Breathable microporous thermoplastic thin film

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 to U.S. Provisional Patent Application No. 61 / 992,438, filed May 13, 2014, U.S. Provisional Patent Application No. 62 / 053,385, filed September 22, 2014, and U.S. Provisional Patent Application No. 62 / 092,351, filed December 16, 2014. [Background technology]

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

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

[0004] Thermoplastic films can be formed by extruding a molten polymer composition onto a chill roller, which immediately cools to form a solid film. The processing of the film involves various stages including heating, cooling, and stretching to produce a final film product that is 72 times thinner than the initial thickness. Stretching in the machine direction (MD) produces a highly oriented thin gauge film, which is called machine direction orientation (MDO). While MDO can be useful, it can also result in qualities such as lower cross direction (CD) tensile strength, impact strength, tear strength, and slow puncture resistance, especially in thin films.

[0005] Current methods for making thin thermoplastic gauge films include the method described in U.S. Pat. No. 7,442,332 (Cancio et al.). In this method, the majority (more than half) of the stretching of the web occurs between the extrusion die and the first nip (i.e., in the "melt curtain"). Two difficulties in such casting processes are a phenomenon known as "draw resonance," which results in non-uniformity in the film thickness, and the formation of holes in the film. These problems become more severe at higher production rates and may further limit the types of polymer compositions that can be used. Resolving these problems requires slower production rates, which ultimately leads to increased costs. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 7,442,332 Summary of the Invention [Problem to be solved by the invention]

[0007] Thus, a need exists for a thin thermoplastic film that has limited MDO and desirable properties such as non-porous, good breathability, good tensile strength, and good tear strength properties, and that can be produced economically and efficiently on high speed manufacturing lines. [Means for solving the problem]

[0008] The present invention satisfies the aforementioned need by providing a breathable thermoplastic film having a low basis weight, substantially free of holes, and having 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, with thicker films generally exhibiting higher tear strength, the films made by the method of the present invention exhibit stronger tear strength than would be expected for a comparable film of similar thickness. In other words, the films of the present invention improve the ratio of tear strength to thickness.

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

[0010] The following are some non-limiting embodiments of the present invention. In one embodiment, a breathable thermoplastic film is provided, the film having a basis weight of about 15 gsm or less and a thermal conductivity of at least about 500 g H2O / 24 hr / m2. 2and the film has a ratio of MD load at break to CD load at break of less than about 10, and at least one of an Elmendorf tear strength in a machine direction notch of at least about 5 g, or a Trapezoid tear strength in a machine direction notch of at least about 15 g.

[0011] In another embodiment, a laminate is provided, the laminate comprising a first layer, the first layer having a basis weight of 15 gsm or less and a thermal conductivity of at least about 500 g H2O / 24 hr / m 2 the ratio of MD load at break to CD load at break is less than about 10, and at least one of an Elmendorf tear strength of a machine direction notch of at least about 5 g, or a Trapezoid tear strength of a machine direction notch of at least 15 g, the first layer having a surface, and a substrate attached to the film surface.

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

[0013] Another embodiment provides the above method, wherein the thermoplastic film has a MD load at break of at least 2.0 N / cm and a CD load at break of at least 0.7 N / cm.

[0014] Another embodiment provides for the above method, wherein the thermoplastic film product has a thickness of from about 5 gsm to about 20 gsm.

[0015] Other embodiments provide for the above methods, where the molten web is cast molded, blown molded, calendared, monoextruded, coextruded, chill cast, nip embossed, or combinations thereof.

[0016] Other embodiments further include at least one additional cooling roller operated at a temperature T and a peripheral speed V in the above given method.

[0017] Other embodiments provide for the above method, comprising at least about 500 g HO / 24 hr / m 2 and further comprising stretching the film in the transverse direction to produce a breathable thermoplastic film product having a water vapor transmission rate (WVTR) of 0.1 to 0.5%.

[0018] In another embodiment, in the method given above, the film is gradually stretched in the transverse direction using intermeshing rollers.

[0019] Another embodiment provides the method described above, where the film advances through a first machine direction orientation section including at least one heated roller having a temperature T3 and at least one stretching roller.

[0020] Another embodiment provides the above-mentioned method, wherein the film advances at least through a second machine direction orientation section including at least one heated roller and at least one stretching roller.

[0021] Another embodiment is a method as provided above, wherein the second machine direction orientation section is located downstream of the cross-machine mating roller section.

[0022] Another embodiment is a method as provided above, wherein the second machine direction orientation section is located upstream of the cross-machine mating roller section.

[0023] Another embodiment is given the above method, where T1 is from about 80°C to about 160°C.

[0024] Another embodiment is given the above method, where T2 is from about 60°C to about 100°C.

[0025] Another embodiment is given the above method, where T3 is from about 80°C to about 150°C.

[0026] In another embodiment, in the methods given above, T is the same as T1.

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

[0028] In another embodiment, in the methods given above, V is the same as V1.

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

[0030] Another embodiment provides the method described above, wherein the cooling roller and the stretching roller form a second gap of about 7.5 cm to about 30 cm.

[0031] Another embodiment is given the above method, wherein the ratio of V2 to V1 is from about 2 to about 8.

[0032] Another embodiment is a multi-layer film in which the film is coextruded in the manner described above.

[0033] Another embodiment is given above the method, wherein the film is a monoextruded film.

[0034] Another embodiment is given the above method, wherein the film is a blown film.

[0035] Another embodiment is provided in the above method, wherein the film has an opacity of at least about 50%.

[0036] Another embodiment provides the above method, wherein the film comprises an olefin block copolymer that is ethylene-based, propylene-based, or a combination thereof.

[0037] In yet another embodiment, a breathable thermoplastic film is provided, the film being produced by a process in which a molten web comprising a thermoplastic polymer is extruded onto a chill roller having a temperature T1 to form a film, the film being fed to a stretching roller downstream of said first chill roller having a temperature T2, and further fed through a first machine direction orientation section having at least one heated roller and at least one stretching roller having a temperature T3, where a limited machine direction orientation is imparted to the film, the film having a basis weight of about 15 gsm or less, at least about 500 g H2O / 24 hr / m 2 and said film has a ratio of MD load at break to CD load at break of less than about 10.

[0038] In another embodiment, the film produced by the above method has an Elmendorf tear strength in the machine direction of at least 5 g.

[0039] In another embodiment, the film produced by the above method has a trapezoidal tear strength in the machine direction of at least 15 g.

[0040] Another embodiment is a film produced by the above method, wherein the film has a MD load at break of at least 2.0 N / cm and a CD load at break of at least 0.7 N / cm.

[0041] In other embodiments, in the films produced by the above methods, the molten web is cast, blown, calendared, monoextruded, coextruded, chill cast, nip embossed, or combinations thereof.

[0042] Another embodiment is a film made by the above method, where the film is a coextruded multilayer film.

[0043] Another embodiment is a film made by the above method, where the film is a monolayer film.

[0044] In another embodiment, the film produced by the above method has a hydrohead pressure of at least 200 psi.

[0045] In another embodiment, the film produced by the above method is gradually stretched in the transverse direction using intermeshing rollers.

[0046] Another embodiment is a film produced by the above method, wherein the film has an opacity of at least about 50%. [Brief description of the drawings]

[0047] [Figure 1] 1 illustrates one non-limiting embodiment of an apparatus suitable for making the films of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Terms used here: "Activation defect," "activation hole," or "pinhole" means a small hole or tear in a film while the film is being formed, laminated, activated, or undergoes other manufacturing or processing steps, which may subsequently result in reduced tear strength, increased porosity, increased leakage, or other undesirable properties.

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

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

[0051] "Skin layer" means one or both outer layers of a multilayer film that serve 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. Herein, tear strength may be measured by Elmendorf notch tear test ASTM D-1922, which is incorporated herein by reference, and / or by trapezoidal tear test ("Trap test") as described herein or by ASTM D-5587. Tests may be performed on either notched or unnotched films, and in either CD or MD. Unless otherwise specified, tear strength herein refers to notched tear strength. Tear strength is related to the thickness of the film, and any comparison of tear strength must be made with the relative basis weight of the control sample in mind.

[0053] "Tear strength" means the load required to cause a break in a film (load at break) in either the CD or MD. Tensile strength is expressed in N / cm or equivalent and is determined by ASTM D822-02 method using the following parameters: Sample direction = MD x CD; Sample dimensions = 1 inch wide x 6 inches long; Test speed = 20 in / min; Grip distance = 2 inches. Grip dimensions = 3 inch wide rubber faced grips that grip the sample evenly.

[0054] "WVTR" stands for "Water Vapor Transmission Rate" and is a measurement of the breathability of a film. WVTR is H2O / 24 hours / m 2 The mass % of the molecule may be expressed in units or equivalent units and may be measured according to ASTM D-6701-01 method.

[0055] film The films of the present invention are thermoplastic monolayer or multilayer films and may have a basis weight of about 5 gsm to about 20 gsm, alternatively about 5 to about 15 gsm, alternatively about 10 to about 15 gsm, alternatively about 8 to about 13 gsm, alternatively about 10 gsm to about 12 gsm, alternatively less than about 15 gsm, alternatively less than 14 gsm, alternatively less than about 12 gsm, and alternatively less than about 10 gsm. The multilayer films of the present invention may include at least 2 layers, alternatively at least 3 layers, alternatively at least 5 layers, alternatively at least 7 layers, alternatively at least 9 layers, alternatively at least 11 layers, alternatively from 2 to about 20 layers, alternatively from 3 to about 11 layers, and alternatively from 5 to 11 layers. The films may or may not include skin layers to reduce tackiness on one or both of the outer surfaces.

[0056] The films of the present invention have a CD load at break of greater than 0.7 N / cm, alternatively greater than about 0.8 N / cm, alternatively greater than about 0.9 N / cm, alternatively from about 0.7 N / cm to about 3.0 N / cm, alternatively from about 0.7 N / cm to about 2.0 N / cm. The films of the present invention have a MD load at break of at least about 2.0 N / cm, alternatively at least about 2.5 N / cm, alternatively at least about 3.0 N / cm, alternatively from about 2.0 N / cm to about 6.0 N / cm, and alternatively 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 MD load to CD load at break, which is a measure of the improved balance between these properties, not present in previously disclosed films. Without wishing to be bound by theory, it is believed that this advantageous ratio is achieved by the reduction in machine direction orientation in the film by the methods disclosed herein. The ratio of MD load to CD load at break for the films of the present invention is from about 1 to about 15, alternatively from about 1 to about 10, alternatively from about 1 to about 9, alternatively from about 1 to about 8, alternatively from about 1 to about 5, alternatively less than about 10, alternatively less than about 9, alternatively less than about 8, alternatively less than about 5, alternatively less than about 4, alternatively about 1.

[0058] The film of the present invention has a resistance of at least 500 g H2O / 24 hours / m 2 , or at least 1,000g H2O / 24 hours / m 2 , or at least 2,000g H2O / 24 hours / m 2 , or at least 3500g H2O / 24h / m 2 , or at least 4500g H2O / 24h / 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 2to approximately 10,000 g H2O / 24 hours / m 2 It further has a water vapor transmission rate (WVTR).

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

[0060] The films of the present invention further have a machine direction trapezoidal (trap) tear strength of at least about 15 g, alternatively at least about 20 g, alternatively at least about 25 g, alternatively from about 15 g to about 150 g, alternatively from about 15 g to about 100 g, alternatively from about 15 g to about 85 g.

[0061] The film of the present invention comprises one or more thermoplastic polymers. Suitable polymers for the film include, but are not limited to, polyolefins, such as polyethylene homopolymers and copolymers, polypropylene, polypropylene homopolymers and copolymers, functionalized polyolefins, polyesters, poly(ester ethers), polyamides, such as nylons, poly(ether amides), polyethersulfones, fluoropolymers, polyurethanes, and mixtures thereof. Polyethylene homopolymers include those with low, medium, or high density, and / or formed by high pressure or low pressure polymerization processes. Polyethylene and polypropylene copolymers include, but are not limited to, copolymers with C4-C8 alpha olefin monomers, such as 1-octene, 1-butene, 1-hexene, and 4-methylpentene. The polyethylene may be substantially linear or branched, and may be formed by a variety of methods known to those skilled in the art using catalysts, such as Ziegler-Natta catalysts, metallocene catalysts, or single-site catalysts, or other catalysts commonly known to those skilled in the art. Examples of suitable copolymers include, but are not limited to, poly(ethylene-butene), poly(ethylene-hexene), poly(ethylene-octene), and copolymers such as 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 polyolefin terpolymers thereof. In one embodiment, the film comprises polyethylene, polypropylene, and combinations thereof. One example of a suitable commercially available polyethylene-based resin is the Exceed 1000 series from Exxon Corporation. TM 3527PA. An example of a suitable commercially available polypropylene copolymer is Borealis BD712 from Borealis.

[0062] Other non-limiting examples of suitable olefin-based polymer compositions are olefin-based block copolymers, olefin-based random copolymers, polyurethanes, rubbers, vinylarylenes, and conjugated dienes, polyesters, polyamides, polyethers, polyisoprenes, polyneoprenes, copolymers of any of the aforementioned compositions, and mixtures thereof. Additionally, the film of the present invention, or a layer thereof, may comprise a brittle polymer, non-limiting examples of which are disclosed in U.S. Pat. No. 7,879,452. In one embodiment, the film comprises an olefin-based block copolymer.

[0063] In one embodiment, the olefin-based block copolymer is polypropylene-based. Non-limiting examples of suitable polypropylene-based olefin-based block copolymers include those available under the trade name INFUSE from Dow Chemical Company, Midland, Michigan. TM Some are sold under the trade name VISTAMAXX® by ExxonMobil Chemical Company, Houston, Texas, and Exxon Impact® copolymers, such as Exxon PD 7623. Both polypropylene and polyester are known to increase the melting point of the formed polymer film, improving the film's resistance to burn through. In another embodiment, the film of the present invention may comprise an ethylene-based olefinic block copolymer.

[0064] The above mentioned thermoplastic polymers may be present in the film, or in individual layers of the film, in an amount of from 0% to about 95%, alternatively from about 0% to about 40%, alternatively from about 10% to about 50%, alternatively from about 35% to about 50%, alternatively from about 20% to about 40%, alternatively from about 1% to about 10%. In one embodiment, the film, or one or more layers of the multilayer film, comprises from about 0.1% to about 90%, alternatively from about 1% to about 60%, alternatively from about 20% to about 50%, alternatively from about 20% to about 40%, alternatively from about 1% to about 10% 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 individual layers 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 (SBC) 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 films of the present invention may contain optional ingredients such as fillers such as calcium carbonate, plasticizers, compatibilizers, drawdown polymers, processing aids, antiblocking agents, viscosity reducing polymers, etc. Other additives include pigments, dyes, antioxidants, antistatic agents, slip agents, foaming agents, heat or light stabilizers, UV stabilizers, etc. Suitable processing aids and antiblocking agents include, but are not limited to, Ampacet, available from Ampacet Corporation. TMIn one embodiment, the polymer composition may include about 0% to about 75%, 1% to 30%, or about 30% to about 60% of a filler. In one embodiment, the polymer composition may include about 0% to about 15%, or about 0% to about 10%, or 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 of greater than 50%, alternatively greater than 55%, or alternatively greater than about 60%.

[0068] Device FIG. 1 illustrates an exemplary configuration of a film-forming apparatus 10 suitable for forming the films of the present invention. When applied to a film or nonwoven material, "machine direction" refers to a direction parallel to the direction in which the film or nonwoven material moves as it is processed in the film-forming apparatus. "Cross direction" refers to 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 interdigitating roller (CDI) section 16. Optionally, the film-forming apparatus 10 may include additional sections, such as an annealer section, a winder, additional machine direction orientation sections, and / or a corona treatment section, as would be apparent to one of ordinary skill in the art. In other embodiments, the order of the sections or components thereof may differ from that shown in FIG. 1, as would also be understood by one of ordinary skill in the art.

[0069] The casting / drawing section 12 includes an extruder 24 followed by at least one cooling roller 28 with a first gap 26 therebetween. As will be appreciated by those skilled in the art, the position of the extruder 24 relative to the cooling roller 28 may be altered from the position shown in FIG. 1 to a position somewhat downstream from that shown, but such that the extruder 24 is still in a position to deliver 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 and extrudes the extrudate across the gap 26 onto the cooling roller 28 to form a web or film 15. The film 15 travels across the second gap 32 into a nip 33 formed between a slave roller 34 and the stretching roller 30. The film 15 then passes over idle rollers 39 towards the machine direction orientation section 14 .

[0070] The webs or films of the present invention may be formed in a variety of ways, as will be understood by those skilled in the art, and may be cast, blown, calendared, monoextruded, coextruded, chill cast, nip embossed, or any other method that will result in a film equivalent to the methods described herein.

[0071] In one embodiment, the thermoplastic polymer film formulation may be compounded in extruder 24 at a temperature of, for example, about 210°C to about 280°C. The exact temperature will depend on the polymer composition formulation. A web or "melt curtain" containing the polymer composition may be extruded (or coextruded if a multilayer film is to be formed) onto chill roller 28. The temperature T1 of chill roller 28 is carefully controlled so that the film 15 may be stretched to a predetermined thickness as it leaves chill roller 28 without substantial MD molecular orientation, but below the melting point of the polymer composition. Consequently, temperatures T1 and T2 depend on the composition of the film. T1 may be greater than 80°C, alternatively from about 80°C to about 160°C, alternatively from about 90°C to about 160°C, alternatively from about 100°C to about 140°C, alternatively from about 80°C to about 120°C, alternatively from about 100°C to about 120°C, alternatively less than about 160°C. The temperature T2 of the drawing rollers 30 may be greater than 40°C, alternatively from about 40°C to about 100°C, alternatively from about 60°C to about 100°C, alternatively from about 60°C to about 90°C, alternatively from about 85°C to about 90°C, or alternatively less than about 100°C.

[0072] In the present invention, the temperature T1 of the chill roller 28 and the temperature T2 of the stretch roller 30 are substantially higher than in any previously disclosed MDO process. In the previous applications, T1 is typically from about 10° C. to about 60° C. and T2 is typically from about 10° C. to about 40° C. The present invention uses temperatures that balance the needs for processability of the film and also allow the amount of MDO to be controllable.

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

[0074] The length of the first gap 26 between the extruder 24 and the chill roller 28 is the shortest distance between the extruder 24 and the chill 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, alternatively from about 2.5 cm to about 25 cm, alternatively from about 3 cm to about 15 cm, alternatively from about 3 cm to about 7.6 cm. The extrudate may undergo melt curtain drawing with a corresponding reduction in thickness of from 10 times to about 25 times (about 10X to about 25X) within the gap 26.

[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. Pat. No. 7,442,332. In other embodiments, the apparatus may include one or more additional cooling rollers. In yet other embodiments, the cooling roller 28 may be replaced by two rollers, where the rollers form an additional nip. The rollers may be a metal roller and a rubber roller, and the metal roller may optionally be embossed. The temperature of the film in the nip is about 120° C. or less, alternatively about 100° C. or less. After passing through the additional nip, the film proceeds through nip 33 and further passes through the processes described herein.

[0076] The speed ratio of the rolls V2 / V1 provides the relative length to which the film is stretched. Thus, a ratio of 1 / 1 (1X) indicates that the film is not stretched. A ratio of 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, alternatively at least 5, alternatively from about 2 to about 8, alternatively from about 3 to about 8, alternatively less than 5.

[0077] The length of the second gap 32 between the chill roller 28 and the nip 33 at the stretch roller 30 is the shortest distance between the chill roller 28 and the stretch roller 30, and in one embodiment is at least about 7.5 cm, alternatively about 7.5 cm to about 30 cm, alternatively about 7.5 cm to about 20 cm, alternatively about 7.5 cm to about 10 cm, alternatively about 30 cm, alternatively about 20 cm, alternatively about 15 cm, alternatively less than 10 cm. After the film 15 has been stretched between the chill roller 28 and the stretch roller 30, it is a substantially nonporous film with limited molecular orientation in the machine direction.

[0078] Here, "imparting limited machine direction orientation to the film" means forming sufficient MD orientation to impart a MD load at break of at least 2.0 N / cm and a CD load at break of at least 0.7 N / cm. Additionally, the film has a ratio of MD load to CD load at break of about 1 to about 15. Although the amount of MDO cannot be directly quantified, the amount of MDO correlates with film properties. Films with limited MDO have improved CD properties, particularly CD Elmendorf tear strength and trapezoidal tear strength, CD tensile strength at break, and an improved balance of CD and MD tensile strength over conventional films.

[0079] Downstream of the casting / drawing section 12, the film 15 passes from stretching roller 30 around idle roller 39 to a 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 heated rollers 35a and 35b followed by stretching rollers 36a and 36b and / or cooling roller 37. At heated rollers 35a and 35b, the film 15 is heated to a temperature T3, which 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., alternatively greater than 95° C., alternatively greater than 120° C.

[0080] As will be appreciated by those skilled in the art, the number of stretching rollers, heating rollers, and cooling rollers within the first MDO section 14, as well as the number of MDO sections, may be varied. Accordingly, 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. By way of example, a second set of heating rollers, stretching rollers, and / or cooling rollers may be disposed in the first MDO section 14, downstream of stretching rollers 36a and 36b, and upstream of cooling roller 37. In alternative embodiments, the second set of heating rollers, stretching rollers, and / or cooling rollers is disposed downstream of CDI section 16 in the second MDO section.

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

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

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

[0084] The film 15 may be transferred from the CDI section 16 to any other component, including but not limited to a corona treatment section, an annealing section, a second MDO section, and / or a winder, to be prepared for its intended use. The films of the present invention are useful for a variety of purposes, including personal hygiene products, such as disposable absorbent products. Non-limiting examples include diapers, training pants, adult incontinence pads and pants, swimwear, sanitary napkins, tampons, panty liners, and the like. In one embodiment, the present invention relates to an absorbent article comprising the film 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 can be any woven or nonwoven material suitable for use with a thermoplastic film, and in one embodiment is a spunbonded nonwoven. The substrate can have a basis weight of 100 gsm or less, alternatively 50 gsm or less, alternatively 25 gsm or less, alternatively 15 gsm or less, or alternatively 10 gsm or less. The substrate can be bonded to the film by various methods, such as adhesive lamination, ultrasonic bonding, extrusion bonding, etc.

[0086] The films and / or laminates of the present invention are suitable for use as diaper backsheets or ears (closure tabs), and may be formed into pouches for packaging personal hygiene products and foods such as sandwiches, fruits, vegetables, and breathable polybags, such as breathable diaper polybags. Other non-limiting examples of articles in which the laminates of the present invention may be used include roofing, upholstery, and architectural applications such as backsheets for flooring and carpeting.

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

[0088] opacity The opacity of a film is measured as follows: The measurement method uses the ratio of reflectance of the sample combined with a white backing to the same sample combined with a black backing. The Hunterlab Colorimeter D25A is calibrated and standardized according to the manufacturer's specifications. The sample is cut large enough to cover the instrument's sight glass opening. The sample is placed in the window with the rubber roll side or 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 samples were gradually stretched (CDI) in the cross direction (CD).

[0089] Alternatively, the opacity of a film may be measured according to ASTM1746.

[0090] Hydro Head Pressure Hydrohead 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 better may be used. The standard test gradient is 60 mbar / min and a 70 gsm spunbond / pattern bonded polypropylene nonwoven is used as the substrate. The test end point is the third drop and the pressure in mbar is recorded when the first, second and third drops penetrate the sample and / or the pressure when the sample bursts is recorded. If no water penetration is observed, the maximum test pressure is recorded.

[0091] Trap tear strength A sample template is cut to have dimensions 3" x 6". From this template, a trapezoidal template is marked with a long side of 4", parallel short sides of 1", and a height (distance between parallel sides measured perpendicular to the sides) of 3". Starting at the center of the short side edge, cut a 5 / 8" long slit perpendicular to the short side. Place the template in the clamps of an Instron Model 1122, 4301 or equivalent tensile tester with constant extension rate. Set the distance between the clamps to 1". Prepare and standardize the load cell according to the instructions. For tensile testers equipped with Series IX software, select the appropriate Series IX test method from the "Method" menu in the software.

[0092] Set the load range on 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. Clamp the template in the upper and lower clamps along the marked non-parallel sides of the trapezoid so that one end of the clamps is aligned with the one inch (1") side of the trapezoid and the slit is halfway between the clamps. Start the testing machine and record the tear force of the specimen.

[0093] Example 1: A film was formed according to the method described above. The polymer formulation included, by weight, 48% polyethylene, 45% calcium carbonate, 6% polypropylene, and 1% processing aids. The formulation was melt blended and extruded as a monolayer at a temperature of about 260°C onto a cooling roller rotating at about 45.7 meters per minute and having a temperature of 116°C. The film was stretched in a stretching roller operating at a speed of V2 (149 meters per minute) and a temperature of 88°C. The film was then stretched in an MDO operating at a speed of 278 meters per minute and a temperature of less than 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 machine direction elongation at break was 269%. The opacity was 59.4% and no TiO2 was added. The water vapor transmission rate (WVTR) was 9,083 H2O / 24hr / m 2 These data points, along with the reduction in material, all exceed the specification for a 16 gsm basis weight.

[0094] Examples 2 to 11 Additional cast films were formed using the method disclosed in Example 1. The samples contained 1% processing aid, polypropylene, and the filler described below, with the remainder of the composition being polyethylene. The physical properties of the films are shown in Table 1. Unless otherwise noted, the films contained 50% calcium carbonate and no titanium dioxide.

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

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

[0097] In Example 5, a monolayer 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, monolayer films were formed containing 33% polypropylene, with V2 / V1 ratios of 4.0 and 3.5, respectively, and V3 / V2 ratios of 1.5 and 1.3, respectively.

[0099] In Example 8, a multilayer film was formed containing 3 layers, 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 thickness percentages of layers A / B / A were 15 / 70 / 15.

[0100] In Examples 9 and 10, monolayer films containing 33% polypropylene were formed as well as rubber additives. 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 monolayer film was formed containing 21% polypropylene and 46% calcium carbonate. 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. To the extent that 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," as that term is interpreted when used as a transitional term in the claims.

[0104] All documents cited in the detailed description of the invention are, in relevant part, incorporated herein by reference. The citation of any document shall not 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 does not coincide with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to the term in this specification shall prevail.

[0105] While particular embodiments of the present invention have been illustrated and described, it would be obvious 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. It is therefore intended to cover in the claims of this invention all such changes and modifications that are within the scope of the invention. [Explanation of symbols]

[0106] 10 Film forming device 12 Casting / Drawing Section 14 Machine Direction Orientation (MDO) Section 15 Web or Film 16 Cross-direction interlocking roller (CDI) section 24 Extruder 26 The First Gap 28 Cooling roller 30 Stretching roller 32 The Second Gap 33 Nip 34 Slave Lola 35a, 35b Heating roller 36a, 36b Stretching rollers 37 Cooling roller 38 Tension roller 39 Idol Lola 40, 42 Mating roller T1, T2, T3 temperature V1, V2, V3 speed

Claims

1. Basis weight between 5gsm and 15gsm; at least 500g H ２ O / 24 hours / m ２ a ratio of MD load at break to CD load at break from 1 to 10; and at least one of an Elmendorf tear strength with a machine direction notch of at least 5 g or a Trapezoid tear strength with a machine direction notch of at least 15 g.

2. 2. The breathable thermoplastic film of claim 1, wherein the basis weight is from 5 gsm to 13 gsm.

3. 3. The breathable thermoplastic film of claim 1 or 2, wherein the basis weight is from 8 gsm to 13 gsm.

4. The breathable thermoplastic film according to any one of claims 1 to 3, wherein the ratio of MD load at break to CD load at break is 1 to 8.

5. 5. The breathable thermoplastic film of 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.

6. 6. The breathable thermoplastic film of claim 1 having an Elmendorf tear strength of a machine direction notch that is at least 5 g.

7. 7. The breathable thermoplastic film of claim 1 having a machine direction notch trapezoidal tear strength of at least 25 g.

8. 8. The breathable thermoplastic film of any one of claims 1 to 7, comprising a propylene-based polymer composition, an ethylene-based polymer composition, an olefin block copolymer, or a combination thereof.

9. 10. The breathable thermoplastic film of claim 8 comprising an olefin block copolymer.

10. 10. The breathable thermoplastic film of claim 8 or 9, comprising a propylene-based polymer composition.

11. 11. The breathable thermoplastic film of claim 10 comprising 1% to 60% polypropylene.

12. 12. The breathable thermoplastic film of claim 11 comprising 30% to 60% by weight of a filler.

13. 13. The breathable thermoplastic film of claim 12, further comprising an ethylene-based polymer composition.

14. 14. The breathable thermoplastic film of any one of claims 11 to 13, comprising 1% to 20% polypropylene.

15. 10. The breathable thermoplastic film of claim 8 comprising an ethylene-based polymer composition.

16. 20. The breathable thermoplastic film of claim 15, wherein the ethylene-based polymer composition comprises from 10% to about 60% polyethylene.

17. 17. The breathable thermoplastic film of claim 16 comprising 30% to 60% by weight of a filler.

18. 20. The breathable thermoplastic film of claim 17, further comprising a polypropylene-based polymer composition.

19. 19. The breathable thermoplastic film of any one of claims 16 to 18, comprising from 20% to about 50% polyethylene.

20. 20. The breathable thermoplastic film of any one of claims 1 to 19 having an opacity of at least 50%.

21. 21. The breathable thermoplastic film of claim 20, which is substantially free of titanium dioxide.

22. 22. The breathable thermoplastic film of any one of claims 1 to 21, which is a coextruded multilayer film.

23. 22. The breathable thermoplastic film of claim 1, which is a monolayer film.

24. extruding a web comprising a thermoplastic polymer; advancing the web over a chill roller to form a film, the chill roller having a first temperature that is below a melting point of the thermoplastic polymer; advancing the film through a machine direction orientation section including at least one heated roller and at least one stretching roller; stretching the film in the machine direction orientation section while maintaining the film at a second temperature to produce a film having a limited machine direction orientation; stretching the film in a transverse direction; 1. A method for making a thermoplastic film comprising: The thermoplastic film has a basis weight of 5 gsm to 15 gsm and a basis weight of at least 500 g H ２ O / 24 hours / m ２ and a ratio of MD load at break to CD load at break that is 1 to 10.

25. 25. The method of claim 24, wherein the second temperature is from about 80°C to about 150°C.

26. 26. The method of claim 24 or 25, wherein the step of advancing the film through the machine direction orientation section follows the step of stretching the film in the transverse direction.

27. 26. The method of claim 24 or 25, wherein advancing the film through the machine direction orientation section precedes stretching the film in the transverse direction.

28. 28. The method of any one of claims 24 to 27, further comprising advancing the film to a second stretching roller immediately downstream of the chill roller.

29. 29. The method of any one of claims 24 to 28, further comprising advancing the film through a second machine direction orientation section comprising a second heated roller and a second stretching roller.

30. 30. The method of any one of claims 24 to 29, further comprising stretching the film using a tenter frame.

31. 31. The method of any one of claims 24 to 30, wherein the cooling roller forms a nip with at least one additional roller.

32. 32. The method of any one of claims 24 to 31, wherein extruding a web comprising the thermoplastic polymer comprises one or more of the steps of casting, blow molding, calendaring, mono-extruding, co-extruding, chill casting, and nip embossing the web.

33. 33. The method of any one of claims 24 to 32, wherein the ratio of MD load at break to CD load at break is from 1 to 8.

34. 34. The method of any one of claims 24 to 33, wherein the thermoplastic film has 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.

35. 35. The method of any one of claims 24 to 34, wherein the thermoplastic film further has at least one of an Elmendorf tear strength of a machine direction notch of at least 5 g or a Trapezoid tear strength of a machine direction notch of at least 15 g.

36. 36. The method of claim 35, wherein the thermoplastic film further has an Elmendorf tear strength of a machine direction notch that is at least 5 g.

37. 37. The method of claim 35 or 36, wherein the thermoplastic film further has a machine direction notch trapezoidal tear strength of at least 25 g.

38. 38. The method of any one of claims 24 to 37, wherein the thermoplastic film is a coextruded multilayer film.

39. 38. The method of any one of claims 24 to 37, wherein the thermoplastic film is a monolayer film.

40. 40. The method of any one of claims 24 to 39, wherein the basis weight is from 5 gsm to 13 gsm.

41. 41. The method of any one of claims 24 to 40, wherein the basis weight is between 8 gsm and 13 gsm.

42. 42. The method of any one of claims 24 to 41, wherein the breathable thermoplastic film comprises a propylene-based polymer composition, an ethylene-based polymer composition, an olefin block copolymer, or a combination thereof.

43. 43. The method of claim 42, wherein the thermoplastic film comprises an olefin block copolymer.

44. 44. The method of claim 42 or 43, wherein the thermoplastic film comprises a propylene-based polymer composition.

45. 45. The method of claim 44, wherein the thermoplastic film comprises 1% to 60% polypropylene.

46. 46. ​​The method of claim 45, wherein the thermoplastic film comprises 30% to 60% by weight of a filler.

47. 47. The method of claim 46, wherein the thermoplastic film further comprises an ethylene-based polymer composition.

48. 48. The method of any one of claims 45 to 47, wherein the thermoplastic film comprises 1% to 20% polypropylene.

49. 43. The method of claim 42, wherein the thermoplastic film comprises an ethylene-based polymer composition.

50. 50. The method of claim 49, wherein the ethylene-based polymer composition comprises from 10% to about 60% polyethylene.

51. 51. The method of claim 50, wherein the thermoplastic film comprises 30% to 60% by weight of a filler.

52. 52. The method of claim 51, wherein the thermoplastic film further comprises a polypropylene-based polymer composition.

53. 53. The method of any one of claims 50 to 52, wherein the thermoplastic film comprises from 20% to about 50% polyethylene.

54. 54. The method of any one of claims 24 to 53, wherein the thermoplastic film has an opacity of at least 50%.

55. 55. The method of any one of claims 24 to 54, wherein the thermoplastic film is substantially free of titanium dioxide.

Images