KR100266044B1 - Irradiated ethylene polymer, process for making it, and use thereor - Google Patents

Abstract

The present invention is characterized by having a high melt strength due to strain hardening, which is believed to be due to the free terminal long side chains of the molecular chains forming the polymer, having a density of 0.89 to 0.97 g / cc, usually solid, gel-free irradiated high A molecular weight ethylene polymer relates.

In addition, the present invention is directed to irradiating high-energy radiation to a high-molecular weight ethylene polymer, which is usually a solid under reduced oxygen, and to maintaining the irradiated material in the environment for a certain period of time, and then deactivating the free radicals in such material A method for producing the polymer.

Description

Process for preparing ethylene polymer material investigated, the polymer material and use thereof

1 is a schematic working flow diagram of a preferred embodiment of a continuous process for converting, for example, polyethylene, which is typically solid, to polyethylene that does not contain gel, which is normally solid, with strain hardening.

2 shows the elongational viscosity versus elongation time of two samples, the free end ego chain branched high density polyethylene obtained with the method of the present invention and the control high density polyethylene.

3 shows the elongation viscosity versus elongation time of the free end long chain branched low density polyethylene and control linear low density polyethylene (LLDPE) samples obtained by the process of the present invention.

The present invention is in the chemical art. In particular, the present invention relates to chemical techniques related to synthetic resins derived from α-olefins or 1-olefins. Specifically, the present invention relates to a synthetic resin formed by polymerizing ethylene alone or together with other olefins.

Synthetic resin produced by polymerizing only ethylene as a monomer is called polyethylene. "Polyethylene" has sometimes been used in the art to include copolymers of ethylene with a small amount of another monomer, such as butene-1, but the term is not used herein as such.

Currently commercially available polyethylenes, such as low density polyethylene (LDPE) and high density polyethylene (HDPE), and copolymers of ethylene and C ₃ -C ₁₀ α-olefins (commonly referred to as linear low density polyethylene (LLDPE)) are known as specific monomers ( S) are usually solid and somewhat soft thermoplastic polymers prepared by polymerization by various methods well known in the art. For example, such polymers can be prepared by free radical polymerization under high pressure or by low pressure processes (eg, gas phase technology of fluidized beds) using molybdenum-based catalysts, chromium-based catalysts and Ziegler-Natta catalyst systems. have. High pressure processes produce polymers with long chain branches and low pressure processes produce essentially linear polymers with a limited degree of short chain branches. In the Ziegler-Natta catalyst system, the catalyst is formed by an inorganic compound (eg aluminum alkyl) of the Group I to III metals of the periodic table and a compound of Group IV to VIII transition metals (eg titanium halide) of the periodic table. Is formed. See Wunderlick & Guar, J. Phys. Chem. Ref. Data, Vol 10, No. Typical crystallinity measured by the method described in 1 (1981)] is about 21 to about 75% by weight. In addition, typical melt indices of such ethylene homopolymers or copolymers are from 0.2 to 50 g / 10 min (measured according to ASTM 1238, condition E). Moreover, the melting point of the crystalline phase of polyethylene, which is a commercially available common solid, is about 135 ° C.

Although commercially available linear polyethylenes have numerous desirable and beneficial properties, they have poor melt strength. Upon melting, these linear polyethylenes exhibit no strain hardening (increase in stretch resistance during stretching of the molten material). Thus, linear polyethylene includes the initiation of edge weave during high-speed extrusion coating of paper or other supports, sheet sag during melt thermoforming, and local lamination and flow instability during coextrusion of laminate structures. Has various drawbacks in melt processing. As a result, the use of these polyethylenes has been limited to potential applications such as, for example, extrusion coating, blow molding, profile extrusion and thermoforming.

In the art, efforts have been made to overcome the melt strength deficiency of such commercially available polyethylene.

Irradiation of polyethylene is known in the art, but such irradiation is required to crosslink the polyethylene, such as products processed from polyethylene at high dose levels, ie greater than 2 Mrads, such as films, petroleum and Sheet). For example, US Pat. No. 4,668,577 describes a method for crosslinking filaments of polyethylene, and US Pat. Nos. 4,705,714 and 4,891,173 describe methods for differentially crosslinking sheets made of high density polyethylene. . Polyethylene crosslinked by these methods has been reported to improve melt strength but decrease solubility and melt flowability. However, cross-linking undesirably reduces the melt extensibility of polyethylene, which typically limits the stretch length required for film or fiber applications.

Another attempt to improve the melt strength and melt extensibility of polyethylene by exposing linear polyethylene to low doses, high energy radiation of 0.05 to 0.3 Mrad, is described in US Pat. No. 3,563,870.

European Patent Application No. 047171 discloses heat aging by pretreatment of polymer granules with a steam atmosphere to reduce the oxygen content in the ethylene polymer granules, and the polymers thus treated are irradiated at a dose of less than 1.5 Mrad. A method is disclosed for irradiating an ethylene polymer by steam treating the irradiated polymer.

British Patent No. 2,019,412 relates to increasing the elongation value at break by irradiating a linear low density polyethylene (LLDPE) film at 2 to 80 Mrad.

US Pat. Nos. 4,586,995 and 4,598,128 disclose terminal vinyl unsaturation in ethylene polymers having no unsaturated end groups or heating endethylenes in polyethylene having no unsaturated end groups by heating the ethylene polymers under gelling and not oxidizing conditions. To increase the unsaturation and irradiate the heat treated ethylene polymer at a dose of 0.1 to 4 Mrad and then cool the resulting irradiated polymer gradually or rapidly to obtain a long chain “Y” branch in the ethylene polymer. .

U.S. Patent No. 4,525,257 discloses an increased elongational viscosity compared to the corresponding uncrosslinked polyethylene by irradiating a narrow and linear low density ethylene / C ₃ -C ₁₈ α-olefin copolymer in a dose of 0.05 to 2 Mrad in a molecular weight range. And methods of making copolymers that are crosslinked but not gelled to a degree sufficient to provide substantially equivalent high shear viscosity. Such irradiated copolymers reduce or eliminate residual radical intermediates without deactivation.

In one embodiment the present invention has a density from 0.89 to 0.97 g / cc, the molecular chains thereof having a significant amount of free-long side chains, a branching index of less than 1, a significant strain hardening elongation viscosity, usually solid and gels. Free irradiated high molecular weight polyethylene.

More broadly, the present invention includes irradiated high molecular weight ethylene polymer materials having a branching index of less than 1, having significant strain hardening elongation viscosity, and which are typically solid and gel-free.

Ethylene polymers of the present invention have a reduced melt index (as evidenced by I ₂ at 190 ° C.) demonstrating an increase in molecular weight, an increase in the melt index ratio (I ₁₀ / I ₂ ) indicating an extended molecular weight distribution, enhanced Melt tension and strain hardening elongation viscosity, and a branching index of less than one.

Ethylene polymers of the present invention are prepared by low dose radiation under controlled conditions.

As used herein, "ethylene polymer material" refers to (a) homopolymers of ethylene, (b) C ₃ -C having a maximum content of polymerized α-olefins of about 20% by weight (preferably about 16% by weight). A random copolymer of ethylene with an α-olefin selected from the group consisting of ₁₀ α-olefins, and (c) said α-olefins having a maximum content of polymer α-olefins of about 20% by weight (preferably about 16% by weight); Ethylene polymer material selected from the group consisting of random terpolymers with ethylene. C ₃ -C ₁₀ α-olefins include straight and branched α-olefins such as propylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4 -Dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene and the like.

If the ethylene polymer is an ethylene homopolymer, its density is typically at least 0.960 g / cm ³ , and if the ethylene polymer is an ethylene copolymer with a C ₃ -C ₁₀ α-olefin, its density is typically 0.91 g / cm ^{It is 3} or more and less than 0.94 g / cm <^3> . Suitable ethylene copolymers are ethylene / butene-1, ethylene / hexene-1, ethylene / octene-1 and ethylene / 4-methyl-1-pentene. The ethylene copolymer can be HDPE or short chain branched LLDPE and the ethylene homopolymer can be HDPE or LDPE. The density of LLDPE and LDPE is typically 0.910g / cm ³ or more and less than 0.940g / cm ^3, the density of HDPE is 0.940g / cm ³ or more, typically 0.950g / cm ³ or more. In general, ethylene polymer materials having a density of 0.89 to 0.97 g / cc are suitable for use in practicing the present invention. The ethylene polymer is preferably LLDPE and HDPE having a density of 0.89 to 0.97 g / cc.

As used herein, "high molecular weight" means that the weight average molecular weight is about 50,000 or more.

The branching index is a quantification of the long chain branching degree. In a preferred embodiment the branching index is preferably less than about 0.9 and most preferably about 0.2 to 0.8.

This is defined as:

Wherein g 'is the branching index, [IV] _Br is the intrinsic viscosity of the branched ethylene polymer material, [IV] _Lin is the corresponding ethylene polymer material, ie the weight average molecular weight is about the same, and the ethylene copolymer and For terpolymers, it is the intrinsic viscosity of an ethylene polymer material which is a common solid with about the same relative molecular ratio (s) of monomer units.

Intrinsic viscosity in the most common sense, also known as the limiting viscosity number, is a measure of the polymer molecule's ability to enhance the viscosity of a solution. This depends on both the size and shape of the dissolved polymer particles. Thus, when comparing a nonlinear polymer with a nearly identical linear polymer of weight average molecular weight, the intrinsic viscosity indicates the form of the nonlinear polymer molecule. Indeed, this ratio of intrinsic viscosity is a measure of the degree of branching of the nonlinear polymer. Methods for determining the intrinsic viscosity of ethylene polymer materials are described in J. App. Poly. Sci., 21, pp 3331-3343 (1977).

The weight average molecular weight can be measured by various methods. However, the process preferably used herein is described in McConnell in Am. Lab., May 1978, in the article entitled "Polymer Molecular weights and Molecular Weight Distribution by Low-Angle Laser Light Scattering".

Elongational viscosity is the resistance to elongation of a fluid or semi-fluid material. This is a melting characteristic of thermoplastics that can be measured with a device that measures the stress and strain of a specimen in the molten state when subjected to tensile strain at a constant rate. One such device is shown and described in FIG. 1 of Munstedt, J. Rheology, 23, (4), 421-425, (1979). A commercial device of similar design is the Rheometrics RER-9000 extensional rheometer. As the molten high molecular weight ethylene polymer material elongates or elongates from a relatively fixed point at a constant rate, the distance increases with elongation rate, and then rapidly decreases until there is little so-called ductile or necking failure. Elongational viscosity tends to be shown. On the other hand, the molten ethylene polymer material of the present invention is about the same in weight as the corresponding molten high molecular weight ethylene polymer material and the test temperature is almost the same, as it is elongated or stretched from a relatively fixed point at about the same elongation rate. The tendency to increase over long distances shows elongational viscosity and is broken or broken by fracture, so-called brittleness or elastic fracture. This property is an index of strain hardenability. In fact, the greater the long chain branching of the ethylene polymer material of the present invention, the greater the tendency for the stretch viscosity to increase as the stretched material approaches defects. The latter tendency is most evident when the branching index is less than about 0.8.

Melt tension also provides an indication of the melt strength of the material. Melt tension is measured using a Gottfert Rheotens melt tension apparatus (manufactured by Gottfert Inc.) by measuring the tension of strands of molten ethylene polymer in centi-newtons as follows. The polymer to be tested is extruded at 180 ° C. through a 20 mm long, 2 mm diameter capillary, and then the strand is drawn using a drawing system with a constant acceleration of 0.3 cm / sec ² . The tension generated from the stretching process described above (in centi-Newtons) is measured. Higher melt tension means higher melt strength values, which in turn are indicative of the strain hardening force of a particular material.

In another aspect the present invention provides a practical process for converting high molecular weight ethylene polymer materials that are typically solids into conventional solid, gel-free ethylene polymer materials having a branching index of less than 1 and having significant strain hardened elongation viscosity.

The method,

(1) the high molecular weight ethylene polymer material,

(a) under an environment where the active oxygen concentration is maintained at less than about 15% by volume of the environment; (b) about 1 to about for a time sufficient to expose to radiation below 2.0 Mrads but insufficient to cause gelation of the material. Irradiated with high energy ionizing radiation in the dose rate in the range of ¹ × 10 ⁴ Mrads / min,

(2) the material so irradiated is kept in this environment for a time sufficient to produce a significant amount of long chain branches,

(3) treating the irradiated material under the above environment to deactivate almost all free radicals present in the irradiated material.

The ethylene polymer material treated according to the method of the present invention may be a high molecular weight ethylene polymer material which is any conventional solid. In general, the intrinsic viscosity of the ethylene polymer starting material, which is an indicator of molecular weight, should be about 1 to 25, preferably 1 to 6, resulting in the desired product having an intrinsic viscosity of 0.8 to 25, preferably 1 to 3. However, ethylene polymer materials with intrinsic viscosities greater and smaller than these general values also exist within the broad scope of the present invention. Ethylene polymer materials having a melt index of at least about 0.01 can be used.

The ethylene polymer material treated according to the process of the invention under the broadest concept of the process of the invention may be in certain physical forms, for example, finely divided particles, granules, pellets, films, sheets and the like. However, in a preferred embodiment of the process of the invention, satisfactory results are obtained when the ethylene polymer material is in the form of pellets or spherical particles. Preferred spherical particle forms with an average diameter of greater than 0.4 mm are preferred.

The active oxygen content of the environment in which three process steps are performed is an important factor. The expression "active oxygen" as used herein refers to oxygen in the form of reacting with the irradiated material and in particular with the free radicals in the material. This includes molecular oxygen (a form of oxygen commonly found in air). The active oxygen content required for the process of the invention can be obtained by using a vacuum or by replacing some or all of the air in the environment with an inert gas such as nitrogen.

Ethylene polymer materials immediately after preparation usually contain little active oxygen. Therefore, it is within the concept of the present invention to carry out the polymerization step and the polymer work-up steps (if the ethylene polymer material is not exposed to air) using the process of the invention. In most cases, however, ethylene polymer materials have active oxygen content because they are stored in air or for some other reason. As a result, in a preferred implementation of the process of the invention, the finely divided ethylene polymer material is first treated to reduce its active oxygen content. A preferred method of carrying out this treatment is to introduce the material into a bed of the same blown with nitrogen, the active oxygen content of which is no greater than about 0.004% by volume. The residence time of the material in the phase should be at least about 5 minutes effective to remove active oxygen from the gaps of particles of the material, preferably long enough to allow the material to be in equilibrium with the environment.

The ethylene polymer material prepared between this preparation step and the irradiation step should be maintained in an environment where the active oxygen concentration is less than about 15% by volume, preferably less than 5% by volume and more preferably less than 0.004% by volume in the gas delivery system. In addition, the temperature of the ethylene polymer material should be maintained above the glass transition temperature of the amorphous fraction of the ethylene polymer material but below about 70 ° C, preferably below about 60 ° C.

The concentration of active oxygen in the environment in the irradiation step is preferably less than about 5% by volume, more preferably less than about 1% by volume. The most preferred concentration of active oxygen is less than 0.004% by volume.

In the irradiation step, the ionizing radiation should have enough energy to penetrate the desired mass of ethylene polymer material to be irradiated. The energy must be sufficient to ionize the molecular structure and then excite the atomic structure, but not enough to affect the atomic nucleus. Ionizing radiation can be of any kind, but most practical kinds include electrons and gamma rays. Preference is given to electrons emitted from an electron generator having an acceleration potential of 500 to 4,000 KV. Satisfactory results in the case of ethylene polymer materials are generally less than about 0.2 to 2.0 Mrads, preferably less than 0.3 to 2.0 Mrads, carried at a dose rate of about 1 to 10,000 Mrads / min, preferably about 18 to 2,000 Mrads / min. Most preferably at a branch dose of ionizing radiation of 0.5 to 1.5 Mrads.

The term "rad" is usually defined as the amount of ionizing radiation that causes it to absorb 100 erg of energy per gram of irradiated material, regardless of the radiation source. As far as the present invention is concerned, the amount of energy absorbed by the ethylene polymer material is not usually measured when irradiated. However, in the general practice of the method, the amount of energy absorption from ionizing radiation is measured using a known conventional dosimeter, which is a measuring device in which a fabric strip comprising a radiation sensitive dye is an energy absorption sensing means. Thus, as used herein, the term "rad" refers to ionizing radiation that absorbs an equivalent amount of energy of 100 ergs per gram of fabric of the radiation meter placed on the surface of the ethylene polymer material being irradiated, whether in the form of particles or films or sheets. It means quantity.

The second step of the process according to the invention should generally be carried out for a time ranging from about 1 minute to about 1 hour and preferably from about 2 to 30 minutes. The minimum time is required for the combination to sufficiently transfer the ethylene polymer chain fragments to the free radical sites, wherein the complete chain is re-formed or long chain branches are formed in the chain. Radical shift times of less than 1 minute [eg, about 30 seconds] are within the broad concept of the present invention, but are not preferred because the amount of free chain long chain branch obtained is very small.

The final step of the process, the free radical deactivation or quenching step, can generally be carried out by applying heat at 60 to about 280 ° C. or by adding an additive (eg methyl mercaptan) that acts as a free radical trap. have.

In one embodiment of the process of the invention, the application of heat comprises a melt extrusion process of the irradiated ethylene polymer material. As a result, the quenching of the free radicals is substantially completed. In this embodiment, the irradiated ethylene polymer material may be blended with other polymers, optionally with additives such as stabilizers, pigments, fillers, etc., prior to extrusion or melt blending. Alternatively, this additive may be incorporated into the extruder as side stream addition.

In another aspect of the process of the invention, the application of heat is accomplished by introducing the irradiated ethylene polymer material into a fluidized or staged fluidized bed system in which the flow medium is, for example, nitrogen or other inert gas. The phase (s) are maintained at a temperature range of at least about 60 ° C. up to the melting point of the polymer, wherein the average residence time of the irradiated ethylene polymer material in the fluidized bed (s) is from about 5 to about 120 minutes, from about 20 to 30 minutes is optimal.

The product thus obtained is a high molecular weight ethylene polymer material which is usually solid and free of gel, characterized by strain hardenability. In addition, the material is characterized by a melt index ratio of greater than 10.

The process of the invention can be carried out batchwise, but is preferably carried out continuously. In one of the continuous embodiments of the process, the finely divided ethylene polymer material is included with or without the preparation step and laminated onto the moving belt in the required environment depending on the active oxygen content of the material. The thickness of the layer depends on the required degree of ionizing radiation and the proportion of irradiated ethylene polymer material needed for the final desired product. The moving speed of the moving belt is selected to pass through the beam of ionizing radiation at a rate at which the finely divided layer of ethylene polymer material receives the desired dose of ionizing radiation. After receiving the required dose of ionizing radiation, the irradiated layer is left on a moving belt in the environment for the time that the movement and combination of free radicals occur, then removed from the belt and operated at the melting temperature of the irradiated material Or into another particular embodiment into a heated or heated phased system of irradiated material particles fluidized with nitrogen or other inert gas. In another embodiment, the irradiated material is released to the atmosphere after at least virtually all free radicals in it are deactivated and cooled rapidly to room temperature. In another embodiment, the irradiated ethylene polymer material is removed from the belt and transferred from the required environment to a support vessel containing the required environment therein and then maintained in the vessel to complete the required free radical transfer time. The irradiated material is then introduced into an extruder running at the melting point of the irradiated material or into a heated inert gas fluidized bed or fluidized staged system of irradiated particles of ethylene polymer material and quenched free radicals. The irradiated polyethylene is then released into the atmosphere.

In another aspect the invention encompasses the use of extensional flow of the modified curable ethylene polymer materials of the invention. Extensible flow occurs when the molten ethylene polymer material is pulled in one or more directions at a rate faster than the flow direction. This occurs in an extrusion coating process in which the molten coating material is extruded onto a support (eg, a moving web of paper or metal sheet) and the extruder or support is moved at a speed faster than the extrusion speed. This occurs in film production which extrudes the molten film and then stretches it to the desired thickness. It is also present in the thermoforming process where the molten sheet is stacked on the plug mold, vacuum is applied and then the sheet is pushed into the mold. This occurs in the manufacture of foam articles which expand the molten ethylene polymer material with a blowing agent. The modified cured ethylene polymer material of the present invention is part of the molten plastic material used in the above-mentioned melt process and other melt processes (eg, profile extrusion during melt spinning of fibers) for producing useful products. (E.g., 0.5 to 95% by weight or more) or in particular almost all.

The invention is further illustrated through the accompanying drawings and embodiments which illustrate aspects of forming the material portions described above.

FIG. 1 introduces finely divided high molecular weight polyethylene through conduit 11 and nitrogen gas through conduit 13 from which a high molecular weight polyethylene with little free radicals is fitted with a solid flow rate regulator 16. The flow bed unit 10 of a conventional construction and operation is shown to be removed through the solid discharge conduit 15. Solids are discharged to the discharge conduit 15 and transferred to the conveyor belt feed hopper 20.

The conveyor belt feed hopper 20 is a capped structure of a conventional design. It is manipulated so that its interior contains a nitrogen atmosphere. At the bottom is a solid discharge outlet where polyethylene particles move to form a layer on the top horizontal actuator of the endless conveyor belt 21.

The conveyor belt 21 is generally arranged horizontally and continuously moves under normal operating conditions. It is contained in a radiation chamber 22. This spinning chamber completely surrounds the conveyor belt and is constructed and manipulated to install and maintain a nitrogen atmosphere therein.

Connected with the radiation chamber 22 is an electron beam generator 25 of conventional design and operation. This generates a high energy electron beam in the direction of the layer of polyethylene particles on the conveyor belt 21 under normal operating conditions. Below the discharge end of the conveyor belt is a solid collector 28 arranged to receive irradiated polyethylene particles falling from it as the conveyor belt 21 is rotated in the opposite travel path. Irradiated polyethylene particles in solid collector 28 are removed by rotary valves or star wheels 28 and moved to solid transfer line 30.

The moving line 30 is connected to the gas-solid separator 31. This unit is a conventional structure and usually a cyclonic separator. The separated gas is removed by the gas exhaust conduit 33 and the separated solid is discharged to the solid discharge line 34 by a rotary valve or star wheel 32. The solid discharge line 34 may be directly connected to the extruder hopper 35.

The extruder hopper 35 fed to the extruder 36 is conventional in structure and operation. Also, it is a sealed structure in which a nitrogen atmosphere is installed and maintained therein. The extruder 36 is of conventional construction and is operated in a conventional manner. The solids in the extruder hopper 35 are transferred into the extruder which is operated at a speed of the extruder sufficient for the time to irradiate the polyethylene and introduce it into the extruder so that a significant amount of free end long chain branch is formed. Thus, the volume of the extruder hopper 35 is chosen to provide the hopper storage time needed to satisfy this jogger, if necessary. The extruder 36 is designed (length of the extruder barrel and screw) and operated at a pressure and melting point sufficient to maintain the free radical containing polyethylene for the time necessary to deactivate nearly all free radicals present.

The finely divided polyethylene thus treated is characterized by almost no gel, has a density of 0.89 to 0.97 g / cc, and is virtually branched into free terminal long chains of ethylene units. It can be used as such or for example by a solid transfer line 38 as solid pellets which can be introduced directly into the pelletizing and cooling unit 37_ and used after being stored or used without being stored. Is moved from.

Similar results are obtained when other specific embodiments of high molecular weight ethylene polymer materials are treated according to the continuous process just described.

The following examples illustrate the high molecular weight polyethylene of the present invention and the preferred embodiment of the method for preparing the same.

Melt index, I ₂ and I ₁₀ are measured according to ASTM D-1238. Melt index ratio is measured by dividing I ₁₀ by I ₂ . The ratio indicates molecular weight distribution, and the larger the number, the wider the molecular weight distribution.

Example 1

Soltex T50-200 polyethylene in pellet form with a MI of 2 and a density of 0.95 is introduced into the closed spinning chamber 22 and purged with nitrogen until the oxygen concentration reaches 40 ppm.

The material is distributed on a moving stainless steel conveyor belt 21 to form an image of polyethylene powder (height 1.3 cm, width 15 cm). The conveyor belt passes the phase into an electron beam produced by a 2MeV Van de Graff generator operating at 50 microamperes (μA) beam current. The absorbed surface dose obtained is 0.40 Mard. In addition, the oxygen content in the environment within the closed spinning chamber 22 or in the rest of the system including the atmosphere and the irradiated polyethylene transfer line 30, solid-gas separator 31 and separator discharge line 34. Is maintained at less than 140ppm.

After irradiation, the polyethylene is moved from the end of the conveyor belt 21 to the belt discharge collector 28 and through the rotating belt 29 to the movement line 30. After separating the gas from the irradiated polymer, the polymer is fed through a separator discharge line 34 to a bag purged with nitrogen.

The irradiated polyethylene is kept for 30 minutes at room temperature in the absence of oxygen. The material is introduced into an extruder feed hopper purged with nitrogen and then extruded at 260 ° C. in a 2.5 ”single screw extruder.

The properties of the gelless final product of Example 1 are summarized in Table I.

[Examples 2 to 4]

The products of Examples 2-4 are prepared using the methods and components of Example 1, except that the absorbed surface doses obtained are 0.6, 0.9 and 1.0 Mrad, respectively. Oxygen concentration is maintained below 60 ppm in the closed spinning chamber 22, the irradiated polyethylene moving line 30, the solid-gas separator 31 and the separator discharge line 34. The properties of the gel-free final product of Examples 2-4 are summarized in Table I.

[Examples 5 to 8]

Dow 04052N polyethylene in pellet form having a MI of 4 and a density of 0.952 and the absorption surface doses obtained were 0.5, 0.7, 0.8 and 1.0 Mrad, respectively, using the method and components of Example 1. Prepare the products of Examples 5-8. The oxygen concentration is maintained at less than 100 ppm in the closed spinning chamber 22, the irradiated polyethylene transfer line 30, the solid-gas separator 31 and the separator discharge line 34. The properties of the gel-free final product of Examples 5-8 are summarized in Table I below.

[Control Examples 1 and 2]

Controls 1 and 2 are unirradiated samples of Soltex T 50-200 and Dow 04052N, respectively.

TABLE I

Example 9 and Control Examples 3 to 8

Radiation Intermediate Aging (RIA) in a restricted environment with less than 15% oxygen content corresponding to irradiation step (IA) corresponding to irradiation step (1) of the process and second step (2) of the process and the process of the invention To show the importance of the radical intermediate inactivation step (RID) corresponding to the final step, the products of Example 9 and Control Examples 4-8 are prepared using the method of Example 1 except for the following:

Instead of Soltex T50-200, use high density polyethylene (manufactured by HIMONT Italia S.r.l.) with a spherical granular MI of 6.90,

The absorbed surface dose obtained is 1.1 Mrad and

The processing environment of the control 3 to 8 is changed as shown in Table II,

Radical deactivation is carried out in a 3/4 "Brabender Extruder at about 260 ° C.

The results are shown in Table II below.

TABLE II

Control Examples 5 and 8 show an unstable melt flow rate over 13 days when compared to Example 9 of the present invention. Control Examples 4, 6 and 7 show a somewhat more stable melt flow rate than Control Examples 5 and 8 but are not as low as Example 9 of the present invention.

[Examples 10 to 15 and Control Examples 9 and 10]

The ethylene polymer used is fed through a separator discharge line 34 into a nitrogen purged hopper of a 3/4 "Brabender extruder, 21 ° C. in the first zone, 215 ° C. in the second zone, and 220 ° C. in the die. The product of Examples 10-15 was prepared using the method of Example 1, except for pelleting by the phosphorous method, and the pellet was then equipped with a 100 rpm Murdock mixer at a flat cross section of 420 ° F. Extruded with 0.1% Irganox 1010 stabilizer in a 1-1 / 4 "Killian single screw extruder. The standing time between irradiation and extrusion is on average about 15 minutes. The properties of the final products of Examples 10-15 are summarized in Table III and are examples 10, 12 and 14, measured using a rheometrics PER 9000 extended flow meter at 180 ° C. at a strain rate of 0.05 to 2.0 sec ⁻¹ . And extensional viscosities of Examples 9 and 10 are shown in FIGS. 2 and 3.

TABLE III

(1) Measured using Gottfert Inc.'s Gottfert rhetens melt tension device by measuring the standard tension of the strand of molten ethylene polymer in centi-Newton units as follows: The polymer is extruded through a capillary tube having a length of 20 mm and a diameter of 2 mm at 180 ° C; The strand is then stretched using a stretching system with a constant acceleration of 0.3 cm / sec ² . The higher the tension, the better the viscoelasticity, and therefore the better the workability of the polymer in the molten state.

(2) Intrinsic viscosity measured in decalin at 135 ° C.

(3) Wyatt Dawn laser in trichlorobenzene at 135 ° C

Weight average molecular weight measured by laser light scattering with a light scattering apparatus (manufactured by Wyatt Technology Corporation).

(4) Branching Index: [IV] _Lin = 2.77 × 10 ^-4 Mw ^0.725

(5) High density polyethylene containing 0.5% propylene monomer units in pellet form with a Dow Chemical melt index (MI) of 3.9.

(6) LLDPE containing 6.1% butene-1 monomer units, mixed at 200 parts per million parts of Irganox 1076 stabilizer (MIMON 7.9, pelletized by HIMONT Italia S.r.1) in MI.

From the results shown in the table above, it can be seen that the ethylene polymer of the present invention has an increased melt index ratio, which demonstrates an increase in molecular weight distribution, an increased melt tension indicating an increase in melt strength, and a branching index indicating the formation of long side chains. have.

The results shown in FIGS. 2 and 3 show that the ethylene polymer of the present invention has an elongational viscosity, which indicates the strain hardening force of the material. The trend for strain hardened elongation viscosity increases with decreasing branching index, i.e., with increasing long chain branching.

The free end long chain branched ethylene polymer material of the present invention is a melt process operation for forming useful products such as foamed and thermoformed products, such as foamed and thermoformed sheet materials, extrusion coated products and fibers, for example. Useful for In addition, the strain curable ethylene polymer materials of the present invention are useful for all melt process operations aimed at high molecular weight ethylene polymer materials with improved melt strength.

Other features, advantages, and aspects of the invention described herein will be apparent to those of ordinary skill in the art upon reading the disclosure herein. In this regard, while certain aspects of the invention have been described in considerable detail, changes and modifications in these aspects can be made without departing from the spirit and scope of the invention described and claimed.

As used herein, the expression “consisting essentially of” permits the presence of one or more unmentioned substances in concentrations that are insufficient to substantially adversely affect the above essential properties and properties, while the essential properties of the composition of the defined material And materials not mentioned at concentrations sufficient to substantially adversely affect the properties.

Claims (11)

(1) a high density polyethylene, and a random copolymer and terpolymer of ethylene and C _3-10 alpha olefin, wherein the ethylene content of the copolymer and terpolymer is at least 80% by weight and the polyethylene, Copolymers and terpolymers are prepared by low pressure polymerization, each using a Ziegler-Natta catalyst system, each having a weight average molecular weight of 50,000 or more, and in the solid state, an ethylene polymer material having no strain hardening elongation viscosity, in the solid state, (B) sufficient to be exposed to radiation of 2.0 Mrad or less, under conditions in which the active oxygen concentration remains above 15 vol% of the environment at temperatures above 70 ° C. but above the glass transition temperature of the amorphous fraction of the ethylene polymer material. 1 to 1 × 10 ⁴ per minute for an insufficient time to cause gelation of the ethylene polymer material Irradiated with high-energy ionizing radiation in the dose rate in the Mrad range, and (2) to obtain free-end long-chain branches sufficient to cause the irradiated material to have a branching index of less than 0.9 and to have a strain hardening elongation viscosity. Maintaining the irradiated material in a solid state under the above-mentioned environment for a sufficient time, and then (3) treating the irradiated material under the above-mentioned environment to deactivate all free radicals present in the irradiated material. A process for producing an irradiated ethylene polymer material having a strain hardening elongation viscosity and which is usually solid, high molecular weight and gel-free from a normally solid ethylene polymer material without strain hardening elongation viscosity. The method of claim 1, wherein in the solid state prior to irradiation, the ethylene polymer material is maintained under the environment described in part (1) (a). The method of claim 1 wherein the active oxygen content in the environment is less than 0.004% by volume. The method of claim 1 wherein the exposure of high energy ionizing radiation is between 1 and 2 Mrads. The method of claim 1 wherein the time of step (2) is in the range of 1 minute to 1 hour. A process for producing a foamed film in which an ethylene composition is extruded into a tube, followed by foaming to form bubbles, wherein the composition consists of an ethylene polymer material produced by the process according to claim 1. (1) a high density polyethylene and a random copolymer and terpolymer of ethylene and C _3-10 alpha olefin, wherein the ethylene content of the copolymer and terpolymer is at least 80% by weight and the polyethylene , Copolymers and terpolymers, in the solid state of (a) the amorphous fraction of the ethylene polymer material, in the solid state prepared by low pressure polymerization using a Ziegler-Natta catalyst system, each having a respective weight average molecular weight of 50,000 or more. Under conditions in which the active oxygen concentration remains set below 15 volume percent of the environment at temperatures above the glass transition temperature but below 70 ° C., (b) gelling of the ethylene polymer material is sufficient to expose to radiation below 2.0 Mrad. Dose rate high energy ions in the range of 1 to 10 ⁴ Mrad per minute for insufficient time to produce Irradiated with irradiated radiation, (2) the material so irradiated is kept in the solid state under the above-mentioned environment for a time sufficient to form a significant amount of free-end long chain branching, and (3) the irradiated material is The branching index of each of the polyethylene, copolymer and terpolymer is less than 0.9 and each of these has a significant strain hardened elongation viscosity by a process comprising deactivating all free radicals present in the irradiated material. A conventional solid, gel-free polymeric material selected from polyethylene, copolymers, and terpolymers investigated by the process, having sufficient free end long chain branching to have. 8. The ethylene polymer material of claim 7, wherein the branching index is from 0.2 to 0.8. Film forming composition consisting of the polymeric material according to claim 7. A film made of the polymeric material according to claim 7. An article consisting of an ethylene polymer composition comprising a substantial amount of the polymer material according to claim 7.