Breathable and microporous thin thermoplastic films

Abstract

To provide breathable thermoplastic films having a low basis weight that are substantially free of holes, and that have physical properties characteristic of films having a much higher basis weight.SOLUTION: Breathable thermoplastic films, laminates, and methods of making the films are provided. The films have a basis weight less than or equal to 15 gsm, and a water vapor transmission rate of at least about 500 g H2O / 24-hour / m2, wherein the film has a ratio of the MD load at break to the CD load at break of less than about 10, and at least one of a machine-direction notched Elmendorf tear strength of at least about 5 g or a machine-direction notched trapezoidal tear strength of at least about 15 g.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 61 / 992,438, filed on May 13, 2014, U.S. Provisional Patent Application No. 62 / 053,385, filed on September 22, 2014, and U.S. Provisional Patent Application No. 62 / 092,351, filed on December 16, 2014.

Background Art

[0002] Thermoplastic films are widely used in personal care articles, for example, as the outer layer of diapers or as other disposable personal hygiene products. For various reasons including cost, comfort, resource conservation, and waste minimization, it is desirable to make the film as thin as possible while maintaining other necessary properties of the film.

[0003] Desirable qualities of thermoplastic films include being liquid impermeable, having vapor permeability (e.g., being breathable), being bondable to other layers of personal hygiene products, and having sufficient physical strength to be processed into the final product. When using a thermoplastic film for packaging, for example, as the outer packaging of consumer goods, strength is an important consideration. A breathable film having sufficient strength and basis weight may be particularly useful as the packaging for products that need to release odors caused by the manufacturing process.

[0004] A thermoplastic film can be formed by extruding a molten polymer composition onto a cooling roller, and the molten polymer composition is immediately cooled to form a solid film. The processing of the film includes various stages including heating, cooling, and stretching, and a final film product having a thickness of 1 / 72 or less compared to the initial thickness is produced. Stretching in the machine direction (MD) forms a highly oriented thin gauge film, which is called machine direction orientation (MDO). MDO can be useful, but it can also result in qualities such as low cross-direction (CD) tensile strength, impact strength, tear strength, and slow puncture resistance, especially in particularly thin films.

[0005] Current methods for making thin thermoplastic gauge films include the method described in U.S. Patent No. 7,442,332 (Cancio et al.). In this method, most (more than half) of the stretching of the web occurs between the extrusion die and the first nip (i.e., within the "melt curtain"). Two difficulties in such a casting process are the phenomenon known as "draw resonance" which results in film thickness non-uniformity, and the formation of holes in the film. These problems become larger as the production speed increases and can further limit the types of polymer compositions that can be used. To solve these problems, it is necessary to slow down the production speed, which ultimately leads to an increase in cost.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Accordingly, there is a need for thin thermoplastic films that are MDO-limited and have desirable properties such as being pore-free, having good breathability, good tensile strength, and good tear strength characteristics, and that can be manufactured economically and efficiently on high-speed manufacturing lines.

Means for Solving the Problem

[0008] The present invention meets the aforementioned needs by providing a breathable thermoplastic film that has a low basis weight, is substantially pore-free, and has physical properties characteristic of films having a higher basis weight. The films of the present invention exhibit excellent tensile strength, tear strength, and breathability. While tear strength is proportional to the thickness of the film and thick films generally exhibit high tear strength, the films produced by the method of the present invention exhibit stronger tear strength compared to what would be predicted in films for comparison having a similar thickness. In other words, the films of the present invention improve the ratio of tear strength to thickness.

[0009] The thermoplastic films of the present invention are considered to be unique in themselves and are stretched in the machine direction at a temperature high enough to prevent detrimental machine direction (MD) orientation, but below the melting point of the thermoplastic polymer, and are produced by a novel method. This method occurs downstream from the cooling roller, in contrast to the method described in U.S. Patent No. 7,442,332. The method of the present invention allows the extrusion process to be carried out at normal manufacturing speeds without the need for additional equipment to reduce draw resonance. As a further advantage, film properties such as opacity can be controlled by additional downstream MD stretching, which reduces or eliminates the need for the addition of opacifying agents.

[0010] Some non-limiting embodiments of the present invention are described below. In one embodiment, a breathable thermoplastic film is provided, the film having a basis weight of about 15 gsm or less and at least about 500 g H2O / 24 hours / m 2having a water vapor transmission rate (WVTR), wherein the film has a ratio of the MD load at break to the CD load at break of less than about 10 and has an Elmendorf tear strength of a machine direction notch of at least about 5 g or a trapezoidal tear strength of a machine direction notch of at least about 15 g.

[0011] In other embodiments, a laminate is provided, the laminate comprising a first layer, the first layer having a basis weight of 15 gsm or less and a water vapor transmission rate (WVTR) of at least about 500 g H2O / 24 hours / m 2 of a breathable thermoplastic film, wherein the film has a ratio of the MD load at break to the CD load at break of less than about 10 and has an Elmendorf tear strength of a machine direction notch of at least about 5 g or a trapezoidal tear strength of a machine direction notch of at least 15 g, and the first layer has a surface, and a substrate attached to the film surface.

[0012] In other embodiments, a method for manufacturing a thermoplastic film product is provided, the method comprising extruding a molten web comprising a thermoplastic polymer onto a first cooling roller from an extruder, the first cooling roller being operated at a peripheral speed V1 and a temperature T1 which is less than the melting point of the thermoplastic polymer, cooling the web to form a film, the space between the extruder and the cooling roller forming a first gap; advancing the film to a stretching roller downstream from the first cooling roller, the stretching roller being operated at a peripheral speed V2 greater than V1 and a temperature T2, advancing the film, further stretching the film in the machine direction to have a substantially uniform thickness, with a limited machine direction orientation, and having a ratio of the MD load at break to the CD load at break of less than about 10 and having an Elmendorf tear strength of a machine direction notch of at least about 5 g or a trapezoidal tear strength of a machine direction notch of at least about 15 g.

[0013] In other embodiments, in the above-described method, the MD load at break of the thermoplastic film is at least 2.0 N / cm, and the CD load at break is at least 0.7 N / cm.

[0014] In other embodiments, in the above-described method, the thickness of the thermoplastic film product is from about 5 gsm to about 20 gsm.

[0015] In other embodiments, in the above-described method, the molten web is cast, blown, calendered, single-extruded, co-extruded, chill-cast, nip-embossed, or a combination thereof is performed.

[0016] In other embodiments, in the above-described method, it further includes at least one additional cooling roller operated at a temperature T and a peripheral speed V.

[0017] In other embodiments, in the above-described method, to produce a thermoplastic film product having a water vapor transmission rate (WVTR) of at least about 500 g H2O / 24 hours / m 2 and having breathability, it further includes the step of stretching the film in the transverse direction.

[0018] In other embodiments, in the above-described method, the film is gradually stretched in the transverse direction using a fitting roller.

[0019] In other embodiments, in the above-described method, the film advances through a first machine direction orientation section including at least one heating roller having a temperature T3 and at least one stretching roller.

[0020] In other embodiments, in the above-described method, the film advances through at least a second machine direction orientation section including at least one heating roller and at least one stretching roller.

[0021] In other embodiments, in the above-described method given, the second machine direction orientation section is located downstream of the lateral mating roller section.

[0022] In other embodiments, in the above-described method given, the second machine direction orientation section is located upstream of the lateral mating roller section.

[0023] In other embodiments, in the above-described method given, T1 is from about 80 °C to about 160 °C.

[0024] In other embodiments, in the above-described method given, T2 is from about 60 °C to about 100 °C.

[0025] In other embodiments, in the above-described method given, T3 is from about 80 °C to about 150 °C.

[0026] In other embodiments, in the above-described method given, T is the same as T1.

[0027] In other embodiments, in the above-described method given, T is different from T1.

[0028] In other embodiments, in the above-described method given, V is the same as V1.

[0029] In other embodiments, in the above-described method given, V is different from V1.

[0030] In other embodiments, in the above-described method given, the cooling roller and the stretching roller form a second gap of from about 7.5 cm to about 30 cm.

[0031] In other embodiments, in the above-described method given, the ratio of V2 to V1 is from about 2 to about 8.

[0032] In other embodiments, in the above-described method given, the film is a coextruded multilayer film.

[0033] In other embodiments, in the above-described method provided, the film is a single-extruded film.

[0034] In other embodiments, in the above-described method provided, the film is a blow-molded film.

[0035] In other embodiments, in the above-described method provided, the film has at least about 50% opacity.

[0036] In other embodiments, in the above-described method provided, the film comprises an olefin block copolymer that is ethylene-based, propylene-based, or a combination thereof.

[0037] In yet other embodiments, a breathable thermoplastic film is provided, the film being produced by a method in which a melt web comprising a thermoplastic polymer is extruded onto a cooling roller having a temperature T1 to form a film, the film being sent to a stretching roller having a temperature T2 downstream of the first cooling roller and further sent through a first machine direction orientation section having at least one heating roller having a temperature T3 and at least one stretching roller, whereby a defined machine direction orientation is imparted to the film, the film having a basis weight of about 15 gsm or less, a water vapor transmission rate of at least about 500 g H2O / 24 hours / m 2 and a ratio of the MD load at break to the CD load at break of the film being less than about 10.

[0038] In other embodiments, in the film produced by the above-described method, the Elmendorf tear strength of the film is at least 5 g in the machine direction.

[0039] In other embodiments, in the film produced by the above-described method, the trapezoid tear strength of the film is at least 15 g in the machine direction.

[0040] In another embodiment, in the film produced by the method described above, the MD load at break of the film is at least 2.0 N / cm, and the CD load at break is at least 0.7 N / cm.

[0041] In another embodiment, in the film produced by the method described above, the molten web is cast, blown, calendered, single-extruded, co-extruded, chill cast, nip embossed, or a combination thereof is performed.

[0042] In another embodiment, in the film produced by the method described above, the film is a co-extruded multilayer film.

[0043] In another embodiment, in the film produced by the method described above, the film is a single-layer film.

[0044] In another embodiment, in the film produced by the method described above, the hydrostatic head pressure of the film is at least 200 psi.

[0045] In another embodiment, in the film produced by the method described above, the film is gradually stretched laterally using a fitting roller.

[0046] In another embodiment, in the film produced by the method described above, the film has an opacity of at least about 50%.

Brief Description of the Drawings

[0047]

Figure 1

Modes for Carrying Out the Invention

[0048] The terms used herein: "Activation defects", "activation holes", or "pinholes" mean small holes or tears in the film while the film is being formed, laminated, activated, or going through other manufacturing or processing steps, which can subsequently lead to a decrease in tear strength, an increase in porosity, an increase in leakage, or other undesirable properties.

[0049] "Gsm" means grams per square meter, is a measure of basis weight, and basis weight is an industrial standard term that quantifies the thickness or unit mass of a film or laminate product.

[0050] "Hydrohead pressure" can be measured according to the AATCC 127 - 2008 method and can be expressed in units of pounds per square inch or psi. The film of the present invention has a hydrohead pressure of at least 200 psi.

[0051] "Skin layer" means one or both outer layers of a multilayer film that function as the outer surface of the film.

[0052] "Tear strength" or "tear force" reflects the ease or difficulty with which a film can be torn and is expressed in grams. Here, tear strength may be measured by the Elmendorf Notch Tear Test ASTM D - 1922, which is incorporated herein by reference, and / or by the trapezoid tear test ("Trap test") as described herein or by ASTM D - 5587. The test may be performed on either a notched or unnotched film and in either the CD direction or the MD direction. Unless otherwise specified, tear strength here is the notched tear strength. Tear strength is related to the thickness of the film, and any comparison of tear strength must be made taking into account the relative basis weight of the control sample.

[0053] "Tear strength" means the load (load at break) required to cause the film to break, either in the CD or MD direction. Tensile strength is expressed in units of N / cm or equivalent units and is determined by the ASTM D822-02 method using the following parameters: sample direction = MD × CD; sample dimensions = width 1 inch × length 6 inches; test speed = 20 in / min; grip distance = 2 inches; grip dimensions = 3 inches wide, rubber surface grips that uniformly grip the sample.

[0054] "WVTR" means "Water Vapor Transmission Rate" and is a measure of the gas permeability of the film. WVTR is expressed in units of H2O / 24 hours / m 2 or equivalent units and may be measured in accordance with ASTM D-6701-01 method.

[0055] Film The film of the present invention is a thermoplastic single-layer or multi-layer film and may have a basis weight of from about 5 gsm to about 20 gsm, or from about 5 to about 15 gsm, or from about 10 to about 15 gsm, or from about 8 to about 13 gsm, or from about 10 gsm to about 12 gsm, or less than about 15 gsm, or less than 14 gsm, or less than about 12 gsm, and / or less than about 10 gsm. The multi-layer film of the present invention may include at least 2 layers, or at least 3 layers, or at least 5 layers, or at least 7 layers, or at least 9 layers, or at least 11 layers, or from 2 to about 20 layers, or from 3 to about 11 layers, and / or from 5 to 11 layers. The film may or may not include a skin layer for reducing the tackiness of one or both of the outer surfaces.

[0056] The film of the present invention has a CD load at break that exceeds 0.7 N / cm, or exceeds about 0.8 N / cm, or exceeds about 0.9 N / cm, or ranges from about 0.7 N / cm to about 3.0 N / cm, or from about 0.7 N / cm to about 2.0 N / cm. The film of the present invention has an MD load at break of at least about 2.0 N / cm, or at least about 2.5 N / cm, or at least about 3.0 N / cm, or from about 2.0 N / cm to about 6.0 N / cm, and / or from about 3.0 N / cm to about 6.0 N / cm.

[0057] However, an important and inventive aspect of the present invention is the ratio of the MD load to the CD load at break, which is a measure of the improved balance between these properties and does not exist in the films disclosed heretofore. Without wishing to be bound by theory, this advantageous ratio is believed to be achieved by reducing the machine direction orientation in the film by the method disclosed herein. The ratio of the MD load at break to the CD load at break of the film of the present invention is from about 1 to about 15, or from about 1 to about 10, or from about 1 to about 9, or from about 1 to about 8, or from about 1 to about 5, or less than about 10, or less than about 9, or less than about 8, or less than about 5, or less than about 4, or about 1.

[0058] The film of the present invention is at least 500 g H2O / 24 hours / m 2 or at least 1,000 g H2O / 24 hours / m 2 or at least 2,000 g H2O / 24 hours / m 2 or at least 3500 g H2O / 24 hours / m 2 or at least 4500 g H2O / 24 hours / m 2 or at least about 6,000 g H2O / 24 hours / m 2 or at least about 7,000 g H2O / 24 hours / m 2 or at least about 9,000 g H2O / 24 hours / m 2 or about 1,000 g H2O / 24 hours / m 2From about 10,000 g H2O / 24 hours / m 2 and further has a water vapor transmission rate (WVTR) of 2 .

[0059] The film of the present invention further has a machine direction Elmendorf tear strength of at least about 5 g, or at least about 10 g, or at least about 15 g, or from about 5 g to about 50 g, or from about 10 g to about 45 g, or from about 15 g to about 45 g.

[0060] The film of the present invention further has a machine direction trapezoid (trap) tear strength of at least about 15 g, or at least about 20 g, or at least about 25 g, or from about 15 g to about 150 g, or from about 15 g to about 100 g, or from about 15 g to about 85 g.

[0061] The film of the present invention contains one or more thermoplastic polymers. Polymers suitable for this film include, without limitation, for example, polyolefins such as polyethylene homopolymers and copolymers, polypropylene, polypropylene homopolymers and copolymers, functional polyolefins, polyesters, poly(ester ethers), polyamides such as nylon, poly(ether amides), polyether sulfones, fluoropolymers, polyurethanes, and mixtures thereof. Examples of polyethylene homopolymers include those formed by low density, medium density, or high density, and / or high pressure polymerization or low pressure polymerization methods. Polyethylene and polypropylene copolymers include, without limitation, copolymers with C4-C8 alpha olefin monomers such as 1-octene, 1-butene, 1-hexene, and 4-methylpentene. Polyethylene may be substantially linear or branched and may be formed in various ways known to those skilled in the art using catalysts such as Ziegler-Natta catalysts, metallocene catalysts, or single-site catalysts, or other catalysts widely known to those skilled in the art. Examples of suitable copolymers include, without limitation, poly(ethylene-butene), poly(ethylene-hexene), poly(ethylene-octene), and poly(ethylene-propylene), poly(ethylene-vinyl acetate), poly(ethylene-methyl acrylate), poly(ethylene-acrylic acid), poly(ethylene-butyl acrylate), poly(ethylene-propylene diene), poly(methyl methacrylate), and / or their polyolefin interpolymers. In one embodiment, the film contains polyethylene, polypropylene, and combinations thereof. An example of a suitable commercially available polyethylene-based resin is Exceed TM 3527PA from Exxon. An example of a suitable commercially available polypropylene copolymer is Borealis BD712 from Borealis.

[0062] Other non-limiting examples of suitable olefinic polymer compositions include olefin block copolymers, olefin random copolymers, polyurethanes, rubbers, vinyl arenes, and conjugated dienes, polyesters, polyamides, polyethers, polyisoprene, polyneoprene, any copolymers of the foregoing compositions, and mixtures thereof. Further, the films of the present invention, or layers thereof, may include brittle polymers, non-limiting examples of which are disclosed in U.S. Patent No. 7,879,452. In one embodiment, the film includes an olefin block copolymer.

[0063] In one example, the olefin block copolymer is polypropylene-based. Non-limiting examples of suitable polypropylene-based olefin block copolymers include those sold under the trade name INFUSE TM by Dow Chemical Company, Midland, Michigan, those sold under the trade name VISTAMAXX® by ExxonMobil Chemical Company, Houston, Texas, and those sold under the trade name Exxon Impact® copolymer such as Exxon PD 7623. Both polypropylene and polyester are known to increase the melting point of the formed polymer film and improve the film's resistance to delamination. In other embodiments, the films of the present invention may include ethylene-based olefin block copolymers.

[0064] The thermoplastic polymers described above may be present in the film or in individual layers of the film in amounts from 0% to about 95%, or from about 0% to about 40%, or from about 10% to about 50%, or from about 35% to about 50%, or from about 20% to about 40%, or from about 1% to about 10%. In one embodiment, one or more layers of a film, or a multilayer film, comprise from about 0.1% to about 90%, or from about 1% to about 60%, or from about 20% to about 50%, or from about 20% to about 40%, or from about 1% to about 10% of polypropylene, a polypropylene-based composition or copolymer, ethylene, an ethylene-based composition or copolymer, or a combination thereof.

[0065] The film of the present invention, or an individual layer thereof, may comprise one or more elastomers, including styrenic block copolymers, elastomeric olefinic block copolymers, and combinations thereof. Non-limiting examples of suitable styrenic block copolymers (SBCs) include styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene (SEP), styrene-ethylene-propylene-styrene (SEPS), or styrene-ethylene-ethylene-propylene-styrene (SEEPS) block copolymer elastomers, polystyrene, and mixtures thereof. In one embodiment, the film comprises styrene-butadiene-styrene, polystyrene, and mixtures thereof. Suitable SBC resins are readily available from Clayton Polymers, Houston, Texas; Dexco Polymers LP, Plaquemine, Louisiana; or Septon Company of America, Pasadena, Texas.

[0066] The film of the present invention may include optional components such as fillers such as calcium carbonate, plasticizers, compatibilizers, draw-down polymers, processing aids, antiblocking agents, viscosity-reducing polymers, and the like. Other additives include pigments, dyes, antioxidants, antistatic agents, slip agents, foaming agents, heat or light stabilizers, UV stabilizers, and the like. Suitable processing aids and antiblocking agents are, without limitation, Ampacet available from Ampacet Corporation TMinclude. In one embodiment, the polymer composition may include from about 0% to about 75%, 1% to 30%, or from about 30% to about 60% filler. In one embodiment, the polymer composition may include from about 0% to about 15%, or from about 0% to about 10%, or from about 0.5% to about 5% of a suitable processing aid.

[0067] In one embodiment, the film is substantially free of titanium dioxide or contains less than 0.1% titanium dioxide. The film may have an opacity greater than 50%, or greater than 55%, or greater than about 60%.

[0068] Device FIG. 1 shows an exemplary configuration of a film forming apparatus 10 suitable for forming the film of the present invention. When used with a film or nonwoven material, the “machine direction” means a direction parallel to the direction in which the film or nonwoven material moves when processed within the film forming apparatus. The “cross direction” means a direction perpendicular to the machine direction. In one non-limiting example, as shown in FIG. 1, the film forming apparatus 10 includes a casting / drawing section 12, a machine direction orientation (MDO) section 14, and a cross direction interlocking roller (CDI) section 16. Optionally, the film forming apparatus 10 may include additional sections, such as an annealing section, a winder, an additional machine direction orientation section, and / or a corona treatment section, which will be apparent to those skilled in the art. In other embodiments, the order of the sections or their components may be different from that shown in FIG. 1, as will also be understood by those skilled in the art.

[0069] The casting / drawing section 12 includes an extruder 24 and at least one cooling roller 28 having a first gap 26 therebetween and following it. As will be understood by those skilled in the art, the position of the extruder 24 relative to the cooling roller 28 may be changed from the position shown in FIG. 1 to a position somewhat downstream of that shown, provided that the extruder 24 is still in a position to send a melt curtain containing the extrudate onto the cooling roller 28. Downstream of the cooling roller 28 having a temperature T1 and rotating at a speed V1 is a stretching roller 30 having a temperature T2 and rotating at a speed V2. The cooling roller 28 is separated from the stretching roller 30 by a second gap 32. In operation, the extruder 24 melts the extrudate and extrudes it across the gap 26 onto the cooling roller 28 to form a web or film 15. The film 15 moves into the nip 33 formed between the slave roller 34 and the stretching roller 30 across the second gap 32. Thereafter, the film 15 passes over an idler roller 39 toward the machine direction orientation section 14.

[0070] The web or film of the present invention may be formed in various ways, as will be understood by those skilled in the art, and may result in a film equivalent to the methods described herein, such as cast molding, blow molding, calender molding, single extrusion, co-extrusion, chill casting, nip embossing, or any other method.

[0071] In one embodiment, the thermoplastic polymer film formulation can be compounded in extruder 24 at a temperature, for example, of from about 210°C to about 280°C. The exact temperature will depend on the formulation of the polymer composition. A web or "melt curtain" comprising the polymer composition can be extruded onto cooling roller 28 (or co-extruded if a multilayer film is being formed). The temperature T1 of cooling roller 28 is carefully controlled such that when film 15 leaves cooling roller 28, it can be stretched to a predetermined thickness without substantially causing MD molecular orientation, provided that it is below the melting point of the polymer composition. As a result, the temperatures T1 and T2 depend on the composition of the film. T1 can be higher than 80°C, or from about 80°C to about 160°C, or from 90°C to about 160°C, or from about 100°C to about 140°C, or from about 80°C to about 120°C, or from about 100°C to about 120°C, or less than about 160°C. The temperature T2 of stretching roller 30 can be above 40°C, or from about 40°C to about 100°C, or from about 60°C to about 100°C, or from about 60°C to about 90°C, or from about 85°C to about 90°C, or less than about 100°C.

[0072] In the present invention, the temperature T1 of cooling roller 28 and the temperature T2 of stretching roller 30 are substantially higher than those in any previously disclosed MDO process. In previous applications, T1 was typically from about 10°C to about 60°C and T2 was typically from about 10°C to about 40°C. The present invention uses temperatures that balance the need for film processability and further enable control of the amount of MDO.

[0073] In one embodiment, there are at least two cooling rollers, each having a speed V and a temperature T. Each of the speed and temperature of the cooling rollers may be the same or different, provided that they are sufficient for the film to be stretched to a desired thickness without causing substantial MD molecular orientation, but below the melting point of the polymer composition. For purposes of non-limiting illustration only, the temperatures may differ by 5 °C, 10 °C, or more. The cooling rollers may each independently be smooth, may have irregularities, may be coated (e.g., having a release treatment), may be the same or different for each roll.

[0074] The length of the first gap 26 between the extruder 24 and the cooling roller 28 is the shortest distance between the extruder 24 and the cooling roller 28 and is large compared to conventional cast MDO processes. In one embodiment, the length of the first gap 26 is greater than 2.5 cm, or is from about 2.5 cm to about 25 cm, or from about 3 cm to about 15 cm, or from about 3 cm to about 7.6 cm. The extrudate may undergo melt curtain stretching, with a corresponding thickness reduction within the gap 26 being from 10-fold to about 25-fold (about 10X to about 25X).

[0075] In one embodiment, the apparatus may include additional rollers and nips between the extruder 24 and the cooling roller 28 as described in U.S. Patent No. 7,442,332. In other embodiments, the apparatus may include one or more additional cooling rollers. In still other embodiments, the cooling roller 28 can be replaced by two rollers, where the rollers form additional nips. The rollers may be metal rollers and rubber rollers, and the metal rollers may optionally be embossed. The temperature of the film within the nip is about 120 °C or less, or about 100 °C or less. After passing through the additional nip, the film proceeds through nip 33 and further through the steps described herein.

[0076] The speed ratio V2 / V1 of the rolls provides the relative length by which the film is stretched. Thus, the ratio 1 / 1 (1X) indicates that the film is not stretched. The ratio 5 / 1 (5X) indicates that the film is stretched 5 times its length before stretching, i.e., the corresponding reduction in film thickness is 0.2 times its thickness before stretching. In one embodiment, the ratio of V2 / V1 is at least 2, or at least 5, or from about 2 to about 8, or from about 3 to about 8, or less than 5.

[0077] The length of the second gap 32 between the cooling roller 28 and the nip 33 in the stretching roller 30 is the shortest distance between the cooling roller 28 and the stretching roller 30, and in one embodiment, is at least about 7.5 cm, or from about 7.5 cm to about 30 cm, or from about 7.5 cm to about 20 cm, or from about 7.5 cm to about 10 cm, or about 30 cm, or about 20 cm, or about 15 cm, or less than 10 cm. The film 15 is a substantially non-porous film having a limited molecular orientation in the machine direction after being stretched between the cooling roller 28 and the stretching roller 30.

[0078] Here, "providing a limited machine direction orientation to the film" means forming a sufficient MD orientation to give the film a breaking MD load of at least 2.0 N / cm and a breaking CD load of at least 0.7 N / cm. Further, the film has a ratio of the MD load to the CD load at break of from about 1 to about 15. The amount of MDO cannot be directly quantified, but the amount of MDO correlates with film properties. Films having a limited MDO have, in particular, improved CD properties such as CD Elmendorf tear strength and trapezoid tear strength, CD tensile strength at break, and an improved balance of CD tensile strength and MD tensile strength compared to conventional films.

[0079] Downstream of the casting / drawing section 12, the film 15 passes around the idler roller 39 from the stretching roller 30 and heads towards the first machine direction orientation (MDO) section 14. The purpose of this section is to further stretch the film in the machine direction while avoiding substantial MD orientation. The MDO section 14 may include heating rollers 35a and 35b, and subsequent stretching rollers 36a and 36b and / or cooling roller 37. In the heating rollers 35a and 35b, the film 15 is heated to the temperature T3. T3 depends on the composition of the film and is sufficient to avoid substantial MD orientation. In one embodiment, T3 is from about 80 °C to about 150 °C, or exceeds 95 °C, or exceeds 120 °C.

[0080] As will be understood by those skilled in the art, the number of stretching rollers, heating rollers, and cooling rollers inside the first MDO section 14, as well as the number of MDO sections, may be varied. Consequently, in alternative embodiments, the apparatus may include one or more additional sets of stretching rollers, heating rollers, and / or cooling rollers to impart desired physical and appearance properties such as porosity and opacity. For illustrative purposes, a second set of heating rollers, stretching rollers, and / or cooling rollers may be disposed downstream of the first MDO section 14, downstream of the stretching rollers 36a and 36b, and upstream of the cooling roller 37. In an alternative embodiment, a second set of heating rollers, stretching rollers, and / or cooling rollers is disposed downstream of the CDI section 16 within the second MDO section.

[0081] The film 15 moves downstream of the MDO section 14 at a speed V3. In one embodiment, the ratio V3 / V1 is greater than 1, or greater than 2, or less than 25, or from about 2 to about 25, or from about 5 to about 15, or from about 5 to about 25. In one embodiment, the ratios V3 / V2 and / or V2 / V1 are greater than 1, or greater than 2, or less than 5, or from about 1 to about 5, or from about 2 to about 5.

[0082] The cross-directional interlocking roller (CDI) section 16, if present, may include a tension roller 38 in front of the interlocking rollers 40 and 42. In the present invention, the interlocking rollers 40 and 42 are designed to stretch the film in the cross direction, resulting in further activation of the film and imparting breathability. In one embodiment, the machine-direction interlocking roller is used either instead of or in addition to the cross-directional interlocking roller, either before or after the CDI section 16. Suitable cross-directional interlocking rollers are described in U.S. Patent No. 7,442,332.

[0083] Instead of or in addition to the MDO section and / or the CDI section, a tenter frame (not shown) can be used to stretch the film. This can be used to effect both MD orientation and CD orientation.

[0084] The film 15 may be moved from the CDI section 16 to any other optional component, which may include, without limitation, a corona treatment section, an annealing section, a second MDO section, and / or a winder, and is prepared for its intended use. The films of the present invention are useful for a variety of purposes, including, for example, personal hygiene products related to disposable absorbent articles. Non-limiting examples include diapers, training pants, adult incontinence pads and pants, swimsuits, sanitary napkins, tampons, pantiliners, and the like. In one embodiment, the present invention relates to an absorbent article comprising a film as described herein. In one embodiment, the absorbent article is a diaper.

[0085] The present invention further describes a laminate comprising the film of the present invention. The laminate comprises a first layer comprising a breathable thermoplastic film as described herein, and a substrate bonded to one or both surfaces of the film. The substrate may be any woven or non-woven material suitable for use with the thermoplastic film, and in one embodiment is a spunbond non-woven fabric. The substrate may have a basis weight of 100 gsm or less, or 50 gsm or less, or 25 gsm or less, or 15 gsm or less, or 10 gsm or less. The substrate may be bonded to the film by various methods such as adhesive lamination, ultrasonic bonding, extrusion bonding, etc.

[0086] The film and / or laminate of the present invention is suitable for use as a diaper backsheet or ear (closure tab), and may be formed into personal hygiene products, as well as pouches for packaging for wrapping foods such as sandwiches, fruits, vegetables, etc., and breathable polybags such as breathable diaper polybags. Other non-limiting examples of articles in which the laminate of the present invention can be used include roofing materials, linings, and architectural applications such as backsheets for flooring and carpets.

[0087] The present invention will be further understood in light of the following detailed examples.

[0088] Opacity The opacity of the film is measured as follows. The measurement method uses the ratio of the reflectance of the same sample combined with a white backing to that combined with a black backing. The Hunterlab Colorimeter D25A is calibrated and standardized according to the manufacturer's specifications. The sample is cut to a size sufficient to cover the opening of the viewing window of the measuring instrument. The sample is placed in a window with the rubber roll side or the curl side up. The sample is covered with an uncalibrated white tile. "Read" and "xyz" are pressed. The white tile is removed. The sample is covered with a black glass tile. "100%" is pressed. The "y" value of the sample is displayed along with the opacity value expressed as a percentage. In all examples, the sample is gradually stretched in the cross direction (CD) (CDI).

[0089] Alternatively, the opacity of the film may be measured in accordance with ASTM 1746.

[0090] Hydrostatic head pressure The hydrostatic head pressure may be measured according to the method described in AATCC 127 - 2008. Specifically, a Textest Instrument FX 3000 Hydrotester III, 05 / 07 s / n 597 or a higher model thereof may be used. The standard test gradient is 60 mbar / min, and a 70 gsm spunbond / patternbond polypropylene nonwoven fabric is used as the support. The end point of the test is the third drop, and when the first, second, and third drops penetrate the sample, the pressure in mbar is recorded and / or the pressure when the sample ruptures is recorded. If no water penetration is observed, the maximum test pressure is recorded.

[0091] Trap tear strength The sample template is cut to have dimensions of 3” × 6”. From this template, mark a trapezoidal template with a long side of 4”, parallel short sides of 1”, and a height (the distance between the parallel sides measured perpendicular to the sides) of 3”. Starting from the center of the short side end, make a slit 5 / 8” in length perpendicular to the short side. Place the template in the clamp of an Instron Model 1122, 4301 or an equivalent tensile testing machine with a constant elongation rate. Set the distance between the clamps to 1”. Prepare and standardize the load cell according to the instructions. For a tensile testing machine equipped with Series IX software, select the appropriate Series IX test method from the “Method” menu of the software.

[0092] Set the load range of the testing machine so that the maximum load occurs at 85% of the full-scale load. Set the crosshead to advance 12 inches (12”) per minute. Secure the template to the upper and lower clamps along the trapezoidal, marked non-parallel sides such that one end of the clamp coincides with the 1-inch (1”) side of the trapezoid and the slit is in the middle between the clamps. Start the operation of the testing machine and record the tearing force of the test piece.

[0093] Example 1: The film was formed according to the method described above. The polymer formulation contained 48% polyethylene, 45% calcium carbonate, 6% polypropylene, and 1% processing aid by weight. This formulation was melt blended and extruded as a single layer at a temperature of about 260 °C, rotated at about 45.7 m per minute, and extruded onto a cooling roller at a temperature of 116 °C. The film was stretched in a stretching roller operating at a speed V2 (149 m per minute) and a temperature of 88 °C. The film was then stretched in an MDO operating at a speed of 278 m per minute and a temperature below 95 °C. The formed film had a basis weight of 11.4 gsm and a CD load at break of 1.14 N / cm. The transverse elongation at break was 446%. In the machine direction, the load at break was 3.16 N / cm. The elongation at break in the machine direction was 269%. The opacity was 59.4%, and no TiO2 was added. The water vapor transmission rate (WVTR) was 9,083 H2O / 24 hours / m 2 These data points exceed all specifications for a 16 gsm basis weight with decreasing material.

[0094] Examples 2 to 11 Using the method disclosed in Example 1, additional cast films were formed. The samples contained 1% processing aid, polypropylene, and the fillers described below, with the balance of the composition consisting of polyethylene. The physical properties of the films are shown in Table 1. Unless otherwise stated, the films contained 50% calcium carbonate and no titanium dioxide.

[0095] According to Example 2, a three-layer film was formed, where the skin layer contained polyethylene with 4% polypropylene and the core layer contained polyethylene with 33% polypropylene. The percentage of the layer A / B / A thickness was 15 / 70 / 15.

[0096] In Example 3, a single-layer film was formed containing polyethylene, 11% polypropylene, and 47% calcium carbonate filler.

[0097] In Example 5, a single-layer film was formed containing 16% polypropylene. The ratio of V2 / V1 was 3.2 and the ratio of V3 / V2 was 2.5.

[0098] In Examples 6 and 7, single-layer films were formed containing 33% polypropylene. The ratios of V2 / V1 were 4.0 and 3.5 respectively, and the ratios of V3 / V2 were 1.5 and 1.3 respectively.

[0099] In Example 8, a multilayer film containing three layers was formed, with the outer layer containing 0% polypropylene and the inner layer containing 33% polypropylene. The ratio of V2 / V1 was 3.2 and the ratio of V3 / V2 was 2.0. The percentage of the thickness of layer A / B / A was 15 / 70 / 15.

[0100] In Examples 9 and 10, single-layer films containing 33% polypropylene were formed in the same manner as the rubber additive. The ratio of V2 / V1 was 3.5, and V3 / V2 was 1.3 in Example 9 and 1.5 in Example 10.

[0101] In Example 11, a single-layer film containing 21% polypropylene and 46% calcium carbonate was formed. The V2 / V1 ratio is 3 and the V3 / V2 ratio is 2.

[0102] [Table 1]

[0103] In all embodiments of the present invention, all ranges are inclusive and combinable. All quantities are understood to be modified by the term "about" unless otherwise specifically indicated. As long as the terms "includes", "including", "contains", or "containing" are used in the specification or claims, they are intended to be inclusive in the same manner as the term "comprising" when judged as a transitional term in the claims.

[0104] All documents cited in the detailed description of the invention are hereby incorporated by reference in their relevant parts. The citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. If the meaning or definition of any term in this specification, etc. does not match the meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to the term in this specification, etc. shall prevail.

[0105] Although specific embodiments of the present invention have been described and recited, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is intended that all such changes and modifications within the scope of the present invention be included in the claims of the present invention.

[0106] [1] A breathable thermoplastic film having a basis weight of about 15 gsm or less and a water vapor transmission rate of at least about 500 g H2O / 24 hours / m 2 having a ratio of the machine direction (MD) load at break to the cross direction (CD) load at break of less than about 10 and having an Elmendorf tear strength of at least about 5 g for machine direction notches or a trapezoidal tear strength of at least about 15 g for machine direction notches. [2] The film according to [1], wherein the MD load at break is at least about 2.0 N / cm and the CD load at break is at least about 0.7 N / cm. [3]The film according to [1], having at least about 50% opacity. [4]The film according to [3], substantially free of titanium dioxide. [5]The film according to [1], comprising an olefin block copolymer. [6]The film according to [5], wherein the olefin block copolymer is a propylene-based polymer composition. [7]The film according to [5], wherein the olefin block copolymer is an ethylene-based polymer composition. [8]The film according to [1], comprising from about 10% to about 60% polypropylene. [9]The film according to [1], comprising from about 30 wt% to about 60 wt% filler.

[10] The film according to [1], which is a coextruded multilayer film.

[11] The film according to [1], which is a monolayer film.

[12] The film according to [1], having a hydrohead pressure of at least 200 psi.

[13] A breathable thermoplastic film, having a basis weight of from about 5 gsm to about 20 gsm, a water vapor transmission rate of at least about 500 g H2O / 24 hours / m 2 , a CD load at break of at least 0.7 N / cm, an MD load at break of at least about 2.0 N / cm, a ratio of the MD load at break to the CD load at break of from about 1 to about 10, and having at least one of an Elmendorf tear strength of at least about 5 g for a machine direction notch or a trapezoidal tear strength of at least about 15 g for a machine direction notch.

[14] The film according to

[13] , having at least about 50% opacity.

[15] The film according to

[13] , comprising an olefin block copolymer.

[16] The film according to

[15] , wherein the olefin block copolymer is a propylene-based polymer composition.

[17] The film according to

[13] , comprising from about 10% to about 60% polypropylene. The film according to

[13] , comprising from about 30% to about 60% by weight of a filler.

[19] The film according to

[13] , which is a coextruded multilayer film.

[20] a. A breathable thermoplastic film having a basis weight of about 15 gsm or less and a water vapor transmission rate of at least about 500 g H2O / 24 hours / m 2 The film has a ratio of the machine direction (MD) load at break to the cross direction (CD) load at break of less than about 10 and has an Elmendorf tear strength of at least about 5 g for machine direction notches or a trapezoidal tear strength of at least about 15 g for machine direction notches, and the first layer having at least one of the above, the first layer having a surface, and a first layer; b. A substrate attached to the film surface; A laminate article comprising.

[21] Extruding a melt web comprising a thermoplastic polymer onto a first cooling roller, the first cooling roller being operated at a first peripheral speed V1, the first cooling roller having a first temperature T1, the temperature T1 being less than the melting point of the thermoplastic polymer, thereby cooling the web to form a film; Advancing the film from the first cooling roller to a stretching roller downstream, the stretching roller rotating at a second peripheral speed V2 greater than V1, the stretching roller having a temperature T2, advancing the film, including; The stretching roller stretches the film in the machine direction, has a substantially uniform thickness, limited machine direction orientation, a ratio of the machine direction load at break to the cross direction load at break of less than about 10, and an Elmendorf tear strength of at least about 5 g for machine direction notches or a trapezoidal tear strength of at least about 15 g for machine direction notches, producing a film having at least one of the above; A method for manufacturing a thermoplastic film product.

Description of the reference numerals

[0107] 10 Film forming apparatus 12 Casting / drawing section 14 Machine Direction Orientation (MDO) Section 15 Web or Film 16 Cross Direction Infeed Roller (CDI) Section 24 Extruder 26 First Gap 28 Cooling Roller 30 Drawing Roller 32 Second Gap 33 Nip 34 Slave Roller 35a, 35b Heating Roller 36a, 36b Drawing Roller 37 Cooling Roller 38 Tension Roller 39 Idler Roller 40, 42 Infeed Roller T1, T2, T3 Temperature V1, V2, V3 Speed

Claims

1. A breathable thermoplastic film having a basis weight of 10 gsm to 15 gsm; a ratio of MD load at break to CD load at break of 1 to 15; and a machine direction notch trapezoidal tear strength of at least 25 g; A film having a water vapor transmission rate of from 500 g H2O / 24 hr / m2 to 10,000 g H2O / 24 hr / m2.

2. A film as described in claim 1, having an MD load at break of at least 2.0 N / cm and a CD load at break of at least 0.7 N / cm.

3. A film as described in claim 1 having an Elmendorf tear strength of a machine direction notch of at least 5 g.

4. A film as described in claim 1 having an opacity of at least 50%.

5. The film described in claim 4, which is substantially free of titanium dioxide.

6. The film of claim 1, comprising a propylene-based polymer composition, an ethylene-based polymer composition, an olefin block copolymer, or a combination thereof.

7. The film of claim 1, comprising 30% to 60% by weight of a filler.

8. The film of claim 1, which is a coextruded multilayer film.

9. The film described in claim 1, which is a single layer film.

10. A laminate comprising a nonwoven substrate and a breathable thermoplastic film having a basis weight of 10 gsm to 15 gsm; a ratio of MD load at break to CD load at break of 1 to 15; and a machine direction notch trapezoidal tear strength of at least 25 g, A laminate wherein the film has a water vapor transmission rate of from 500 g H2O / 24 hr / m2 to 10,000 g H2O / 24 hr / m2.

11. The laminate of claim 10, wherein the film comprises a propylene-based polymer composition, an ethylene-based polymer composition, an olefin block copolymer, or a combination thereof.

12. The laminate described in claim 10, wherein the film contains 10% to 60% polypropylene.

13. The laminate of claim 10, comprising an adhesive.

14. The laminate of claim 10, comprising an ultrasonic bond.

15. An article of manufacture comprising the film of claim 1.

16. The article of manufacture of claim 15, which is packaging for a personal hygiene product.

17. An article of manufacture comprising the laminate of claim 10.

18. The article of manufacture of claim 17, which is a diaper backsheet, a closure tab, roofing material, upholstery, flooring backsheet, or carpet backsheet.

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