MXPA01007846A - Microfibers and method of making - Google Patents

Abstract

Microfibers and microfibrillated articles are provided by imparting fluid energy to a surface of a highly oriented, highly crystalline, melt-processed polymeric film. The microfibers and microfibrillated articles are useful as tape backings, filters, thermal and acoustical insulation and as reinforcement fibers for polymers or cast building materials such as concrete.

Description

MICROFIBRAS AND METHOD OF MANUFACTURE OF THE SAME Field of the Invention The present invention relates to microfibers processed from a melt, high modulus, high strength, films having a microfibrillated surface and methods for making them. The microfibers of the invention can be prepared by transmitting fluid energy, typically in the form of ultrasound or high pressure water jets, to a film processed from a highly crystalline, highly crystallized melt to release microfibers from the same The microfibrillated films of the invention find use as backings of tapes, filters, fibrous mats and thermal and acoustic insulation. The microfibers of the invention, when removed from the film matrix, find use as reinforcing fibers for molded polymers or building materials. such as concrete.

BACKGROUND OF THE INVENTION Polymeric fibers have been known essentially from the beginning of the development of commercial polymers. The production of polymer fibers of polymer films is also well known. In REF: 132001 in particular, the ease with which films produce fibers (ie, fibrillated) can be correlated to the degree of molecular orientation of the polymer fibrils that form the film. The orientation of crystalline and polymeric films and fibers has been realized in numerous forms, including melt spinning, (co) extrusion of melt transformation, coextrusion in the solid state, gel stretching, solid state coiling, stretching with nozzle, stretched in solid state, and roller-trusion, among others. Each of these methods has been successful in preparing high-modulus, oriented polymer and fiber films. Most solid-state processing methods have been limited to slow production speeds, in the order of a few cm / min. Methods involving gel stretching can be quick, but require additional steps of solvent handling. A combination of winding and stretching of solid polymer sheets, particularly polyolefin sheets, in which a piece of polymer is biaxially deformed in a two-roll calender has been described, is then stretched further along (that is, the address of the machine). Methods that relate to other tissue handling equipment have been used to achieve molecular orientation, including an initial clamping or a calendering step followed by stretching in both the machine direction or transversely to the length of the film . The release of the fibers of high modulus, oriented polymer films, particularly of high molecular weight crystalline films, has been carried out in numerous ways, including abrasion, mechanical stripping by rapidly rotating circular wire brushes, jet collision water to crumble or cut the film, and application of ultrasonic energy. The water jets have been used extensively to cut the films into longitudinal, continuous, wide, flat fibers for binding or reinforcement purposes. It has been shown that the ultrasonic treatment of a volume oriented polyethylene film (that is, a film roll immersed in a fluid, subjected to ultrasonic treatment for a period of hours) produces small amounts of microfibrils.

Brief Description of the Invention The present invention is directed to novel polymeric microfibers processed from a melt, highly oriented, having an average, effective diameter of less than 20 microns, generally from i. "0.01 micras at 10 microns, and substantially rectangular in cross section, having a transverse dimensional relationship (width to thickness) of 1.5: 1 to 20: 1, and generally about 3: 1 to 9: 1. Since the microfibers are substantially rectangular, the effective diameter is a measure of the average value of the width and thickness of the microfibers. The rectangular cross-section advantageously provides a larger surface area (relative to fibers of the same diameter having a round or square cross section) making the microfibers (and microfibrillated films) especially useful in applications such as filtration and as reinforcing fibers in molded materials. The surface area is generally greater than about 0.25 m2 / cm, typically around 0.5 to 30 m2 / g. In addition, due to their highly oriented morphology, the microfibers of the present invention have a very high modulus, for example, typically above 109 Pa for the polypropylene fibers, making them especially useful as reinforcing fibers in a thermosetting resin and the concrete. present invention is further directed towards the preparation of highly oriented films having a microfibrillated surface by the steps of providing a semi-crystalline, highly oriented polymer film, stretching the film to give a surface with micro-gaps the same, then microfibrillating the surface with micro-lagoons to the transmit enough fluid energy to it. Optionally, the microfibers can be collected from the microfibrillated surface of the film. Advantageously, the process of the invention is capable of high production speeds, is suitable as an industrial process and uses readily available polymers. The microfibers and microfibrillated articles of this invention, which have an extremely small fiber diameter and both high strength and high modulus, are useful as tape backings, tie materials, films with unique optical properties and a high surface area, low reinforcements. density for thermosetting products, impact modifiers or prevention of the propagation of fissures in matrices such as concrete, and as fibrillar forms (dental floss and nonwovens, for example).

Brief Description of the Figures Figure 1 is a digital image of an electron micrograph for a thorough examination of the microfibers of Example 1 at an extension of 1000 X. _? ii_l_á_í_i_.

Figure 2 is a digital image of an electron micrograph for a detailed examination of the microfibers of Example 1 at an enlargement of 3000 X Figure 3 is a digital image of a confocal light micrograph of a cross section of the microlabeled film of Sample 2-7 at an enlargement of 3000 X. Figure 4 is a histogram of average fiber axis diameter effective of the microfibers of Example 1. Figure 5 is a schematic diagram of the process of the invention. Figure 6 is a digital image of an atomic force micrograph (derivation mode) of a microfiber of the invention Detailed Description Polymers useful in the present invention include any crystalline, semicrystalline or crystallizable polymer that can be manufactured from a melt. Semicrystalline polymers consist of a mixture of amorphous regions and crystalline regions. The crystalline regions are more ordered and the segments of the chains are actually packed in crystalline lattices. Some crystalline regions can be more ordered than others. If the crystalline regions are heated above -tl-tt --- «fl-l-Íirf! É _ÍÍÍÍ the temperature of fusion of the polymer, the molecules become less ordered or more random. If they cool quickly, this less ordered feature "freezes" instead and the resulting polymer is said to be amorphous. If cooled slowly, these molecules can be packaged again to form crystalline regions and the polymer is said to be semi-crystalline. Some polymers are always amorphous and show no tendency to crystallize. Some polymers can be made semicrystalline by thermal treatments, elongation or orientation and by solvent, and these processes can control the true degree of crystallinity. Many semicrystalline polymers produce spherulites in crystallization, initiating nucleation through various stages of crystal growth. Spherulites are birefringent, usually spherical structures that are generally observed by optical techniques such as optical polarization microscopy. Spherulites are not individual crystals, preferably these are aggregates of smaller crystalline units called crystallites. The crystallites vary in diameter, depending on the polymers and processing conditions, from 10"5 to 10" m. The lower limit for the size of the spherulites has been estimated to be approximately 10 ~ 6 m according to the microscopy studies, but the upper limit is restricted by the number of nucleation sites in the crystallization of the polymer. The spherulites result from the radial growth of fibrillar subunits, the individual fibrils or bundles of fibrils that constitute the basic unit for the spherulites. The fibrils themselves are of submicroscopic dimensions and often only visible by the electron microscope. However, if the subunits are of sufficient size, they can be observed microscopically. These fibrils of larger dimensions are generally composed of microfibrillar bundles, which in turn are composed of crystallite subunits. The observations suggest that the fibrillar growth of the spherulites occurs radially from the nucleation site and that the individual molecules are oriented perpendicular to the radii (see, for example, LH Sperling, Introduction to Physical Polymer Science, John Wiley and Sons, NY, NY 1986). The perpendicular orientation of the polymer chains with respect to the fibrillar axis is a consequence of chain folding, which leads to the tangential orientation of the molecules in spherulites, since the fibrils grow radially from the nucleation site.

The terms "amorphous", "crystalline", "semicrystalline" and "orientation" are commonly used in the description of polymeric materials. The true amorphous state is considered to be a randomly entangled mass of polymer chains. The X-ray diffraction pattern of an amorphous polymer is ur. diffuse halo indicative of the non-regularity of the polymer structure. Amorphous polymers exhibit softening behavior at the transition temperature of the vitreous state, but no true fusion or first order transition. The semicrystalline state of the polymers is one in which the long segments of the polymer chains appear in both amorphous and crystalline states or phases. The crystalline phase comprises multiple lattices e :? which the polymer chain assumes a conformation of bent chains (lamellae) in which there is a highly ordered register in adjacent folds of the various chemical portions of which the chain is constructed. The ordering of packaging (short order orientation) within the reticle is highly regular in both its chemical and geometric aspects. The semicrystalline polymers show characteristic melting points, above which the crystal lattices become disordered and quickly lose their identity. Either the concentric rings or a symmetric arrangement of spots, which are indicative of the nature of the crystalline order, generally distinguish the X-ray diffraction pattern of semi-crystalline polymers (or copolymers). Semi-crystalline polymers useful in the present invention include, but are not limited to, polyethylene, polypropylene, polyoxymethylene, poly (vinylidine fluoride), poly (methyl pentene), poly (ethylene-chlorotrifluoroethylene), poly (vinyl fluoride), poly (ethylene oxide), poly (ethylene terephthalate), poly (butylene terephthalate), nylon 6, nylon 66, high and low density polybutene and thermotropic liquid crystal polymers. Examples of suitable thermotropic liquid crystal polymers include aromatic polyesters which exhibit liquid crystal properties when melted and which are synthesized from aromatic diols, aromatic carboxylic acids, hydroxycarboxylic acids and other similar monomers. Typical examples include a first type consisting of parahydroxybenzoic acid (PHB), terephthalic acid and bifenc, a second type consisting of PHB and 2,6-hydroxynaphthoic acid and a third type consisting of PHB, terephthalic acid and ethylene glycol. Preferred polymers are polyolefins such as polypropylene and polyethylene which are readily available at low cost and can provide highly desirable properties in microfibrillated articles such as high modulus and high tensile strength. The molecular weight of the polymer should be selected so that the polymer is processable from a melt under the processing conditions. For polypropylene and polyethylene, for example, the molecular weight may be from about 5000 to 500,000 and is preferably from about 100,000 to 300,000. Organic polymers typically comprise long molecular chains that have a backbone of carbon atoms. The theoretical strength of the polymers and the ease with which the surface of a polymer film can be microfibrillated are often not realized due to the random orientation and entanglement of the polymer chains. In order to obtain the maximum physical properties and render the polymer film operable for fibrillation, the polymer chains need to be oriented substantially parallel to each other and partially unraveled. The degree of molecular orientation is generally defined by the stretch ratio, that is, the ratio of the final length to the original length. This orientation can be effected by a combination of techniques in the present invention, including the steps of calendering and longitudinal orientation. Films are generally defined, for example, by Modern Plastics Encyclopedia, as thin in relation to width and length, and having a nominal thickness of no more than about 0.25 mm. Thicker materials are generally defined as sheets. As used herein, the term "film" will also encompass the sheets and it may also be understood that other configurations and profiles such as tubes may be provided with a microfibrillated surface with equal ease using the process of this invention. In the present invention, a processed film is provided from a highly oriented, semicrystalline melt having an induced crystallinity. The induced crystallinity is the maximized crystallinity that can be obtained by an optimal combination of molding and subsequent processing such as calendering, annealing, elongation and recrystallization. For polypropylene, for example, the crystallinity is above 60%, preferably above 70%, more preferably above 75%. The crystallinity can be measured by differential scanning calorimetry (DSC) and the comparison with extrapolated values for 100% crystalline polymers. For example, see B. Wunderlich, Thermal Analysis, Academic Press, Boston, MA, 1990. Generally, the crystallinity of commercially available molded films must be increased to be useful in the process of the invention. Molded films, such as those prepared by extrusion of a melt followed by quenching in a cooled molding cylinder, exhibit a "spontaneous crystallinity" that results from the conventional processing conditions. For example, molded isotactic polypropylene films typically exhibit crystallinity of 59-61% by DSC analysis. When such a polypropylene film is used in the process of the invention, it is desirable to increase the crystallinity at least 20% above this "spontaneous crystallinity" value, to about 72% or higher. It is believed that maximizing the crystallinity of the film will increase the microfibrillation efficiency. Any suitable combination of the processing conditions can be used to give maximum induced crystallinity and orientation to the processed film from a melt. These can include any combination of molding, tempering, annealing, calendering, orientation, stretch in state solid, roller-trusion and the like. This processing also generally serves to increase the degree of crystallinity of the polymeric film as well as the size and number of the spherulites. The suitability of a film for the subsequent process steps can be determined by measuring the degree of crystallinity of the polymer film by, for example, X-ray diffraction or differential scanning calorimetry (DSC). The highly oriented polymeric films, suitable for subsequent processing to give a micro-pool morphology, are known and / or commercially available. These have been described, for example, by Nippon Oil, Tokyo; Polteco, CA; Cady Industries Inc. Memphis TN; and Signode Packaging Systems, Glenview IL. Micro-lagoons are microscopic pools in the film, or on the surface of the film, which occur when the film is unable to undergo the imposed deformation process. By "unable to submit" it is implied that the film is unable to relax sufficiently to reduce the stress caused by the imposed deformation. The highly crystalline, highly oriented polymeric films are elongated under plastic flow conditions that exceed the capacity of the polymer to undergo the imposed deformation, to give due to that a micro-lagoon morphology thereto. In conventional film orientation processes, such excessive stresses are avoided since they lead to weakening in the film and can result in a break during orientation. During a step of the orientation process of the present invention, small tears or tears occur (microlagunas) when the deformation stress due to the orientation exceeds the unraveling speed of the polymer molecules. See, for example, Roger S. Porter and Li-Hui Wang, Journal of Macromolecular Science-King Macromol Chem. Phys. C35 (l), 63-115 (1995). Depending on how the film is processed to induce crystallinity and how the film is oriented, one or both surfaces may have a significant micro-lacquer content, in addition to the significant micro-lacquer content in the film volume.

When the film is oriented by elongation in the machine direction, the micro-gaps are typically distributed across the x, y and z axes of the film, generally beyond the boundaries of the fibrils, and appear as microscopic defects or fissures. The microlagunas are of relatively flat form, of irregular size and lack of different limits.

The micro-gaps on the surface of the film are generally transverse to the direction of the machine (direction of orientation) of the film, while those in the film matrix are generally in the plane of the film, or perpendicular to the plane of the film. film with main axes in the machine direction (direction of orientation). The size, distribution and quantity of the micro-lagoons in the film matrix can be determined by techniques such as small-angle X-ray scattering (SAXS), confocal microscopy or density measurement. Additionally, visual inspection of a film may reveal increased opacity or a silvery appearance due to the significant micro pond content. Generally, the higher the microlaguna content, the greater the performance of the microfibers by the process of this invention. Preferably, when preparing an article having at least one microfibrillated surface, at least one major surface of the polymeric film must have a microlaguna content in excess of 5%, preferably in excess of 10%, when measured by density; that is, the ratio of the density of the film with micro-lagoons to that of the starting film. Films with microlagunas useful in the present invention can be distinguished from other films or articles with gaps, such as microporous films or cellular or cellular articles in which the micro-gaps are generally non-cellular, relatively flat and have principal axes in the machine direction (direction of orientation) of the film. The micro-lagoons do not interconnect generally, but they can intercept the adjacent micro-lagoons. In practice, the films can be first subjected to one or more processing steps to give the desired degree of crystallinity and orientation, and can be further processed to give the micro-gaps, or the micro-gaps can be given coinciding with the (the) step (s) of the process that give crystallinity. In this way, the same calendering or stretching steps that orient the polymer film and increase the crystallinity (and orientation) of the polymer can concurrently give the micro-lagoons. In one embodiment of the present invention, the polymer is extruded from a melt through a nozzle in the form of a film or sheet and is tempered to maximize the crystallinity of the film by retarding or minimizing the rate of cooling. As the polymer cools from the melt, it begins to crystallize and spherulites are formed at p > Artir of the development of crystallites. If it rapidly cools from a temperature above its melting point to a temperature well below the crystallization temperature, a structure comprising crystallites surrounded by large amorphous regions is produced, and the size of the spherulites is minimized. In one embodiment, the film is tempered in a heated molding cylinder that is maintained at a temperature above the glass transition temperature, but below the melting temperature. Normally, polypropylene, for example, is cold tempered at approximately 24 ° C (75 ° F) - but in the present process, for example, hot tempering of a melt is used at approximately 220 ° C (450 ° F) at an annealing temperature of approximately 82 ° C (180 ° F). This higher tempering temperature allows the film to cool slowly and the crystallinity of the film to increase due to annealing. Preferably, tempering occurs at a rate to not only maximize the crystallinity, but to maximize the size of the crystalline spherulites. The effect of the molding temperature and the cooling rate on the crystallinity is known and can be referred to S. Piccarolo et al., Journal of Applied Polymer Science, vol. 46, 625-634 (1992) * "-" - * - * »- '* Alternatively to molding in a hot molding cylinder, the film can be tempered in air or in a fluid such as water, which can be heated, to allow the film to be Cool more slowly and allow the crystallinity and size of the spherulites to be maximized. The tempering with air or water can ensure the uniformity of the crystallinity and the content of spherulites through the thickness of the film. Depending on the thickness of the extruded article and the temperature of the molding roll, the morphology of the polymer may not be the same across the thickness of the article, that is, the morphology of the two surfaces may be different. The surface in contact with the hot molding cylinder can be substantially crystalline, while the remote surface of the molding cylinder can have a similar morphology due to exposure to ambient air where the heat transfer is less efficient. Small differences in morphology do not normally prevent the formation of a microfibrillated surface on any major surface on the film, but if microfibrillated surfaces are desired on both surfaces of the article, it is preferred that the temperature of the molding wheel be carefully controlled for ensure uniform crystallinity through the thickness of the article.

Alternatively, when casting on a hot molding wheel, the film can be rapidly tempered at a temperature below the crystallization temperature and the crystallinity can be increased by stress-induced crystallization. example, by stretching a stretch ratio of at least 2.1. The stretching tension must be sufficient to produce the alignment of the molecules and the deformation of the spherulites when inducing the plastic deformation required above that produced by the flow stretching. After molding (and stretching, if any), the polymer can be characterized by a relatively high crystallinity and the formation of the signifying spherulites. The size and number of the spherulites is dependent on the molding conditions. The degree of crystallinity and the presence of spherulite structures can be verified by, for example, X-ray diffraction and electron microscopy. The thickness of the film will be selected according to the desired end use and can be achieved mechanically by controlling the process conditions. Molded films will typically have thicknesses of less than 2.5 mm (100 mils), and preferably between 0.8 to 1.8 mm (30 and 70 mils). However, depending on the characteristics desired for the resulting article, these can be molded in thicknesses outside this range, In a preferred embodiment, the molded film is calendered after annealing. Calendering allows a higher molecular orientation to be achieved by making possible subsequent, higher stretch ratios. In the absence of a calendering step, the subsequent stretch ratios in the orientation step above the natural stretch ratio (7: 1 for polypropylene) are not generally achieved without the risk of rupture. Calendering at the appropriate temperature can reduce the average size of the crystallites through the cutting and splitting of the entanglements, and can impose a dimensional relationship on the spherulites (ie, flattening in the transverse direction and lengthening in the direction of the machine ). The calendering is preferably carried out at or above the alpha crystallization temperature. The crystallization temperature alpha, Tac, corresponds to the temperature at which the crystallite subunits are capable of being moved within the largest laminar crystal unit. Above this temperature, a laminar crack can occur, and extended chain crystals form, with the effect that the degree of crystallinity increases as the amorphous regions of the polymer are stretched in the laminar crystal structure. The calendering step has the effect of orienting the fibrils within the plane of the film of the radially oriented, original sphere. The crystallites are divided due to the cutting forces, which can be verified by wide-angle X-rays. In this way, the individual fibrils without greatly radial nucleation site, but are in the same plane. After calendering, the article is then oriented in the machine direction by stretching under plastic flow conditions, which are insufficient to cause a catastrophic failure of the film (i.e., in excess of the polymer's ability to undergo the deformation). By using polypropylene, for example, the films can be stretched at least 5 times their length. In a preferred embodiment, when considering the steps of both calendering and orientation, the combined draw ratio is at least 10: 1 and preferably in the range of 10: 1 to about 40: 1 for the polypropylene. The orientation step (stretching) is preferably done immediately after the calendering step, that is, the calendered film is fed directly from the contact line between the rollers of the calender to the longitudinal orientation equipment. A minimum opening between the line of contact between rollers of the calender to the first longitudinal orientation roller minimizes cooling and prevents folding of the film. The tension of the longitudinal orientation machine is maintained so that essentially no relaxation occurs during the orientation step and the orientation imparted during calendering is maintained. Preferably, the longitudinal orientation apparatus comprises a plurality of orientation rollers, whose relative speeds are controlled to give a stretch or gradual orientation to the film. In addition, the temperature of the plurality of rollers can be controlled to provide a gradual decrease in temperature to the oriented film and thereby minimize orientation. The elongation conditions are selected to give the micro-gaps (in excess of 5% as measured by the change in density) to the surface of the film. Generally, the elongation conditions can be selected such that, under plastic flow (at a given minimum temperature and a maximum stretch ratio), the temperature is reduced by approximately 10 ° C or more. the imposed deformation increases approximately 10% (stretched approximately 10 additional) to induce the micro-lagoons. Also, the _a__tt_ta_ The temperature can be lowered and the stretch ratio increased at the same time, since conditions are selected to exceed the ability of the polymer to undergo the imposed deformation and avoid a catastrophic failure of the film. Micro-gaps are small defects that occur when the film is stretched to a tension, under plastic flow conditions, that exceeds that in which the film is capable of undergoing the imposed stress, or at a speed that is faster than the speed of relaxation of the film (the speed of unraveling the chains of polymers). The occurrence of a significant amount of micro-lagoons will give an opalescent or silvery appearance to the surface of the film due to diffusion of light from the defects. In contrast, surfaces of the film that lack significant micro-lagoons have a transparent appearance. The presence of micro-lagoons can be verified by small angle X-rays or density measurement, or by microscope. The appearance can serve as an empirical test of the convenience of a film oriented for the production of a microfibrillated surface. It has been found that an oriented film lacking a significant amount of microlagur.as is not easily microfibrillated, although the film may be divided longitudinally, as is characteristic of highly oriented polymeric films having a fibrous morphology. In the orientation step, the individual fibrils of the spherulites are drawn substantially parallel to the direction of the machine (direction of orientation) of the film and in the plane of the film. The calendered, oriented fibrils can be visualized as having a rope-like appearance. See Figure 6. Through microscopy of confocal light, the microtome film reveals a microfibrous morphology in which microlagunas can be observed. See Figure 3. The final thickness of the film will be determined in part by the molding thickness, the calendering thickness and the degree of orientation. For most uses, the final thickness of the film prior to fibrillation. it will be 0.025 to 0.5 mm (1 to 20 mils), preferably 0.075 to 0.25 mm (3 to 10 mils). The highly crystalline, highly oriented film is then microfibrillated by giving sufficient fluid energy to the surface to release the microfibers from the polymer matrix. Optionally, prior to microfibrillation, the film can be subjected to a fibrillation step by a conventional mechanical means to produce macroscopic fibers of the highly oriented film. The conventional means of mechanical fibrillation utilizes a rotating cylinder or roller having cutting elements such as needles or teeth in contact with the moving film. The teeth can completely or partially penetrate the surface of the film to give a fibrillated surface thereto. Other similar macropofibrillation treatments are known and include mechanical actions such as torsion, brushing (as with a sawtooth cylinder), rubbing, for example with leather pads, and bending. The fibers obtained by such conventional fibrillation processes are macroscopic in size, generally several hundred microns in cross section. Such macroscopic fibers are useful in a number of products such as particulate filters, as oil absorption media, and as electrettes. The oriented film is microfibrillated by transmitting sufficient fluid energy thereto to give a microfibrillated surface, for example, by contacting at least one surface of the film with a high pressure fluid. In a microfibrillation process, relatively large amounts of energy are transmitted to the surface of the film to release the microfibres, in relation to that of a conventional mechanical fibrillation process. Microfibrils are several orders of magnitude smaller in diameter than fibers obtained by a mechanical means (such as with a sawtooth cylinder) that vary in size from less than 0.01 microns to 20 microns. In the present invention, microfibers can be obtained (using polypropylene for example) having a degree of crystallinity in excess of 75%, a modulus of tension in excess of ~ 7 GPa (one million psi). Surprisingly, the microfibres obtained in this manner are rectangular in cross section, having a transverse dimensional relationship (width transverse to the thickness) that varies from approximately 1.5: 1 to approximately 20: 1 as can be seen in Figures 1 and 2. In addition , the sides of the rectangular-shaped microfibers are not smooth, but have a serrated or scalloped appearance in the cross section. Atomic force microscopy reveals that the microfibers of the present invention are single or unitary fibril bundles, which together form the rectangular or ribbon-like microfibers. See Figure 6. In this way, the surface area exceeds that which can be expected from rectangular-shaped microfibers, and such a surface increases the bond in matrices such as concrete and thermoset plastics.

A method of microfibrillating the surface of the film is by means of fluid jets. In this process one or more jets of a stream of fine fluid impact the surface of the polymeric film, which can be supported by a wire drum or band in motion, thereby releasing the microfibers of the polymeric matrix. One or both surfaces of the film can be microfibrillated. The degree of microfibrillation is dependent on the exposure time of the film to the fluid jet, the pressure of the fluid jet, the cross-sectional area of the fluid jet, the contact angle of the fluid, the properties of the polymer and, to a lesser degree , the fluid temperature. Different types and sizes of wire drums can be used to support the film. Any type of liquid or gaseous fluid can be used. Liquid fluids may include water or organic solvents such as ethanol or methanol. Suitable gases such as nitrogen, air or carbon dioxide can be used, as well as mixtures of liquefies or gases. Any of these fluids is preferably non-bulking (ie, not absorbed by the polymer matrix), which reduces the orientation and degree of crystallinity of the microfibers. Preferably the fluid is water. The temperature of the fluid can be raised, although suitable results can be obtained by using fluids at room temperature. The fluid pressure must be sufficient to impart some degree of microfibrillation to at least a portion of the film, and suitable conditions may vary widely depending on the fluid, the nature of the polymer, including the composition and morphology, the configuration of the Fluid, the angle of impact and temperature. Typically, the fluid is water at room temperature and pressures of at least 3400 kPa (500 psi), although lower pressure and longer exposure times may be used. This fluid will generally impart a minimum of 5 watts or 10W / cm2 based on the calculations assuming incompressibility of the fluid, a smooth surface and without losses due to friction. The configuration of the fluid jets, ie the transverse shape, can be nominally round, but other shapes can be used as well. The jet or the jets may comprise a groove which passes through a section or which passes through the width of the film. The jet (s) can be stationary (s), while the film is transported relative to the jet (s), the jet (s) can be moved relative to a stationary film, or both the film and the jet can be moved relative to each other. For example, the film can be transported in the direction of the machine (longitudinal) by means of feed rollers while the jets move transverse to the fabric. Preferably, a plurality of jets is employed, while the film is transported through the fibrillation chamber by means of rollers, while the film is supported by a wire drum or thin canvas, which allows the fluid is drained from the microfibrillated surface. The film can be microfibrillated in a single pass, or alternatively the film can be microfibrillated using multiple passes beyond the jets. The jet (s) can be configured such that all or part of the surface of the film is microfibrillated. Alternatively, the jets can be configured so that only selected areas of the film are microfibrillated. Certain areas of the film can also be hidden, using conventional concealment agents to leave selected areas free of microfibrillation. In the same way, the process can be conducted so that the microfibrillated surface only partially penetrates, or completely through the thickness of the start film. If it is desired that the microfibrillated surface extends through the thickness of the film J the conditions can be selected such that the integrity of the article is maintained and the film is not separated into individual threads or fibers. A hydraulic entangling machine, for example, one or both surfaces can be used to microfibrilate on exposing the fibrous material to the fluid jets. Hydraulic entanglement machines are generally used to increase the volume of microfibers or yarns by using high-speed water jets to wind or knot the individual microfibers in a fabric bonding process, also referred to as jet lacing or spinning lashing. Alternatively, a jet of water under pressure can be used, with a vortex or oscillating head, which allows manual control of the collision of the fluid jet. The microfibrillation can be conducted by immersing the sample in a high-energy cavitation medium. One method to achieve this cavitation is by applying ultrasonic waves to the fluid. The speed of microfibrillation is dependent on the intensity of cavitation. Ultrasonic systems can vary from cleaning baths, low power ultrasonic baths, low acoustic amplitude, to focused low amplitude systems to high amplitude, high intensity sounding systems. A method which comprises the application of ultrasonic energy involves the use of a probe system in a liquid medium in which the fibrous film is immersed. The horn or horn (probe) must be submerged at least partially in the liquid. For a probe system, the fibrous film is exposed to ultrasonic vibration by placing it between the oscillating horn and a perforated metal or screen mesh (other methods of placement are also possible) in the middle. Advantageously, both main surfaces of the film are microfibrillated when ultrasound is used. The depth of microfibrillation in the fibrous material is dependent on the cavitation intensity, the amount of time that passes in the cavitation medium and the properties of the fibrous material. The intensity of the cavitation is a factor of many variables such as the amplitude applied and the frequency of the vibration, the liquid properties, temperature of the fluid and applied pressure and location in the cavitation medium. The intensity (energy per unit area) is typically the highest below the horn, but this can be affected by the focus of the sonic waves.

The method comprises placing the film between the ultrasonic horn or horn and a film support in a cavitation medium (typically water) maintained in a tank. The support serves to restrict the movement of the film away from the speaker due to the extreme cavitation that takes place in this region. The film can be supported by various means, such as a screen mesh, a rotary device that can be punctured or by adjusting the tension rollers which feed the film to the ultrasonic bath. The tension of the film against the horn can be used alternatively, but the correct placement provides a better fibrillation efficiency. The distance between the opposite faces of the film and the speaker and the screen is generally less than about 5 mm (0.2 inches). The distance from the film to the bottom of the tank can be adjusted to create a standing wave that can maximize the cavitation energy on the film, or alternatively other focusing techniques can be used. Other distances from the speaker to the film can also be used. The best results typically occur when the film is placed near the speaker or at wavelength distances from the horn, however, this is dependent on factors such as the shape of the fluid container and the radiation surface used. . It is generally preferred to place the sample near the horn, or the first or second wavelength distance. The amplitude of the ultrasonic pressure can be represented as: P0 = 2pB /? = (2p /?) Pc2ymax The intensity can be represented as: I = (P0) 2 / 2pc where P0 = amplitude of the maximum acoustic pressure (] peak) I = acoustic intensity B = volume module of the medium? = wavelength in the medium ymax = peak acoustic amplitude p = density of the medium, and c = velocity of the wave in the medium The ultrasonic cleaning bath systems can typically vary from 1 to 10 watts / cm2 while the horn systems ( probe) can reach 300 to 1000 watts / cm2 or more. Generally, the levels of energy density (energy per unit area, or intensity) for these systems can be determined by the energy delivered divided by the surface area of the radiation surface. However, the actual intensity may be somewhat lower due to the attenuation of waves in the fluid. The conditions are selected to provide acoustic cavitation. In general, higher amplitudes and / or applied pressures provide more cavitation in the medium. Generally, the higher the cavitation intensity, the faster the production rate of microfibers and the finer (smaller diameter) the microfibers that are produced. While not wishing to be bound by theory, it is believed that high pressure shock waves are produced by the collapse of incipient cavitation bubbles, which impact the film resulting in microfibrillation. The ultrasonic oscillation frequency is usually 20 to 500 kHz, preferably 20-200 kHz and more preferably 20-100 kHz. However, sonic frequencies can also be used without departing from the scope of this invention. The energy density (energy per unit area, intensity) can vary from 1 W / cm to 1 kW / cm2 or more. In the present process it is preferred that the energy density be 10 watts / cm 2 or more, preferably 50 watts / cm 2 or more. The opening between the film and the horn may be, but is not limited to, 0.03 to 76 mm (0.001 to 3.0 inches), preferably 0.13 to 1.3 mm (0.005 to 0.05 inches). The temperature may vary from 5 to 150 ° C, preferably 10 to 100 ° C and more preferably from 20 to 60 ° C. A surfactant or other additive may be added to the cavitation medium or incorporated into the fibrous film. The treatment time depends on the initial morphology of the sample, the thickness of the film and the intensity of cavitation. This time may vary from 1 millisecond to one hour, preferably from 1/10 of a second to 15 minutes and more preferably 1/2 second to 5 minutes. In the present process, the degree of microfibrillation can be controlled to provide a low degree or high degree of microfibrillation. A low degree of microfibrillation may be desired to increase the surface area by partially exposing a minimal amount of microfibers on the surface and thereby giving a fibrous texture to the surface of the film. The increased surface area consequently increases the adhesion of the surface. Such articles are useful, for example as substrates for abrasive coatings and as receiving surfaces for printing, as hook and loop fasteners, as interlayer adhesives and as tape backings. Conversely, a high degree of fibrillation may be required to give a highly fibrous texture to the surface to provide cloth-like films, insulation articles, filter articles or to provide subsequent collection of individual microfibers (i.e. removal of the microfibers from the polymer matrix). In any microfibrillation process, most microfibers remain attached to the tissue due to incomplete release of the microfibers from the polymer matrix. Advantageously, the microfibrillated article, which has microfibers secured to a fabric, provides a convenient and safe means of handling, storing and transporting the microfibers. For many applications it is desirable to retain the microfibers secured to the fabric. In addition, integral microfibers can be extremely useful in many filtering applications - the present microfibrillated article provides a large filtering surface area due to the microscopic size of the microfibers while the non-fibrillated surface of the film can serve as an integral support. Optionally, the microfibers can be collected from the surface of the film by a mechanical means such as with a cylinder with teeth, scraper and the like. The collected microfibers generally retain their volume (foamed) due to the high modulus of the individual microfibers and, as such, are useful in many thermal insulation applications such as clothing. If necessary, the foaming can be improved by a conventional means, such as those used to increase the swelling of blown microfibers, for example by the addition of staple fibers. If desired, adjuvants may be added to the polymer melt to improve the efficiency of microfibrillation, such as silica, calcium carbonate or micaceous materials or to give a desired property to microfibers, such as static electricity reducers or dyes . In addition, nucleating agents can be added to control the degree of crystallinity or, when polypropylene is used, to increase the proportion of β-phase polypropylene in the crystalline film. A high proportion of ß-phase is believed to make the crystalline film more easily microfibrillated. The β-phase nucleating agents are known and described, for example, in Jones et al., Makromol Chem., Vol. 75, 134-158 (1964) and J. Karge-Kocsis, Polypropilene: Structure, Blends and Compositions, vol. 1, 130-131 (1994). A beta nucleating agent of this class is N ', N' -dicyclohexyl-2,6-naphthalene dicarboxamide, available as NJ-Star NO-100MR from New Japan Chemical Co. Chuo-ku, Osaka, Japan. With reference to Figure 5, the extruder! (10) supplies an amorphous polymer, melted by means of a roller contact line or extruder orifice having a predetermined profile to produce a semi-cast film (12). The film is molded on a molding cylinder (14), having a temperature control means for tempering the film to the desired temperature and maximizing the crystallinity of the film. The molding cylinder can be heated to a temperature above the vitreous temperature or can be maintained at a temperature suitable for tempering, cold. If cold tempering is desired, the molded film is preferably stretched immediately by means of a longitudinal orientation device (not shown). The molding wheel for example can be solid or hollow and heated by means of a circulating fluid, resistance heaters, air shock or thermal lamps. The molded film is fed by means of the tension guide rollers (16), (18) and (20) to the calendering apparatus (22) wherein the profile of the film is reduced by a stretch ratio of at least 2: 1 to impart a degree of orientation to it. The temperature of the calendering apparatus (22) is controlled to subject the desired deformation and maximize the division of the crystallites. The calendered film is fed to a longitudinal orientation apparatus (24) by means of powered rollers (not shown) whereby the film is stretched beyond the natural stretch ratio in the machine direction. The longitudinal orientation apparatus may comprise a plurality of rollers which provide tension in the machine direction. Generally, the rollers below the fabric rotate at faster speeds than the rollers above the fabric to maintain the desired tension i. Preferably the rollers are maintained at optimum temperatures to orient a particular polymer, for example about 130 ° C for the polypropylene. More preferably, the rollers are maintained in a temperature decreasing sequence so that the highest possible stretching speeds can be achieved. After orientation, the film is cooled in a cooling wheel (not shown) and removed from the apparatus by the take-off rollers (not shown). Preferably, the calendering apparatus and the longitudinal orientation apparatus are arranged in this manner to provide a minimum opening between the press rollers of the calendering apparatus and the guide rollers of the orientation apparatus to prevent the calendered film from relaxing before orientation. longitudinal.

The highly oriented film can be fed to the fibrillation apparatus 30 as shown in the figure, or it can be stored for later use. Preferably, the film is fed directly to the microfibrillation apparatus (30) by means of the rollers 28. The microfibrillation of the film can optionally include a macro-fibrillation step whereby the film is subjected to a mechanical fibrillation by means of a sawtooth cylinder (26) to expose a larger surface area of the fiber or bundles of fibers. In the present process it is not generally necessary to mechanically microfibrillate the film, although subsequent microfibrillation can be increased by corrugation of the surface. The microfibrillation apparatus (30) may comprise one or more jets of fluid (32) which impact the film with sufficient fluid energy to microfibrillar the surface. The film can be transported on a support band (34) driven by the rollers (36). The web is typically in the form of a screen that can provide mechanical support and allow the fluid to be drained. Alternatively, the apparatus may comprise an ultrasonic horn immersed in a cavitation fluid as previously described. The film is transported by guide rollers (not shown) which place the film against a support screen at a predetermined distance from the ultrasonic horn. The present invention provides microfibers with an effective, small average diameter (width and average thickness), generally less than 20 μm) of fibrous polymeric materials. The small diameter of microfibers provides advantages in many applications where efficiency or performance is improved by a small fiber diameter. For example, the surface area of the microfibers (or the microfibrillated film) is proportionally inverse to the diameter of the fiber allowing the preparation of more efficient filters. The high surface area also increases the yield when they are used as adsorbents, such as in mats or blocks of fibrous oil adsorbent material used in the cleaning of spills and oil stains. Other potential uses include strong reinforcing microfibers in the manufacture of composite materials to increase interfacial bonding, multilayer constructions where the capillary absorbance effect of the microfibrous surface is used to increase the adhesion or integrity of multiple layers, and micro- Loops in the applications of hooks and loops. Microfibers are especially useful as a reinforcing agent in concrete, due to the high surface area (which helps the bond), high tensile strength (which prevents the formation and migration of fissures), rectangular and low cross section elasticity. Microfibrillated films can be useful as backings of tapes or strips to produce an extremely strong tape due to the high modulus and tensile strength of the microfibrillated films. The non-fibrillated surface i can be coated with a pressure sensitive adhesive for use as adhesive tapes.

TEST PROCEDURES Voltage Modulus, Voltage Resistance Voltage modulus and tensile strength were measured using an Instron tension testing machine, Model 1122 (Inston Corp., Park Ridge :, IL) equipped with a battery Piezo 5 KN, model 251 -317. A crosshead speed of 0.05 m / min was used for a total test. We used freestanding samples measuring 12.7 cm x 6.4 mm. The tests were conducted at 23 ° C unless otherwise specified.

Mechanical Dynamic Analysis (DMA) The self-stable strips of each sample were clamped in the jaws of a Seiko Instruments DMA 200 Rheometer (Seiko Instruments, Torrance, CA) equipped with a tensional assembly for samples. The samples were tested at -60 to 200 ° C at 2 ° C / minute and 1 Hz. The separation between the jaws was 20 mm.

Differential Scanning Calorimetry (DSC) The known quantities of the sample to be analyzed were weighted in Perkin-Elmer DSC stainless steel trays (Perkin-Elmer Corp. Norwalk, CT). A DSC scan was performed on each specimen using a Seiko Instruments SSC / 5220H DSC instrument Seiko Instruments, Torrance, CA) in which samples were cooled to -60 ° C for 15 minutes followed by heating at 200 ° C to 10 ° C / min.

Dielectric Constant Dielectric constant measurements were taken at 1 GHz in accordance with the IPC-TM-650 method (Institute for Interconnecting and Packaging Electronic Circuits, Northbrook, IL), using an HP 42921 Impedance Material Analyzer equipped with an HP 16451B Dielectric Test Fixture (Hewlett Packard Co. Palo Alto, CA).

Fiber Diameter (EFD) The microfibrillated fabrics of the invention were evaluated for air flow resistance by measuring the pressure drop (? P) through the tissue in mm of H20 as summarized in the ASTM F 778 method. 88 The Effective Diameter of the Average Fiber (EFD) of each tissue in microns was calculated using an air flow velocity of 32 L / min according to the method described in Davies, CN, "The Separation of Airborne Dust and Particles", Institution of Mechanical Engineers, London, Proceedings IB, 1952.

Relationship between Transverse Dimensions of the Fiber and Transverse Area The relation between dimensions and the measurements of the area of the microfibers obtained from the microfibrillation procedures were measured from the photomicrographs. The fiber samples were mounted on an aluminum fragment and plated by gold / palladium deposition, then examined using an 840 Scanning Electron Microscope (JEOL USA, Inc., Peabody, MA) at a normal viewing angle for the surface of the fragment. The scanning electron micrographs can be observed as Figures 1 and 2.

Surface Area The surface area measurements were made with a Horiba instrument model SA-6201 (Horiba Insruments, Inc., Irvine, CA) using nitrogen as the adsorbate. The samples were conditioned at 20 ° C and a pressure of approximately 760 mm Hg, then measured at room temperature (approximately 23 ° C) with a differential saturation pressure of 20 mm Hg. The samples were degassed at 60 ° C for 800 minutes before measurement. A calibration constant of 2.84 was used. A surface area material known as a control material was used to determine the repeatability of the test.

Density The density of the microfibrillated materials was measured at 25 ° C in deionized water according to the method of ASTM D792-86. Samples were cut into 1.27 x 2.54 cm pieces, weighed on a Mettler AG245 high precision scale (Mettler-Toledo, Inc., Hightstown, NJ), and placed under water. The displaced water mass was measured using the density measurement assembly.

Oil Adsorption Microfibrillated samples were weighed, then immersed in MP404MR lubricating oil (Henkel Surface I Technologies, Madison Heights, MI) or Castrol Hypoy gear oil (Castrol Industrial North America Inc, Downers Grove, IL) for 60 seconds, then drained in a sieve for one hour and reweighed. All steps were performed at 23 ° C. The results were recorded as grams of oil adsorbed per gram of the adsorbent material.

Electric Charge A. Corona Effect Charge. The sample was subjected to corona treatment upon passage of the sample, in contact with an aluminum ground plane, under a positive DC corona source once at a velocity of 3.8 m / min at 40 kV, with the current maintained. at approximately 0.01 mA / cm from the corona source, The source of the corona effect was approximately 4 cm from the ground plate, B. Filtration performance. The filtration performance and the pressure drop of the charged and uncharged samples with the corona effect were measured by the penetration of dioctyl phthalate (DOP) using a TSI Model 8010 instrument (TSI), Inc., St. Paul, MN) at a flow rate of 32 L / min. For each sample, the filtration performance was evaluated according to a GF Quality Factor, defined as QF = -In. { P (%) / 100} /? p (mm H20) Where P was the PDO penetration and? p was the pressure drop. An increase in QF indicated an improvement in filtration performance.

Acoustic Absorption Acoustic absorption was measured essentially in accordance with the method of ASTM E 1050-90. A heavy sample to be analyzed was placed in a double microphone impedance tube, model 4026, 29 mm in diameter (Bruel &Kjaer, Decatur, GA) at a depth of 45 mm and subjected to a frequency range. A dual-channel signal analyzer model 2032 (Bruel &Kjaer) was used to analyze the sound absorption of the sample. The data is presented as a coefficient of absorption against the frequency such that an absorption coefficient of 1 indicates the complete sound dissipation at the specified frequency.

Film Preparation Sample 1. Highly Oriented Polypropylene A molded polypropylene film (ESCORENE 4502-E1, Exxon Chemical Co., Houston, TX) was prepared by extrusion. The extruder settings were 235 - 250 - 270 - 250 ° C from the inlet end to the nozzle, at 60 rpm. The extruded material was cooled in a roll cooled with water at 36 ° C, to produce a film of approximately 2.54 mm in thickness. The extruded film was longitudinally oriented at 135 ° C in a stretch ratio of 5: 1 in the machine direction and collected on a roller. The film was fed in a 4 roller calender apparatus, with each roller heated with steam at about 150 ° C, at 1.5 m / min. A clamping force between the third and fourth rollers effected a biaxial stretching ratio of 2: 1 on the film, which was then fed into a longitudinal orienter with only a gap of 2.54 cm between the pressure roller and the first roller. longitudinal orientation. The longitudinal orienter used a series of rollers in such a way that an additional 10: 1 stretch ratio was achieved, while the roll temperature was lowered to 23 ° C. The oriented film was passed through a pressure roller to maintain tension, then stretched on a roller. A total stretch ratio of 20: 1 was achieved such that the film produced was approximately 0.25 mm thick.

The resulting film had a voltage modulus of 8.9 GPa and a tensile strength of 496 MPa. The dynamic mechanical tension analysis (DMA) showed an increase of approximately 10 times in the module on the non-oriented polypropylene at temperatures of -50 ° to 150 ° C. The sample exhibited a degree of crystallinity of approximately 95%, calculated from differential scanning calorimetry (DSC) measurements. The dielectric constant in the z-direction (ie, in the direction of film thickness) at 1 GHz was 1.92, with a delta dissipative toast of 0.15 milliunits.

Sample 2. Highly Oriented Polypropylene The polypropylene film was prepared by extruding the polypropylene homopolymer (FINA 3374X or FINA 3271, commercially available from Fina Inc., Dallas, TX) at 40 rpm with an extruder temperature profile of 229 ° C. -239 ° C - 247 ° C - 246 ° C from feed to tip. The neck tube and mouthpiece were maintained at 246 ° C. Films having a thickness of 1.6 mm were prepared using a casting wheel temperature of either 23 ° C (cold casting) or 90 ° C ("hot casting"). The cast films were calendered using a calender of two. rollers at 150 ° C, with the first set of rollers (input) at 0.31 m / min and 4.15 MPa and the -_ .. da ..i. second set of rollers (tensioners) at 2.13 m / min. The elongation ratios of 12: 1 were measured using the deformation of a reticule etched onto the film. A method of longitudinal orientation of the films of the invention used a series of six preheated rolls of 15 cm diameter (90 ° C) arranged such that each side of the film comes into contact with three rollers (Brückner Maschinenbau GmbH, Siegsdorf, Germany). The rollers had a peripheral speed of 1 m / min. The film was stretched between two rolls of 7.3 cm diameter heated to 90 ° C, the first of which had a peripheral speed of 1 m / min and the second one that had a peripheral speed of 4 m / min. The elongated film then passed over two additional 15 cm diameter rollers heated to 90 ° C, such that each side of the film came into contact with a roller, in order to heat the film. The film was immediately wound on a receiving or winding reel. The longitudinal, additional orientation of the film was carried out in an elongated oven having a temperature profile of 160 ° C in zones 1, 2 and 3 and 145 ° C in zone 4. The film was introduced into the oven at 1 m / min and was stretched at the exit end at 3.6 m / min. The oriented film was cooled to 23 ° C on a series of unheated rolls, then wound onto a receiving roll. The stretch ratio for this procedure was 1.6: 1, measured using the lattice deformation as previously described. The total stretch ratio for all orientations was 19: 1. The tensile properties of the films are shown in Table 1. The microlaguna morphology of Samples 2-7 can be observed with reference to Figure 3. All the films described in Table 1 were calendered as described above. In addition, some films were oriented longitudinally i (LO). All the films were either cold molded (CC) or hot molded (HC), as indicated in the table. The values of the tensile strength and the Module are reported as the average of five readings taken at 23 ° C in the center of the film after the orientation procedure was completed.

The data in Table 1 show that | the highest combinations of tension modulus and tensile strength can be obtained when the film is both hot molded and longitudinally oriented (Exhibits 2-1, 2-3, 2-6 and 2-7).

Sample 3. Oriented Polypropylene Film The oriented polypropylene film was prepared by extruding the polypropylene (Type 3374X, Fina, Inc.) using a 4.4 cm diameter extruder equipped with a 15 cm nozzle. The initial film (1.63 mm thick) was molded on a molding cylinder at 85 ° C, then oriented longitudinally by calendering between two rolls held at 152 ° C, exerting a pressure of 5520 kPa on the film, followed by the additional longitudinal orientation between a hot roll (138 ° C) and a cold roll (14 ° C). The stretch ratio ».--». resulting was 12.7: 1. The oriented film exhibited a modulus of 2.1 GPa and a tensile strength of 124,200 kPa, and had a surface morphology with fibrous-pitted microlagunas on one side away from the molding wheel, while being smooth on the side of the molding wheel.

Sample 4. Oriented Polypropylene Film The oriented polypropylene film was prepared by extruding the polypropylene (FINA 3374X, Fina Inc.) at 50 rpm in a single screw extruder with a temperature profile of 230 ° C -240 ° C -250 ° C -245 ° C from the feed to the tip. The neck tube and mouthpiece were maintained at 245 ° C. A 1.6 mm thick cast sheet was obtained using a molding wheel maintained at 90 ° C. The molded sheet was oriented longitudinally without ur, calendering step using six 15 cm rolls heated at 95 ° C, as described in Sample 2, at a stretch ratio of 6: 1. The additional longitudinal orientation of the film was carried out in a tenter oven having a temperature profile of 150 ° C in zone 1 and 130 ° C in zones 2, 3 and 4. The film was placed in the oven in 1 m / min and was stretched at the exit end at 3.6 m / min. The oriented film was cooled to 23 ° C on a series of unheated rolls, then wound onto a receiving roll. The stretch ratio for! this procedure was 1.25: 1, measured using the lattice deformation as previously described. Finally, the stretched film was further elongated in a retensioning apparatus in which the second set of rollers was maintained at 120 ° C, to produce an additional 1.5: 1 elongation. The total stretch ratio for all operations was 11: 1, producing a film that had 71% crystallinity (DSC). The tensile modulus of the film obtained in this way was 8.3 GPa (1.2 x 106 psi), the tensile strength was 331 MPa (47,900 psi).

EXAMPLE 1. Fluid Jet Microfibrillation (SRL-24, pp. 3-12) Fibrillation of the polypropylene films oriented by a fluid jet was carried out using a Model 2303 hydraulic entangling machine (Honeycomb Systems Inc., Bridgeport, ME) equipped with a 61 cm nozzle that had 0.13 mm diameter holes separated by 0.39 mm (spacing). Deionized water (23 ° C) was used at a pressure of 8280 kPa to 9660 kPa for all the examples. The typical line speed was between 0.9 and 1.3 m / min, unless otherwise noted. In a typical procedure, the highly oriented polypropylene film, as described above, was supported on a continuous mesh screen and it was passed under the hydraulic entanglement jets at the prescribed speed at a distance of approximately 3 cm from the nozzle. The resultant microfibrillated film was wound on a receiving roll. The highly oriented polypropylene film, Sample 2-7, was subjected to microfibrillation of fluid jet using the general procedure described above. In this way, a sample of the film of 1.27 cm in width and 0.125 mm in thickness was passed under the hydraulic entanglement nozzle at a distance of approximately 3 cm, in a sieve having openings of 1.25 mm x 1.25 mm, under pressure of the water jet of 8280 kPa. The resulting microfibrillated tissue was 0.375 mm thick. The physical properties of the microfibrillated tissue were: Orientation Module, MPa Maximum Load Resistance in Stress Deformation, Mpa Break, N Break,% Direction of 2,300 72.5 123 8.6 the machine (DM) Direction 138 0.26 0.44 272 transversal (DT) Effective Diameter of the Fiber (EFD): 0.5 - 0.7 micrometers. Surface area: 4.01 m2 / g Density: 0.104 g / cc Oil Adsorption (lubricant MP404): 14.42 g / g Oil Adsorption (Hypoy C Gear Oil): 19.29 g / g Filtration performance, before corona loading: QF = 0.03. Filtration performance, after corona loading: QF = 0.33. Ratio between average dimensions: 6 ± 3: 1 (n = 24) Average transversal area: 1.4 ± 0.7 μm (n = 24) Acoustic Absorption: Absorption coefficient greater than 0.85 between 650 and 5000 Hz. Scanning electron micrographs (SEMs) ) of the microfibers can be seen in Figures 1 and 2, revealing the new microfibers similar to a batten of the invention. A histogram of the average fiber effective size was recorded in a diagram like Figure 4. In Figure 4, the relationships between dimensions (width to thickness) were averaged to obtain the reported diameters.

EXAMPLE 2. Ultrasonic Microfibrillation A 0.255 mm thick sample of the highly oriented polypropylene film, described in the preparation of Sample 1, was subjected to ultrasonic microfibrillation. An Autotrack 3000 ultrasonic system (Dukane Corp., St. Charles, IL) was used in a water tank filled with water with the horn or horn placed such that the working surface of the horn was approximately 3 cm below the water level . A high gain bar horn with a top diameter of 5 cm and a rectangular bottom of 9.5 x 51 mm (3/8 x 2 inches) was used, in conjunction with a 0.6: 1 amplifier. The amplitude was 0.045 mm peak-to-peak. The film remained in close proximity to the speaker. The resulting film was microfibrillated on both sides such that the total thickness in the microfibrillated zone was approximately 0.375 mm in thickness, while the non-microfibrillated portion 0.125 mm in thickness remained in the core, between the microfibrillated surfaces. The contact time for microfibrillation was 2 minutes. Microfibrils having diameters in the range of 0.1 to 10 microns were observed by scanning electron microscopy. It is believed that the microfibers below the detection limit of the SEM were also present.

SI & -Example 3. Ultrasonic Microfibrillation The oriented polypropylene film described in the preparation of Sample 3 was subjected to ultrasonic microfibrillation. A water tank that had inlet and outlet slots on each side was filled with water approximately 7.5 cm deep. An Autotrack 3000 ultrasonic system (Dukane Corp., St. Charles, IL was used with a horn placed such that the horn was below the water level and above the screen that had 3 mm holes mounted in an open ring approximately 3.5 cm The distance between the horn and the screen was kept to a minimum, for example, 0.25 mm for a 0.225 mm thick film sample, and a high amplitude bar horn was used. an upper part of 5 cm in diameter and a rectangular bottom of 9.5 x 51 mm (3/8 x 2 inches), in conjunction with a 1.5: 1 amplifier.The oriented film was conducted inside the input slot, under the speaker Ultrasonic, that is, under water, and out of the outlet slot under sufficient tension to keep the film in close contact with the working surface of the speaker.The amplitude was 0.185 mm.The contact time for microfibrillation was approx. 2 M / minute (~ 6 feet / minute). Microfibrillation was observed only on the surface - * > - * •• - _ ^^^ fibrous-chopped earlier of the film). It was observed that this microfibrillation took place on the fibrous-pitted surface if the surface was facing or away from the ultrasonic horn.

EXAMPLE 4. Water Jet Microfibrillation The oriented polypropylene film obtained as described in Sample 4 was subjected to microfibrillation with water jets using a balanced, neutral, three-hole, 10 cm vortex head attached to a cutting table. of Jet Edge water equipped with three-axis controls that were adjusted to produce 7.6 x 10"3 m3 (2 gallons) of water at 248 Mpa (36,000 psi) (Jet Edge, Minneapolis, MN) The actual water pressure was 34.5 MPa (5000 psi) at a film speed of 1.3 m / mi.n beyond the stationary vortex head.The microfibres obtained from the film were shown by the SEM to be relatively flat, ribbon-like fibers that have their dimension wider than less than 1 micrometer to about 9 micrometers and a thickness of about 0.5 micrometer, such that the ratios between fiber dimensions were from 2: 1 to about 18: 1.

Claims (3)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. 1. Polymeric microfibers processed from a melt, characterized in that they comprise bundles of unitary fibrils, microfibers having an average effective diameter of less than 20 microns and a transversal dimensional relationship of 1.5: 1 to 20: 1.
2. 2. The microfibers according to claim 1, characterized in that they have an effective average diameter of 0.01 microns to 10 microns.
3. 3. The microfibers according to claim 1, characterized in that they have an average effective diameter of less than 5 microns 4. The microfibers according to claim 1, characterized in that the polymer is selected from the group consisting of polyethylene, polypropylene, polyoxymethylene , poly (vinylidene fluoride), poly (methyl pentene), poly (ethylene-chlorotrifluoroethylene), poly (vinyl fluoride), poly (ethylene oxide), poly (ethylene terephthalate, poly (butylene terephthalate), nylon 6) , nylon 66, high and low density polybutene and liquid crystal polymers, thermotropic. (c) microfibrillating the microlabeled surface by imparting sufficient fluid energy to the surface to release the polymeric matrix of the polymeric microfibers processed from a melt of the film comprising bundles of unitary fibrils, the microfibers having a diameter Effective average of less than 20 micras and a transversal dimensional relationship of 1.5: 1 to 20: 1. 10. The process according to claim 9, characterized in that the fluid energy is imparted with a fluid at high pressure. The process according to claim 9, characterized in that the microfibrillation step comprises holding the film to the cavitation energy while it is immersed in a fluid. The process according to claim 9, characterized in that the microfibrillation step comprises contacting the film with one or more jets of high pressure fluid. The process according to claim 9, characterized in that the highly oriented polymer film is prepared by the steps of (a) extruding a crystalline polymer that can be processed from a melt; (b) molding the polymer to maximize crystallinity; Y (c) calendering the polymer in a stretch ratio of at least 2: 1. The process according to claim 9, characterized in that the polymer is elongated in a ratio of at least 10: 1 to produce a highly oriented film having a plurality of micro-gaps. 15. The process according to claim 9, characterized in that the film, before microfibrillation, is .025 to 0.5 millimeters thick. 16. The process according to claim 13, characterized in that the film is calendered at or above the alpha crystallization temperature of the polymer. 17. The process according to claim 9, characterized in that the film has a micro-lagoon content in excess of 5%. 18. The process according to claim 9, characterized in that the film has a micro-lagoon content in excess of 10%. 19. The process according to claim 9, characterized in that the fluid energy is a minimum of 10 watts / cm2. 20. The process according to claim 12, characterized in that the fluid is water at a pressure of at least 3400 kPa 21. The process according to claim 9, characterized in that the film is 0.8 to 1.8 millimeters thick before elongation