MXPA99010243A - Texturized microporosa film, stable dimensionally, and method for factory - Google Patents

Abstract

The present invention relates to a soft, texturized, dimensionally stable microporous film, which comprises: about 45 to 60% by weight of a filler, and the rest between a mixture of a linear low density polyethylene and a high polyethylene. density, or other heat resistant polymer. This texturized, dimensionally stable microporous film is formed by extruding the formulation as a film, and orienting the film by passing it through at least one set of interengaged gear rolls. The oriented film is tempered, reheated and, optionally, enhanced to form a microporous, soft textured film, which is dimensionally stable at elevated temperatures.

Description

TEXTURIZED MICROPOROSA FILM. STABLE DIMENSIONALLY. AND METHOD TO MANUFACTURE Antecedent-bes The present invention is found in the general field of microporous films. The invention relates particularly to microporous films that are dimensionally stable at elevated temperatures and to a method for making these films. The microapplication of a film is typically expressed in terms of the wet steam transmission rate or MVTR. It is also commonly referred to as the breathability of the film. One method of determining the MVTR of a film is to use the test procedures provided in ASTM E96-93. Uses readily considered of the present invention include a liquid impervious layer in such products as disposable absorbent articles, which include disposable garments for sanitary purposes and catamenial towels, diapers, incontinence articles or for hospital towels, surgical bandages, beds and other products, such as sleeping bag liners, and the like. Absorbent articles, such as diapers, catamenial products, surgical draperies and the like, are designed to receive and retain a liquid within an absorbent core. The absorbent article contains a cover or back sheet on the outside thereof, which prevents the absorbed liquid from escaping or penetrating through the absorbent core. The liquid-proof backsheet significantly reduces the self-drying of the absorbent article by any evaporation of the fluid retained in the core. The outer, liquid-proof back sheet can contribute to making the absorbent article moist, hot and finally not comfortable to use. Therefore, it would be an advantage to have a breathable material that allows the exchange of vapors, but retain the fluid as in a subsequent liquid-proof sheet. One type of breathable film is a microporous film, which has a plurality of interconnected micropores, through tortuous paths extending from one outer surface of the film to another outer surface of the film. This type of microporous film can be formed by preparing and stretching a film containing at least one type of filler material. This filler can be removed from the film, allowed to remain intact within the film or compressed under pressure to supply the pores in the film. The filler particles can also be made to separate from the thermoplastic polymers during a stretching process, to form interconnected micropores. Several patents, which show the general principle of using a filler material within a plastic material, to produce a microporous film, include those of Aoyama et al., U.S. Patent No. 4,841,124 and 4,921,653; Nishizawa et al, U.S. Patent No. 4,626,252; Sugimoto, U.S. Patent No. 4,472,328; Sch arz, U.S. Patent Nos. 4,833,172, 4,116,892, 4,289,832, 4,153,571 and 4,091,164. Still other patents that teach modifying inorganic fillers, which use additional ingredients to produce a microporous film include that of Hwang, U.S. Patent No. 4,824,718; Toyoda et al, patent of E.U.A., No.4, 418, 112; Takashi et al, U.S. Patent No. 4,319,950; Suzuki, U.S. Patent No. 3,969,562; Ikeda et al, Reexpedición patent of E.U.A., No. 28,608; Ikeda et al, U.S. Patent Nos. 3,738,904 and 3,903,234; Elton et al, U.S. Patent Nos. 3,870,593 and 3,844,865; Ita et al, U.S. Patent No. 4,705,812; Hogue, U.S. Patent No. 4,350,656; Antoon, Jr. et al, U.S. Patent Nos. 5,008,296 and 4,879,078; Okuyama et al, U.S. Patent Nos. 4,704,2328 and 4,585,604; Doi et al, U.S. Patent Nos. 4,335,193, 4,331,622 and 4,210,709; Kaneko et al, U.S. Patent No. 5,445,862; McCormick, PCT Application W095 / 16562; Sheth, US Patents, Nos. 4,929,303 and 4, 777, 073; Sheth et al, U.S. Patent No. 5,055,338; Cancio et al, U.S. Patent Nos. 5,055,338, 4,380,564 and 4,298,647; Gure itz, U.S. Patent No. 5,364,695; Seiss et al, U.S. Patent No. 4,716,197; Sheth, U.S. Patent No. 4,777,073; and Exxon, PCT Application WO 98/05397. While it would be convenient to use high amounts of the filler material in a textured microporous film, various difficulties occur when the currently known film forming technologies discussed above are used. In order to improve the physical properties of the thermoplastic films, various methods have been used to stretch and orient the films. One method involves moving the film through sets of rollers that operate at different speeds. Another method involves passing the film through interengaged gear rollers that stretch the film. Several patents, which show the general principle of using interengaged gears to stretch a film include: Sch arz, U.S. Patents, Nos. 4,116,892; 4,144,008; 4,153,751; 4,251,585; 4,223,059; 4,285,100; 4,289,832; 4,368,565 and 4,438,167, all of which are hereby expressly incorporated by reference. While interengage gear gearing processes have been used in the past to stretch the film, until the present invention, none has stretched uniaxially or biaxially, successfully a film containing a large amount of filler, to supply a textured microporous film, flexible and dimensionally stable. In the past, microporous films containing fillers were not acceptably soft and flexible and none were candidates for use in disposable products. In the past, microporous films were enhanced to increase the texture of the film, softness and flexibility. However, microporous films having a high filler content are difficult to enhance without significantly reducing the physical properties of this film. Enhancing the melt or embossing before orientation causes the film to have thinner and thicker areas before orientation. Thin areas are more likely to develop small holes and tears during orientation or during the subsequent process. In addition, the reheating enhancement of the microporous films generally results in a lower breathability. The presence of large amounts of filler in a microporous film increases the thermal conductivity of the film. The increase in thermal conductivity results in the polymer that surrounds the filler particles relaxing during the embossing cap. Relaxation of the polymer causes this polymer to flow into the voids of the film and reduce the porosity of the film. Until the present invention, this phenomenon has caused microporous films to have a significantly reduced respirability after embossing. The presence of a filler in the film formulation presents additional limitations in the process of forming this film. The presence of large amounts of filler in a film changes the thermal conductivity of the film. Until the present invention, the heat generated during extrusion and the film forming processes have made it virtually impossible to achieve a microporous, textured, dimensionally stable film, without causing damage to the micropores in the film. When a formulation with a high content of filler is going to be processed or subsequently converted into a final product, the thermal characteristics of the film containing the filling cause additional problems, since the filling is heated quickly, the subsequent application of heat, hot rubber or adhesives to the film cause shrinkage, puckering and / or holes in the microporous film.

When prior art films are used in disposable products, such as in diapers or catamenial products, there is usually an adhesive strip that is used to secure the disposable article. Frequently, due to the presence of filler particles on the surface of the generally flat microporous films, the adhesive bonds to the disposable product make it difficult to detach the adhesive strip from the film, or to detach the film from an article to which it is attached. This high detachment force often results in the tearing of the film or article to which it is attached, which is not acceptable to the consumer. Until the present invention, it was virtually impossible to reduce the adhesive forces of release of the microporous films. It is well known in the art that oriented films have reduced dimensional stability at elevated temperatures. This lack of dimensional stability at elevated temperatures is aggravated by the increased thermal conductivity of the microporous films. This creates problems during the subsequent shipment process. For example, a tow truck can reach a temperature of 60 seconds, which can cause the film to shrink. This is not acceptable because the shrinkage will cause the layers of the film in the roll to stick together, preventing unwinding of the film. Until the present invention, the microporous films had poor dimensional stability at elevated temperatures. The presence of a large amount of filler in a film, in the past, limited the physical properties of the film, including the ability of such film to be stretched. Since the landing material is not elastic, the film containing the filling is stretched only by a limited amount before reaching its elastic point. Once the film has passed its elastic point, it quickly reaches its breaking point. This narrow gap between the elastic point and the point of rupture prevents the film from having the capacity to be subsequently carried out in subsequent processes or conversion stages. Any elongation or further processing of the film by an end user in converting the film into a disposable absorbent product, caused the degradation of the physical properties of the film. Such prior art films were rather rigid and had paper-like properties. These films of the prior art do not have the soft and flexible characteristics of the film of the present invention. While several formulations have been used in the past to produce thermoplastic films, none has produced a dimensionally stable textured microporous film having a high percentage of the filler material and a polyolefin blend comprising a high density polyethylene, or other polymer resistant to heat, and a linear low density polyethylene. Optionally the formula of the film may include low density polyethylene and process aids. Therefore, it is a primary object of the present invention to provide a microporous, texturized, dimensionally stable film or sheet useful in disposable articles, and a process for the preparation of such a film. The added feature of the invention of dimensional stability provides an even greater utility of such microporous film. Therefore, it is another object of the present invention to provide an improved method for forming a microporous, dimensionally stable film that can be subsequently cast during the conversion and still meets the requirements of the final use of the film.

SUMMARY OF THE INVENTION The present invention provides a textured microporous film, which is vapor permeable, impermeable to liquid and dimensionally stable at elevated temperatures. For the first time, a method for manufacturing a microporous, texturized, dimensionally stable film is disclosed.yes.

According to the present invention, the film formulation provides a balance of high amounts of a filler, which is a mixture of polyolefins of a linear low density polyethylene and a high density polyethylene or other heat reant polymer, and , in certain embodiments, a low density polyethylene, to supply a film with desired physical properties. In one embodiment, heat-reant polymers can be incorporated into the mixture to create a mixture having a primary melting point, when evaluated by differential scanning calorimetry (DSC), equal to or greater than 120 ° C; however, mixtures with a primary melting point below 120 ° C can also be used. The heat reant polymers may include other thermoplastic or elastomeric polymers, with a melting point greater than 120SC. The primary melting point is defined as that peak with the largest area or endothermic energy flow. Examples of heat reant polymers include, but are not limited to, polypropylenes, rubber modified high density polyethylene, linear density medium polyethylene, ethylene-propylene copolymers, and block copolymers containing styrene. Among the advantages obtained from the film forming process is that the film is easily oriented to provide the desired controllable permeability, without the formation of minute holes. The improved moisture vapor transmission properties of the film result from a combination of factors. The first factor is that the formulation of the film comprises a high percentage of filler material. The second factor is the orientation of the intergrain gear of the film when a balanced orientation of the film is achieved. The third factor is the employee of the oriented film, when the temperature and tension in the tempering element hardens or cures the micropores of the film. Optionally, the fourth factor is the overheating and embossing of the tempered film, when the temperature and tension of the embossing between the reheating rolls and the engraving rolls provide smoothness to the film, without diminishing the desired wet steam transmitting properties. Another advantage obtained from the film forming process, described above, is the property of residual film elongation. The residual elongation makes it possible for the film to be stretched further during the conversion of the film into a final use product. The property of residual elongation, ie the difference between the elongation at break of the film and the elastic elongation of the film is related to the orientation of the geared gear of the film in the machine and the transverse directions and to the depth of the coupling used in the gearing gear orientation. The property of the residual elongation is also dependent on the formulation of the film. The ability of the film to be oriented depends on the mixture of the polymer used in the film formulation. The ability of the film to be oriented tells us how much of the film should be elongated in order to have the desired properties of wet steam transmission. An advantage of the formulation of the film of the present invention is the low elongation required to achieve the desired vapor transmission rates. Still another advantage is that the film has good reance to calpr, despite having a high content of filler. The thermal reance of the film prevents damage to the film from occurring during further heat applications to the film. In particular, the heat reance of the film prevents the formation of holes in this film when an adhesive material of a hot melt is applied to the film during the conversion of the film into a final use product. Still another advantage is that the film has dimensional stability at high temperatures and does not shrink easily. Such dimensional stability is related to the interengagement gear orientation and the film formulation. The subsequent dimensional stability is provided to the film during the tempering process, controlling the tension between the rollers, the temperature of the hardening rollers and the period of time in which the film is in contact with the hardening rollers. The dimensional stability of the film is also increased by controlling the embossing preheating temperature and the tension between the preheating rolls and the engraving rolls of the embossing element. Yet another advantage of the film of the present invention is the impact resistance of the film. The impact resistance of the film is improved by the balance of the machine and the orientation of the transverse direction. Still another advantage is the production of a film having a desired texture, which improves the aesthetics of the film and decreases the adhesive release forces of the film. The embossing of the film reduces the surface area of contact between an adhesive and the microporous film. A decrease in the peel force is an advantage when the film is used in disposable products, such as diapers and catamenial towels. The microporous film of the present invention allows the fastener tape to be removed or the film to be removed from the article to which it is attached, without tearing the film. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a system for producing a textured, microporous, dimensionally stable film. Figure 2 is a graph showing the moisture vapor transmission rate for several films with high filler content. DETAILED DESCRIPTION The present invention relates to a textured, dimensionally stable microporous film, and to a method for manufacturing it. The film is formed using a combination of a high density polyethylene, or other heat resistant polymers, with a low density polyethylene. The film also contains a filler that creates the micropores when the film is subjected to stretching forces. In one embodiment, the microporous film is tempered to provide greater dimensional stability to the film, when this film is subjected to elevated temperatures. In yet another modality, the film is enhanced. The balance between high-density polyethylene (or other heat-resistant polymer) and linear low-density polyethylene, together with filler, provides a film that has the desired properties of moisture vapor transmission rate, along with the strength to the desired impact, dimensional stability (resistance to shrinkage), and elongation properties. Increasing the amount of high density polyethylene increases the moisture vapor transmission rate and the heat resistance of the film due to the higher level of crystallinity. However, amounts greater than 20% of the high density polyethylene affect the characteristics of the module, rigidity and noise of the film, which result in a reduced attraction to the consumer. The linear low density polyethylene material allows the film to have the quality of a soft touch necessary for disposable products. The linear low density polyethylene also allows the film to be easily drawn due to the extensibility of this component. The presence of linear low density polyethylene in the formulation also increases the elongation properties of the film. The film of the present invention is formed using a polyolefin film formulation, comprising about 45 to 65%, preferably about 50 to 55%, of a filler material, about 25 to 55% of a polyethylene. low density, around 0 to 20% of a high density polyethylene, or other heat-resistant polymer, around 0 to 5% of low density polyethylene, around 0 to 3% of process aids and around 0 to 10% pigmenting agents, such as bleaches or other color agents. Preferably, the thermoplastic film formulation comprises about 50 to 56% of the calcium carbonate filler, about 30 to 40% of the linear low density polyethylene, about 5 to 10% of high density polyethylene, or other resistant polymer to heat, about 2% of a process aid, comprising a Von® fluorocarbon in a low density polyethylene, and around 2% of a white concentrate, comprising the titanium dioxide in a low density polyethylene. The film of the present invention has very good heat resistance. The polyolefin blend of the present invention combines a material with a higher melting point (such as high density polyethylene, which has a melting point of about 130SC) with a material having a somewhat lower melting point temperature ( such as a linear low density polyethylene having a melting point of about 122se). The heat resistance of the film is surprising, since the film has a large amount of filler. In the past, several hot melt adhesives tended to cause puckering, shrinkage or holes, when applied to a microporous film. However, when the high filler formulation used in the present invention was quenched, there was no damage to the film, such as puckering, shrinkage or holes in the gum areas. The breathability,. or MVTR, of the film, is affected by the amount and size of the filler particles and by the ratio between the types of resins used in the film. The percentage of the filler that may be present in the film depends, in part, on the size of the filler particles. These filler particles of a certain predetermined size range have defined ranges of circumference (or surface area) and volume. Both the circumference and the volume of the filler particles affect the moisture vapor transmission rate of a film. The circumference and the volume of the filler particles cause the formation in the film of a certain size of holes and trajectories. The filler particles have a size of about 12.5 microns or larger, when used with the resins specified above, they cause the resulting film to have tiny holes through which liquids can escape. It has been found that the filler particles have an average size of about 0.5 to 5 microns and a preferred average size of about 1 to 3 microns works particularly well to produce a film with the desired level of breathability. Various inorganic fillers can be used, including, but not limited to, calcium carbonate, talc, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, barium sulfate, calcium sulfate, magnesium sulfate, magnesium hydroxide, aluminum hydroxide, magnesium oxide, calcium oxide, zinc oxide, titanium oxide, alumina, mica, glass powder and the like. These fillers can be used separately or in combination. A particularly suitable filler material is calcium carbonate. This calcium carbonate can be coated, at least partially, with stearic acid or other stearate compounds, which allow the calcium carbonate to have a more uniform dispersion throughout the resin composition. The breathability of a film, which has 38% filler by weight, based on the weight of the film, is relatively low, while a film that has a 53 to 55% filler will have a high MVTR. While additional filler, greater than 53 to 55%, can be added to the film, there is no substantial increase in the humidity vapor transmission rate. Filler levels greater than 60% will cause the film to become brittle and more paper-like, rather than soft and flexible. The textured filmDimensionally stable, of the present invention, also has improved breathability properties, due to the orientation of the film by the intergrain gear (IMG) stretch of the film. When the film is stretched in the machine direction only, the preferred stretch is about 5 to 100% and more preferably about 15 to 100%. It has been found that a film stretched by at least 15% supplies an MVTR of about 1000 to 1500 g / m / day (grams per square meter per day). The degree to which the gears overlap or interengage in these intermeshing gears, known as the "engagement depth", can vary to change the amount of orientation or stretch of the film. An increase in the coupling depth of the intergrain gears increases the breathability of the film. The distance between the feelings in the intergrain gears, known as "pitch", can also vary to change the amount of orientation of the film. In practice, it has been found that a distance of about 762 to 5080 microns between teeth ("pitch") and about 127 to 5080 microns depth of coupling (DOE) on the MG rolls, can be used to produce a film with an MVTR of approximately 500 to 5000 g / m2 / day. A preferred passage interval of about 1270 to 2540 microns and a preferred depth of coupling of 508 to 1905 microns provides a film having an MVTR of about 1500 to 3000 g / m2 / day. The film formation in combination with the orientation step of the present invention allows the film to have a sufficient residual elongation so that the film can be stretched further. This further stretching of the film is often done by a customer during the conversion of the film into a disposable product. An important characteristic that allows the additional stretch of the film is the residual elongation, or the difference between the elastic elongation and the elongation at the break of the film. This elongation is measured by a voltage tester, as specified in ASTM D882. The difference between the percent elastic elongation and the percent elongation at break provides an "elongation window," which is not found in other films. The film of the present invention has a residual elongation greater than 75% in the machine direction and greater than 300% in the transverse direction, as measured by the difference between the percent of the elongation at break and the per cent. one hundred of the elastic elongation. It has been found that a film with a residual elongation greater than about 150% in the machine direction (MD), and greater than 500% in the transverse direction (TD) works particularly well. This increases the impact resistance of the film. The combination of the film formulation and the orientation of the intergrain gear also affects the impact resistance of the film. Impact resistance can be measured by dropping a dart onto the film, as specified by STM D1709-80. When a film is stretched only in one direction, there is less impact resistance. Also, the higher the level of stretch imparted to the film, the lower the impact resistance. However, in the mode of the molded film, it is convenient to stretch the film in the transverse direction rather than in the machine direction, due to the lack of the direction of direction TD in the molded films. It is also convenient to balance the orientation in the direction of the machine made to the film during manufacture, with at least some amount of orientation in the transverse direction. In the blown film mode, the inherent orientation of the transverse direction can be such that this orientation in the IMG transverse direction is unnecessary. In the formulation of the present invention, a higher percentage of filling together with a highly orientable mixture of polymers in the film, provides breathability and allows smaller amounts of stretch. The film of the present invention has improved dimensional stability at elevated temperatures over the films of the prior art. The oriented film is tempered to provide the dimensional stability at high temperatures and the heat resistance of the film. The tempering allows a slight molecular relaxation of the polymer chains stretched by the polyolefins in the film formulation. The tempering step applies heat to the film at a controlled tension to relieve the stress that would result from the formation and orientation steps. Due to the relaxation that occurs in the tempering stage, there is less than 15% shrinkage of the film, after exposure to 76.6 ° C in the are for 30 minutes. When the tempered film is subjected to further process steps, the film will not shrink when exposed to temperatures of, or below, the tempering temperature. The tempered film can be subjected to further heating, such as when the film is subjected to a conversion and / or transport process. The film can be easily used in subsequent conversion steps, such as when a hot gum is used to secure the misroporous film to other components of a construction. During the tempering stage, the tension between the hardening rollers is important in its control. It is not convenient to have a positive pull between the hardening rollers. Positive pulling stretches the film and undesirably reduces dimensional stability at elevated temperatures. It is usually desired to have a negative draw as the film passes through the quenching rolls, so that the first roll is faster than the second roll. When the first roller goes faster than the second roller, the speed of the film decreases somewhat and the film is allowed to relax. The relative speeds of the rollers determine the relaxation of the film. The second speed of the quenching roller is preferably about 0.90 to 1.00 times the speed of the first quenching roller. However, excessive loosening will cause the micropores of the film to close. For example, if the second speed of the roller is about 0.85 to 0.89 times the speed of the tempering roller, then the micropores in the film will tend to close and reduce the breathability of the film. During the tempering stage, there will be a smaller increase in the thickness of the film due to the relaxation of this film. As previously explained, the dimensional stability of the film is only increased at the temperature at which the film is tempered. Therefore, it is necessary to balance the tempering temperatures against the softening point of the film formulation and the expected end-use temperatures of the film. The surface temperature of the quenching rolls should not be higher than the softening temperature of the film, when it begins to stick to the quenching rolls. In addition, the tempering temperature is preferably greater than the temperatures that the film undergoes or in the subsequent conversion steps (application of hot gum to secure the film apart from a disposable product) or in situations experienced by the film or the disposable product (high temperatures, when transported or stored). In most modalities, the film is tempered at about 82 to 93SC. The film is in contact with the quenching rollers for a prolonged period to allow the film to be heated sufficiently. It is important to heat the film to a desired temperature before the film relaxes between the rollers. In preferred embodiments, the residence time in each tempering roller is less than about 1 second. Tempering relieves tensions in the film, hardens the film, prevents the film from shrinking and prevents the closing of the micropores of the film. The tempered film can be reheated and enhanced without loss of any desired moisture vapor transmission regime, dimensional stability or elongation properties. If a film is oriented using an orientation process of interengaged gears and is enhanced without a tempering step, the micropores will be closed and the breathability of the film will be damaged. In certain embodiments, the film of the present invention can be enhanced. The embossing step provides the desired texture to the microporous oriented and tempered film. The texturing provided by the embossing stage improves aesthetics and provides other physical advantages to the film. A particularly useful advantage is that the embossing of the film reduces the contact surface area between any pressure sensitive adhesive and the microporous film, so that less detachment force is needed to remove the adhesive strip from the film or pull the film from an article, to which it joins. Figure 1 is a schematic illustration of a system used to produce a microporous film of soft, dimensionally stable texture. In the embodiment shown in Figure 1, a film formulation with high filler content is extruded from a die 10 as a blown pipe 12. However, it should be understood that other embodiments of a molding extrusion method can be used for form a movie Various methods for forming blown and / or molding films can be practiced in the present invention. For ease of illustration, only the blown film method is shown in Figure 1. The pipe 12 is crushed by passing it through a set of squeezing rollers 14. The pipe 12 passes through a grooving apparatus 30 that divides the pipeline. 12 in two separate layers of film 16 and 18. The two layers, 16 and 18, are oriented biaxially by passing them through a first set of intergrander gear rollers 20, which stretch the film in the transverse direction, the two layers, 16 and 18, then pass through a second set 24 of interengaging gear rollers, which stretch the two layers in the machine direction. In other embodiments, it is considered that the layers can be oriented uniaxially by passing the pipe through the inter-gearing gears in the machine direction or the inter-gearing gears in the transverse direction.

In the embodiment shown, the two film layers, 16 and 18, are separated after being oriented. The film 18 passes through a set of hardening rollers 40 and is at an approximate temperature of 82 to 93se. The tempered film 18 passes adjacent to a heating element 50, which reheats the tempered film 18 to a temperature of about 82 to 932C. The superheated tempered film 18 can pass through a set of embossing rollers 60, which supplies the tempered film 18 with an embossing pattern, which gives softness and texture to the film 18. It is also within the scope of the invention. present invention that the film 18 can pass from the quenching rolls 40 and pass through the embossing rolls without being subjected to further heat. It is desirable that the film be at a temperature below the melting temperature, but above the softening temperature of the film formulation, when this film is enhanced. In the embodiment shown, the enhanced film 18 passes through a corona treatment element 70, which applies a high voltage to the surface of the film 18. However, it will be understood that the film 18 can be treated with the corona . This film 18 passes through reels 80 and is wound onto a roller 82. In the embodiment shown in Figure 1, the film 16 also passes through a hardening element 140, a reheating element 150, embossing element 160, element 170 of corona treatment, and will be rolled onto a roller 180, in the manner described for the above film 18. It is also within the considered scope of the present invention that the layers of the film, 16 and 18, can be oriented separately. In the embodiment shown in outline in Figure 1, the pipe 12 passes through the router apparatus 30, which divides the pipe into two separate layers of film, 16 'and 18. The film 16' is oriented biaxially by passing through a first set of interrengaging gear rollers 120, which stretch the film in the transverse direction. The film 16 'then passes through a second set 124 of intergrander gear rollers, which stretch the film 16' in the machine direction. The film 16 'then passes through the hardening rollers 140, the heating element 150 and the embossing rollers 180, as described above. The invention is further described in the following examples, although it should be understood that these examples are for purposes of illustration and are not intended to limit the scope of the invention.

EXAMPLE 1 The relationship between the moisture vapor transmission rate and the various formulations of the film in the present invention was evaluated. The balance between the high density polyethylene component and the linear low density polyethylene component in the film affects the transmission of moisture vapor in the microporous films that have been formed by the use of intergrander gear rollers to stretch the film in the direction of the machine. The following formulation was used in this example: 50% by weight of calcium carbonate, X% by weight of high density polyethylene, 46-x% by weight of linear low density polyethylene, 2% by weight of white concentrate in the Low density polyethylene and 2% by weight of a fluorocarbon process aid in low density polyethylene, All films were produced with a thickness of 38 microns and were oriented in the machine direction using intergrain gears to a depth coupling of 1270 microns. The results of the moisture vapor transmission regime for these formulations is shown in Table 1 below. The breathability test results, MVTR, in Table 1 were determined using ASTM E96-93 at 382C and 75% relative humidity, using a sample cup that has an open area of about 12.89 cm2.

TABLE 1 Microporous LLDPE / HDPE Mixtures EXAMPLE 2 Samples of films of various formulations were tested to measure the performance of "rubber burning through the film". This "burning of rubber through the film" means that the film develops holes or melts in the area that the rubber makes contact during the subsequent conversion. Burning rubber is an unacceptable feature in the films used for disposable items. The results of the rubber burn are presented on a scale from 0 to 3, with 0 being unburned and 3 being a massive burn. They were measured by the observations of an operator conducting the test. The data shown in the following Table 2 show the results of the burning of rubber through the film.

TABLE 2 EXAMPLE 3 The relationship between the amount of filler content in the film formulation and the moisture vapor transmission rate was evaluated. Figure 2 shows the results of the moisture vapor transmission rate of the films oriented in the machine direction, comprising x% by weight of the calcium carbonate filler, 86-X% by weight of the linear low density polyethylene, 10% by weight of the high density polyethylene, 2% by weight of the white concentrate in the low density polyethylene and 2% by weight of the fluorocarbon process aid in the low density polyethylene. This formulation was used to produce a 38 micron thick film, which was oriented in the machine direction using intergrander gear rollers at a coupling depth of 1270 microns. There is a significant increase in the moisture vapor transmission rate as the fill percentage approaches 50%. In preferred embodiments, the filler content ranges from about 45 to 60%. The most preferred amount of filler is about 50-54%. The moisture vapor transmission rate no longer increases exponentially when the percentage of calcium carbonate increases beyond about 54-55%.

EXAMPLE 4 The effects of tempering on the physical properties of the microporous oriented interengaging gear film were evaluated. The tempering of. The films reduce the tendency of microporous films to exhibit a shrinkage without reducing the breathability. Tests were conducted using a film containing 50% by weight of filler, 34.06% by weight of LLDPE, 12% by weight of HDPE, 1% by weight of LDPE, 2% by weight of concentrate of titanium oxide, and 0.04% by weight of a fluoropolymer concentrate processing aid. The depths of the transverse direction and the direction of the coupling machine in the intergrander gear rollers were kept constant at 508 and 1270 microns, respectively. The quenching rollers were maintained at a constant temperature of 82se. The speed of the rollers was measured in two levels, 13 and 35 meters per minute. Control films were produced by passing the films through the unhardened intermeshing gear rollers. The tempered films were passed through the quenching rolls having a negative draw, in order to minimize the band tension and allow the molecular loosening to occur. Shrinkage tests were conducted at 7isc, without restriction for five (5) minutes. The following Table 3 shows the percentage of shrinkage, which is from about% to% that of the non-tempered, controlled film, without reduction in breathability. The values of the MVTR in Table 3 were obtained using ASTM 96-93, as modified in Example 1.

TABLE 3 Physical Properties of Microporous Films EXAMPLE 5 The effect of the orientation of the intergrander gear roller of a pipe was evaluated rather than simple layers of the film. The pipeline was not blocked after the orientation of the interengranado and tempered gear. Rather, the pipe easily separated into simple layers. The orientation of the intergrander gear roller and the quenching of a blown pipe produced two equivalent layers of film.

EXAMPLE 6 The effect of embossing on a microporous oriented MD IMG tempered film was evaluated. A microporous MD IMG tempered film was reheated and enhanced using three embossing patterns. A precursor film of 35.56 microns was comprised of the following formulation: 54% by weight of CaCO3; 33.96% by weight of LLDPE; 10% by weight of HDPE; 0.67% by weight of LDPE; 1.33% by weight of titanium dioxide; and 0.04 wt% fluorocarbon. The films were extruded, stretched and tempered. The microporous MD IMG oriented microporous films were reheated and enhanced to a compression pressure of 66,075 kg / cm. The temperature of the pre-embossing roller was 88 seconds, the temperature of the engraving roller was 52 seconds and the temperature of the cooling roller was 35 ° C. for all samples. The line speed was 45.72 m / min for all samples. The three embossing patterns, a macro-hexagonal (Mac) pattern, large diamond and small diamond, were enhanced in a MD IMG oriented microporous film, without significantly changing the values of the MVTR or heat shrinkage, as shown in next Table 4. The texture level can be correlated with the differences in the low load thickness, before and after embossing. As shown in Table 4, the enhancement increased the texture present after the IMG orientation. The MVTR values in Table 4 were obtained using ASTM 96-93, as modified in Example 1.

TABLE 4 EXAMPLE 7 The following Table 5 shows a comparison of the film of the present invention to other films currently used as backsheets of diapers. The key physical properties of breathable films for use in posterior sheets of diapers are: breathability (MVTR), residual elongation, dimensional stability at elevated temperatures during conversion and during transport, impact resistance in use, and texture. The values of the MVTR in Table 5 were obtained using the ASTM 96-93 standard, as modified in Example 1. The following examples were tested. Comparative Sample 1 is a HTS-5 film sold by Tredegar Industries, a previously used diaper backsheet film. Comparative Sample 2 is a CPC 2 film sold by Tredegar Industries as a diaper backsheet film, currently used. Comparative Sample 3, Exxon® Exxaire is a breathable film, commercially available, Example A is an IMG-oriented non-tempered breathable film. Examples B-1 and B-2 are IMG oriented tempered respirable films. Example C is a breathable tempered and embossed film, oriented IMG. Examples A, B-1, B-2 and C comprise: 55% by weight of CaCO 3; 31% by weight of LLDPE, 10% by weight of HDPE; 2% by weight of white concentrate and 2% by weight of fluorocarbon concentrate, Viton®. The film of the present invention has a preferred residual elongation of approximately 200% in the machine direction and approximately 300% in the transverse direction, as measured by the difference between the percent elongation at break and the per cent. Elastic elongation belt. While particular embodiments of the present invention have been illustrated and described, those skilled in the art will recognize that various changes and modifications can be made without departing from the spirit and scope of the invention. It is intended to cover in the appended claims, all these modifications that are within the scope of this invention.

TABLE 5 Physical Properties Data

Claims (28)

1. CLAIMS 1. A microporous film, soft, textured, dimensionally stable at elevated temperatures, oriented by interengaged gears, comprising approximately 45 to 65% by weight of a filler; about 25 to 55% by weight of a linear low density polyethylene; about 0 to 20% by weight of a high density polyethylene or other heat resistant polymer; about 0 to 5% by weight of a low density polyethylene; about 0 to 10% by weight of a pigmenting agent; and about 0 to 3% by weight of an auxiliary of the process.
2. 2. The film of claim 1, wherein this film has a moisture vapor transmission rate of at least about 500 g / m2-day.
3. 3. The film of claim 1, wherein this film has a shrinkage percentage of less than about 15%, after being exposed to a temperature of 76.6SC for 30 minutes.
4. 4. The film of claim 1, wherein this film has a residual elongation greater than about 75% in the machine direction and greater than about 300% in the transverse direction, as measured by the difference between the percentage of the elongation at the rupture and the percentage of elastic elongation.
5. 5. The film of claim 1, wherein this film has a residual elongation of greater than about 150% in the machine direction and greater than about 400% in the transverse direction, as measured by the difference between the percentage of elongation at the rupture and the percentage of elastic elongation.
6. 6. The film of claim 1, wherein the filler comprises calcium carbonate.
7. 7. The film of claim 6, wherein the filling of. Calcium carbonate is coated, at least partially, with stearic acid or another stearate compound.
8. 8. The film of claim 7, wherein the formulation comprises: about 50 to 56% by weight of the calcium carbonate filler; about 30 to 35% by weight of the linear low density polyethylene; about 10 to 12% by weight of the high density polyethylene, or a heat resistant polymer; about 0 to 5% by weight of the low density polyethylene; about 9 to 2% by weight of titanium dioxide; and approximately 0. to 0.05% by weight of the process aid that includes a fluorocarbon.
9. 9. The film of claim 8, wherein the formulation comprises approximately 53 to 56% by weight of calcium carbonate.
10. 10. The film of claim 9, wherein the calcium carbonate has an average size of about 0.5 to 5 microns.
11. 11. A microporous, soft, textured, dimensionally stable film at elevated temperatures, oriented by interengaged gears, comprising: about 50% by weight of the calcium carbonate filler; about 35% by weight of the LLDPE; about 12% by weight of the HDPE; about 1% by weight of the LDPE; about 2% by weight of the titanium dioxide and about 0.04% by weight of the process aid including a fluorocarbon.
12. 12. A microporous, soft, textured, dimensionally stable film at elevated temperatures, oriented by interengaged gears, comprising: about 56% by weight of the calcium carbonate filler; about 30% by weight of the LLDPE; about 10% by weight of the HDPE; approximately 0.67% by weight of LDPE; about 1.33% by weight of the titanium dioxide and about 0.04% by weight of the process aid including a fluorocarbon.
13. 13. A method for forming a microporous, soft, textured, dimensionally stable film at elevated temperatures, having a formulation comprising: about 45 to 65% by weight of a filler; approximately 25 to 55% by weight of a linear low density polyethylene; about 0 to 20% by weight of a high density polyethylene, or other heat resistant polymer; about 0 to 5% by weight of a low density polyethylene; about 0 to 10% by weight of a pigmenting agent; and about 0 to 3% by weight, of a process aid including a fluorocarbon, this method comprises: extruding the formulation as a film; introducing the film into at least one set of interengaged gear rollers, to orient this film; and pass the film oriented through a tempering element, to temper this film.
14. 14. The method of claim 13, further comprising reheating the tempered film and enhancing this superheated film by passing it through the tightening space of the embossing rolls, to impart an embossed pattern on the film.
15. 15. The method of claim 13, wherein the embossed film is subjected to a corona discharge treatment.
16. 16. The method of claim 13, wherein the film is extruded using a molding extrusion method.
17. 17. The method of claim 13, wherein the film is extruded using a blown film method.
18. 18. The method of claim 17, wherein the film is extruded as a bubble and the method includes crushing the bubble to form a two-layer pipe and orienting both layers of the pipe together.
19. 19. The method of claim 17, wherein the film is extruded as a bubble and the method includes crushing the bubble to form a two-layer pipe and separating the pipe in a first film layer and a second film layer, and orienting each layer separately.
20. 20. The method of claim 13, wherein the set of interengaged gear rollers orients the film in the machine direction.
21. 21. The method of claim 20, further including a second set of intermeshing gear rollers which orientates the film in the transverse direction.
22. 22. The method of claim 13, wherein the set of interengaged gear rollers > Orient the film in the transverse direction.
23. 23. The method of claim 13, wherein the film is stretched by about 5% to 100% in the machine direction and / or the transverse direction.
24. 24. The method of claim 13, wherein ? the film is stretched by approximately 15% to 60% in the machine direction and / or the transverse direction.
25. 25. The method of claim 13, wherein the inter-geared gears, which orient the film, have a plurality of interengaging teeth, spaced by a distance or pitch of about 760 to 5080 microns, and a plurality of interengaged teeth having a coupling depth of about 127 to 5080 microns.
26. 26. The method of claim 25, wherein the pitch varies from about 1270 to 2540 microns and the depth of coupling varies from about 508 to 1905 microns.
27. 27. A method for forming a microporous, soft, textured, dimensionally stable film at elevated temperatures, having a formulation comprising: about 50% by weight of calcium carbonate; about 35% by weight of a linear low density polyethylene, about 12% by weight of a high density polyethylene; about 1% by weight of a low density polyethylene; about 2% by weight of titanium dioxide; and about 0.04% by weight of a process aid that includes a fluorocarbon, this method comprises: extruding the formulation as a film; introducing the film into at least one set of intergrander gear rollers, to orient the film; passing the oriented film through a tempering element, to temper the film; reheat the tempered film; and enhancing the overheated film by passing it through the tightening space of the embossing rolls to impart an embossing pattern on the film.
28. 28. A method for forming a microporous, soft, textured, dimensionally stable film at elevated temperatures, having a formulation comprising: about 56% by weight of calcium carbonate; about 30% by weight of a linear low density polyethylene, about 10% by weight of a high density polyethylene; about 0.67% by weight of a low density polyethylene; approximately 1.33% by weight of titanium dioxide; and about 0.04% by weight of a process aid that includes a fluorocarbon, this method comprises: extruding the formulation as a film; introducing the film into at least one set of intergrander gear rollers, to orient the film; passing the oriented film through a tempering element, to temper the film; reheat the tempered film; and enhancing the overheated film by passing it through the tightening space of the embossing rolls to impart an embossing pattern on the film.