,5,6-tetrachloro-4(methylsulphonyl)-pyridine and

2,3,6-trichloro-4(isopropylsulphonyl)-pyridine; tetrachloro-isophthalonitrile;

benzimidazomethyl-carbamate; thiocyanatomethylthiobenzthiazoie;

methylene bisthiocyanate, iodopropargyl-n-butyl-carbamate; triazines such

as 2-tert-butylamino-4-ethylamino-6-methylmercapto-1 ,3,5-triazine and

2-methylthio-4-tert-butylamino-6-cyclopropylamino- 1 ,3,5-triazine;

N-( 1 -methyl- 1 -naphthyl) maleamide; dichlorofluanide, (fluoro)-captan and

(fluro)-folpet. Other microbiocidal compounds which may be employed

include phenoxarsines (including bisphenox-arsines), phenarsazines

(including bisphenarsazines), maleimides, isoindole dicarboximides, having

a sulfut atom bonded to the nitrogen atom of the dicarboximide group,

halogenated aryl alkanols and isothiazolinone compounds. Examples of

these phenoxarsines and phenarsazines include 1 O-chloro-phenoxarsine;

1 0-iodophenoxarsine; and 1 0-bromophenox-arsine. Microbiocidal

maleimides are exemplified by N-(2-methylnaphthyl)maleimide. The

isoindole dicarboximides are exemplified by N-trichloromethylthio

phthalimide. The halogenated aryl alkanols are exemplified by 2,4-dichlorobenzyl alcohol. An isothiazolinone compound is exemplified

by 2-(n-octyl-4-isothiazolin-3-one). Bisphenoxarsines and bisphenarsazines

a re exemplified by 1 0, 1 0'-oxybisphenoxarsine and

1 0, 1 0'-oxybisphenarsazine. Amounts are preferably in the general range

of 0.3 to 1 percent by weight.

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 embossing and 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.

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. 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 unembossed or microembossed

microporous film has a gauge or a thickness between about 0.0008 and

0.002 inch and, most preferably about 0.001 inch. The nonwoven fibrous

webs of the strip or patch laminated sheet normally have a weight of

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

about 20 to about 40 grams per square yard. The 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 or

preceded by stretching in the machine direction (MD) to form a composite

which is stretched in both CD and MD directions. As indicated above, the

microembossed microporous films or laminates 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-Formable Laminates

A number of different stretchers and techniques may be

employed to stretch the starting or original 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 slidabie 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 4y2 ° 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 0.100" 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,

0.1 00" pitch, 30 diametral pitch, 14V2° 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

laminate of nonwoven fibrous web and microporous-formable film to form

the microporous laminate of this invention. The stretching operation is

usually 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 0.025 inch to 0.1 20

inch at speeds from about 700 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 example illustrates the method of making

antibacterial films 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 microembossed and flat microporous films.

FIG. 5 is a graph demonstrating the moisture vapor

transmission rate can be adjusted by heating the precursor film.

FIG. 6 is a graph demonstrating the impact strengths of the

microembossed and flat films which have been incrementally stretched.

FIG. 7 is a graph demonstrating the tear strength of the

microembossed and flat films which have been incrementally stretched.

EXAMPLES 1 -5

Blends of LLDPE and LDPE having the compositions reported

in the following TABLE 1 were extruded to form both antibacterial flat

(non-embossed) and microembossed films and the films were then

incrementally stretched to provide antibacterial microporous films. The antibacterial microembossed 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, preferably 250 lines per inch, with

engraving depth to produce about 0.0008 inch to 0.002 inch, preferably

about 0.001 inch to 0.001 5 inch, of embossed depth in a 0.001 inch

thick film. This pattern is disclosed, for example, in U. S. Patent

No. 4,376, 147 which is incorporated herein by reference. This

microembossed pattern provides a matte finish to the film but is

undetectable to the naked eye. The flat film was made with a flat chrome

roller.

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. + 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 diagrammatically 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. A microembossed metal roll and a flat chrome roll were each

used to make the microembossed and flat films, respectively, for

comparison. Where extrusion lamination is practiced, there is an incoming web strip 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 both the microembossed and non-embossed microporous films. 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

diagrammatically in FIG. 3.

FIG. 4 is a graph demonstrating the moisture vapor

transmission properties of both microembossed 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/m /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. As stated above, the embossed film was made

with a metal embossing roller having a rectangular engraving of CD and

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

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

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

undetectable to the naked eye.

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/m /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

diagrammatically 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 meta) 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 ⁰C 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.

EXAMPLES 7 - 16

Blends of LLDPE and LDPE having a composition of

Example 2 described above were slot die extruded in accordance with the

same procedures for Examples 1 -5 to produce both flat (non-embossed)

and microembossed films which were then incrementally stretched to

provide microporous films. In the case of Examples 7-1 1 , Example 7 was

a 0.001 inch film made for comparison with Examples 8-1 1 of the

microembossed microporous film of this invention. The microembossed

film had a rectangular pattern of 250 lines per inch in both the CD and MD

with an engraved depth of about 0.001 inch to about 0.001 5 inch and

about 0.001 inch in thickness. In the case of Examples 1 3-1 6, a flat

chrome metal roller was used to produce the non-embossed microporous

films of about 0.001 inch in thickness, and Example 1 2 was made for

comparison. The conditions of incremental stretching, resulting film basis weight, air cooling conditions, film impact strength and notched tear

strength are all provided in the following Table 3.

TABLE 3

FIGS. 6 and 7 are graphs demonstrating the impact strengths

of the microembossed and non-embossed microporous films which have

been incrementally stretched in accordance with the procedures of

Examples 8-1 1 and 1 3-1 6. With reference to Table 3, Examples 1 3-1 6,

where the non-embossed films were incrementally stretched to produce

micropores in the films, the microporous films lost their mechanical

properties, such as elongation at break and impact strength. However, in

contrast, Examples 8-1 1 demonstrate that the microembossed films of

this invention upon incremental stretching to provide microporosities did

not lose their impact strength to the same extent as the flat film. Thus,

Table 3 and FIGS. 6 and 7 demonstrate unexpectedly higher impact

strengths for microembossed microporous film which has been

incrementally stretched when compared to non-embossed film.

Furthermore, the tear strengths of both the microembossed as well as the

non-embossed film are comparable, as demonstrated by Table 3 and

FIGS. 6 and 7.

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

filed September 14, 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:

1 . An antibacterial microporous film having a high

moisture vapor transmission rate (MVTR) comprising a thermoplastic

polymer film containing a dispersed phase of particles selected from the

group consisting of an inorganic filler and an organic material, said film

having

(a) a film thickness of about 0.0008 to about 0.002 inch

with incrementally stretched areas in the film to provide

microporosity in the film with an MVTR greater than about

1 000 gms/m²/day according to ASTM E96E, and

(b) said film microporosity having a pore size distribution

wherein the largest pore size is about 0.22 micron as

determined by PMI capillary flow porometry.

Claims

2. The film of claim 1 wherein the smallest pore size is

about 0.05 micron.

3. The film of claim 1 wherein about 80% of the pores

range from about 0.05 to about 0.08 micron.

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

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

5. The film of claim 1 wherein the thermoplastic

composition is a polymer selected from the group consisting of

polyethylene, polypropylene, and copolymers thereof.

6. The film of claim 1 wherein said thermoplastic

composition is an elastomeric polymer.

7. The film of claim 6 wherein said elastomeric polymer

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

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

poly (sty rene-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.

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

selected from the group consisting of calcium carbonate and barium

sulfate.

9. The film of claim 1 having a portion thereof laminated

to a strip or patch of a fibrous web.

1 0. The film of claim 9 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.

1 1 . The film of claim 9 wherein the fibrous web has a

weight from about 5 to about 70 gms/yd².

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

on the order of about 0.001 inch and a microembossed rectangular

pattern of about 1 65 to about 300 embossed lines per inch across the

width of the film which intersect with embossed lines of about 1 65 to

about 300 lines per inch across the length of the film said pattern having

an embossed depth of about 0.001 to about 0.001 5 inch.

1 3. 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 4. The film of claim 1 3 wherein the composition further

contains high density polyethylene and titanium dioxide.

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

additionally contains an antibacterial agent.

1 6. An antibacterial microporous film having a high

moisture vapor transmission rate (MVTR) comprising a thermoplastic

polymer film containing a dispersed phase of calcium carbonate particles,

said film having

(a) a microembossed rectangular pattern of about 250

embossed lines per inch, across the width of the film which

intersect with embossed lines of about 250 lines per inch

across the length of the film, said pattern having an

embossed depth of about 0.0008 to about 0.002 inch,

(b) a film thickness of about 0.0008 to about 0.002 inch

with incrementally stretched areas in the film to provide

microporosity in the film with an MVTR greater than about

2000 to about 4500 gms/m²/day according to ASTM E96E,

(c) a film impact strength of greater than about

1 50 grams according to ASTM D1 709, and

(d) . said microporosity having a pore size distribution

wherein the largest pore size is about 0.22 micron as

determined by PMI capillary flow porometry.

1 7. The film of claim 1 6 wherein the smallest port size is

about 0.05 micron.

1 8. The film of claim 1 6 wherein about 80% of the pores

range from about 0.05 to about 0.08 micron.

1 9. The film of claim 1 6 wherein the thermoplastic

composition is a polymer selected from the group consisting of

polyethylene, polypropylene, and copolymers thereof.

20. The film of claim 1 6 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,

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

carbonate filler particles, and

(d) an antibacterial agent.

21 . A high speed method of making an antibacterial

microporous thermoplastic film comprising

meltblending a thermoplastic polymer and filler

particles to form a 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 0.0008 to about 0.002 inch at a

speed on the order of at least about 550 fpm to about 1 200 fpm without

draw resonance,

applying an incremental stretching force to said film at

said speeds along lines substantially uniformly across said film and

throughout its depth to provide a microporous film with an MVTR greater

than about 1 000 gms/m²/day according to ASTM E96E,

said film microporosity having a pore size distribution

wherein the largest port size is about 0.22 micron as determined by PMI

capillary flow porometry.

22. The film of claim 21 wherein the smallest pore size is

about 0.05 micron.

23. The film of claim 21 wherein about 80% of the pores

range from about 0.05 to about 0.08 micron.

24. The film of claim 21 wherein the MVTR is on the order

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

25. The high speed method of claim 21 comprising

introducing a strip of nonwoven fibrous web into said nip of rollers and

controlling the compressive force between the strip and the film at the nip

to bond the surface of the strip to only a portion of the film to form a

laminated microporous sheet.

26. The high speed method of claim 25 wherein said

fibrous web comprises polyolefin fibers.

27. The high speed method of claim 26 wherein said fibers

are selected from the group consisting of polypropylene, polyethylene,

polyesters, cellulose, rayon, nylon and blends or coextrusions of two or

more such fibers.

28. The high speed method of claim 27 wherein the

fibrous web has a weight of from about 5 to about 70 gms/yd² and the

microporous film has a thickness on the order of about 0.001 to about

0.001 5 inch.

29. The high speed method of claim 28 wherein said web

is formed from staple fibers or filaments.

30. The high speed method of claim 21 wherein said

incremental stretching step is conducted at ambient temperature.

31 . The high speed method of claim 21 wherein said film

has a thickness on the order of about 0.001 inch and an embossed depth

of about 0.001 to about 0.001 5 inch and said roller has a microembossed

rectangular pattern of about 250 lines per inch in each direction.

32. The high speed method of claim 21 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 0.0008 to about

0.002 inch.