MXPA97002365A - Polypropylene escined by radiation and fibrashechas from my - Google Patents

Abstract

The present invention relates to a propylene homopolymer, having an adhesion point of 320 cm or less, during spinning of the melt, an oligomer content of less than 1500 ppm, without a post-polymerization treatment to remove the oligomers and a flow rate of the melt greater than 300 dg / min

Description

POLYPROPYLENE ESCINED BY RADIATION AND FIBERS MADE FROM IT This invention relates to propylene polymer materials cleaved by radiation and to fibers, films and other articles obtained therefrom. Propylene polymers can be chain broken to produce products of lower molecular weight, a process commonly referred to in the English language as visbreaking. This process not only decreases the molecular weight and raises the melting flow rate of the polymers, but also leads to a narrowing of the molecular weight distribution. Generally speaking, the higher molecular weight leads to better physical properties, but also poor process properties. Conversely, lower molecular weight leads to poorer physical properties, but better process properties. A low molecular weight polymer, with a narrow molecular weight distribution, provides good physical and process properties in many manufactured articles. Therefore, it has been a common procedure in the past to polymerize the propylene at a higher molecular weight than desired for the final application and then to cleave the same at the desired molecular weight. Several different types of gum reactions, which are well known, can be used to cleave propylene polymers. An example is thermal pyrolysis, which is achieved by exposing a polymer at high temperatures, for example in an extruder at 350 ° C or more. Another approach is to expose powerful oxidizing agents. Another approach is exposure to ionizing radiation. For example, U.S. Patent No. 4,282,076 describes a process for reducing the molecular weight of a propylene polymer, by activating a first portion of the polymer, by exposure to ionizing radiation, adding the irradiated polymer to a second portion of the polymer. Non-irradiated polymer, add a stabilizing amount of an antioxidant to the mixture and split by cutting mixture in an extruder. Another method, which is used almost exclusively in commercial practice, is the addition of a prodegradante agent to the polymer, before the formation of pellets. A prodegradant agent is a substance that promotes chain scission when mixed with the polymer, which is then heated under extrusion conditions. The prodegradant agents used in current commercial practice are mainly alkyl hydroperoxides or dialkyl peroxides. These materials initiate a chain reaction of free radial at elevated temperatures, resulting in the cleavage of polypropylene molecules. The use of alkyl hydroperoxide prodegrants or dialkyl peroxide has been a satisfactory method of cleaving polymers in many aspects, but there is considerable room for improvement. An objectionable characteristic is the presence of decomposition products of the prodegradants that remain in the polymer as contaminants. These decomposition products can be harmful during the subsequent treatment of the polymer and during the use of the products obtained from the polymer. The irradiation of the polymers can also be used to produce the convenient properties, in addition to the reduction in molecular weight and the narrowing of the molecular weight distribution. For example, the patent of E. U. A., No. 4,916,198, describes a process for obtaining gel-free polypropylene, which has a deformation viscosity of the hardening elongation of propylene which does not have such a set strain elongation viscosity. The polymer is irradiated in the essential absence of oxygen until a substantial chain cleavage of the linear propylene polymer has occurred, without causing gel formation of the polymer, and keeping the polymer irradiated in such medium for a sufficient period of time for the Significant formation of long chain branches. The irradiated polymer is then treated in the essential absence of oxygen to deactivate the free radicals. The patent of E. U. A., No. 5,047,446 discloses a process for treating a high molecular weight, irradiated propylene polymer material containing a free radical, to further increase long chain branching and free radical formation, induced by radiation, and to make to the stable polymer in storage for prolonged period, in the presence of air. A two-fluid bed process is used in which the first stage employs an intermediate temperature for the recombination of the radical and the second stage employs a higher temperature for the deactivation of the radical. When alpha-olefins are polymerized, the product is a mixture of molecular chains or chains of alpha-olefin units, which have many different chain lengths. While the lengths of most chains represent thousands of carbon atoms, inevitably there are chains of much shorter lengths, which can be as low as two units of alpha-olefin. Molecules of shorter chain length are referred to as oligomers. In this specification, "oligomer" is defined as a chain alpha-olefin units whose number of carbon atoms is less than 40. The oligomers can be separated from the polymer particles in a process of removing an unreacted monomer, generally executed after the polymerization stages. The oligomers can also be formed into a polymer as a result of post-polymerization treatments, such as, for example, the splitting and extrusion of the melt. In most commercial alpha-olefin polymers, the concentration of the oligomers in the polymer particles is not high enough to cause a problem. Indeed, the presence of oligomers may have a beneficial effect on the melting rheology of the polymers. However, especially in the case of substantially crystalline propylene polymers with high melt flow rates (>10 dg / min, ASTM D 1238, Condition L (230SC, 2.16 kg)) in which the concentration of the oligomer is frequently in the range of 1000 to 10,000 parts per million parts in. polymer weight, a substantial concentration of the oligomers in the polymer causes the emission of "smoke" from the polymer when it is extruded by melting, for example, when it is converted into fibers. However, not all oligomers are emitted from the molten polymer after it leaves the die and before cooling to room temperature, to which it solidifies. The residual oligomer in the extruded polymer can result in unpleasant taste and odor in the articles, such as fibers, packaging films and containers made from the extruded polymer. A particular area of interest is the production of melted and blown polypropylene fibers and non-woven materials made from these fibers. Commercial resins tried for this use are currently obtained in two stages. First, propylene granules of high melt flow rate (MFR), for example an MFR of 400, are produced in a reactor. Because the molecular weight distribution (MWD) is too wide for proper spinning, peroxide is added to the granules to break the molecular chain, thus narrowing the MWD while increasing the MFR. For example, 500 ppm of peroxide can be added to polymer granules with an MFR of 400, to decrease the MWD from 4.0 to 3.2. At this stage, the MFR increases to 800. This technology has a number of limitations. First and foremost, the content of the polymer oligomer is sufficiently high to produce defects in the product. The oligomers, of light weight, tend to become gaseous products during spinning at high temperatures, producing smoke and condensate during spinning operations, which can cause health problems, as well as defects in the product. In some polymerization processes, a washing column is installed to wash the oligomers of the polymer granules. In addition, the amount of the peroxide to be added should be limited, because the polymer granules have a limited absobency capacity for the liquid peroxide and because too much peroxide leaves a residue that can cause irritation to the skin. Therefore, the polymers produced by this process have limitations on the maximum MFR that can be achieved, as well as in the MWD range. There is still a need for a process in which the MFR and the MWD of the propylene polymer material can be controlled over a wide range, while producing a product with a low oligomer content, ie less than 1500 ppm, without some post-polymerization treatment to remove the oligomers. The propylene homopolymers of this invention have a point of adhesiveness of 30 cm or less during spinning of the melt, an oligomer content of less than 1500 ppm without the post-polymerization treatment, to remove the oligomers, and a of the melt flow greater than 300 dg / min. The method of this invention for treating an irradiated propylene polymer comprises (1) exposing an irradiated propylene polymer material, containing a free radical, selected from the group consisting of (a) propylene homopolymers having an isotactic index of minus 90, (b), random copolymers of propylene and ethylene or butylene, or random terpolymers of propylene, ethylene and butylene, in which the maximum content of ethylene, or ethylene plus butylene, is 10% by weight, which has a isotactic index of at least 80 and (c) heterophasic propylene polymer materials, which essentially consist, by weight, of: (i) 99 to 55% of a polymeric material, selected from the group consisting of a propylene homopolymer having an isotactic index greater than 90, and a crystalline copolymer of propylene and alpha-olefin of the formula CH2 = CHR, where R is H or an alguyl group, linear or branched, of 2 to 6 carbon atoms, having an isotactic index of at least 80, this alpha-olefin being less than 10% of the copolymer e (ii) from 1 to 45% of an elastomeric olefin polymer of propylene and an olefinic material selected from the group consisting of alpha-olefins of the formula CH 2 = CHR, wherein R is H or an alkyl group, linear or branched, from 2 to 6 carbon atoms, the alpha-olefin is from 50 to 70% of the elastomeric polymer. to a controlled amount of active oxygen of more than 0. 0004% and less than 15% by volume at a temperature T ^ of 40-1100C, (2) heating the temperature T2 of at least HOSC, in the presence of a quantity of controlled oxygen, within the same range as in the stage ( i), and (3) maintaining the polymer at a temperature T2, in the presence of 0.004% or less in volume of active oxygen.

The use of the process of this invention for the radiation cleavage of the propylene polymer materials, the melt flow rate and the molecular weight distribution of the polymers can be varied within wide limits to accommodate the specific requirements in obtaining the melt and blown and non-woven materials joined by spinning, in the case of propylene homopolymer, and other manufactured articles. The propylene polymer materials obtained by this method have a much lower oligomer content than the current commercial grades of the propylene polymer, without the need for post-polymerization treatment to remove the oligomers, and are essentially odor free, thus avoiding the need to deodorize, It is also possible to obtain polymers with a higher MFR, which can be obtained by extrusion and pelletization of the peroxide-cleaved polymers, where the practical limit is an MFR of 100 to 200 dg / min, using a typical commercial team. In addition, the properties of the polymer product, for example, the melt flow rate and viscosity, are more uniform than in the case of polypropylene cleaved by peroxide, currently in commerce. The propylene polymer materials obtained by the radiation-cutting process according to this invention can be used, for example, for the production of films and fibers, extrusion coating and injection molding. Figure 1 is a schematic flow diagram of the fluid bed system for obtaining cleaved propylene polymer materials, according to this invention. The propylene polymer material used as a starting material in the process of this invention is selected from the group consisting of (a) propylene homopolymers having an isotactic index of at least 90, preferably from 95 to 98.; (b) random copolymers of propylene and ethylene or butylene, or random terpolymers of propylene, ethylene and butylene, or random terpolymers of propylene, ethylene and butylene, in which the maximum content of ethylene or ethylene plus butylene is 10%, preferably from 1 to 5% by weight, having an isotactic index of at least 80, preferably of 85 or more; and (c) heterophasic propylene polymer materials, which consist, by weight, essentially of: (i) from 99 to 55% of a polymeric material, selected from the group consisting of a propylene homopolymer having a higher isotactic index of 90, and a crystalline copolymer of propylene and an alpha-olefin of the formula CH 2 = CHR, where R is H or an alkyl group, linear or branched, having 2 to 6 carbon atoms, having an isotactic index of at least 80 , this alpha-olefin being less than 10% of the copolymer; e (ii) from 1 to 45%, preferably from 8 to 25% and more preferably from 10 to 20%, of an elastomeric propylene polymer and an olefinic material selected from the group consisting of alpha-olefins of the formula CH2 = CHR where R is H or a linear or branched alkyl group of 2 to 6 carbon atoms, this alpha olefin is 50 to 70%, preferably 40 to 70% and more preferably 55 to 70% of the elastomeric copolymer. When a propylene homopolymer is used as the starting material, any propylene homopolymer having an isotactic index of at least 90% can be used. If the polymer is to be used to obtain fibers, it should preferably be in the form of flakes or spheres of high porosity, ie physical forms with a high surface / volume ratio. Pellets or spheres with normal density are not suitable for fiber applications when the polymer is treated by the process of this invention. For different applications of fibers, for example molding, films and extrusion coating, the propylene polymer material can be in any physical form, for example of finely divided particles, granules or pellets.

The propylene polymer material is exposed to a high ionizing energy radiation in an essentially oxygen-free environment, in which the concentration of active oxygen is established and maintained at less than 15%, preferably less than 5% and more preferably 0.004% or less in volume. The ionizing radiation must have sufficient energy to penetrate the desired extent in the mass of the irradiated propylene polymer material. Ionizing radiation can be of any kind, but the most practical class is electrons and gamma rays. Preferred are electrons radiated from an electron generator having an acceleration potential of 500-4,000 kilovolts. Satisfactory results are obtained at a dose of ionization radiation of about 0.1 to 15 mega-rads, preferably about 0.5 to 4.0 mega-rads. The term "rad" is usually defined as the amount of ionizing radiation that results in the absorption of 100 ergs of energy per gram of irradiated material, using the process described in the previously mentioned U.S. Patent No. 4,916,198. The energy absorption of the ionizing radiation is measured by the well-known conventional dosimeter, a measuring device in which a strip of the polymer film containing a radiation-sensitive dye is the energy absorbing detector element. Therefore, as used in this specification, the term "rad" means that amount of ionizing radiation that results in the absorption of the equivalent of 100 ergs of energy per gram of the polymer film of a dosimeter placed on the surface of the material of propylene polymer that is irradiated, either in the form of a bed or layer of particles, or a film or sheet. The irradiated propylene polymer material, which contains the free radical, is then subjected to a series of oxidative treatment steps. The preferred way to carry out the treatment is to pass the irradiated polymer through a fluid bed assembly operating in T ^, in the presence of a controlled amount of oxygen, passing the polymer through the second fluid bed assembly which operates in, in the presence of an amount of oxygen, within the same range as in the first stage and then maintain the polymer in T2, in the substantial absence of oxygen, that is, an oxygen concentration equal to or less than 0.004% in volume, in a third fluid bed assembly. In a commercial operation, a continuous process using three separate fluid beds is preferred. However, the process can also be carried out in a batch mode in a fluid bed, using a fluidizing gas stream, heated to the desired temperature for each treatment step. Unlike some techniques, such as melt extrusion methods, the fluidized bed method does not require the conversion of the irradiated polymer into the molten state and the subsequent re-solidification and fractionation into the desired form. The first stage of treatment consists in heating the irradiated polymer in the presence of a controlled amount of the active oxygen of more than 0.004%, but less than 15% by volume, preferably less than 8% and more preferably less than 3%, to a temperature from 40 to 1102C, preferably from about 80SC. Heating to the desired temperature is achieved as quickly as possible, preferably in less than 10 minutes. The polymer is then maintained at the selected temperature, typically for about 90 minutes, to increase the rate of reaction of the oxygen with the free radicals in the polymer. The retention time, which can be easily determined by a person skilled in the art, depends on the properties of the starting material, the concentration of the active oxygen used, the irradiation dose and the temperature. The maximum time is determined by the physical restrictions of the fluid bed. In the second stage of treatment, the irradiated polymer is heated in the presence of a controlled amount of oxygen, in the same range used in the first treatment step, at a temperature of at least 1102C to the softening point of the polymer (1402C for the homopolymer). The polymer is then maintained at the selected temperature, typically for about 90 minutes, to increase the rate of chain cleavage and minimize recombination to form long chain branches. The retention time is determined by the same factors discussed in relation to the first stage of treatment. In the third treatment step, the polymer is maintained at the selected temperature for the second treatment step for about 10 to 120 minutes, preferably about 60 minutes, in the substantial absence of active oxygen, ie 0.004% by volume or less, preferably less, to produce a product that is stable during subsequent storage under ambient conditions. After the third stage of treatment, the polymer is cooled to a temperature of about 70 ° C for a period of about 10 minutes in an atmosphere essentially free of oxygen, before being discharged from the bed. The term "active oxygen" means oxygen in a form that will react with the irradiated material of the propylene polymer. It includes molecular oxygen, which is in the form of oxygen normally found in the air. The requirement of the active oxygen content of the process of this invention can be achieved by the use of a vacuum or by replacing part or all of the air in the environment with an inert gas, such as, for example, nitrogen. The control of the oxygen level in the gas stream of the fluid bed is achieved by the addition of air to the suction side of the blower. Air or oxygen must be added constantly to compensate for the oxygen consumed by the formation of peroxides in the polymer. The fluidizing medium can be, for example, nitrogen or any other gas which is inert with respect to the free radicals present, for example argon, krypton and helium. In the flow diagram shown in Figure 1, the conveyor belt feed hopper 1 is a cover with a conventional design. It operates so that its interior contains an atmosphere essentially free of active oxygen, for example a nitrogen atmosphere. It has a discharge outlet of bottom solids through which the polymer particles move and form a layer on the upper horizontal run of an endless conveyor belt 2. The band 2 of the horizontal conveyor is contained in the radiation chamber 3 and moves continuously under normal operating conditions. The radiation chamber completely encloses the conveyor belt and is constructed and operated to establish and maintain an atmosphere essentially free of active oxygen therein. In combination with the radiation chamber 3 is the electron beam generator 4 ** of conventional design and operation. Under normal operating conditions it generates a beam of high-energy electrons directed at the polymer particle layer in conveyor belt 2. Beneath the discharge end of the conveyor belt is a solids collector 5, arranged to receive the irradiated polypropylene material falling from the conveyor belt 2, as it rotates in its opposite travel path. The particles irradiated in the collector 5 of solids are removed by a rotary valve or star wheel 6 and delivered to a solid transfer line 7. The transfer line 7 leads to a gas-solids separator 8. This unit is of conventional construction and is usually a cyclone separator. The gas that is separated is removed, for example, by the gas discharge conduit 10, while the separated solids are discharged, for example, by a rotary valve or star wheel 9, in a solids discharge line 11. The solids discharge line 11 leads to a fluid bed unit 12. This fluid bed is of conventional design, is sealed and is constructed and operated to establish and maintain an atmosphere containing a controlled amount of active oxygen therein. A gas stream containing a controlled amount of active oxygen is introduced, via conduit 16, into the bed 12 by means of a closed circuit assembly containing the blower 13, the buffer 14 and the heat exchanger 17. The butterfly damper 14 is used to control and maintain the desired gas velocity through the fluid bed. The circulating gas passes through the heat exchanger 17, where it is heated to the desired temperature. An oil circulation system, consisting of the oil heaters 20 and 21, the heat exchanger 19 and the temperature control circuit 18, is used to maintain the desired temperature in the gas stream. Two separate oil heaters, 20 and 21, are used to minimize the time required to change the temperatures during the polymer process, having the heaters adjusted to the desired temperatures and directing the oil at the proper temperature to the heat exchanger 17. The heat exchanger 19 is a conventional oil-to-water heat exchanger used to provide additional temperature control for the hot oil system. The heated gas passes through the conduit 16 in the lower side of the plenum chamber of the fluidized bed and through the manifold plate. The velocity of the gas is maintained in order to produce a fluidizing action in the particle bed of the polymer. The fluid bed is operated in a batch mode. Thus, the residence time is controlled by the amount of time that the propylene polymer material is maintained in the fluid bed. The propylene polymer material leaves the unit through the manually controlled valve and passes through the discharge line 15 into a collection vessel. Knowing the MFR of the starting material, the dose during the irradiation step, the oxygen level during the first and second treatment steps, the temperature and time can be adjusted to obtain this MFR in the cleaved product. The propylene homopolymer cleaved by radiation, according to this invention, is characterized by having an adhesion point of 30 cm or less, during spinning of the melt; an oligomer content of less than 1500 ppm, without the subsequent polymerization treatment, to remove the oligomers, and a melt flow rate greater than 300 dg / min.

The radiation-split propylene homopolymer, prepared by the process described above, can be used to spin fibers that become non-woven materials blown in molten form and spin-bonded, and can also be used in other applications, where the MFR and The MWD have to be adjusted to meet specific end-use requirements. Techniques for the formation of non-woven webs by melt blowing and spinning are well known in the art. The blown fibers in a molten form are very thin and typically have a diameter of about 3 μm, which is smaller by an order of magnitude than the fibers linked by traditional smaller spinning. A special die uses a heated pressurized fluid, usually air, to attenuate the filament of the molten polymer as it leaves the hole in the die or nozzle. Weak staple fibers are deposited on a shaping screen as a random matted band. In the preparation of spin-bonded materials, the polymer is continuously extruded through a spinneret to form discrete filaments. Next, the filaments are stretched pneumatically without breaking, in order to orient the polymer filaments and achieve tenacity. The continuous filaments are then deposited in a substantially random manner on a carrier band to form a band. The propylene polymer material, prepared by the process of this invention, can be used, for example, for extrusion coating, film production, particularly molded films, fiber melt spinning and injection molding, particularly for the mold from thin walled containers. The propylene polymer materials can also be blended with 5 to 95% of a linear, semi-crystalline, predominantly isotactic, usually solid propylene polymer material for use in the melting process and other operations to obtain useful articles. The point of adhesion of a polymer is determined as follows: In polymeric materials, stress-induced crystallization is the dominant mode of solidification during spinning of the melt, during which a high degree of orientation is achieved. The crystallization regime is a function of the molecular structure of the material that is processed. Therefore, the measurement of the solidification point during spinning can be used for different polymer differences. The solidification point is measured by sliding a metal bar along a line of moving yarn starting from 70 cm away from the face of the row. As the bar moves upward, it reaches a point where the polymer is still molten. At this point, the line of thread sticks to the bar and breaks. The "adhesion point" is defined as the distance from the face of the row to the point at which the line of the thread sticks to the bar and breaks. Low values for the measurement of the adhesion point are convenient. The spinning of the melt of the fibers for the test is carried out at a total rate of 0.5 g / hole / minute, without the forced air cooling, a melting temperature of 1902C and a spinning speed of 1000 m / minute. The hole diameter of the die is 0.5 mm and the length / diameter ratio of the troguel is 4. The percentage of xylene solubles, at room temperature, is determined by dissolving 2.5 g of the polymer in 250 ml of xylene in a container equipped with an agitator, which is heated to 1352C, with stirring, for 20 minutes. The solution is cooled to 252C, while continuing to stir, and then allowed to stand, without agitation, for 30 minutes, so that the solids can settle. The solids are filtered with filter paper, the solution is really evaporated by its treatment with a stream of nitrogen and the solid residue is vacuum dried at 802C until reaching the constant weight. In the examples, the following methods were used to determine the physical properties of the radiation-split polymers and the fabricated materials or articles prepared from these polymers: melt flow rate (MFR) - ASTM-D 1238, Condition L, resistance to trapezoid tear - ASTM-D 1117-80, air permeability - ASTM-D 1117-80 and hydraulic head - Test Method AATCC 127-1989. The Polydispersity index (Pl) was used as a measure of the molecular weight distribution in the polymer. The separation of the module at the low value of the module, ie 500 Pa, was determined at a temperature of 2002C using a RMS-800 parallel plate rheometer model, available from Rheometrics (USA), operating at an oscillation frequency which increases from 0.1 to 100 rad / second. From the module separation value, the value of Pl can be derived, using the following equation: Pl = (module separation) -1-76 where the separation of the module is defined as:frequency at G1 = 500 Pa module separation = frequency at G "= 500 Pa where G 'is the storage module and G "is the value of the module selected for the test, unless otherwise mentioned, all parts and percentages in this specification are by weight.

Example 1 This example illustrates how the process conditions may vary to obtain a polymer product with approximately the same melt flow rate (MFR). Propylene homopolymer flakes, having a nominal MFR of 20.3, commercially available from Montell USA Inc., were irradiated and exposed to the controlled amount of oxygen, shown in Table 1. The depth of the polymer bed in the conveyor belt it was adjusted to an equal bed depth of entry and exit, placing dosimeters in the conveyor belt and advancing this conveyor belt under the loading hopper and the leveling device of the bed. The conveyor belt was stopped and a second dosimeter was placed on top of the polymer bed. The Van de Graaff accelerator was activated and adjusted to the desired operating conditions of 2.0 MeV of the acceleration voltage and 75 microamps of the beam current. The conveyor belt operated at 38 centimeters per minute to transport the polymer bed and the dosimeters through the electron beams. After irradiation, the dosimeters at the top and bottom of the polymer bed were recovered and measured to determine both the correct depth of the bed and the total dose delivered. The polymer used during this test was removed from the system. The feed hopper of the conveyor belt and conveyor belt enclosure were closed to form a gas-tight enclosure, and nitrogen purge was activated to create an oxygen-free atmosphere. At the same time, the pneumatic conveyor system and the fluid bed system were purged with nitrogen. The hot oil systems were adjusted to the proper operating conditions, while progressing the nitrogen purge. The first oil heater was adjusted to control the temperature of the gas stream to 802V and the second oil heater to 140fiC. When the oxygen concentration in the fluid bed system has been reduced to less than 7%, the blower is started from the fluid bed. When the oxygen concentration has been reduced to the desired point by the nitrogen purge, the air is mixed with nitrogen gas stream to maintain the proper concentration of oxygen. Both flow rates of nitrogen and air are adjusted by manual flow meters. After 45 minutes, the concentration of oxygen in the conveyor belt feed hopper, the polymer conveyor belt enclosure and the pneumatic conveyor system is less than 40 ppm of oxygen, as measured by trace oxygen analyzers connected to the conveyor belt enclosure and the pneumatic transport system. During this period of time, the hot oil systems and the fluid bed system have reached a temperature of equilibrium and oxygen concentration. The sample is irradiated using the Van de Graaff accelerator. The conveyor belt is operated at 38 centimeters per minute for 15 minutes and the irradiated polymer is continuously delivered to the fluid bed by the pneumatic transport system. At the end of the 15 minute period, the conveyor belt and the Van de Graaff accelerator are deactivated. The gas flow in the fluid bed is manually adjusted using a valve in the gas stream, while observing the infiltrating action of the polymer. The polymer is treated, in a first step, with the flow of the fluidizing gas, at a temperature of 80 ° C and at the oxygen concentration indicated in Table 1 (24,500 ppm = 2.4% by volume). At the end of the first stage of treatment, the first oil heater is isolated from the heat exchanger of the fluid bed gas stream and the oil heater is deactivated. At the same time, the second oil booster is placed in service, and the temperature of the fluidizing gas stream is raised to 14ose. There is a transition of about 30 minutes before the temperature of the polymer in the fluid bed reaches the gas stream temperature. During this second treatment step, the oxygen concentration is maintained at the previous level for a period of 60 minutes, after the transition time. Following the second stage of treatment, the addition of air is terminated and the rate of flow of nitrogen to the maximum volume is increased. After a five minute transition, the oxygen concentration of the fluidizing gas stream is reduced to less than 40 ppm, while maintaining a temperature of 140QC for 60 minutes. At the end of the third stage of treatment, the first oil heater, which has been cooled, is put back into service and the water flows to the water-to-oil heat exchanger is maximized. During the cooling cycle, the temperature of the polymer in the fluid bed is reduced to less than 802C. The cooling cycle lasts 45 minutes, after which the polymer is discharged from the fluid bed and collected in a stainless steel container. After the polymer has cooled to room temperature, the melt flow of the polymer is measured under the conditions specified by ASTM 1238-D, condition L. The data in Table 1 show that, when the dose varies of radiation, the concentration of oxygen to which the irradiated polymer is exposed, must also be varied in order to obtain the same MFR in the polymer product.

Table 1 This example illustrates the effect on the properties of the cleaved polymer when the concentration of oxygen to which the irradiated polymer is exposed is kept constant and the radiation dose varies. The propylene homopolymer used as the starting material is the same as that described in Example 1. The process conditions and polymer properties are given in Table 2. The flow rate of the melt increases as the dose increases of radiation.

Table 2 EXAMPLE 3 This example illustrates the effect on the properties of the cleaved polymer when the radiation dose, during irradiation, and the concentration of the oxygen to which the irradiated polymer is exposed are kept constant, as well as the duration of the treatment in each of the three stages of treatment, and the temperature in the first stage is varied. The starting material of the propylene homopolymer is the same as that described in Example 1. Process conditions and polymer properties are given in Table 3. The MFR of the cleaved polymer decreases as the temperature in the first stage of the polymer increases. treatment.

Table 3 Example 4 The propylene homopolymer, described in Example 1, it was irradiated at a dose of 2 Mrad and exposed to 20,000 ppm of oxygen under the conditions indicated in Table 3. The content of the oligomer of the starting polymer is 1900 ppm and the content of the oligomer of the cleaved polymer is 727 ppm.

Comparative Example 5 This example shows the effect of MFR over time, when the third treatment step, that is, maintaining the oxygen concentration equal to or less than 0.004% by volume at temperature T2, was omitted after irradiation of the propylene homopolymer. Polymers A and B, both propylene homopolymers, are irradiated and exposed to oxygen, as described in Example 1. Polymer A, commercially available from Montell USA INC. , is a highly porous propylene homopolymer, having xylene solubles (% by weight) at room temperature, 3.5, an MFR of 9.0, a fraction of the pore volume of 0.28, in which more than 90% of the pores they have a diameter greater than 1 miera, and a porosity of 0.45 cc / g. Polymer B is a flake propylene homopolymer, which has an MFR of 23.8 and is commercially available from Montell USA Inc. The MFR of the polymers was measured at regular intervals to determine if this MFR remains stable over time. It can be seen from Table 4 that the MFR increases stably over time when the three stages of the process of this invention are omitted.

Table 4 Example 6 This example shows the effect on polymer properties when the propylene / ethylene random copolymer is irradiated according to the process described in Example 1. The process conditions are shown in Table 5. Polymer C is a copolymer random of propylene and ethylene containing 3.2% ethylene and has a nominal melt flow rate of 1.9 dg / min. Polymer D is a random copolymer of propylene and ethylene, which contains 3.2% ethylene and has a nominal MFR of 13.3. Polymer E is a random propylene / ethylene copolymer containing 3.2% ethylene, having a nominal MFR of 5.5. All random copolymers are commercially available from Montell USA Inc. The polymer properties are shown in Table 5. Polymer E has an oligomer content, before irradiation, of 469 ppm, and an oligomer content of 214 ppm after of irradiation.

Table 5 Example 7 This example shows the effect on polymer properties when a heterophasic propylene polymer material is irradiated according to the process described in Example 1. The heterophasic composition has an MFR of 3.6 and a total ethylene content of 8.9% and it contains 85% of 1 propylene homopolymer and 15% of an ethylene / propylene rubber, which contains 60% ethylene units. The heterophasic material is commercially available from Montell USA Inc. The process conditions and polymer properties are shown in Table 6.

Table 6 Example 8 A polymer cleaved by radiation was obtained by the process described in Example 1, by subjecting the same flakes of propylene homopolymer at a dose of 0.4 Mrad and exposing the irradiated polymer to 24,000 ppm of oxygen in the first and second stages of treatment . Prior to radiation treatment, the propylene homopolymer had a nominal MFR of 20 dg / min and an oligomer content of 1200 ppm. The irradiated polymer was analyzed by the MFR, the polydispersity index (Pl), and the oligomer content. The "peroxide-cleaved polymer" in the table was obtained from a propylene homopolymer having a nominal MFR of 400 dg / min, containing 500 ppm of the peroxide Lupersol 101, available from Atochem, 1000 ppm of the Irganox 1076 antioxidant, available from Ciba Geigy, and 300 ppm of calcium stearate. The polymer is commercially available from Montell USA Inc. The reaction with the peroxide takes place during heating for the determination of the MFR. The results of the analyzes are given in table 7.

TABLE 7 The radiation-split polymer, obtained by the process of this invention, has a narrower MWD and a much lower oligomer content than the peroxide-cleaved propylene homopolymer. Example 9 The polymers described in Example 8 were obtained in blown fabrics in molten form, using a pilot meltblowing line. The spinning conditions used are: Setting rate 0.4 g / hole / min Fusing temperature 232oc Air temperature 232 to 2602C Basic weight 34 g / m2. The fabrics were tested on trapezoid tear strength, bending length, hydraulic head and air permeability. In the table, gsm = grams / m2. The results are given in Table 8.

TABLE 8 MD = Machine Direction - CD = Cross Direction The radiation-split polymer, prepared according to the process of this invention, produces fabrics by blowing the melt, with better trapezoidal strength, in both the length of bending (a measure of the softness of the fabric), the air permeability and the hydrodylic head are similar to those of the tissues obtained from propylene homopolymer fibers cleaved by peroxide. EXAMPLE 10 A small line of laboratory fibers, designated PMSD (stretch of precision cast yarns), was used to determine the solidification point of the polymer samples during spinning of the melt, the "adhesion point" of the polymer . The spinning conditions used are: Setting rate 0.5 g / hole / min Melting temperature 1902C Spinning speed 1000 m / min Cooling air at rest The polymer from which the peroxide split fibers were spun is the same as the one used to obtain the polymer cleaved by peroxide in Example 8. The reaction with the peroxide took place when the polymer was heated for spinning. Radiation-cleaved polymers were prepared as described in Example 1. The radiation dose and the oxygen concentration to which the irradiated polymer is exposed after radiation are indicated in Table 9, as are the results of the measurements of the point of adhesion. TABLE 9 Type of Polymer Point of Adhesion (cm) Cleaved by peroxide 45 Cleaned by radiation at 0.5 Mrad; 30 28,500 ppm 02 Cleaned by radiation at 1 Mrad; 25 21,000 ppm 02 Cleaned by radiation at 2 Mrad; 25 15,500 ppm O2 All three samples of radiation-split polymers have a shorter adhesion point than the polymer cleaved by peroxide. The point of adhesion decreases steadily as the dose level increases. This indicates that the crystallization rate increases with irradiation and that the effect is greater at higher doses. Example 11 In this, example, the plates and test bars were molded of a polymer cleaved by radiation and a polymer cleaved by peroxide, and the physical properties and content of the oligomer were measured and compared. The starting material in both cases is commercially available from Montell USA Inc., and is a random copolymer of propylene and ethylene containing 3.2% ethylene units, with an MFR of 2 dg / min. The polymer is irradiated as described in Example 1, using a radiation dose of 0.5 Mrads and the irradiated polymer was exposed to 15,000 ppm (1.5% by volume) of oxygen under the conditions shown in Table 5. The polymers were mixed with 0.12 parts of the phenolic antioxidant / phosphite B-215, available from Ciba Geigy, 0.05 parts of calcium stearate and 0.20 parts of Millad 3988, a clarification agent available from Milliken. This polymer to be cleaved with peroxide also contains sufficient Lupersol 101 peroxide, available from Elf Atochem, to produce a melt flow of 35 dg / min and 0.06 parts of Atmer 122, an antistatic agent, available from ICI. All parts are by weight per hundred parts of the polymer. The polymer compositions were extruded in a conventional single screw extruder and formed into pellets. The pellet composition was then cast into plates and tested on rods in a 200-ton HPM molding machine, at a melting temperature of 182se and a molding temperature of 60se. The physical properties were measured by the following methods: flexural modulus - ASTM-D 790; Izod slotted resistance - ASTM-D 256; turbidity - ASTM-D 1003-92. The oligomers were determined as volatile by gas chromatography. The color was measured in accordance with ASTM-D 1925-70, Section I, using a Hunter D25P colorimeter in a total transmission mode, which was first standardized using air as a reference. Yellowness is defined as the deviation of the target in the dominant wavelength range of 570 to 580 nm. The yellowness index (Yl) is a measure of the magnitude of the yellowness in relation to the standard reference of magnesium oxide. The smaller the number, the better the color will be. The results of the measurements are given in table 10.

Table 10 The data shows that the polymer cleaved by radiation has mechanical properties that are comparable or better than the product cleaved by peroxide and that this product cleaved by radiation has a much lower volatile content than the polymer cleaved by peroxide. Due to the low volatile content, the irradiated resin has low taste and odor properties. Example 12 This example illustrates the use of the radiation excised polymers of this invention in the extrusion coating.

A propylene homopolymer, having a nominal MFR of 2 dg / min and commercially available from Montell USA Inc., was irradiated according to the procedure described in Example 1. The radiation dose is 1.0 Mrad and the irradiated polymer is exposed to 12,000 ppm (1.2% by volume) of oxygen in the first and second stages. The polymer was maintained at a temperature of 80 ° C for 90 minutes in the first stage and at 140 ° C for 60 minutes in the second stage. In the third stage, the polymer was maintained at 1402C for 60 minutes, in the presence of less than 40 ppm (0.004% by volume) of oxygen. The product had an MFR of about 35 dg / min. A phenolic antioxidant (0.1 part) and calcium stearate (0.07 part) were added to 100 parts of the irradiated polymer and the mixture was extruded in a conventional screw extruder at 230SC and formed into pellets, all parts are by weight . The pellet composition was then extruded through a 6.35 cm Davis-Standar Extruder, with a cylinder length ratio to the diameter of 26: 1 and a metering type screw, with 5 compression flights and 13 metering flights in a central feed, keyhole type of 40.6 cm wide Egan die. The composition was extruded into a moving substrate just before the substrate enters the space between a cooling roller and a squeezing roller. The following conditions apply to the formation of the extrusion coated product. Cylinder temperatures 104, 160, 288 and 3042C Adapter temperature 321SC Die temperature 3212C Air gap 8.9 cm Coolant roller temperature 162C Tightening pressure 13 kg / cm2 Substrate 13.6 kg / ream (500 sheets, 61 cm x 91.4 cm) unbleached kraft paper Line speed range of the intake system 30 m / min - 305 m / min.

Extrusion rate 36.3 kg / h Example 13 This example illustrates the use of the radiation excised polymers of this invention, in obtaining a blown film. A random copolymer of propylene and ethylene, containing 3.2% ethylene, with a nominal MFR of 1.9 dg / min and commercially available from Montella USA Inc., was irradiated according to the process described in Example 1. The radiation dose is 0.5 Mrad and the irradiated polymer was exposed to 3,000 ppm (0.3% by volume) of oxygen, in the first and second stages. The polymer was maintained at a temperature of 80 seconds for 90 minutes in the first stage and at a temperature of 120 seconds for 60 minutes in the second stage. In the third step, the polymer was maintained at a temperature of 12 ° C for 60 minutes in the presence of less than 40 ppm oxygen. The excised product had an MFR of 9 dg / min. A phenolic antioxidant (0.1 part) and calcium stearate (0.07 part) were added to 100 parts of the irradiated polymer in a conventional single screw extruder at 23 ° C and the mixture formed into pellets. All parts are in weight. The composition in pells was then extruded in a chilled water-cooled, modified film, Chi Chang, comprising a 50 mm extruder, with a length-to-cylinder ratio of 26: 2, and an annular diameter die of 100 mm without the usual water ring, but with a larger capacity blower connected to the air ring. This air ring is a single lip with a lip angle of 45S and is located at 4.25 cm below the die. The hollow of the air ring is adjustable, but it was placed at 9 mm. The height of the tower is 1.9 meters. The polished squeezing rollers are driven by a variable speed motor that allows the linear output speed of the film to be adjusted. The following conditions apply to the formation of the blown film product: Process temperature 200se Extrusion rate 14.4 kg / h Derating ratio, MD / CD 6.7 / 2.7 MD = Address of the machine CD = Direction transverse to the machine Other features, advantages and embodiments of the invention described herein will be readily apparent to those of ordinary skill in the art after reading the above description. In this regard, while specific embodiments of the invention have been described in considerable detail, variations and modifications of these embodiments can be made, without departing from the spirit and scope of the invention, as described and claimed.

Claims (15)

1. CLAIMS 1. A propylene homopolymer, having an adhesion point of 30 cm or less, during spinning of the melt, an oligomer content of less than 1500 ppm, without a post-polymerization treatment to remove the oligomers, and a flow rate of the melt greater than 300 dg / minute.
2. 2. A fiber, which comprises the propylene homopolymer according to claim 1.
3. 3. A nonwoven material, blown in molten form, which comprises the fibers according to claim 2.
4. 4. A non-woven material joined by spinning, the which comprises the fibers according to claim 2.
5. 5. A method for treating an irradiated propylene polymer material, this method comprises: (J) exposing an irradiated propylene polymer material, containing a free radical, selected from the group consisting of of (a) propylene homopolymers, having an isotactic index of at least 90, (b) random copolymers of propylene and ethylene or butylene, or random terpolymers of propylene, ethylene and butylene, in which the maximum ethylene content or content of ethylene plus butylene, is 10% by weight, having an isotactic index of at least 80 and (c) heterophasic materials of propylene polymers, which consist essentially, by weight, of (i) 99-55% d and a polymeric material, selected from the group consisting of a propylene homopolymer, having an isotactic index greater than 90, and a crystalline copolymer of propylene and an alpha-olefin of the formula CH2 = CHR, where R is H or a group alkyl, linear or branched, with 2 to 6 carbon atoms, having an isotactic index of at least 80, the alpha-olefin being less than 10% of the copolymer; e (ii) from 1 to 45% of an elastomeric olefin polymer of propylene and an olefinic material selected from the group consisting of alpha-olefins of the formula CH2 = CHR, where R is H or an alkyl group, linear or branched, of 2 to 6 carbon atoms, the alpha-olefin being from 50 to 70% of the elastomeric polymer, to a controlled amount of active oxygen of more than 0.004% and less than 15%. % by volume, at a temperature T ^ of 40 to lyso, (//) heating the polymer to a temperature T2 of at least 110se, in the presence of a controlled amount of oxygen, within the same range as in the stage (1) ) and (///) keep the polymer at temperature T2, in the presence of 0.004% or less in volume of active oxygen.
6. 6. A propylene polymer material, obtained by the process of claim 5.
7. 7. A composition for forming films, consisting essentially of the propylene polymer material of claim 6.
8. 8. An extrusion coating composition, consisting essentially of the propylene polymer material of claim 6.
9. 9. A composition for forming films , which consists essentially of the propylene polymer material of claim 6.
10. 10. An injection molding composition, which consists essentially of the propylene polymer material of claim 6.
11. 11. A film comprising the propylene polymer material. 7. A fiber comprising the propylene polymer material of claim 6. 13. A non-woven material, which comprises the fiber of claim
12. 12. 14. An injection molded article, which it comprises the propylene polymer material of claim 6. 15. A mixture of the propylene polymer material of the reivi 6 and from 5 to 95% by weight of a linear polymer material of propylene, semi-crystalline, predominantly isotactic, normally solid.