A thin, breathable, microporous thermoplastic 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 priority rights to U.S. Provisional Patent Application No. 61 / 992,438 filed on 13 May 2014, U.S. Provisional Patent Application No. 62 / 053,385 filed on 22 September 2014, and U.S. Provisional Patent Application No. 62 / 092,351 filed on 16 December 2014. [Background technology]

[0002] Thermoplastic films are widely used in personal care products, for example, as the outer layer of diapers or in 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 retaining other necessary properties of the film.

[0003] Desirable qualities of thermoplastic films include liquid impermeability, vapor permeability (e.g., breathability), bondability to other layers of personal hygiene products, and sufficient physical strength to be processed into the final product. Strength is an important consideration when thermoplastic films are used for packaging, for example, as outer packaging for consumer goods. Breathable films with sufficient strength and basis weight can be particularly useful for packaging products that require the release of odors introduced during the manufacturing process.

[0004] Thermoplastic films can be formed by extruding a molten polymer composition onto a cooling roller, where the molten polymer composition is immediately cooled to form a solid film. Film processing involves various steps, including heating, cooling, and stretching, to produce a final film product with a thickness of no more than 1 / 72nd of the initial thickness. Stretching in the machine direction (MD) forms a highly oriented thin gauge film, known as machine direction orientation (MDO). While MDO can be useful, especially in thin films, it can also provide qualities such as low transverse (CD) tensile strength, impact strength, tear strength, and slow puncture resistance.

[0005] Current methods for producing thin thermoplastic gauge films include the method described in U.S. Patent No. 7,442,332 (Cancio et al.). In this method, the majority (more than half) of the web stretching occurs between the extrusion die and the first nip (i.e., within the “melt curtain”). Two drawbacks in such a casting process are a phenomenon known as “draw resonance,” which results in non-uniformity of film thickness, and the formation of pores within the film. These problems become more pronounced with increasing production speed and can further limit the types of polymer compositions that can be used. Solving these problems requires slowing down the production speed, but this ultimately leads to increased costs. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Publication No. 7,442,332 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Therefore, with respect to thin thermoplastic films, there is a need for them to have limited MDO, desirable properties such as non-porous, good breathability, good tensile strength, and good tear strength, and to be able to be manufactured economically and efficiently on a high-speed production line. [Means for solving the problem]

[0008] The present invention satisfies the aforementioned need by providing a breathable thermoplastic film having a low basis weight, being substantially porosity-free, and possessing physical properties characteristic of films with higher basis weights. The film of the present invention exhibits excellent tensile strength, tear strength, and breathability. While tear strength is proportional to the thickness of the film, and thicker films generally exhibit higher tear strength, the film produced by the method of the present invention exhibits stronger tear strength than that predicted for a comparative film of similar thickness. In other words, the film of the present invention improves the ratio of tear strength to thickness.

[0009] The thermoplastic film of the present invention is considered unique in itself and is produced by a novel method in which the film is stretched in the machine direction at a temperature high enough to prevent harmful machine direction (MD) 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. Patent No. 7,442,332. The method of the present invention allows the extrusion process to be carried out at normal production speeds without requiring additional equipment to reduce draw resonance. A further advantage is that 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] 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 / m² 2The film has a water vapor transmission rate (WVTR) of less than 10, and the ratio of the MD load at break to the CD load at break is less than 10, and the film has at least one of the following: 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 another embodiment, a laminate is provided, the laminate having a first layer having a basis weight of 15 gsm or less and at least about 500 g H2O / 24 hours / m² 2 The first layer comprises a breathable thermoplastic film having a water vapor permeability (WVTR), wherein the ratio of the MD load at break to the CD load at break is less than about 10, and the film has at least one of an Elmendorf tear strength of a machine-directed notch of at least about 5 g, or a trapezoidal tear strength of a machine-directed notch of at least 15 g, and the first layer has a surface; and a substrate attached to the surface of the film.

[0012] In another embodiment, a method for manufacturing a thermoplastic film product is provided, the method comprising: an extrusion step of extruding a molten web containing a thermoplastic polymer from an extruder onto a first cooling roller, the first cooling roller being operated at a peripheral speed V1 and a temperature T1, the temperature being below the melting point of the thermoplastic polymer, and cooling the web to form a film, the space between the extruder and the cooling roller forming a first gap; and a step of advancing the film from the first cooling roller to a stretching roller downstream, the stretching roller being operated at a peripheral speed V2 greater than V1 and a temperature T2, the film being further stretched in the machine direction to produce a film having substantially uniform thickness, limited orientation in the machine direction, a ratio of MD load at break to CD load at break of less than about 10, and having 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] In other embodiments, in the above-described method given, 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 given, 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 given, the molten web is cast, blow molded, calendered, single extruded, coextruded, chill cast, nip embossed, or combinations thereof are performed.

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

[0017] In other embodiments, in the above-described method given, in order 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 air permeability, it further includes the step of stretching the film in the transverse direction.

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

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

[0020] In other embodiments, in the above-described method given, 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 another embodiment, in the given method described above, the second machine-oriented section is located downstream of the transversely fitting roller section.

[0022] In another embodiment, in the given method described above, the second machine-oriented section is located upstream of the transversely fitting roller section.

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

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

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

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

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

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

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

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

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

[0032] Another embodiment is a multilayer film obtained by co-extruding the film in the given method described above.

[0033] In another embodiment, the film in the given method described above is a single-extruded film.

[0034] In another embodiment, the film in the given method described above is a blow-molded film.

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

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

[0037] In yet another embodiment, a breathable thermoplastic film is provided, the film being manufactured by extruding a molten web containing a thermoplastic polymer onto a cooling roller having a temperature T1 to form a film, the film being fed downstream of the first cooling roller onto a stretching roller having a temperature T2, and further fed through a first machine orientation section having at least one heating roller and at least one stretching roller having a temperature T3, thereby giving the film a limited machine orientation, the film having a basis weight of about 15 gsm or less, and at least about 500 g H2O / 24 hours / m² 2 The film has a water vapor permeability of 0, and the ratio of the MD load at the time of fracture to the CD load is less than approximately 10.

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

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

[0040] In another embodiment, the film produced by the method described above has an MD load of at least 2.0 N / cm at the time of film breakage and a CD load of at least 0.7 N / cm at the time of breakage.

[0041] In other embodiments, in a film produced by the method described above, the molten web is cast, blow-molded, calendered, single-extruded, co-extruded, cold-cast, nip-embossed, or a combination thereof.

[0042] Another embodiment is a multilayer film in which the film is co-extruded, in the film manufactured by the method described above.

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

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

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

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

[0047] [Figure 1] One non-limiting embodiment of an apparatus suitable for producing the film of the present invention is shown. [Modes for carrying out the invention]

[0048] Terms used here: "Activation defects," "activation pores," or "pinholes" refer to small holes or tears within a film during its formation, lamination, activation, or other manufacturing or processing stages, which may subsequently result in reduced tear strength, increased porosity, increased leakage, or other undesirable properties.

[0049] "Gsm" stands for grams per square meter and is a measure of basis weight, which is a standard industrial 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 or psi per square inch. The film of the present invention has a hydrohead pressure of at least 200 psi.

[0051] The term "skin layer" refers to 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 of tearing a film and is expressed in grams. Here, tear strength may be measured by the Elmendorf notch tear test ASTM D-1922, incorporated herein by reference, and / or by the trapezoidal tear test ("Trap test") as described herein or by ASTM D-5587. The test may be performed on either notched or non-notched films, and in either the CD direction or the MD direction. Unless otherwise specified, tear strength here refers to notched tear strength. Tear strength is related to the thickness of the film, and any comparison of tear strengths must be made considering the relative basis weight of the control sample.

[0053] "Tear strength" refers to the load required to cause the film to break (load at break) in either CD or MD. Tensile strength is expressed in N / cm or equivalent units and is determined by the ASTM D822-02 method using the following parameters: sample orientation = MD × CD; sample dimensions = 1 inch wide × 6 inches long; test speed = 20 in / min; grip distance = 2 inches. Grip dimensions = 3 inches wide. Rubber grip for uniformly holding the sample.

[0054] "WVTR" stands for "Water Vapor Transmission Rate" and is a measure of the breathability of a film. WVTR is H2O / 24h / m² 2 It may be expressed in units or equivalent units and measured according to the ASTM D-6701-01 method.

[0055] film The film of the present invention is a thermoplastic single-layer or multilayer film that may have a basis weight of about 5 gsm to about 20 gsm, or about 5 to about 15 gsm, or about 10 to about 15 gsm, or about 8 to about 13 gsm, or 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 multilayer 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 2 to about 20 layers, or 3 to about 11 layers, and or 5 to 11 layers. The film may or may not include a skin layer to reduce the tackiness of one or both of the outer surfaces.

[0056] The film of the present invention has a CD load at breakage exceeding 0.7 N / cm, or exceeding about 0.8 N / cm, or exceeding about 0.9 N / cm, or 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 a MD load at breakage 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 breakage, 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 breakage to the CD load at breakage 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 has 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 approximately 10,000 g H2O / 24 hours / m 2 It also has a water vapor transmission rate (WVTR).

[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 trapezoidal (trap) tear strength of at least about 15 g, or at least about 20 g, or at least about 25 g, or about 15 g to about 150 g, or about 15 g to about 100 g, or about 15 g to about 85 g.

[0061] The film of the present invention comprises one or more thermoplastic polymers. Suitable polymers for this film include, but are not limited to, polyethylene homopolymers and copolymers, polyolefins such as polypropylene, polypropylene homopolymers and copolymers, functional polyolefins, polyesters, polyamides such as poly(ester ethers), nylon, poly(etheramides), polyethersulfones, fluoropolymers, polyurethanes, and mixtures thereof. Polyethylene homopolymers include those formed by low-density, medium-density, or high-density polymerization and / or high-pressure polymerization or low-pressure polymerization. Polyethylene and polypropylene copolymers include, but are not limited to, copolymers with C4-C8 alphaolefin 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 various methods 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, 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-propylenediene), poly(methyl methacrylate), and / or polyolefin terpolymers thereof. In one embodiment, the film comprises polyethylene, polypropylene, and combinations thereof. An example of a suitable commercially available polyethylene resin is Exxon's Exceed. TM The value is 3527PA. An example of a suitable commercially available polypropylene copolymer is Borealis BD712 from Borealis.

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

[0063] In one example, the olefin-based block copolymer is polypropylene-based. A non-limiting example of a suitable polypropylene-olefin-based block copolymer is the trade name INFUSE from Dow Chemical Company, Midland, Michigan. TM These are sold under the trade name VISTAMAXX® by ExxonMobil Chemical Company in Houston, Texas, and 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, improving the film's resistance to melting. In other embodiments, the film of the present invention may contain an ethylene-based olefinic block copolymer.

[0064] The above-mentioned thermoplastic polymer may be present in the film or in individual layers of the film in amounts ranging 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 multilayer film contain polypropylene, a polypropylene-based composition or copolymer, ethylene, an ethylene-based composition or copolymer, or a combination thereof, in amounts of about 0.1% to about 90%, or about 1% to about 60%, or about 20% to about 50%, or about 20% to about 40%, or about 1% to about 10%.

[0065] The film of the present invention, or its individual layers, may contain one or more elastomers, including styrene-based block copolymers, elastomer-olefin-based block copolymers, and combinations thereof. Non-limiting examples of suitable styrene-based 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 contain optionally selected components such as fillers such as calcium carbonate, plasticizers, compatibilizers, drawdown polymers, processing aids, antiblocking agents, and viscosity-reducing polymers. Other additives include pigments, dyes, antioxidants, antistatic agents, slip agents, foaming agents, heat or light stabilizers, and UV stabilizers. Suitable processing aids and antiblocking agents include, without limitation, Ampacet, which is available from Ampacet Corporation. TMExamples include: In one embodiment, the polymer composition may contain about 0% to about 75%, 1% to 30%, or about 30% to about 60% of filler. In one embodiment, the polymer composition may contain about 0% to about 15%, or about 0% to about 10%, or about 0.5% to about 5% of suitable processing aids.

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

[0068] Device Figure 1 shows an exemplary configuration of a film forming apparatus 10 suitable for forming the film of the present invention. When used with films or nonwoven materials, “machine direction” means the direction parallel to the direction in which the film or nonwoven material moves as it is processed within the film forming apparatus. “Transverse direction” means the direction perpendicular to the machine direction. In one non-limiting embodiment, as shown in Figure 1, the film forming apparatus 10 includes a casting / drawing section 12, a machine direction orientation (MDO) section 14, and a transverse fitting roller (CDI) section 16. Optionally, the film forming apparatus 10 may include additional sections, such as an annealer section, a winder, an additional machine direction orientation section, and / or a corona treatment section, which would be obvious to those skilled in the art. In other embodiments, the order of the sections or their components may differ from that shown in Figure 1, which would also be understood to those skilled in the art.

[0069] The casting / drawing section 12 includes an extruder 24 and at least one cooling roller 28, with a first gap 26 between them. 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 Figure 1 to a position slightly downstream from that shown, but in a position where the extruder 24 still feeds the melt curtain containing the extruded material onto the cooling roller 28. Downstream of the cooling roller 28, which has a temperature T1 and rotates at a speed V1, is a stretch roller 30, which has a temperature T2 and rotates at a speed V2. The cooling roller 28 is separated from the stretch roller 30 by a second gap 32. In operation, the extruder 24 melts the extruded material and pushes it across the gap 26 onto the cooling roller 28 to form a web or film 15. The film 15 moves across the second gap 32 into a nip 33 formed between the slave roller 34 and the stretch roller 30. The film 15 then passes over the idler roller 39 toward the machine orientation section 14.

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

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

[0072] In the present invention, the temperature T1 of the cooling roller 28 and the temperature T2 of the stretching roller 30 are substantially higher than those in any previously disclosed MDO method. In previous applications, T1 is typically about 10°C to about 60°C, and T2 is typically about 10°C to about 40°C. The present invention uses temperatures that strike a balance between the need for processability of the film and further controllability 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. The speed and temperature of the cooling rollers may be the same or different, but sufficient to stretch the film to the desired thickness without causing substantial MD molecular orientation, but below the melting point of the polymer composition. For non-limiting illustrative purposes only, the temperatures may differ by 5°C, 10°C, or more. Each cooling roller may independently be smooth, have a textured surface, be coated (e.g., with a release treatment), and may be the same or different at 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 larger compared to the conventional cast MDO method. In one embodiment, the length of the first gap 26 is greater than 2.5 cm, or about 2.5 cm to about 25 cm, or about 3 cm to about 15 cm, or about 3 cm to about 7.6 cm. The extruded material may undergo melt curtain stretching, and the corresponding thickness reduction within the gap 26 is 10 to about 25 times (about 10X to about 25X).

[0075] In one embodiment, the apparatus may include additional rollers and a nip between the extruder 24 and the cooling roller 28, as described in U.S. Patent No. 7,442,332. In another embodiment, the apparatus may include one or more additional cooling rollers. In yet another embodiment, the cooling roller 28 can be replaced by two rollers, which 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, or about 100°C or less. After passing through the additional nip, the film proceeds through the nip 33 and further through the processes described herein.

[0076] The roll speed ratio 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 to five times its original length, i.e., the corresponding reduction in film thickness is 0.2 times its original thickness. In one embodiment, the V2 / V1 ratio is at least 2, or at least 5, or about 2 to about 8, or 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 about 7.5 cm to about 30 cm, or about 7.5 cm to about 20 cm, or 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, after being stretched between the cooling roller 28 and the stretching roller 30, is a substantially non-porous film having a limited molecular orientation in the machine direction.

[0078] Here, "to give the film a limited machine orientation" means to form a sufficient MD orientation such that the film receives a rupture MD load of at least 2.0 N / cm and a rupture CD load of at least 0.7 N / cm. Furthermore, the film has an MD load-to-CD load ratio of approximately 1 to 15 at rupture. 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 rupture, and an improved balance between CD tensile strength and MD tensile strength compared to conventional films.

[0079] Downstream of the casting / drawing section 12, the film 15 passes from the stretching roller 30 around the idler roller 39 and proceeds toward 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. At the heating rollers 35a and 35b, the film 15 is heated to a temperature T3. T3 depends on the composition of the film and is sufficient to avoid substantial MD orientation. In one embodiment, T3 is about 80°C to about 150°C, or above 95°C, or above 120°C.

[0080] As those skilled in the art will understand, the number of stretching rollers, heating rollers, and cooling rollers within the first MDO section 14, and the number of MDO sections, may be modified. 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 cosmetic properties, such as porosity and opacity. For illustrative purposes, a second set of heating rollers, stretching rollers, and / or cooling rollers may be located downstream of the first MDO section 14, the stretching rollers 36a and 36b, and upstream of the cooling roller 37. In alternative embodiments, the second set of heating rollers, stretching rollers, and / or cooling rollers may be located downstream of the CDI section 16 within a 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 about 2 to about 25, or about 5 to about 15, or about 5 to about 25. In one embodiment, the ratio V3 / V2 and / or V2 / V1 is greater than 1, or greater than 2, or less than 5, or about 1 to about 5, or about 2 to about 5.

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

[0083] The film can be stretched using a tenter frame (not shown) instead of, or in addition to, the MDO and / or CDI sections. This can be used to achieve both MD and CD orientation.

[0084] The film 15 may be moved from the CDI section 16 to any other component, which may include, but is 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 film of the present invention is 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 may be any woven or nonwoven material suitable for use with the thermoplastic film, and in one embodiment is a spunbond nonwoven 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, or extrusion bonding.

[0086] The films and / or laminates of the present invention are suitable for use as backsheets or closure tabs of diapers, and may be formed into pouches for packaging personal hygiene products, as well as foods such as sandwiches, fruits, and 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 building applications such as roofing materials, linings, and backsheets for flooring and carpets.

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

[0088] opacity The opacity of the film is measured as follows: The measurement method uses the ratio of the reflectance of the same sample with a white backing to that of the same sample 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 large enough to cover the opening of the instrument's viewing window. The sample is placed in a window with a 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 sample was gradually stretched transversely (CD) (CDI).

[0089] Alternatively, the opacity of the film may be measured according to ASTM 1746.

[0090] Hydrohead 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 a higher-end model may be used. The standard test gradient is 60 mbar / min, and 70 gsm spunbond / pattern-bonded polypropylene nonwoven fabric is used as the support. The endpoint of the test 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 at which the sample bursts. If no penetration of water is observed, the maximum test pressure is recorded.

[0091] Trap tear strength The sample template is cut to have dimensions of 3" x 6". From this template, mark a trapezoidal template with a long side of 4", a parallel short side of 1", and a height (distance between the parallel sides, measured perpendicular to the sides) of 3". Starting from the center of the short side end, make a 5 / 8" slit perpendicular to the short side. Place the template in the clamps of an Instron Model 1122, 4301, or equivalent tensile testing machine with a constant elongation speed. Set the distance between the clamps to 1". Prepare and standardize the load cell according to the instructions. For tensile testing machines 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 marked, non-parallel sides of the trapezoid, so that one end of the clamps coincides with the 1-inch (1") side of the trapezoid and the slit is midway between the clamps. Start the testing machine and record the tear force of the specimen.

[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 approximately 260°C, rotating at approximately 45.7 m per minute and extruded onto a cooling roller at a temperature of 116°C. The film was stretched on a stretching roller operated at a speed V2 (149 m per minute) and a temperature of 88°C. The film was then stretched on an MDO operating at a speed of 278 m 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 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 / m³. 2 These data points, along with the decrease in material, all exceed the specifications for 16gsm basis weight.

[0094] Examples 2 to 11 Further cast films were formed using the method disclosed in Example 1. The samples contained 1% processing aid, polypropylene, and the fillers described below, with the remainder of the composition being polyethylene. The physical properties of the films are shown in Table 1. Unless otherwise stated, the films contained 50% calcium carbonate and did not contain titanium dioxide.

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

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

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

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

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

[0100] In Examples 9 and 10, single-layer films containing 33% polypropylene were formed in the same manner as with rubber additives. The V2 / V1 ratio was 3.5, and the V3 / V2 ratio 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 was 3, and the V3 / V2 ratio was 2.

[0102] [Table 1]

[0103] In all embodiments of the present invention, all scopes 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,” “includes,” “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 the term is determined when used as a conjugate in a claim.

[0104] All documents cited in the detailed description of the invention are incorporated herein by reference in the relevant sections. The citation of any document is not construed as prior art relating to the present invention. If there is any conflict between the meaning or definition of any term in this specification and any meaning or definition of the same term in any document incorporated by reference, the meaning or definition assigned to the term in this specification shall prevail.

[0105] While specific embodiments of the present invention have been described and explained, it will 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. Accordingly, all such changes and modifications that fall within the scope of the invention are intended to be included in the claims of the present invention.

[0106] [1] Basis weight of approximately 15 gsm or less, and at least approximately 500 g H2O / 24 hours / m² 2 A breathable thermoplastic film having a water vapor permeability of , wherein the ratio of the MD load at break to the CD load at break is less than about 10, and the film has at least one of the following: an Elmendorf tear strength of a machine-directed notch of at least about 5 g, or a trapezoidal tear strength of a machine-directed notch of at least about 15 g. [2] The film according to [1], wherein the MD load at the time of fracture is at least about 2.0 N / cm and the CD load at the time of fracture is at least about 0.7 N / cm. [3] The film according to [1] having at least about 50% opacity. [4] The film described in [3], which is 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 polymer composition. [7] The film according to [5], wherein the olefin block copolymer is an ethylene-based polymer composition. [8] The film described in [1], comprising approximately 10% to approximately 60% polypropylene. [9] The film according to [1], comprising approximately 30% to approximately 60% by weight of filler.

[10] The film according to [1], which is a co-extruded multilayer film.

[11] The film described in [1], which is a single-layer film.

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

[13] A thermoplastic film that is breathable, Basis weight of approximately 5 gsm to 20 gsm, at least 500 g H2O / 24 hours / m² 2 A breathable thermoplastic film having a water vapor permeability, 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 about 1 to about 10, and at least one of the following: an Elmendorf tear strength of a machine-directed notch of at least about 5 g or a trapezoidal tear strength of a machine-directed notch of at least about 15 g.

[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 polymer composition.

[17] The film described in

[13] , comprising approximately 10% to approximately 60% polypropylene.

[18] The film according to

[13] , comprising approximately 30% to 60% by weight of filler.

[19] The film according to

[13] , which is a co-extruded multilayer film.

[20] a. Basis weight of approximately 15 gsm or less, and at least approximately 500 g H2O / 24 hours / m² 2 The first layer comprises a breathable thermoplastic film having a water vapor permeability of , wherein the ratio of the MD load at break to the CD load at break is less than about 10, and the first layer has at least one of the following: an Elmendorf tear strength of a machine-directed notch of at least about 5 g or a trapezoidal tear strength of a machine-directed notch of at least about 15 g, and the first layer has a surface, b. A substrate attached to the film surface, Laminated articles containing the above.

[21] An extrusion step of extruding a molten web containing a thermoplastic polymer onto a first cooling roller, wherein the first cooling roller is operated at a first peripheral speed V1, the first cooling roller has a first temperature T1, the temperature T1 is below the melting point of the thermoplastic polymer, and thereby cools the web to form a film; The process includes the step of advancing the film from the first cooling roller to a stretching roller located downstream, wherein the stretching roller rotates at a second peripheral speed V2 greater than V1, and the stretching roller has a temperature T2, The stretching roller stretches the film in the machine direction to produce a film having a substantially uniform thickness, limited orientation in the machine direction, a ratio of machine-direction load at break to lateral load at break of less than about 10, and having at least one of an Elmendorf tear strength of a machine-direction notch of at least 5 g or a trapezoidal tear strength of a machine-direction notch of at least 15 g. A method for manufacturing thermoplastic film products. [Explanation of Symbols]

[0107] 10 Film forming apparatus 12 Casting / Drawing Section 14. Machine Directional Orientation (MDO) Section 15 Web or film 16. Lateral Mating Roller (CDI) Section 24 Extruder 26. The first gap 28 Cooling rollers 30 stretching rollers 32. The second gap 33 Nips 34 Slave Roller 35a, 35b Heating roller 36a, 36b Stretching roller 37 Cooling rollers 38 Tension Roller 39 Idol Laura 40, 42 Fitting rollers 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 trapezoidal tear strength of a machine-direction notch of at least 25 g; A film having a water vapor transmission rate ranging from 500 g H₂O / 24 hours / m² to 10,000 g H₂O / 24 hours / m².

2. The film according to claim 1, wherein the MD load at the time of fracture is at least 2.0 N / cm and the CD load at the time of fracture is at least 0.7 N / cm.

3. The film according to claim 1, having an Elmendorf tear strength of at least 5 g in the machine direction notch.

4. The film according to claim 1, having at least 50% opacity.

5. The film according to claim 4, which is substantially free of titanium dioxide.

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

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

8. The film according to claim 1, wherein it is a co-extruded multilayer film.

9. The film according to claim 1, wherein it is a single-layer film.

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

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

12. The laminate according to claim 10, wherein the film comprises 10% to 60% polypropylene.

13. The laminate according to claim 10, comprising an adhesive.

14. The laminate according to claim 10, comprising an ultrasonic bonding portion.

15. A manufactured article comprising the film described in Claim 1.

16. The manufactured article according to claim 15, which is a package for personal hygiene products.

17. A manufactured article comprising the laminate described in Claim 10.

18. The manufactured article according to claim 17, which is a backsheet for a diaper, a closure tab, roofing material, lining, a backsheet for flooring, or a backsheet for carpet.

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