Method and apparatus for making a microporous lamianate sheet or a microporous film

Method and apparatus for manufacturing a microporous laminated sheet or a microporous film

Background of the invention

Methods for the production of microporous films are well known in the art. For example, U.S. Patent No. 3,870,593 describes a process in which a microporous film is produced by:

(1) dispersing finely divided particles of a non-hygroscopic inorganic salt such as calcium carbonate in a polymer; (2) form a film from the polymer; and (3) stretch the film to provide microporosity. Such microporous films are used for a variety of purposes, such as breathable barriers (for example, in diapers).

Although there are numerous prior art references that disclose microporous films, most (such as U.S. Patent No. 4,353,945) do not define the stretching process other than to specify unidirectional or biaxial stretching. The three most common stretching techniques are MDO (machine direction orientation), tension furnaces and annular gearing rollers (also called interleaving rollers). MDO stretching units were available in the early days of microporous films from suppliers such as Marshall & Williams, Inc. of Providence, Rhode Island. Typical MDO stretching units have heated rollers and spaces, with downstream rollers that run at a faster speed in order to provide stretching in the machine direction only.

Tension furnaces were also available from several suppliers, including Marshall & Williams. Tension furnaces work by grasping the edges of a film that passes through a heated oven and stretching the film in a direction transverse to the machine. The films stretched in the transverse direction leave the oven substantially wider than its original width.

Interleaving or gearing stretching devices were produced during this early period by suppliers such as Biax-Fiberfilm of Neenah, Wisconsin. US Patent No. 4,153,751, for example, describes the use of interleaving rollers having grooves that extend substantially parallel to the axis of the rollers in order to stretch the films in the direction transverse to the machine.

Methods of manufacturing composites of a microporous film and a nonwoven textile material are also known in the art. A microporous film can be attached directly to the textile material by a variety of means, including adhesive, thermal and / or ultrasonic bonding. As discussed further below, such composite materials have also been prepared by extrusion coating a polymeric extrudate on a nonwoven textile material and then making the film microporous (such as by stretching).

It may also be desirable to stretch microporous film / textile material composites, however, stretching has its disadvantages. For example, for microporous films, the typical positive effects of stretching include superior vapor breathability and improved surface aesthetics. Vapor breathability (also called water vapor transmission rate, "WVTR") can be estimated by laboratory test methods, and is a function of the size and frequency of micropores in the film. Further stretching of an already microporous film is known to increase the size of existing pores and create new pores. Therefore, microporous film / textile material composites and highly stretched microporous films generally have superior vapor breathability compared to similar materials that have been stretched to a lesser extent.

Likewise, it is known that surface touch and fall improve with stretching. Composite film / textile materials tend to be stiffer and rougher than any single component alone. The stretching of such composite materials tends to decompose the rigid structure, thereby providing a softer surface touch and an improved fall.

On the other hand, stretching of microporous film / textile material composites can result in a decrease in bond strength and an increase in perforation. Stretching improves softness and fall by destroying the connection between the film and the textile material. This results in a decrease in the strength of the joint in the laminate. Stretching can also cause unwanted damage to the laminate, such as perforation, tearing or crushing of the film, the textile material or the composite as a whole.

Instead of attaching a microporous film to a textile material, it is also possible to first attach a non-porous film to a textile material, and then stretch the resulting composite material in order to make the film microporous. For example, U.S. Patent No. 5,865,926 describes a method in which the material

composite film / nonwoven material is stretched progressively. US Patent No. 5,910,225 uses MDO stretching and / or tension oven stretching. In some cases, prior art methods have only been partially satisfactory due to damage to the composite material caused by the stretching process. The damage includes, but is not limited to, perforations, tears and other functional and aesthetic defects.

Similarly, U.S. Patent No. 6,013,151 teaches that a nonwoven film / textile laminate can be made microporous and breathable with progressive stretching at high speeds. The resulting microporous laminates have a high water vapor transmission rate (WVTR). It has also been found that a flat film / nonwoven laminate can be progressively stretched more evenly than a embossed printed film / nonwoven laminate. More uniform stretching provides superior WVTR and fewer perforations.

The bonding of a film and textile material can also be carefully controlled to avoid creating other functional and aesthetic problems. For example, in the case of extrusion coating of an extruded polyethylene product on a spunbonded non-woven polypropylene web, process conditions such as melt temperature and rolling pressure determine the intrusion of fibers into the fiber. movie structure. At the minimum level of intrusion, however, the film and the textile material have little or no bond, and therefore tend to exfoliate. At the maximum extrusion level, on the other hand, the film and the textile material essentially mold together and become one. However, such a laminate acquires the worst properties of the two individual components and tends to be both rigid and fragile. It is also known that too much bond strength limits the amount of stretching that can be performed without the risk of forming perforations. Simply put, if the bond in the film and the textile material is too large, the stretched film will break a few times before exfoliating, leaving a perforation.

There is a continuing need for improvements in the performance and appearance of microporous films and composites of microporous films and nonwoven textile materials. In particular, improvements are desired to produce microporous films and microporous film / textile composite materials having superior breathability, while perforations and other functional and aesthetic defects are avoided.

Summary of the invention

The present invention provides a method of manufacturing a microporous laminated sheet or a microporous film according to claim 1.

An embodiment of the present invention provides a method of manufacturing a microporous laminated sheet comprising a first layer of film and a second layer. The method comprises:

<dl><dt>(to)</dt><dd> bonding a first film layer to a second layer in order to form a laminated sheet, in which the first film layer includes a pore initiator; and</dd></dl>

<dl><dt>(b)</dt><dd> stretch the laminated sheet using at least one CD gearing stretch element and at least one MDO stretching unit. </dd></dl>

In one embodiment, the second layer comprises a layer of textile material, while in another embodiment the second layer comprises another layer of film that includes a pore initiator. In a particular embodiment of this method, the laminated sheet can be stretched by at least one CD gearing stretch element.

<dl>&lt;dt /&gt;<dd>either immediately before or immediately after stretching by at least one MDO stretching unit. The coupling depth of the CD gearing stretch element may be from about 0.025 to about 0.1 inches and the MDO stretch ratio may be between about 1.1: 1 and about 4: 1.</dd></dl>

The film layer can be formed from a thermoplastic composition. When the second layer is a textile material, the step of joining the film layer to the layer of textile material may comprise extruding the thermoplastic composition onto said layer of textile material. For example, the thermoplastic composition can be extruded in a space station between casting rollers together with the layer of textile material, the space station between casting rollers including a pair of rollers having a space between them.

The thermoplastic composition may be based on polyolefin and comprise:

<dl><dt>-</dt><dd> at least one functionalized polypropylene, polyethylene or polyolefin; and</dd></dl>

<dl><dt>-</dt><dd> calcium carbonate as pore initiator. </dd></dl>

A particular composition comprises:

<dl><dt>-</dt><dd>one or more polyethylenes; </dd></dl>

<dl><dt>-</dt><dd> from about 40% to about 60% calcium carbonate; and</dd></dl>

<dl><dt>-</dt><dd> from about 1% to 10% of one or more additives chosen from the group consisting of: pigments, processing aids, antioxidants and polymer modifiers. </dd></dl>

The weight of the first film layer of the laminate can be between about 10 and about 40 gsm.

The layer of textile material can be a nonwoven material based on polyolefin. For example, the layer of textile material can be chosen from the group consisting of: spun nonwoven polypropylene; spun nonwoven polyethylene; and thermally bonded polypropylene, carded. The weight of the layer of textile material can be between about 10 and about 30 gsm, and the resulting laminate can have a water vapor transmission rate of more than about 500 grams per square meter per day and a hydrostatic head greater than approximately 60 cm

Another embodiment of the present invention provides a method of manufacturing a microporous film, which comprises the steps of:

<dl><dt>(to)</dt><dd> extrude a thermoplastic film from a polymer composition that includes a pore initiator; and</dd></dl>

<dl><dt>(b)</dt><dd> stretch the film using at least one CD gearing stretch element and at least one MDO stretching unit. </dd></dl>

In a particular embodiment, the microporous film is stretched by at least one CD gearing stretch element either immediately before or immediately after stretching by at least one MDO stretching unit.

Yet another embodiment of the present invention provides a method of manufacturing a microporous laminated sheet comprising at least two layers of film, comprising the steps of:

<dl><dt>(to)</dt><dd> bonding a first film layer to a second film layer in order to form a laminated sheet, in which the first film layer includes a pore initiator; and</dd></dl>

<dl><dt>(b)</dt><dd> stretch the laminated sheet using at least one CD gearing stretch element and at least one </dd></dl>

MDO stretch unit. In a particular embodiment, each of the film layers is formed from a thermoplastic composition, and the step of joining the first film layer to the second film layer comprises coextruding said thermoplastic compositions.

The present invention also provides an apparatus according to claim 17. Brief description of the drawings Figure 1 is a schematic view of an apparatus for producing a laminated sheet according to an embodiment of the

present invention;

Figure 2 is a schematic view of a pair of annular gearing rollers CD according to an embodiment of the present invention; Figure 3 is a MEB photomicrograph of a film stretched by CD gearing rollers; Figure 4 is a MEB photomicrograph of a film stretched by an MDO stretching unit; Figure 5 is a MEB photomicrograph of a film stretched by CD gearing rollers, followed by

MD gear rollers; Figure 6 is a MEB photomicrograph of a film stretched by CD gearing rollers, followed by an MDO stretching unit;

Figure 7 is a photomicrograph of MEB of the surface of an A / B / A film laminate drawn by an MDO unit;

Figure 8 is a MEB photomicrograph of the cross section of an A / B / A film laminate drawn by an MDO unit;

Figure 9 is a MEB photomicrograph of the surface of an A / B / A film laminate drawn by CD gearing rollers, followed by an MDO stretching unit; and

Figure 10 is a MEB photomicrograph of the cross section of an A / B / A film laminate drawn by CD gearing rollers, followed by an MDO stretching unit.

Detailed description of the invention

The present invention provides a method of manufacturing microporous films that exhibit exceptional physical and aesthetic properties. These microporous films may comprise a single layer of film, or may comprise a laminate of two or more layers of film. Such film laminates can be formed, for example, by coextrusion of two or more thermoplastic extrudates. The present invention also provides a method of manufacturing a laminated sheet comprising at least one layer of microporous film and at least one layer of textile material. Such laminated sheets can be manufactured by attaching a microporous film to a layer of textile material. Alternatively, a precursor film can be attached to a layer of textile material to form a laminate, and then the laminate stretched to provide microporosity in the film layer. Regardless of which technique is used, the resulting laminated sheet having a microporous film layer and a layer of textile material provides a breathable composite material satisfactory for any of a variety of end uses, particularly those that require a non-exfoliated composite material , act as a barrier against liquids that have high water vapor permeability and / or soft and similar to a fabric (such as for use in hygiene applications, for example, diaper backsheets).

Applicants have found that, by proper selection of stretching methods, microporous and laminated films can be produced that have improved properties. In particular, by sequentially stretching the film or the laminate with annular rollers of CD gearing and an MDO unit, microporous and laminated films are produced which have unexpectedly improved properties. Unless otherwise indicated, the term "laminate" refers to film laminates comprising two or more layers of film, as well as film / textile laminates comprising at least one layer of film and at least one layer. of textile material.

In one embodiment, a film / textile laminate is prepared and then stretched to provide microporosity. A polymer composition that can be activated to make it microporous is coated by extrusion onto a textile material and then stretched using the methods described herein to form a breathable composition satisfactory for many end uses, such as a liquid barrier. It has high water vapor permeability.

The most desirable property of a laminate or a breathable, microporous film is the combination of high WVTR with a low incidence of perforations. The optimal pore size distribution to achieve this combination is a high frequency of small pores. Scanning electron microscopy (MEB) analysis of film prototypes stretched only with a CD gearing unit (see Figure 3) revealed pores that were located at specific locations along lanes running in the machine direction, due to the nature of the metal rollers that come into physical contact with the film. When this film was subsequently stretched by an MD gear unit (see Figure 5), the pores formed by the CD gear unit enlarged although few new pores were formed. Therefore, CD gearing followed by MD gearing is not the optimal process. However, when the film was processed by CD gearing followed by MDO gearing (see Figure 6), the results greatly improved. New pores were easily created in lanes that did not contain pores only after CD gearing. Since the film must be stretched generally until the desired WVTR is achieved, this CD plus MDO gearing technique can produce high WVTR creating a larger number of smaller pores with less perforation frequency. If an attempt was made to achieve the same level of WVTR using only CD gearing or only MDO stretching, drilling would be more frequent.

The method of the present invention can be used to form microporous films (and laminated film layers) from any suitable polymer (or mixture of polymers) that can form a film and that includes a pore initiator (such as an inorganic filler ) dispersed in it. The polymer composition, which has one or more pore initiators dispersed therein, is formed in a film, such as a continuous film formed by extrusion. The resulting film is then stretched using one or more geared stretch elements in the machine transverse direction (CD) and one or more stretch units in the

machine direction orientation (MDO). In one embodiment, stretching by a CD gearing stretching element either immediately precedes or immediately follows stretching by an MDO stretching unit. As used herein, the phrases "immediately precedes" and "follows immediately" simply mean that no other stretching is performed between the stretching by a gear stretch element CD gear stretch element and the stretch by MDO stretch unit. It is contemplated that other types of stretching units may be employed either before or after this sequence, and it is also contemplated that the film can be stretched only by one or more CD-mesh stretching elements and one or more MDO stretching units.

Using CD gear stretch in combination with MDO stretch, applicants have found that the resulting micropores are more numerous, smaller and more uniform in size and shape (see Figure 6) compared to films stretched with a gear stretch element CD only (see figure 3), an MDO stretch element alone (see Figure 4) or a CD gear stretch element followed by an MD gear stretch element (see Figure 5).

In order to form a laminate of microporous film / textile material, after preparing the microporous film in the manner described above, the microporous film can be attached to one or more layers of textile material to form a laminated structure. Alternatively, a non-microporous film may first be attached to one or more layers of textile material to form a laminated structure, and this laminated structure can then be stretched in the manner described above in order to make the film layer microporous. The layers of film and textile material can be joined together by any of a variety of methods, such as adhesive bonding, electromagnetic bonding, hot plate bonding and ultrasonic bonding. In one embodiment, the film-forming polymer having one or more pore initiators dispersed therein can be extruded onto a textile material in order to form a laminate comprising a film layer bonded to a layer of textile material. The resulting laminated sheet can then be stretched in the same manner as described above in order to make the film microporous. Even when extrusion coating is used to adhere the film to the textile material, the bonding can be improved by the use of any of a variety of additional bonding methods, such as adhesive bonding, electromagnetic bonding, hot plate bonding and ultrasonic bonding. It should also be noted that the film / textile laminates of the present invention may include any number of layers of film and textile material, in any desired arrangement.

The same techniques used to form film / textile laminates can also be used to form film laminates comprising two or more film layers, in which at least one of the film layers is microporous. Therefore, a microporous film can be attached to one or more other layers of film to form a laminated structure. Alternatively, a non-microporous film may first be attached to one or more other layers of non-microporous film to form a laminated structure, and this laminated structure can then be stretched in the manner described above in order to make the film layers microporous The film layers can be joined together by any of a variety of methods, such as adhesive bonding, electromagnetic bonding, hot plate bonding and ultrasonic bonding. Film laminates can also be formed by coextrusion. Film-forming polymer compositions having one or more pore initiators dispersed therein can be coextruded in order to form a laminate comprising two or more layers of film bonded together. The resulting laminated sheet can then be stretched in the same manner as described above in order to make the film layers microporous.

The composition of each film layer in the film laminate can be selected in order to achieve the desired properties for each film layer, and therefore the composition of each film layer can be the same or different. For example, one or more layers of film may include a greater amount of pore initiator so that more pores will be formed in that layer during stretching. In this way, properties such as WVTR can be individually controlled for each film layer in the resulting film laminate. In an exemplary embodiment, a film laminate comprising three microporous layers can be formed, in which the middle layer has a smaller amount of charge compared to the two outer layers.

Figure 1 is a schematic illustration of an embodiment of an apparatus that can be used to produce a laminated sheet according to an embodiment of the present invention, in which the film layer is a thermoplastic film and the textile layer is a fibrous web. non-woven Using the apparatus of Figure 1, the thermoplastic film is laminated into the nonwoven fibrous web during extrusion by introducing the nonwoven web into the space of a pair of rollers together with the thermoplastic extrudate. The resulting laminated sheet is then stretched in the manner described above. If only a microporous film is desired instead of a laminate, the web of nonwoven fabric 33 on the roller 32 can be removed. Also, if a film laminate is desired, multiple thermoplastic extrudates can be introduced into the space of the pair of rollers, thereby providing a coextruded film laminate.

In order to produce a continuous laminated sheet, the thermoplastic composition of the film layer is fed from an extruder press 21 through a slot nozzle 22 to form the extruded product 26 (corresponding to the film layer of the sheet resulting laminate). The extruded product 26 is fed into the space ("casting station space") between a casting roller 24 (usually a metal roller) and a support roller 25 (usually a rubber roller). An air knife 23 may be used to aid in the removal of the stretching resonance, as described in, for example, US Patent No. 4,626,574. Alternatively, the air cooling devices described in US Patent Application Serial No. 09 / 489,095 (filed January 20, 2000) can be employed to prevent stretching resonance. A strip of nonwoven textile material 33 is pulled from the roller 32 into the space of the casting station between the rollers 25 and 24. In this space, the textile material 33 is coated by extrusion with the molten film 26 (or extruded product) that just exited through the slot nozzle 22. In essence, the fibers are embedded in, and encapsulated by, the film during the extrusion lamination process.

After the laminated sheet leaves the space between rollers 24 and 25, the laminated sheet is then stretched at two or more stretching stations. In one embodiment, the laminated sheet is stretched using one or more CD gear stretch elements and one or more MDO stretch units, wherein the sheet is stretched by one of the CD gear stretch elements immediately before or immediately after to stretch using one of the MDO stretch units. In addition, one or more temperature controlled rollers (such as roller 45) may be provided in order to heat the laminate before stretching.

In the embodiment of FIG. 1, a gearing stretch element CD is provided in a first stretching station 28, and an MDO stretching unit is provided in a second stretching station 29. A CD gearing stretch element generally comprises a pair of rollers that are located such that they form a space between them. Therefore, the CD stretch element in a first stretch station 28 generally comprises progressive stretch rollers 30 and 31. While the stretching rollers 30 and 31 may be of any of a variety of configurations, Figure 2 is a schematic view of an exemplary embodiment of the annular rollers 30 and 31 of CD gearing. Each annular roller has a plurality of grooves that extend around the surface of the roller, parallel to the circumference of the roller. When the rollers are carried together in tight engagement, the grooves in one roller will engage with the grooves in the other roller. When a film or laminate is passed between the two rollers, the film or laminate will be progressively stretched in the transverse direction, as is known to those skilled in the art.

In the exemplary embodiment of Figure 2, each progressive stretching roller (or "annular roller") essentially comprises a cylindrical roller 37 and a plurality of annular rings 38 attached to the outer circumference of the cylindrical roller 37. The annular rings 38 are generally uniformly spaced along the length of the cylindrical roller 37. However, the rings in the stretching roller 30 are offset with respect to the rings in the stretching roller 31 so that when the rings are worn together in the manner shown in 2, the rings (and the grooves between them ) of the stretching roller 30 will be engaged with the rings (and the grooves between them) of the stretching roller 31. Thus, as the laminated sheet is passed between the stretching rollers 30 and 31, the laminated sheet will be progressively stretched in the transverse direction (i.e., perpendicular to the machine direction in the apparatus of Figure 1 ).

In an exemplary embodiment, the axes of the annular rollers may be arranged between two side plates of the machine, the lower axis being located on fixed supports and the upper axis being located on supports on vertically sliding elements. The sliding elements can be adjusted in the vertical direction by means of wedge-shaped elements that can be operated by adjusting screws. Screwing

or unscrewing the wedges will move the vertically sliding element respectively downward or upward to further engage or disengage the teeth similar to a gear of the upper gear roller with the lower gear roller. Micrometers mounted on the side frames can be operated to indicate the depth of engagement of the teeth of the gearing roller.

Air cylinders can be used to keep the sliding elements in their lower engaged position firmly against the adjustment wedges to oppose the upward force exerted by the material being stretched. These cylinders can also be retracted to decouple the upper and lower gearing rollers from each other for the purpose of threading material through the gearing equipment or in conjunction with a safety circuit that would open all machine space points when activated.

Since the CD gearing elements can often have large coupling depths, it may be necessary for the equipment to incorporate a means to make the axes of the two gearing rollers remain parallel when the upper axis is rising or falling. This may be necessary to ensure that the teeth of one gearing roller always fall between the teeth of the other gearing roller and avoiding potentially harmful physical contact between gearing teeth. This parallel movement is guaranteed by a gear and rack arrangement in which a stationary gear rack is attached to each side frame in juxtaposition with the vertically sliding elements. A shaft crosses the racks

lateral and works on a support in each of the vertically sliding elements. A gear resides at each end of this axis and works in the coupling with the zippers to produce the desired parallel movement.

The drive of the CD gear stretch element will generally operate both the top and bottom gear rollers, except in the case of gear stretch of materials having a relatively high coefficient of friction. However, the drive does not need backstop, because a small amount of misalignment of the machine direction or drive offset will not cause problems. The reason for this will be evident with a description of the CD gearing elements.

In the exemplary embodiment of Figure 2, the CD gearing elements can be machined from a solid material but can best be described as an alternating rack of two discs of different diameter. In one embodiment, the gearing discs will be 6 "in diameter, 0.031" thick, and have a full radius at their edge. The spacer discs that separate the gearing discs will be 51/2 ”in diameter and 0.069” thick. Two rollers of this configuration can be geared up to 0.231 ”leaving a clearance of 0.019” for material on all sides, and this configuration of CD gearing elements will have a thread pitch of 0.100 ”. Alternatively, the CD gearing rollers may comprise cylindrical rollers having a series of annular rings that extend around the circumference of the rollers.

Although the CD gearing rollers described above may have greater coupling depths, the coupling depth may be advantageously selected to be between about 0.025 and about 0.1 inches, more advantageously between about 0.04 and about 0.075 inches. Such coupling depths can prevent damage to the film.

In the exemplary embodiment of Figure 1, after passing through the CD gearing rollers, the film or composite material moves through the second stretching station 29 which includes an MDO stretching unit. The typical MDO stretching equipment known to those skilled in the art can be quite complicated although the principles are simple. The film or composites of film / textile material are passed through the spaces of two pairs of rollers. However, the second pair of rollers is rotated at a faster speed than the first pair of rollers, so that the second pair of rollers will pull the film or the composite material of film / textile material and therefore stretch into The machine address.

In some roller assemblies of an MDO stretching unit, one or more of the rollers are heated to aid in the stretching process. Alternatively, a separate heated roller can be included and at least one of the roller assemblies can therefore comprise three rollers. In such an arrangement, the first roller is an internally heated roller that heats the film or composite material before presentation to space. This first heated roller is not in physical contact with any other roller in the roller assembly. The second roller is coated with a flexible material such as rubber to allow pinching (i.e. physical contact) with the third roller, which is metal, without damage. Normally, only one of the two rollers is operated in contact with each other, such as the third metal roller. However, the non-driven roller will rotate due to the contact between the two rollers. Although both rollers can be operated in contact with each other, if desired, such an arrangement requires more precise speed control.

In the exemplary embodiment of Figure 1, an MDO stretching unit is provided in the second stretching station 29. The first roller assembly of the MDO stretching unit comprises a heated roller 50, a second coated roller 51 and a third metallic roller 52 (which is driven). The film or composite material is passed through the space between rollers 51 and 52. The second set of rollers of the MDO stretching unit in Figure 1 is similar to the first, however, the second set of rollers only comprises a coated roller 61 and a driven metal roller 62 (without an additional heated roller). The film or composite material is passed through the space between rollers 61 and 62.

During operation, both spaces of the MDO stretch unit are closed. The film or composite material is clamped between rollers 51 and 52 and between rollers 61 and 62. However, rollers 61 and 62 are driven at a circumferential speed faster than rollers 51 and 52, thereby causing The film or composite material is stretched in the air gap between the two spaces. A typical air gap dimension is between about 0.005 "and about 0.550", or between about 0.005 "and about 0.050".

In an MDO stretch unit, the "MDO stretch ratio" is defined as the ratio of the speed of the second pair of rollers with respect to the speed of the first pair of rollers. In the embodiment of Figure 1, the stretching ratio MDO is the ratio of the speed of the roller 62 with respect to the speed of the roller 52. In one embodiment, the MDO stretch ratio can be advantageously selected to be between about 1.1: 1 and about 4: 1, more advantageously about 2: 1. Such reasons of MDO stretching can prevent damage to the film. After leaving the MDO stretch element unit, the film or composite material will be longer and thinner than its initial dimensions.

The apparatus and method of the present invention are particularly suitable for producing laminated sheets comprising at least one layer of microporous film and at least one layer of textile material. The film composition that is extruded into space can include filler particles (a pore initiator) so that, when the laminated sheet is stretched, micropores will form in the film layer at the locations of the filler particles. The textile layer may comprise, for example, a nonwoven fibrous web of cut fibers or spun nonwoven filaments. In addition, the progressive stretching provided by the CD gearing stretch provides a very soft fibrous finish to the composite material that looks like cloth. The result of such progressive or geared stretching is a composite material that has excellent barrier properties against liquids and breathability, as well as textures similar to soft fabric.

Materials for film and composite

Methods for the production of microporous films are well known in the art. The film is produced by combining finely divided particles of an inorganic filler (such as calcium carbonate or other salt) in a suitable polymer, forming a film of the charged polymer, and stretching the film to provide microporosity and breathability.

A microporous film is often characterized by the size of the pores present. It is known that pores with equivalent diameters in the range of 0.01 to 0.25 microns prevent the flow of non-wetting liquids. If the frequency of these pores is high enough, the material will allow a reasonable passage of water vapor while maintaining an effective barrier to liquid water.

According to an embodiment of the present invention, the film (including the film layer of a composite film / textile material and the individual film layer of a film laminate) may comprise a polyolefin-based composition, such as one or more polypropylenes, polyethylenes, functionalized polyolefins or combinations thereof. A suitable composition comprises a combination of one or more polyethylenes (such as a combination of LLDPE and LDPE) and a pore initiator. The type and quantity of each polyethylene used will depend, in large part, on the intended use of the film or laminate. In one embodiment, from about 40% to about 60% of a pore initiator can be included. For example, a particular formulation for the film according to an embodiment of the present invention can be obtained by first blending a composition comprising:

<dl><dt>(to)</dt><dd> from about 35% to about 45% by weight of a linear low density polyethylene ("LLDPE"), </dd></dl>

<dl><dt>(b)</dt><dd> from about 3% to about 10% by weight of a low density polyethylene ("LDPE"), </dd></dl>

<dl><dt>(c)</dt><dd> from about 40% to about 60% by weight of calcium carbonate filler particles (such as calcium carbonate with the surface coated with a fatty acid), and</dd></dl>

<dl><dt>(d)</dt><dd> optionally, from about 1% to about 10% by weight of one or more of the following additives: pigments, processing aids, antioxidants and polymer modifiers. </dd></dl>

The above composition can be extruded in the space between two rollers (such as rollers 24 and 25 described above) in order to form a film at a speed of about 550 fpm to about 1200 fpm (or faster), without stretching resonance . In one embodiment, the resulting film layer may have a weight of between about 10 and about 40 gsm (g / m2), more particularly between about 20 and about 30 gsm. The resulting film can then be stretched in the same manner described above.

A particular film composition may comprise about 51% by weight of polyethylene, and about 44% by weight of calcium carbonate filler particles having an average particle size of about 1 micron. Polyethylene can be provided as a combination of LLDPE and LDPE, depending on the amount of each type of the intended use for the film or laminate, including the desired physical and aesthetic properties (including properties such as drop and surface touch). In some cases, it may be desirable to include high density polyethylene in order to increase stiffness. The color of the film (whiteness) can be controlled including one or more pigments. A white film may be provided, for example, including up to about 4% by weight of titanium dioxide. A processing aid such as a fluorocarbon polymer may also be added in an amount of about 0.1% to about 0.5% by weight, such as 1-propene-1,1,2,3 copolymer, 3,3-hexafluoro with 1,1difluoroethylene. Antioxidants such as Irganox 1010 and Irgafos 168 can also be added at a total concentration of about 500 to about 4000 ppm.

Although the film compositions described above can be used to form microporous films

using the stretching methods described herein, composite structures can also be formed by joining a film layer (such as those formed from the compositions described above) to a layer of textile material or another film layer. The film layer can be made microporous by stretching before joining the textile material or the additional film layer. Alternatively, an unstretched film layer of the compositions described above can be attached to a layer of textile material or another film layer and then the resulting composite structure is stretched in order to make the film layer (s) be (n) microporous (s).

As yet another alternative, a layer of textile material can be fed into the space between two rollers (such as rollers 24 and 25 described above) together with the extruded product. In this way, the polymer composition of the film layer is extruded onto the layer of textile material. The resulting laminated sheet is then stretched in the same manner as described above to provide a laminated sheet having a microporous film layer and a layer of textile material. In one embodiment, the layers of textile material of the various laminated structures described herein may have a weight of between about 10 and about 30 gsm, or even between about 15 and about 25 gsm. The WVTR of the laminate may be greater than approximately 500 grams per square meter per day and the hydrostatic head of the laminate may be greater than approximately 60 cm (measured as the minimum height of a water column that causes leaks in the laminate). In one embodiment, the WVTR can exceed approximately 1000 grams per square meter per day, or even exceed approximately 3000 grams per square meter per day.

Similarly, two or more extrudates can be fed into the space between two rollers (such as rollers 24 and 25 described above). In this way, the polymer compositions are coextruded in order to form a laminate of two or more layers of film. The resulting laminated sheet is then stretched in the same manner as described above to provide a laminated sheet having two or more layers of microporous film.

Layers of suitable textile material include natural or synthetic fibers or filaments, which are joined or otherwise consolidated to give a web structure. Suitable textile materials include woven and nonwoven textile materials such as bands of melt spun, hydrolyzed, carded or thermally or adhesively bonded textile material. Exemplary textile materials that can be used include spun nonwoven polypropylene, spun nonwoven polyethylene and thermally bonded, carded polypropylene.

Test methods

The properties of the films and laminated sheets produced according to the present invention can be tested in a variety of ways. For example, the rate of water vapor transmission ("WVTR") can be determined according to ASTM E 96, "conventional test methods for the transmission of water vapor from materials". A known amount of desiccant is placed in a cup-like container along with the sample and securely held by a retaining ring and a gasket. The assembly is placed in a constant temperature (40 ° C) and humidity (75% RH) chamber for 5 hours. The amount of water absorbed by the desiccant is determined gravimetrically and used to estimate the WVTR (units of g / m2 · 24 h) of the sample.

ASTM E 1294-89 can be used: "conventional test method to determine the pore size characteristics of membrane filters using automated liquid porosimeter" to measure the maximum pore size (TPM). This method measures the TPM (units of microns) for microporous films and laminated sheets using a liquid displacement technique that depends on the capillary increase created by the surface tension and uses the Washburn equation to calculate the pore diameter.

The number of perforations can be determined using the Clopay perforation test method (HCTM02) that measures the resistance of laminated and coated textile materials to the penetration of an alcohol solution (100 ml of 70% isopropyl alcohol with 1.0 ml of food coloring of red color). This test is performed by exposing approximately six square feet of composite material to 72 ml of the solution on the film side of the sample. The solution is spread evenly with a brush to cover the demarcated area of ​​the sample. The solution is allowed to stand for ten minutes, then it dries with cloths. The sample is turned around and the dye marks are counted. The number of perforations in the area under test is notified.

Examples

The following examples illustrate a method of preparing films, film laminates and film / textile laminates according to an embodiment of the present invention. In view of these examples and this additional detailed description, it will be apparent to one of ordinary skill in the art that variations thereof can be made without departing from the scope of this invention. The enumeration of these examples is provided merely

to show a person skilled in the art how to apply the principles of this invention as discussed herein. These examples are not intended to limit the scope of the claims appended to this invention.

In the following examples, an apparatus similar to that shown in Figure 1 was used. However, in Example 1, since only a microporous film was formed and not a laminate, the nonwoven web of material 33 was not used on the roller 32, as well as the rollers 24 and 25 that form the space of the casting station.

EXAMPLE 1:

A film formulation containing 50% calcium carbonate, 47% polyethylene resin and 3% titanium dioxide was extruded using conventional processing conditions and cast film equipment. The speed of the extruder press and the line speed were set so that a 45 g / m2 film layer was produced. This was movie 1A. The 1B film was created by passing the 1A film through a pair of annular CD gearing rollers. The annular rollers had rings every 0,100 inches. Figure 3 is a photomicrograph of film 1 B. Film 1C was created by passing film 1A through an MDO stretching unit only. Figure 4 is a photomicrograph of the 1C film. The 1D film was created by stretching the 1A film with both the CD and MDO drives. The final film thickness of 1D was such that the weight of the film was approximately 23 g / m2 for an MDO stretch ratio of approximately 2: 1. Figure 6 is a photomicrograph of the 1 D film. For comparison, the 1A film was also stretched with the CD gearing unit and then an MD gearing unit (machine direction), to create the 1 E film. 5 is a photomicrograph of the film 1 E.

The results of the physical properties shown in Table # 1 represent typical data for films prior to the coupling depth on the CD gearing rollers and the ratio of speeds in and out of the MDO unit specified above. As indicated in the table, the properties of the film stretched by the CD gearing rollers followed by the MDO stretching unit are superior to any other option. The photomicrographs of Figures 3-6 also demonstrate that the stretching methods of the present invention provide a large number of small, round diameter pores that are responsible for the high MVTR (or WVTR) compared to the other films. The "air flow" measurement reported in Table 1 was obtained by applying high pressure air to the film and measuring the air flow through the film over a short period of time (five seconds).

TABLE 1

<dl><dt>Sample Description </dt><dd>Weight (g / m2) Perforation count (# / m2) Air flow (ml / min. At 90 psi) MVTR (g / m2 / day) </dd></dl>

&lt;p /&gt;

<dl><dt>1A - precursor </dt><dd> 45 0 0 100 </dd></dl>

<dl><dt>1B - Eng. CD only </dt><dd> 35 0 1128 1800 </dd></dl>

<dl><dt>1C - MDO only </dt><dd> 25 0 1511 2500 </dd></dl>

<dl><dt>1D - Eng. CD and MDO </dt><dd> 31 0 6030 3400 </dd></dl>

<dl><dt>1E - Eng. CD and eng. MD</dt><dd> 23 0 4400 3000 </dd></dl>

EXAMPLE 2:

A film formulation containing 50% calcium carbonate, 47% polyethylene resin and 3% titanium dioxide was extruded using conventional processing conditions and cast film equipment. A carded polypropylene band, joined by thermal points of 20 g / m2 of the unwinder was threaded into the space of the casting station so that it was brought into contact with the molten film stream during the execution conditions. The speed of the extruder and the speed of the line were set so that a layer of 40 g / m2 film was added to the textile material. This created the 2A laminate. The film / textile laminate 2A was then passed through the annular CD gearing rollers to make the laminate 2B. The annular rollers had rings every 0,100 inches. Laminate 2C was created by passing laminate 2A through an MDO stretch unit only. 2D laminate was created by stretching laminate 2A with both CD and MDO units. For comparison, the laminate 2A was also stretched with the CD gear unit and then the MD gear unit, to create the laminate 2E. The results of the physical properties shown in table # 2 represent typical data for these prototypes depending on the depth of engagement in the CD gearing rollers and the ratio of speeds in and out of the MDO unit. As indicated in the tables, the properties of the laminate stretched by the CD gearing rollers followed by the MDO stretching unit are superior to any other option.

Table 2

<dl><dt>Sample Description </dt><dd>Weight (g / m2) Perforation count (# / m2) Air flow (ml / min. At 90 psi) MVTR (g / m2 / day) </dd></dl>

&lt;p /&gt;

<dl><dt>2A - precursor </dt><dd> 60 0 0 50 </dd></dl>

<dl><dt>2B - Eng. CD only </dt><dd> 53 0 414 1100 </dd></dl>

<dl><dt>2C - MDO only </dt><dd> 49 0 611 1200 </dd></dl>

<dl><dt>2D - Eng. CD and MDO </dt><dd> 46 0 1780 3169 </dd></dl>

<dl><dt>2E - Eng. CD and eng. MD</dt><dd> 51 0 872 1743 </dd></dl>

EXAMPLE 3:

Conventional processing conditions and cast film equipment were used to prepare a laminate of

10 coextruded film that comprised three layers of film (A / B / A) and had a weight of 85 g / m2. The polymer composition for the first and third layers contained 57% calcium carbonate and 43% polyethylene resin, and had a weight of 30 g / m2. The polymer composition for the middle layer contained 54% calcium carbonate and 46% polyethylene resin, and had a weight of 25 g / m2. None of the layers contained titanium dioxide. This was called film 3A. The 3B movie was created by passing the 3A movie through

fifteen an MDO stretch unit only. The MDO stretch at 215 F was performed, using a stretch ratio of 2.5 and a stretch gap of 5,000. Figure 7 is a photomicrograph of the surface of the film 3B, and Figure 8 is a photomicrograph of a cross section of the film 3B. The 3C film was created by stretching the # 3A film with a CD gearing unit followed by stretching with an MDO unit. Stretching of CD gearing at 75F was performed using a coupling depth of 0.040 ”. Stretching was done

twenty MDO at 215 F, using a stretch ratio of 2.0 and a stretch gap of 5 thousand. Figure 9 is a photomicrograph of the surface of the film 3C, and Figure 10 is a photomicrograph of a cross section of the film 3C.

The results of the physical properties for films 3A, 3B and 3C are shown in Table No. 3. As indicated in the table, the properties of the film stretched by the CD gearing rollers followed by the

25 MDO stretch unit are superior to the stretched film only with an MDO unit. The photomicrographs of Figures 7-10 also demonstrate that the stretching methods of the present invention provide a large number of round, small diameter pores that are responsible for the high MVTR (or WVTR) compared to the other films.

TABLE 3 10

<dl><dt>Sample Description </dt><dd>Weight (g / m2) Perforation count (# / m2) MVTR (g / m2 / day) </dd></dl>

&lt;p /&gt;

<dl><dt>3A-forerunner </dt><dd> 85 0 50 </dd></dl>

<dl><dt>3B -MDO only </dt><dd> 36 0 2850 </dd></dl>

<dl><dt>3C - Eng. CD and MDO</dt><dd> 33 0 9946 </dd></dl>