Film, laminated sheet and methods of making same

Description of the invention

The invention relates to a method of producing a microporous laminate sheet and a microporous film and a device for stretching the film and / or film / fabric laminate.

The present invention relates generally to the production of microporous films and laminates, in particular by using stretching devices including at least one CD stretching device.

Processes for making microporous films are well known in the art and, for example, US Patent No. 3,870,593 discloses a method in which a microporous film is produced by (1) dispersing particulate non-hygroscopic inorganic salt such as calcium carbonate in a polymer (2). ) forming a film from a polymer; and (3) stretching the film to make it porous. Such microporous films are used for various purposes such as breathable barriers (e.g. in diapers).

While there are a great number of publications in the art for which microporous films are known, most of them (for example, US Patent No. 4,353,945) do not specify a stretching process other than unidirectional or biaxial stretching. The three most common stretching techniques include MDO (machine direction orientation), stretching furnaces, and associated circumferential rollers (also called comb rollers). MDO stretching devices have been available since the early advent of porous films by suppliers. Typical MDO stretching machines have heated rollers and nips with the following rollers running faster to provide only machine direction stretching.

Stretching furnaces are also available. Stretching furnaces operate by grasping the edges of the film passing through the heated furnace and stretching the film in a direction transverse to the machine direction. The transversely stretched films exit the oven much wider than their initial width.

Stretching devices with cooperating or comb rollers were manufactured during an earlier period. From US 4,153,751 it is known, for example, to use comb rollers, which have grooves extending substantially parallel to the roller axis, for stretching the film in a cross machine direction.

Methods for producing microporous film and nonwoven composites are also known in the art. The microporous film can be bonded directly to the fabric by a variety of means, including adhesive bonding, thermal bonding, and possibly ultrasonic bonding. As will be discussed later, such composites were also obtained by extrusion coating a polymeric extrudate onto a nonwoven fabric and then porousing the film (e.g., by stretching).

It may also be desirable to stretch the microporous film / fabric composites, but such stretching also has disadvantages. For example, microporous films, typically due to forced stretching, have higher vapor permeability and a better surface appearance. Vapor transmission susceptibility (also called water vapor transmission rate, WVTR) can be assessed by laboratory testing and is a function of the size and frequency of micropores in the film. Additional stretching of an already microporous film is known to increase the size of the existing pores and create new pores. Hence, highly stretched microporous films and microporous film / fabric composites generally have higher vapor permeability compared to similar materials which have been stretched less.

Better surface feel and stretchability are likewise known. Film / fabric composites tend to be more stiff and hard than any of the individual components. The stretching of such composites tends to break the rigid structure, thereby providing a softer surface feel and better formability.

On the other hand, stretching of microporous film / fabric composites may result in lower bond strength and a greater propensity to form point defects. The stretching improves softness and formability by destroying the joints between the film and the non-woven fabric, which in turn results in lower bond strength in the laminate. The stretching can also cause undesirable damage to the laminate, such as dot defects, tears, or fraying of the film, fabric, or composite as a whole.

Instead of bonding (bonding) the microporous film to the fabric, it is also possible to bond the non-porous film to the fabric first and then stretch the resulting composite to give it a

Of the microporosity film. For example, US 5,865,926 discloses a method in which the film / nonwoven composite is gradually stretched. In accordance with US Patent No. 5,910,225, MDO stretching and optionally oven stretching are used. Under certain conditions, the previous methods have proved to be useful only partially due to the failure of the composite due to stretching. Damage includes, but is not limited to, pinpoint defects, tears, and other functional and aesthetic defects.

Similarly, from US Patent No. 6,013,151, it is known that a film / nonwoven laminate can be made microporous and breathable after gradual stretching at high speeds. The resulting microporous laminates have a high water vapor transmission rate (WVTR). It has been found that the film / nonwoven laminate can gradually be stretched more uniformly than the patterned / nonwoven film laminate. More uniform stretching results in higher WVTR and fewer point defects.

The bonding of foil and fabric can be carefully adjusted to avoid other functional and aesthetic problems. For example, in the case of extrusion coating a polyethylene extrusion product on a spunbond polypropylene web, processing conditions such as melting point and nip pressure determine fiber entry into the film structure. However, at the minimum entry level, the film and fabric are bonded (bonded) weakly or not (bonded) at all, and therefore tend to delaminate. On the other hand, at the maximum entry level, the film and fabric are essentially pressed together and become one whole. Such a laminate, however, acquires inferior properties to the two individual components and tends to be stiff and brittle. It is also known that too high a bond strength limits the amount of stretching which can be carried out without risking the formation of point defects. Simply put, if the bond between the film and the fabric is too great, the stretched film will sometimes break before delamination, leaving spot defects.

Hence, there is a continuing need to improve the production efficiency and appearance of porous films and composites of porous films and nonwovens. Improvement is desirable in particular when producing microporous films and microporous film / fabric composites that are more breathable while avoiding point defects and other functional and aesthetic defects.

A method of producing a microporous laminate sheet comprising a first film layer and a second layer which are bonded and formed a laminate sheet, wherein the first film layer comprises a pore initiator, according to the invention, is characterized in that producing a microporous laminate sheet by stretching the laminate sheet, wherein at least one CD stretcher with intermeshing rollers and at least one MDO stretching device are used, and the CD tenter depth with intermeshing rollers is from about 0.635 to about 2.54 mm, and the MDO stretch ratio is from about 1.1: 1 to about 4: 1.

Preferably, the laminate sheet is stretched first with at least one CD tenter with intermeshing rollers and then with at least one MDO stretching device.

Preferably, the second layer comprises a fabric layer.

Preferably, the second layer comprises another foil layer that includes a pore initiator.

Preferably, the laminate sheet is stretched by at least one CD tenter with intermeshing rollers immediately before or immediately after stretching by at least one MDO stretching device.

Preferably, the film layer is formed from a thermoplastic composition, and in the step of bonding the film layer to the fabric layer, this thermoplastic composition is extruded onto the fabric layer constituting the second layer.

Preferably, the thermoplastic composition is extruded into a forming roller nip station together with the fabric layer, the forming roller nip station comprising a pair of rollers having a nip therebetween.

Preferably, a thermoplastic composition is used which is based on a polyolefin and comprises at least one polypropylene, polyethylene or polyolefin with functional groups and calcium carbonate as pore initiator.

Preferably, a polyolefin-based thermoplastic composition is used comprising at least one polyethylene, from about 40 to about 60% calcium carbonate and from 1% to about 10% of at least

One additive selected from the group consisting of pigments, processing aids, antioxidants and polymer modifiers.

₂

Preferably, the basis weight of the first film layer of the laminate is from about 10 to about 40 gsm².

Preferably, a polyolefin-based nonwoven material is used as the fabric layer constituting the second layer.

Preferably, the fabric layer is selected from the group consisting of spunbond polypropylene, spunbond polyethylene, and carded thermally bonded polypropylene.

₂

Preferably, the fabric layer has a basis weight from about 10 to about 30 gsm².

The method of producing a microporous film comprising an extruded thermoplastic polymer film containing a pore initiator according to the invention is characterized in that the microporous film is produced by stretching a thermoplastic polymer film with at least one CD tenter with intermeshing rollers and at least one MDO stretching device. and the CD tenter depth with intermeshing rollers is from about 0.635 to about 2.54 mm, and the MDO stretch ratio is from about 1.1: 1 to about 4: 1.

Preferably, the polymer film is stretched first with at least one CD tenter with intermeshing rollers and then with at least one MDO stretching device.

Preferably, the micro-porous film is stretched by at least one CD tenter with intermeshing rollers immediately before or immediately after stretching by at least one MDO stretching device.

Preferably, a polyolefin-based polymer composition is used which comprises at least one functionalized polypropylene, polyethylene or polyolefin and calcium carbonate as pore initiator.

Preferably, a polyolefin-based polymer composition is used comprising at least one polyethylene, from about 40 to about 60% calcium carbonate and from about 1 to about 10% of at least one additive selected from the group consisting of pigments, processing aids, antioxidants and modifiers. polymers.

₂

Preferably, the basis weight of the film laminate layer is from about 10 to about 40 gsm².

A method of producing a microporous laminate sheet comprising a first film layer and a second layer which are bonded together to form a laminate sheet, the first film layer comprising a pore initiator, according to the invention, that the microporous laminate sheet is produced by stretching the laminate sheet by by means of at least one CD stretcher with intermeshing rollers and at least one MDO stretching device, and the CD tenter depth with intermeshing rollers is from about 0.635 to about 2.54 mm, and the MDO stretch ratio is from about 1.1: 1 to about 4: 1.

Preferably, the laminate sheet is stretched first with at least one CD tenter with intermeshing rollers and then with at least one MDO stretching device.

Preferably, each film layer is made of a thermoplastic composition, and the thermoplastic composition is coextruded in the step of bonding the first film layer to the second film layer.

Preferably, each of the thermoplastic compositions is based on a polyolefin and comprises at least one polypropylene, polyethylene or polyolefin with functional groups and calcium carbonate as the pore initiator.

The device for stretching a film or a film / fabric laminate according to the invention is characterized in that it comprises a CD stretcher with intermeshing rollers and a MDO stretching unit, the CD tenter with intermeshing rollers and the MDO stretching unit being arranged such that the film or foil laminate / the fabric is preferably stretched by a CD tenter with intermeshing rollers either immediately before or immediately after being stretched by an MDO stretching device, while a CD interceptor stretcher has a depth of about 0.635 to about 2.54 mm, and the MDO stretching device provides an MDO stretch ratio of about 1 , 1: 1 to about 4: 1.

A preferred effect of the present invention is to provide a method of producing a microporous laminate sheet consisting of a first film layer and a second layer, the method comprising bonding the first film layer to a second layer to form a laminate sheet, the first film layer comprising a pore initiator. and drawing the laminate sheet using at least one CD tenter with intermeshing rollers and at least one MDO stretching device.

In one embodiment, the second layer is a fabric layer, and in another embodiment, the second layer is another film layer that includes a pore initiator. In a particular embodiment of this method, the laminate sheet can be stretched with the at least one CD tenter with intermeshing rollers either immediately before or immediately after stretching with the at least one MDO stretching device. The CD tenter depth with intermeshing rollers can be from about 0.635 mm to 2.54 mm (0.025 to about 0.1 inch) and the MDO stretch ratio can be from about 1.1: 1 to about 4: 1.

The foil layer may be formed from a thermoplastic composition. When the second layer is a fabric, the step of bonding the foil layer to the fabric layer may consist of extruding the thermoplastic composition onto said fabric layer. For example, the thermoplastic composition may be extruded in a nip station for forming rollers together with the fabric layer, the nip station for casting rolls comprising a pair of rollers having a nip therebetween.

The thermoplastic composition may be based on a polyolefin and comprises at least one polypropylene, polyethylene or polyolefin functionalized polyolefin and calcium carbonate as pore initiator.

One of the particularly recommended compositions includes:

- one or more polyethylenes,

from about 40 to about 60% by weight of calcium carbonate and

- from about 1 to about 10% by weight of one or more additives selected from the group consisting of pigments, processing aids, antioxidants and polymer modifiers.

The basis weight of the first film layer of the laminate may be from about 10 to about 40 gsm².

The fabric layer may be a polyolefin based nonwoven material. For example, the fabric layer may be selected from the group consisting of spunbond polypropylene, spunbond polyethylene and thermally bonded carded polypropylene. The fabric layer weight may be from about 10 to about 30 gsm²and the resulting laminate may have a water vapor transmission rate of greater than about 500 grams per square meter per day and a hydraulic height of greater than 60 cm.

In accordance with another embodiment of the present invention, there is provided a method of producing a microporous film comprising the steps of extruding a thermoplastic film from a polymer composition that includes a pore initiator and stretching the film using at least one CD tenter with intermeshing rollers and at least one MDO stretching device.

In a particular embodiment, the microporous film is stretched by at least one CD tenter with intermeshing rollers either immediately before or immediately after stretching by at least one MDO stretching device.

In accordance with yet another embodiment of the present invention, there is provided a method of making a microporous laminate sheet of at least two film layers comprising the steps of bonding a first film layer to a second film layer to form a laminate sheet, the first film layer comprising a pore initiator and stretching the laminate sheet. using at least one CD tenter with intermeshing rollers and at least one MDO stretching device.

In a particular embodiment, each of the film layers is formed from a thermoplastic composition and the step of bonding the first film layer to the second film layer comprises co-extruding said thermoplastic compositions.

According to the present invention, a device for stretching a film or a film / fabric laminate is also provided, consisting of a CD tenter with intermeshing rollers and an MDO stretching device, in which the CD tenter with intermeshing rollers and the MDO stretching device are so arranged that the film or film / fabric laminate can be stretched by a CD tenter with intermeshing rollers either immediately before or immediately after being stretched through the MDO stretching device.

Fig. 1 is a schematic view of a device for producing a laminate sheet according to one embodiment of the present invention, Fig. 2 is a schematic view of a pair of cooperating CD rollers with rings according to an embodiment of the present invention, Fig. 3 - SEM photomicrograph of film stretched by cooperating CD rollers, Fig. 4 - SEM photomicrograph of film stretched by MDO stretching device, Fig. 5 - SEM micrograph of the film stretched by cooperating CD rollers and then through

Intermeshing MD rollers, Fig. 6 - photomicrograph of film stretched by cooperating CD rollers and then through an MDO stretching device, Fig. 7 - SEM photomicrograph of an A / B / A film laminate surface stretched by an MDO device, Fig. 8 - SEM photomicrograph of an A / B / A foil laminate cross-section stretched by an MDO device, Fig. 9 - SEM photomicrograph of the surface of the A / B / A film laminate stretched by the cooperating CD rollers and then by the MDO stretching device, and Fig. 10 - SEM photomicrograph of the A / B / A film laminate cross-section stretched by the cooperating CD rollers and then by the stretching device MDO.

In accordance with the present invention, a method of producing microporous films which have unique physical and aesthetic properties has been provided. These microporous films may consist of a monolayer or may consist of a laminate of two or more film layers. Such film laminates can be formed, for example, by coextruding two or more thermoplastic extrusion products. According to the present invention, there is also provided a method of producing a laminated sheet consisting of at least one microporous film layer and at least one fabric layer (material). Such laminated sheets can be produced by bonding (bonding) a microporous film to a fabric / material layer. Alternatively, the pre-film may be bonded to a fabric / material layer to form a laminate and the laminate then stretched to provide porosity in the film layer. Regardless of the technique used, the resulting laminated sheet, which has a microporous film layer and a fabric layer, produces a composite breathable and suitable for any of the many end uses, especially those applications that require a composite that will not delaminate, acts as a liquid barrier which has high water vapor permeability and possibly is soft and of a fabric / material type (such as for hygienic applications, e.g. in backing sheets for diapers).

Applicants have found that improved microporous films and laminates can be produced by proper selection of stretching methods. In particular, microporous films and laminates with unexpectedly improved properties can be produced by sequentially stretching the film or laminate by means of cooperating CD rollers with rings and a MDO stretching machine. Unless otherwise indicated, the term laminate refers to film laminates consisting of two or more film layers as well as film / fabric laminates consisting of at least one film layer and at least one material layer / e.g. fabrics.

In one embodiment, the film / fabric laminate is prepared and then stretched to provide porosity. A polymer composition that can be activated to become porous is extruded onto the fabric and then stretched using the methods described herein to form a breathable composite suitable for many end uses such as liquid barrier, high water vapor permeability.

The most advantageous property of a microporous breathable film or laminate is the combination of a high WVTR with a low incidence of point defects. The optimal pore size distribution achieved with this combination is associated with the high frequency of small pores. Scanning electron microscope (SEM) analysis of foil prototypes stretched only with a CD device with intermeshing rollers (see Fig. 3) revealed pores that were located at specific locations along the machine direction tracks due to the nature of the metal rollers in physical contact with the film. When this film was later stretched through the MD device with intermeshing rollers (see Fig. 5), the pores formed by the intermeshing rollers CD device were larger but few new pores were formed. Thus, the cooperation of the CD rollers and then the cooperation of the MD rollers was not an optimal process. However, when the film was processed by cooperating the CD rollers and then stretching the MDO (see Fig. 6), the results were much better. New pores formed easily in those tracks that had no pores only after the co-operation of the CD shafts. Since the film should generally stretch until a desired WVTR is achieved, this roller co-operation plus MDO technique can provide a high WVTR by creating a large number of smaller pores and a lower incidence of point defects. If one tried to achieve the same level of WVTR using only CD roll cooperation or only MDO stretching, the formation of point defects would be more frequent.

The methods of the present invention can be used to form microporous films (and film laminate layers) from any suitable polymer (or polymer blend) that is suitable for film formation and that contains a pore initiator (such as an inorganic filler) dispersed therein. The polymer composition that has one or more pore initiators dispersed therein is formed into a film, such as a continuous molded film.

Extrusion. The resulting film is then stretched using one or more cross machine direction (CD) stretching machines and one or more machine direction (MDO) stretching devices. In one embodiment, stretching with a CD intermeshing tenter either immediately precedes or immediately follows stretching by an MDO stretching unit. As used herein, the terms immediately precedes and immediately follows simply means that no other stretching is performed between stretching with a CD intermeshing roller tenter and stretching with an MDO stretching device. It is contemplated that other types of stretching devices may be used before or after this sequence of operations, and it is also contemplated that the film can only be stretched by means of one or more CD intermeshing stretchers and one or more MDO stretching devices.

Using CD intermeshing roll stretching in conjunction with MDO interlocking, 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 by just a tenter alone with CD intermeshing rollers. (see Fig. 3), the MDO stretcher itself (see Fig. 4) or CD mating rollers, followed by MD mating rollers (see Fig. 5).

To form a porous film / fabric (material) laminate, after preparing the microporous film as described above, the microporous film may be bonded (bonded) to one or more fabric layers to form a laminate structure. Alternatively, the non-microporous film may first be bonded (bonded) to one or more layers of fabric / material to form a laminate structure, and the laminate structure may then be stretched in the manner described above to render the film layer microporous. The foil and fabric layers can be bonded together by any of a variety of methods, such as adhesive bonding, electromagnetic bonding, and ultrasonic bonding. In one embodiment, a film-forming polymer that has one or more pore initiators dispersed therein may be extruded onto a fabric to form a laminate consisting of a film layer bonded to a material / fabric layer. The resulting laminate sheet can then be stretched in the same manner as described above to make the film microporous. Even when extrusion coating is used to adhere the film to the fabric, bonding (bonding) can be improved by using any of a variety of additional bonding methods such as adhesive bonding, electromagnetic bonding, hot plate bonding, and ultrasonic bonding. It should also be shown that the film / fabric laminates of the present invention can include any number of film and material / fabric layers, in any desired configuration.

The same techniques used to form film / fabric laminates can also be used to form film laminates that include two or more film layers, at least one of which is microporous. Thus, the microporous film may be bonded to one or more film layers to form a laminate structure. Alternatively, the non-microporous film may be bonded first to one or more layers of the non-porous film to form a laminate structure, and the laminate structure may then be stretched as described above to render the film layers microporous. The foil layers can be bonded together in any of a variety of ways, such as adhesive bonding, electromagnetic bonding, hot plate bonding, and ultrasonic bonding. Film laminates can also be formed by coextrusion. Film-forming polymer compositions that contain one or more pore initiators dispersed may be coextruded to form a laminate having two or more film layers bonded together. The resulting laminate sheet can then be stretched in the same manner as previously described to make the film layers microporous.

The composition of each foil layer in the foil laminate can be selected to achieve the desired properties of each foil layer, and thus the composition of each foil layer can be the same or different.

For example, one or more of the foil layers may contain a greater amount of pore initiator so that more pores will form in the layer during stretching. In this way, the properties such as WVTR of each foil layer can be individually adjusted in the resulting foil laminate. In one example embodiment, a film laminate can be formed of three microporous layers, the middle layer of which contains less filler than the two outer layers.

PL 207 635 B1

Figure 1 is a schematic representation of one embodiment of an apparatus that can be used to manufacture a laminate sheet in accordance with one embodiment of the present invention, wherein the film layer is a thermoplastic film and the fabric layer is a fibrous nonwoven web. When using the device of Fig. 1 the thermoplastic film is laminated during extrusion onto the fibrous nonwoven web by inserting the nonwoven web into the nip of a roller pair together with the thermoplastic extrusion product. The obtained laminate sheet is then stretched as previously described. If only a microporous film rather than a laminate is desired, the nonwoven web constituting the second layer 33 on the roller 32 can be eliminated. Likewise, if a film laminate is desired, a plurality of thermoplastic extrusion products may be introduced into the nip of a roller pair, thereby obtaining a coextruded film laminate.

To produce a continuous laminate sheet, the thermoplastic film layer composition is fed from an extruder 21 through a slot die 22 to form an extrusion product (which corresponds to the film layer 26 of the resulting laminate sheet). The extrusion product is applied to a nip (nip of the forming station) between the forming roller 24 (typically a metal roller) and a support roller 25 (typically a rubber roller). An air blade can be used to assist in the elimination of drag resonance, as is known, for example, from US Patent No. 4,626,574. Alternatively, air cooling devices known from US Serial No. 09/489095, Public No. US 6,951,591 can be used to prevent resonance due to drag. The nonwoven web / fabric layer 33 from the roller 32 is pulled to the nip of the forming station, between rollers 25 and 24. In this nip, the fabric layer 33 is extrusion coated with a molten film (or extrusion product) 26 that has just left the slit mouthpiece 22. During the extrusion lamination process, the fibers substantially sink into the film and are surrounded by the film.

After the nip between the rollers 24 and 25 has been exited by the laminate sheet, it is then stretched at two or more stretching stations. In one embodiment, the laminate sheet is stretched using one or more CD mating rollers and one or more MDO tensile devices, wherein the sheet is stretched by one of the CD mating rollers immediately before or immediately after being stretched by one of the MDO tensile devices. In addition, one or more temperature-controlled rollers (such as roller 45) may be provided to heat the laminate prior to stretching.

In the embodiment shown in Fig. 1, a CD stretcher 28 with intermeshing rollers is provided in the first stretching station, and an MDO stretching device 29 is provided in the second stretching station. A CD puller with intermeshing rollers generally consists of a pair of rollers which are positioned so as to form a nip therebetween. Thus, a CD tenter with intermeshing rollers 28 in the first stretching station generally consists of incrementally stretching rollers 30 and 31, while the stretching rollers 30 and 31 may have any of a variety of configurations. Fig. 2 shows schematically one example of cooperating rollers CD 30 and 31 equipped with rings. Each ring roller has a plurality of grooves that extend around the surface of the roller, parallel to the circumference of the roller. When the shafts are brought together into close engagement, the grooves on one shaft will mate with the grooves on the other shaft. As the film or laminate passes between the rollers, they will incrementally extend in the transverse direction as is known to the person skilled in the art.

In the example embodiment of FIG. 2, each incremental draw roller (or roller equipped with rings) consists essentially of a cylindrical roller 37 and a plurality of circumferential rings 38 attached to the outer circumference of the cylindrical roller 37. The circumferential rings 38 are generally uniformly spaced along their length. cylindrical shaft 37. However, the rings on the stretching roller 30 are offset with respect to the rings on the stretching roller 31, so that when the rings are brought together as shown in Fig. 2, the rings (and the grooves therebetween) of the spreading roller 30 will engage (cooperate). with rings (and grooves between them) of the spreading roller 31. Thus, as the laminate sheet passes between the draw rollers 30 and 31, the laminate sheet will incrementally extend in the transverse direction (i.e., perpendicular to the machine direction in the apparatus of Figure 1).

In one exemplary embodiment, the shafts of the shafts provided with rings may be interposed between two machine side plates, with the lower shank located in fixed bearings and the upper shank located in the bearings in vertically sliding members. The sliding members are vertically adjustable by wedge-shaped movable

Elements by means of adjusting screws. Screwing in or out of the wedges will move the slide member vertically downward or upward, respectively, to further engage or engage the gear-type teeth of the upper mating shaft with the lower mating shaft. Micrometers mounted on the side frames work to indicate the engagement depth of the teeth of the mating shaft.

Air cylinders can be used to firmly hold the sliding members in their downward engagement position relative to the adjustable wedges to counter the upward force exerted by the material being stretched. These cylinders can also be retracted to disengage the upper and lower intermeshing shafts for threading material through associated equipment or in conjunction with a safety circuit which, when activated, would open all the machine's gripping points.

Since CD mating members are often susceptible to large tooth depths, it may be necessary for the equipment to include a means for causing the shafts of the two mating rollers to remain parallel as the upper shank is raised or lowered. It may be necessary to ensure that the teeth of one mating shaft always fall between the teeth of the other mating shaft, avoiding potential damaging physical contact between the mating teeth. This parallel movement is provided by a rack arrangement in which a stationary rack is attached to each side frame in a side by side position with vertically sliding members. The stem extends through the side frames and runs in a bearing in each of the vertically sliding members. The gear rests at each end of the shank and works in mesh with the racks to produce the desired parallel movement.

A CD tenter drive with intermeshing rollers will generally act on the upper and lower intermeshing rollers, except when stretched by intermeshing rollers materials that have a relatively high coefficient of friction. The drive does not need to compensate for the tooth clearance, but a small amount of drive misalignment or slip will not cause any problem. The reason for this will be apparent from the description of the cooperating CD components.

In the embodiment of Fig. 2, CD mating members may be machined from a solid material, but can best be described as an alternating arrangement of two discs of different diameters. In one embodiment, the mating wheels would be 15.24 cm (6 ") in diameter, 7.9 mm (0.031) thick, and had a full radius at its edge. The spacer discs separating the mating discs would be 129.54 / 5.08 cm (51/2) in diameter and 0.18 cm (0.069) in thickness. Two rollers of this configuration could be countersunk up to 0.587 cm (0.231) leaving a clearance of 0.048 cm (0.019) for the material on all sides and this CD mating member configuration would have a pitch of 0.254 cm (0.100). Alternatively, the CD intermeshing rollers may consist of cylindrical rollers that have a series of circumferential rings extending around the circumference of the rollers.

While the CD mating shafts described above may exhibit greater tooth depths, such depths may preferably be from about 0.064 cm to 0.254 cm (0.025 to about 0.1 inch), and more preferably from about 0.10 cm to 0.19 cm (0 .04 to about 0.075 inches). Such groove depths make it possible to avoid damage to the film.

In the exemplary embodiment of Fig. 1, after passing through the intermeshing CD rollers, the film or composite passes through a second stretching station that includes an MDO stretching device 29. Typical MDO stretching equipment known to one skilled in the art may be rather complex, but the principles are simple. The film or film / fabric composites (material) are passed through the nips of two pairs of rollers, however, the second pair of rollers rotates faster than the first pair of rollers, so that the film or film / fabric composite will be pulled by the second pair of rollers and thus stretched. in the machine direction.

In some roll assemblies of an MDO stretching unit, one or more rollers are heated to facilitate the stretching process. Alternatively, a separate heated roller may be provided, in which case at least one of the roller units may therefore consist of three rollers. In such an arrangement, the first roll is an internally heated roll that heats the film or composite prior to reaching the nip. This heated first roller is not in physical contact with any other roller of the roller assembly. The second roller is coated with a resilient material, such as rubber, to allow gripping without damage (i.e., physical contact) with the third roller, which is a metal roller. Typically only one of the two shafts in contact with each other, such as a metal third shaft, is driven. At the same time, however, not driven

The roller will rotate due to the contact between the two rollers. While the two shafts may be driven while they are in contact with each other, such an arrangement requires more precise speed control if desired.

In the exemplary embodiment of Fig. 1, an MDO stretching unit 29 is provided in the second stretching station. The first roll set of the MDO stretching unit comprises a heated roller 50, a coated second roller 51, and a third metal roller 52 (which is driven). The film or composite is passed through the nip between rollers 51 and 52. The second set of rollers of the MDO stretching unit in FIG. 1 is similar to the first set, but the second roll set includes only a coated roller 61 and a driven metal roller 62 (no additional heated roller). The foil or composite is passed through the nip between rollers 61 and 62.

In operation, the two nips of the MDO stretching device are closed and the foil or composite is gripped between the rollers 51 and 52 and between the rollers 61 and 62. However, the rollers 61 and 62 are driven at a greater peripheral speed than the rollers 51 and 52, causing is the stretching of the film or composite in the air gap between the two nips. A typical size of the air gap is from about 0.013 cm to 1.4 cm (0.005 to about 0.550).

In an MDO stretching unit, the MDO stretch ratio is defined as the ratio of the speed of the second roller pair to the speed of the first roller pair. In the embodiment illustrated in FIG. 1, the MDO stretch ratio is the ratio of roller speed 62 to roller 52 speed. In one embodiment, the MDO stretch ratio may preferably be selected from about 1.1: 1 to about 4: 1, and more preferably about 2: 1. These MDO stretch ratios make it possible to avoid damaging the film. Upon exiting the MDO stretching unit, the film or composite will be longer and thinner than its original dimensions.

The apparatus and methods of the present invention are particularly suitable for producing laminate sheets having at least one microporous film layer and at least one fabric layer. The film composition that is extruded into the nip may contain filler particles (pore initiator) so that when the laminate sheet is stretched, micropores are formed in the film layer at the locations of the filler particles. The fabric layer may be a non-woven fibrous web of staple fibers or spunbonded monofilaments. In addition, the incremental stretching provided by stretching with the cooperating CD rollers gives the composite a very soft fibrous finish that then looks like a fabric. The result of such incremental stretching or stretching by cooperating rollers is a composite that has excellent breathability and barrier properties, as well as a soft fabric type texture.

Methods for making microporous films are well known in the art. The film is made by mixing particulate mineral filler (such as calcium carbonate or other salt) into a suitable polymer by mixing to form a filled polymer film, and then stretching the film to make it microporous and breathable.

A microporous film is often characterized by the size of the pores present. Pores with 0.01 to 0.25 micron equivalent diameters are known to prevent the flow of non-wetting liquids. If the frequency of these pores is sufficiently high, the material will allow the rational passage of water vapor while at the same time providing an effective barrier to liquid water.

In accordance with one embodiment of the present invention, the film, including the film layer of the film / fabric composite and the individual film layers of the film laminate, can be comprised of a polyolefin-based composition such as one or more polypropylenes, polyethylenes, functional grouped polyolefins, or combinations thereof. One suitable composition comprises a mixture of one or more polyethylenes (such as a mixture of LLPDE and LDPE) and a pore initiator. The type and amount of each polyethylene used will depend very much on the intended use of the film or laminate. In one embodiment, from about 40% to about 60% pore initiator may be incorporated. For example, one particular composition for a film according to an embodiment of the present invention may first be prepared by melt blending a composition comprising:

(a) from about 35 to about 45% by weight of linear low-density polyethylene (LLDPE); (b) from about 3 to about 10% by weight of low-density polyethylene (LDPE).

(C) from about 40 to about 60% by weight of calcium carbonate filler particles (where the surface of the calcium carbonate is coated with a fatty acid), and (d) optionally from about 1 to about 10% by weight of one or more with the following additives: pigments, technological adjuvants, antioxidants and polymer modifiers.

The above composition can be extruded into a nip between two rolls (such as rolls 24 and 25 previously described) to form a film at a speed of about 2.79 m / s to 6.1 m / s (550 fpm to about 1200 fpm) (or larger) without drag resonance. In one embodiment, the resulting film layer may have a basis weight of about 10 to about 40 gsm²most preferably from about 20 to about 30 g / m2². The resulting film can then be pulled out in the manner described previously.

One particular film composition may contain about 51 wt% polyethylene and about 44 wt% calcium carbonate filler particles that have an average size of about 1 micron. Polyethylene can be supplied as a blend of LLDPE and LDPE with any type of amount depending on the intended use of the film or laminate, including required aesthetic and physical properties (including properties such as formability and surface feel). In some circumstances, it may be desirable to include high-density polyethylene to increase stiffness. The color of the film (whiteness) can be adjusted by incorporating one or more pigments. For example, a white colored film can be obtained by incorporating up to about 4% by weight of titanium dioxide. A processing aid such as a fluorocarbon polymer, e.g. propene-1,1,1,2,2,3,3,3-hexafluorocopolymer from 1, may also be added in an amount of from about 0.1 to about 0.5% by weight. 1-difluoroethylene. Antioxidants such as Irganox 1010 and Irgafos 168 may also be added in a total concentration of from about 500 to about 4000 ppm.

While the above-described film compositions can be used to make microporous films using the stretching methods described herein, composite structures can also be formed by bonding a film layer (such as a film layer formed from the compositions described above) to a fabric layer or other film layer. The film layer can be made porous by stretching it prior to bonding to the fabric layer or an additional film layer. Alternatively, an unstretched film layer having the compositions described above may be bonded to a fabric layer or other film layer and then stretched the resulting composite structure to render the film layer (s) microporous.

In yet another alternative, a fabric layer may be nipped between two rollers (such as rollers 24 and 25 previously described) along with the embossing product. In this way, the polymeric composition of the film layer is extruded onto the fabric layer. The resulting laminate sheet is then stretched in the same manner as previously described to obtain a laminate sheet that has a microporous film layer and a material (woven) layer. In one embodiment, the fabric / woven layers of the various laminate structures described herein may have a basis weight of about 10 to about 30 gsm.²and even from about 15 to about 25 gsm². The WVTR of the laminate can be greater than about 500 grams per square meter per day and the hydraulic height can be greater than about 60 cm (measured as the minimum height of the water column that causes water to leak in the laminate). In one embodiment, the WVTR may exceed about 1,000 grams per square meter per day, and even exceed about 3,000 grams per square meter per day.

Likewise, two or more extrusion products may be provided to the nip between the two rollers (such as the rollers 24 and 25 previously described). In this way, the polymeric compositions are coextruded to form a laminate of two or more film layers. The resulting laminate sheet is then stretched in the same manner as described previously to obtain a laminate sheet that has two or more microporous film layers.

Suitable fabric layers include natural or synthetic fibers or monofilaments which are bound or otherwise integrated into a web structure. Suitable fabrics include woven and non-woven fabrics, such as melt-spun, spin-laced, carded, heat-bonded or adhesive-bonded fabrics. Exemplary fabrics that can be used include spunbond polypropylene, spunbond polyethylene, and carded thermally bonded polypropylene.

The properties of the films and sheets of laminates made according to the present invention can be tested in various ways. For example, the water vapor transmission rate (WVTR) can be determined according to ASTM E 96, Standard Test Methods for Water Vapor Transmission of Materials. Known

The amount of desiccant is placed with the sample in a cup-shaped container and held securely by the retaining ring and gasket. The assembly is placed in a constant temperature (40 ° C) and constant humidity (75% RH) chamber for 5 hours. The amount of moisture absorbed by the drying agent is determined gravimetrically and used to determine the WVTR of the sample (units g / m² 24 hours).

ASTM E 1294-89: Standard Test Method for Pore Size Characteristics of Membrane Filters using Automated Liquid Porosimeter can be used to measure the maximum pore size (MPS). This method measures the MPS (micron units) of microporous films and laminate sheets using a liquid displacement technique that depends on the capillary rise created by surface tension and uses the Washburn equation to calculate the pore diameter.

The number of spot defects can be determined using the Clopay Pinhole Test Method (HCTM-02) which measures the resistance of coated and laminated fabrics to penetration of an alcoholic solution (100 ml of 70% isopropyl alcohol with 1.0 ml of red food dye). This test is carried out by an exposure path of approximately (six square feet) (0.56 m²) of the composite by exposure to 72 ml of the solution on the foil side of the sample. The solution is evenly spread with a brush to cover the marked area of ​​the sample. The solution is allowed to rest for ten minutes and then tapped with napkins to dry. The sample is then inverted, the color marks are counted and the number of point defects in the test area is reported.

Examples

The following examples illustrate one method of making films, film laminates, and film / fabric laminates according to one embodiment of the present invention. In light of these examples and the following detailed description, one skilled in the art will appreciate that changes can be made thereto without departing from the scope of the present invention. The listing of these examples is only provided to show those skilled in the art how to apply the principles of the present invention as discussed herein. These examples are not intended to limit the protection scope of the present invention.

The following examples used a device similar to that shown in Fig. 1, but in Example 1, however, since only a microporous film and not a laminate was formed, the nonwoven web was not used as a fabric layer 33 on the roll 32, as well as in Example 1. rollers 24 and 25 that form the nip of the forming station.

Example 1

A film composition containing 50% calcium carbonate, 47% polyethylene resin and 3% titanium dioxide was extruded using standard cast film equipment and processing conditions. The extruder speed and the line speed were adjusted so that a film layer with a basis weight of 45 g / m was produced² and it was foil 1A. Film 1B was formed by passing film 1A through a pair of CD rollers with mating rings. The ring rollers had rings every 0.254 cm (0.100 inch). Fig. 3 shows a photomicrograph of the film 1B. Film 1C was formed by passing film 1A only through an MDO stretching unit. Fig. 4 shows a photomicrograph of the film 1C. The 1D film was created by stretching the 1A film with both a CD and MDO stretching device. The final thickness of the 1D film was such that (specific surface area) the basis weight of the film was about 23 g / m2² with a stretch ratio of MDO of about 2: 1. Fig. 6 shows a photomicrograph of the 1D film. For comparison, the film 1A was also stretched using a CD stretching device with intermeshing rollers, and then an MD device with intermeshing rollers (machine direction) to form the film 1E.

The physical property measurement results shown in Table # 1 show typical data for the above films with the above mentioned groove depth on the CD mating rollers and the speed ratio in and out of the MDO device. As indicated in the table, the properties of the film stretched by CD intermeshing rollers and then by MDO stretching machine are better than any other option. The micrographs in Fig. 3-6 also show that the stretching methods of the present invention provide a large number of small diameter round pores which are responsible for a high MVTR (or WVTR) compared to other films. The air flow measurement reported in Table 1 was obtained by applying high pressure air to the film and measuring air flow through the film for a short period of time (five seconds).

PL 207 635 B1

Table 1

<td>Sample description</td><td>Surface proper (g / m²)</td><td>The number of defects spotlights (# / m²)</td><td>Air flow (ml / min @ 90psi) (621 kPa)</td><td>MVTR (g / m²/day)</td>

<td>Precursor 1A</td><td> 45</td><td> 0</td><td> 0</td><td> 100</td>

<td>1B - only cooperating CD shafts</td><td> 35</td><td> 0</td><td> 1128</td><td> 1800</td>

<td>1C - only MDO</td><td> 25</td><td> 0</td><td> 1511</td><td> 2500</td>

<td>1D - CD, cooperating CD &amp; MDO rollers</td><td> 31</td><td> 0</td><td> 6030</td><td> 3400</td>

<td>1E - cooperating CD &amp; MD rollers</td><td> 23</td><td> 0</td><td> 4400</td><td> 3000</td>

Example 2:

A film composition containing 50% calcium carbonate, 47% polyethylene resin and 3% titanium dioxide was extruded using standard cast film equipment and process conditions. Carded polypropylene web, thermally point bonded, with a specific surface area of ​​20 g / m 2²threaded from the unwinder to the nip of the casting station so that it is in contact with the stream of molten film under operating conditions. The extruder speed and the line speed were adjusted so that a film layer with a basis weight of 40 g / m was added to the fabric.²which resulted in a 2A laminate. The film / fabric laminate 2A was then passed through CD rollers with mating rings to form laminate 2B. The ring rollers had rings every 0.254 cm (0.100 inch). The 2C laminate was formed by passing the 2A laminate only through an MDO stretching unit. The 2D laminate was formed by stretching the 2A laminate with both a CD and MDO stretching device. For comparison, laminate 2A was also stretched using a CD device with intermeshing rollers, and then an MD device with intermeshing rollers to form a 2E laminate. The physical property results shown in Table # 2 show typical data for these prototypes as a function of the depth of the groove on the mating CD shafts and the speed ratio in and out of the MDO device. As shown in the table, the properties of the laminate stretched with CD intermeshing rollers followed by an MDO stretching device are better than any other option.

Table 2

<td>Sample description</td><td>Surface proper (g / m²)</td><td>The number of defects spotlights (# / m²)</td><td>Air flow (ml / min @ 90psi) (621 kPa)</td><td>MVTR (g / m²/day)</td>

<td>Precursor 2A</td><td> 60</td><td> 0</td><td> 0</td><td> 50</td>

<td>2B - only cooperating CD shafts</td><td> 53</td><td> 0</td><td> 414</td><td> 1100</td>

<td>2C - MDO only</td><td> 49</td><td> 0</td><td> 611</td><td> 1200</td>

<td>2D-CD, cooperating CD &amp; MDO rollers</td><td> 46</td><td> 0</td><td> 1780</td><td> 3169</td>

<td>2E - cooperating CD &amp; MD rollers</td><td> 51</td><td> 0</td><td> 872</td><td> 1743</td>

Example 3:

When obtaining a co-extruded foil laminate consisting of three foil layers (A / B / A) and a grammage of 85 g / m² standard cast film equipment and process conditions were used. The polymer composition for the first and third layers contained 57% calcium carbonate and 43% polyethylene resin and had a basis weight of 30 g / m2². The polymer composition for the middle layer contained 54% calcium carbonate and 46% polyethylene resin and had a basis weight of 25 g / m2². Neither of the layers contained titanium dioxide and was designated as film 3A. Film 3B was formed by passing film 3A only through an MDO stretching unit. MDO stretching was performed at 102 ° C (215 F) using a draw ratio of 2.5 and a draw gap of 0.127 mm

PL 207 635 B1 (5 mils). Fig. 7 shows a photomicrograph of the surface of the film 3B and in Fig. 8 a photomicrograph of the cross-section of the film 3B. Film 3C was formed by stretching film # 3A with a CD intermeshing roller and then stretching with an MDO stretching machine. Stretching with CD intermeshing rollers was performed at 24 ° C (75 F) using a 1 mm (0.040) tooth depth. Stretching for MDO was performed at 102 ° C (215 F) using a draw ratio of 2.0 and a draw rest of 0.127 mm (5 mils). Fig. 9 is a photomicrograph of the surface of the film 3C, and Fig. 10 is a photomicrograph of a cross section of the film 3C.

The physical property results for films 3A, 3B and 3C are shown in Table # 3. As shown in the table, the properties of the film stretched with the cooperating CD rollers, followed by the MDO stretching device, are better than that of the film stretched with the MDO device only. The micrographs of Fig. 7-10 also show that the stretching methods of the present invention provide a high number of small diameter round pores which are responsible for a high MVTR (or WVTR) compared to other films.

Table 3:

<td>Sample description</td><td>Specific surface</td><td>Number of point defects (#m²)</td><td>MVTR (g / m²/day)</td>

<td>3A - precursor</td><td> 85</td><td> 0</td><td> 50</td>

<td>3B - only MDO</td><td> 36</td><td> 0</td><td> 2850</td>

<td>30 - cooperating shafts CD &amp; MDO</td><td> 33</td><td> 0</td><td> 9946</td>

Patent claims