JPH0693033A - High-melt-strength ethylene polymer, its production and its use - Google Patents

Abstract

PURPOSE: To provide an irradiated ethylene polymer material usable for melt processing operation for production of thermoformed products, extrusion coated products, fibers, etc., having excellent melt strength, etc.

CONSTITUTION: This polymer is a normally solid, high mol.wt., gel-free, irradiated ethylene polymer material of a branching index of less than 1, having a density of 0.89-0.97 g/cc, with strain hardening elongational viscosity.

COPYRIGHT: (C)1994,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to chemical technology. More particularly, the present invention relates to chemical techniques related to alpha-olefins or synthetic resins derived from 1-olefins. In particular, the invention relates to synthetic resins produced by the polymerization of ethylene alone or the polymerization of ethylene with other olefins.

[0002]

BACKGROUND OF THE INVENTION A synthetic resin produced by polymerizing ethylene as a single monomer is called polyethylene. "Polyethylene" has become increasingly used in the art to include copolymers of ethylene and small amounts of other monomers, such as butene-1, but the term is not so used herein. Polyethylenes such as low density polyethylene (referred to as LDPE) and high density polyethylene (referred to as HDPE), and commercial ethylene and C _3-10 α-olefin copolymers (commonly referred to as linear low density polyethylene (LLDPE)) Is a normally solid, produced by polymerization of one or more special monomers by various methods known in the art,
It is a slightly flexible, thermoplastic polymer. For example, such polymers may be prepared by high pressure free radical polymerization or by low pressure processes such as fluidized bed, gas phase techniques using molybdenum-based catalysts, chromium-based catalysts, and Ziegler-Natta catalyst systems. The high pressure method produces polymers with long chain branching, and the low pressure method produces substantially linear polymers with controlled amounts of short chain branching. In the Ziegler-Natta catalyst system, the catalyst is an inorganic compound of a metal of Group I to III of the Periodic Table (eg, alkylaluminum) and a compound of a transition metal of Group IV to VIII of the Periodic Table (eg, halogenated). Titanium). Typical crystallinity is Wund
erlick & Guar, J.Phys.Chem.Ref.Data, Volume 10, Issue 1 (1981)
It is about 21 to about 75% by weight. Also, the typical melt index of the ethylene homopolymer or copolymer is 0.2 to 50 g / 10 min (ASTM 1238, measured according to condition E). Further, the melting point of the crystalline phase of commercially available normal polyethylene is about 135 ° C.

While commercially available linear polyethylenes have many desirable and beneficial properties, they have poor melt strength. When melted, they do not exhibit strain hardening (increased resistance to stretching during elongation of the molten material). Thus, linear polyethylene is the starting material for edge weave during high speed extrusion coating of paper or other substrates, sagging and local thinning of sheets during melt thermoforming (loc.
Al thining), as well as various melt processing drawbacks, including flow instability during coextrusion of laminated structures. As a result, their use has been limited to potential applications such as extrusion coating, blow molding, profile extrusion, and thermoforming.

Certain efforts have been made in the art to overcome the lack of melt strength of commercially available polyethylene. Irradiation of polyethylene is known in the art, but such irradiation is predominantly processed from polyethylene at high dose levels, ie dose levels greater than 2 megarads, to crosslink polyethylene, for example, It was done for films, fibers and sheets. For example, U.S. Pat.No. 4,668,577 discloses cross-linking of polyethylene filaments, and U.S. Pat.Nos. 4,705,714 and 4,891,173 disclose differentially cross-linking sheets made from high density polyethylene. Disclosure. Polyethylene cross-linked by these methods is reported to have improved melt strength and reduced solubility and melt flow. However, cross-linking resulted in an undesired reduction in polyethylene melt elongation, thereby limiting the draw length typically required for film or fiber applications.

Low levels of linear polyethylene, ie 0.05
Another attempt to improve the melt strength and melt elongation of polyethylene by exposure to high energy radiation of .about.0.3 megarads is disclosed in US Pat. No. 3,563,870. European Patent Application 0 471 171 discloses the heat aging of ethylene polymer granules by pre-treating them in a steam atmosphere to reduce the oxygen content in the granules, thus reducing the treated polymers to less than 1.5 megarads. Of an ethylene polymer by irradiating it with a dose of 1 and then steaming the irradiated polymer. British Patent No. 2,019,412
It relates to irradiation of linear low density polyethylene (LLDPE) films at 2-80 megarads to give increased elongation at break.

US Pat. Nos. 4,586,995 and 4,598,12
No. 8 describes ethylene polymer under non-gelling conditions, non-acid
When heated under oxidative conditions, ethylene
Occurrence of terminal vinyl unsaturation in the limer, or unsaturated terminal
Increase terminal vinyl unsaturation in polyethylene containing groups,
Illuminate the heat-treated ethylene polymer with a dose of 0.1 to 4 megarads.
And then the resulting irradiated polymer is gradually or rapidly
Long chains in ethylene polymer due to rapid cooling
It relates to a method of obtaining a "Y" branch. U.S. Pat.No. 4,525,257
Is a narrow molecular weight, linear, low density ethylene / C
_3-18Release α-olefin copolymer from 0.05 to 2 megarads
Irradiate at a radiation dose and compare with the corresponding uncrosslinked polymer
The increase in extensional viscosity and
To an extent sufficient to give substantially equal high shear viscosities
It is possible to produce copolymers that are crosslinked without gelation.
Is disclosed. Irradiated copolymers are residual free radical intermediates
Is not deactivated to reduce or eliminate.

[0007]

In one aspect, the invention features a density of 0.89 to 0.97 g / cc, a molecular chain having a significant amount of long branches with free ends, and less than 1 branching. It comprises a normally solid, high molecular weight, gel-free, irradiated ethylene polymer with a branching index and with a considerable strain hardening elongational viscosity. More generally, the invention comprises a normally solid, gel-free, high molecular weight, irradiated ethylene polymer material having a branching index of less than 1 and having a significant strain hardening elongational viscosity.

The ethylene polymers of the present invention have a reduced melt index (as evidenced by I ₂ at 190 ° C.) which is an increase in molecular weight, melt index ratio (I ₁₀
/ I ₂ ), which exhibits a broadened molecular weight distribution, improved melt tension and strain hardening elongational viscosity, and a branching index of less than 1. The ethylene polymers of this invention are produced by low levels of radiation under controlled conditions.

As used herein, "ethylene polymer material" means (a) a homopolymer of ethylene, (b) a random copolymer of ethylene and an α-olefin selected from the group consisting of C _3-10 α-olefins. (Having a polymerized α-olefin content of about 20% by weight (preferably about 16% by weight)),
And (c) a random terpolymer of ethylene and the aforementioned α-olefin (provided that the maximum polymerized α-olefin content is about
Mean ethylene polymer material selected from the group consisting of 20% by weight (preferably about 16% by weight). C _3-10 α-olefin is, for example, propylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1.
-Including linear α-olefins and branched α-olefins such as butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene and the like.

When the ethylene polymer is an ethylene homopolymer, it typically has a density of 0.960 g / cm ³ or more, and when the ethylene polymer is a copolymer of ethylene and a C _3-10 α-olefin, it is Typically 0.
It has a density of 91 g / cm 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-.
Contains methyl-1-pentene. Ethylene copolymer is HDPE
Or it may be a short chain branched LLDPE and the ethylene homopolymer may be HDPE or LDPE. Typically LLDPE and LDPE has a density of less than 0.940 g / cm ³ at 0.910 g / cm ³ or more and HDPE is greater than 0.940 g / cm ^3, usually 0.
It has a density of 950 g / cm ³ or more. Generally, 0.89-0.97g /
Ethylene polymer materials having a density of cc are suitable for use in the practice of this invention. 0.89 for ethylene polymer
LLDPE and HDPE with a density of 0.97 g / cc are preferred.

As used in this application, "high molecular weight" means a weight average molecular weight of at least about 50,000. The branching index quantifies the extent of long chain branching. In a preferred embodiment, the branching index is preferably less than about 0.9, most preferably about 0.2-0.8. It is defined by

[0012]

[Equation 1]

(Where g'is a branching index,
[IV] _Br is the intrinsic viscosity of the branched ethylene polymer material, and [IV] _Lin is substantially the same weight average molecular weight (and in the case of copolymers and terpolymers, substantially the same related molecular moiety or monomer). Part of the unit) is the corresponding ethylene polymer material, ie the intrinsic viscosity of a normally solid ethylene polymer material)

Intrinsic viscosity, also known as intrinsic viscosity number, is in its most general sense a measure of a polymer molecule's ability to increase the viscosity of a solution. This depends on both the size and shape of the dissolved polymer particles. Therefore,
When comparing a non-linear polymer to a linear polymer of substantially the same weight average molecular weight, it is an indication of the shape of the non-linear polymer molecule. In fact, the above ratio of intrinsic viscosities is a measure of the degree of branching of non-linear polymers. A method for measuring the intrinsic viscosity of ethylene polymer materials is J.App.Poly.Sci., 21.
Vol. 3331-3343 (1977). The weight average molecular weight can be measured by various operations. However, the procedure preferably used here is that of laser light scattering photometry, which is described in "Polymer Molecular Weights a
nd Molecular Weight Distribution by Low-Angle Lase
r Light Scattering "(Am. Lab.'s McConnell
, May 1978).

Elongation viscosity is the resistance of a liquid or semi-liquid substance to elongation. It is the melting property of a thermoplastic material, which can be measured by a device that measures the stress and strain of a molten specimen when subjected to tensile strain at a constant rate. One such device is Munstedt, J. Rheology, 2
3, (4), 421-425, (1979) and shown in FIG. A commercially available device of similar design is Rheometrics (Rhe
ometrics) RER-9000 Elongation rheometer. The molten high molecular weight ethylene polymer material exhibits elongational viscosity,
It increases as the material is stretched or stretched at a constant rate from a relatively fixed position, over a distance that depends on the rate of elongation, until it is no longer thin (so-called , Ductile fracture or necking fracture) tends to decrease rapidly. On the other hand, a melted ethylene polymer material of the present invention having substantially the same weight average molecular weight and substantially the same test temperature as its corresponding melted high molecular weight ethylene polymer material exhibits an elongational viscosity which is , When stretched or stretched from a relatively fixed position at substantially the same rate of elongation, tends to increase over longer distances, and it decomposes by so-called brittle or elastic fracture. Or it will be damaged. These features indicate strain hardening. In fact, the longer the ethylene polymer material of the invention has longer chain branching,
As the stretched material approaches fracture, the elongational viscosity tends to increase. This last trend is most apparent when the branching index is less than about 0.8.

The melt tension also gives an indication of the melt strength of the substance. Melt tension is measured on a Gottfert Rheotens melt tension device from Gottfert by measuring the tension (centimeter-Newton) of the melted strands of ethylene polymer as follows. . The polymer to be tested is extruded at 180 ° C. through a 20 mm long, 2 mm diameter capillary. The strand is then subjected to stretching using the stretching system with a constant acceleration of 0.3 cm / sec ² . The tension (centi-Newton) resulting from the above stretching is measured. Higher melt tensions mean higher melt strength values, which in turn indicate the strain hardening capacity of a particular material.

In another aspect, the present invention relates to a normal solid, high molecular weight, ethylene polymer material, a normal solid, gel having a branching index of less than 1 and having a significant strain hardening elongational viscosity. It provides a practical method of converting to an ethylene polymer material that is free of. The method is sufficient to provide (1) (a) exposure to up to 2.0 megarads of radiation in an environment where the active oxygen concentration is established and maintained below about 15% by volume of the environment. , But about 1 to about 1x10 / min for a period of time insufficient to cause gelation of the material.
Irradiating the ethylene polymer material with high-energy ionizing radiation at a dose rate in the range of ⁴ megarads, and (2) exposing the material thus irradiated for a period sufficient to form a significant amount of long chain branching. Maintaining in such an environment, and then (3) treating the irradiated material while in such environment to quench substantially all of the free radicals present in the irradiated material. .

The ethylene polymer material treated by the method of the present invention can be any normally solid, high molecular weight ethylene polymer material. Generally, the intrinsic viscosity of the raw ethylene polymer material (which indicates its molecular weight) is
Generally from about 1 to 25, preferably from 1 to 25 to yield a final polymer having an intrinsic viscosity of 0.8 to 25, preferably 1 to 3.
Should be 6. However, ethylene polymer materials having an intrinsic viscosity above or below these general values are within the broad scope of the present invention. Ethylene polymer materials having a melt index of about 0.01 or greater can be used. The ethylene polymer material, which is treated according to the method of the present invention in its broadest sense, has any physical form, such as fine particles, granules, pellets, films,
It can be a sheet, etc. However, in a preferred embodiment of the method of the present invention, the ethylene polymer material is in pellet or spherical particle form, which gives satisfactory results. Spherical granular morphology with a weight average diameter greater than 0.4 mm is preferred.

The active oxygen content of the environment in which the three steps are performed is an important factor. The expression "active oxygen" as used herein means oxygen in the form which reacts with the irradiated substance, more particularly the free radicals in that substance. It contains molecular oxygen, which is the form of oxygen normally found in air. The active oxygen content requirement of the method of the present invention may be achieved by the use of vacuum or by replacing some or all of the air in the environment with an inert gas such as nitrogen. The as-prepared ethylene polymer material is typically substantially free of active oxygen. Therefore, it is within the concept of this invention to follow the polymerization and polymer treatment steps (if the ethylene polymer material is not exposed to air) according to the method of this invention. However, under most circumstances, ethylene polymer materials have an active oxygen content because they have been stored in air or for some other reason. Therefore, in a preferred practice of the method of the present invention, the finely divided ethylene polymer material is first treated to reduce its active oxygen content. The preferred way to do this is to introduce the material into a bed of the material which is blown with nitrogen, the active oxygen content of which is less than about 0.004% by volume. The residence time of the material in the bed should generally be at least about 5 minutes in order to effectively remove active oxygen from the interstices of the material's particles, preferably long enough for the material to equilibrate with the environment. .

Between this preparation step and the irradiation step, the ethylene polymer material prepared has an active oxygen concentration in the gas transport system of less than about 15%, preferably less than 5%, more preferably 0.004% by volume of the environment. Should be kept in an environment that is. In addition, the temperature of the ethylene polymer material should be maintained above the glass transition temperature of the amorphous portion of the material at about 70 ° C or less, preferably about 60 ° C or less. In the irradiation step, the active oxygen concentration of the environment 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 sufficient energy to penetrate to the desired degree into the mass of ethylene polymer material to be irradiated. The energy should be sufficient to ionize the molecular structure and excite the atomic structure, but not enough to affect the nucleus. The ionizing radiation may be of any type, but the most practical types include electron beams and gamma rays. Electrons emitted from an electron generator having an acceleration potential of 500 to 4,000 kilovolts are preferred. For ethylene polymer materials, generally about 0.2 to 2.0 megarads, preferably 0.3 to 2.0, delivered at a dose rate of about 1 to 10,000 megarads per minute, preferably about 18 to 2,000 megarads per minute.
Satisfactory results are obtained with low doses of ionizing radiation of megarads, most preferably 0.5-1.5 megarads.

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, regardless of the source of the radiation.
As far as the invention is concerned, the amount of energy absorbed by the ethylene polymer material when it is irradiated is usually not measured. However, in the normal practice of the method, energy absorption from ionizing radiation is measured by known conventional dosimeters, in which the strip of cloth containing the radiation sensitive dye is the energy absorption sensing means. Therefore, as used herein, the term "rad" is 100 per gram of dosimeter cloth placed on the surface of an ethylene polymer material that is irradiated in the form of a bed or layer of particles, or a film or sheet. It refers to the amount of ionizing radiation that produces absorption corresponding to the energy of an erg.

The second step of the method of the present invention should generally be conducted for a period in the range of about 1 minute to about 1 hour, preferably about 2 to 30 minutes. Sufficient migration of the ethylene polymer chain fragment to the free radical site and reforming of the complete chain,
Or minimal time is required for in situ compounding to form long branches in the chain. Less than 1 minute, eg about
Free radical transfer times of 0.5 minutes are within the broad concept of the invention, but are not preferred. This is because the amount of long-chain branch at the free end obtained is very small. The final step of the process, i.e. the free radical quenching or quenching step, is generally by the application of heat of at least 60 ° C to about 280 ° C, or of an additive that acts as a free radical trap such as, for example, methyl mercaptan. It can be performed by addition.

In one embodiment of the method, applying heat comprises melt extruding the irradiated ethylene polymer material. As a result, the quenching of the free radicals is substantially complete. In this embodiment, prior to extrusion or melt compounding, the irradiated ethylene polymer material may optionally be blended with other polymers and additives such as stabilizers, pigments, fillers, and the like. Also, such additives may be incorporated as a sidestream addition to the extruder. In another embodiment of the method of the present invention, the application of heat is carried out by introducing the irradiated ethylene polymer material into a fluidized bed or staged fluidized bed system, where the fluidizing medium is, for example, nitrogen or other. It is an inert gas. One or more floors created, at least about 60
C. to a temperature not exceeding the melting point of the polymer, the average residence time of the irradiated ethylene polymer material in the one or more fluidized beds is about 5 minutes to about 120 minutes, about 20 to 30 minutes.
Minutes are optimal. The product thus obtained is a normally solid, high molecular weight, gel-free ethylene polymer material characterized by strain hardening. The material is also characterized by a melt index ratio greater than 10.

Although the process of the invention can be carried out batchwise, it is preferably carried out continuously. In one continuous embodiment of the process, depending on the active oxygen content of the material, finely divided ethylene polymer material with or without a preparation step is layered on a moving belt in the required environment. To be The thickness of the layer depends on the desired degree of penetration of ionizing radiation in the layer and the proportion of irradiated ethylene polymer material desired in the final product. The speed of movement of the moving belt is selected so that the layer of fine ethylene polymer material passes through one or more beams of ionizing radiation at a rate that receives the desired dose of ionizing radiation. After receiving the desired dose of ionizing radiation, the irradiation layer can be left on the moving belt in said environment for the period of time during which free radical migration and compounding occur, and then removed from the belt to determine the melting temperature of the irradiated material. A heated bed of particles of radiation material introduced into an extruder operated in, or in another special embodiment, fluidized with nitrogen or other inert gas,
Alternatively it is introduced into a staged heating bed system. In either embodiment, the irradiated material is vented to the atmosphere and rapidly cooled to room temperature after at least substantially all of the free radicals therein have been deactivated. In another embodiment, the irradiated ethylene polymer material is discharged from the belt and held in a required environment, the interior of which has the required environment.
And then held in a container to complete the required free radical transfer time. The irradiated material is then introduced into an extruder operated at the melting temperature of the irradiated material, or into a heated inert gas fluidized bed of irradiated particles of ethylene polymer material, or a staged fluidized bed system, after quenching of the free radicals. Irradiated polyethylene is discharged into the atmosphere.

In yet another aspect, the invention provides an extensional flow of the strain-hardening ethylene polymer material of the invention.
flow) is included. Stretch flow occurs when the molten ethylene polymer material is pulled in these directions at a faster rate than it normally flows in one or more directions.
It occurs during extrusion coating operations, in which the molten coating material is extruded onto a support, such as a moving web of paper or metal sheets, and the extruder or support is moving faster than the extrusion speed. It is done during film production, where the molten film is extruded and then stretched to the desired thinness. It is present during the thermoforming operation, in this case the molten sheet is clamped into the plug mold, vacuum is applied,
The sheet is pressed against the mold. It occurs during the production of foamed products, where the molten ethylene polymer material is foamed with a blowing agent. The strain-hardening ethylene polymer material of the present invention is part of the molten plastic material used in these and other melt processing processes to produce useful articles (eg, as little as 0.5% by weight up to 95% by weight). weight%
(Up to the above order of magnitude) or substantially all of the molten plastic material.

The invention is illustrated by the drawings, which form an essential part of these disclosures, and the examples below. More specifically, FIG. 1 shows a fluidized bed unit of conventional construction and operation.
10 shows a fine high molecular weight polyethylene conduit
11 is introduced, nitrogen gas is introduced by conduit 13,
The high molecular weight polyethylene, which is substantially free of active oxygen, is then removed by solids discharge conduit 15, which also has a solids flow controller 16. The solids discharge conduit 15 leads to a conveyor belt feed hopper 20. The conveyor belt feed hopper 20 has a conventional design of a lid fastening structure. It is operated so that its interior contains a nitrogen atmosphere. It has a lower solids discharge outlet through which the polyethylene particles move and form a layer on the upper horizontal run of the endless conveyor belt 21. The conveyor belt 21 is generally arranged horizontally and moves continuously under normal operating conditions. It is contained in the radiation room 22. This chamber is constructed and operated to completely enclose the conveyor belt and to create and maintain a nitrogen atmosphere within it.

An electron beam generator 25 of conventional design and operation is associated with the radiation chamber 22. Under normal operating conditions, it produces a high energy electron beam that is directed to the layer of polyethylene particles on the conveyor belt 21. As the conveyor belt 21 rotates in its path of opposite travel,
Below the discharge end of the conveyor belt is a solids recovery device 28 arranged to receive the irradiated polyethylene particles falling from the conveyor belt 21. The irradiated polyethylene particles in the solids recovery unit 28 are then removed therefrom by a rotary valve or star wheel 29 and thereby delivered to the solids transfer tube 30. The transfer pipe 30 leads to a gas-solid separator 31. This unit is of conventional construction, usually a cyclone separator. The gas separated in the gas exhaust pipe
The separated solids are removed by 33, while the separated solids are then discharged to a solids discharge pipe 34 as by a rotary valve or star wheel 32. The solid discharge pipe 34 leads directly to the extruder hopper 35.

The extruder hopper 35, which feeds the extruder 36, is conventional in construction and operation. Also, it is a closed structure suitable for creating and maintaining a nitrogen atmosphere inside. The extruder 36 is of conventional construction and operates in a conventional manner. The solids in the extruder hopper 35 then move to the extruder, which is sufficient to form a significant amount of free-chain long-chain branching between the irradiation of polyethylene and its entry into the extruder. It is operated at a rate of extrusion that produces a period of time between. Therefore, the volume of the extruder hopper 35 is selected as necessary to provide the desired amount of hopper storage time that meets this condition. The extruder 36 is designed (extruder barrel and screw length), and the amount of time required to deactivate polyethylene with free radicals therein, substantially all of the free radicals present. Operated at the melt temperature with sufficient pressure to maintain The finely treated polyethylene is characterized by being substantially gel-free, having a density of 0.89-0.97 g / cc and being substantially branched with a long chain at the free end of the ethylene unit. And It can be used as it is, or, for example, introduced directly into the pelletizing and cooling unit 37 and solid pellets (which can be stored and then used,
Or it can be used without storage) and then carried away as by solid transport tube 38.

Similar results are obtained when the high molecular weight ethylene polymer material of the other particular embodiment is treated by the continuous process described above. The following examples illustrate the high molecular weight polyethylene of the present invention, and the above-described preferred embodiments of its method of manufacture. Melt index, I ₂ and I ₁₀
Is measured according to ASTM D-1238. The melt index ratio is determined by dividing I ₁₀ by I ₂ . The ratio shows a molecular weight distribution, the higher the number, the broader the molecular weight.

[0031]

EXAMPLES introduced Sol tex (Soltex) T50-200 polyethylene in pellet form having a density of melt index and 0.95 of Example 1 2 in a closed radiation chamber 22 and purged with nitrogen until the oxygen content of 40ppm can be obtained . The material is distributed over a moving stainless steel conveyor belt 21, height 1.3 cm, width 15 cm.
Forming a polyethylene floor. The floor is passed by a conveyor belt 21 into an electron beam generated by a 2 MeV van der Graaf generator operated with a beam current of 50 microamps. The resulting absorbed surface dose is 0.40 megarads. In addition, in the closed radiation chamber 22, and the irradiation polyethylene transfer pipe 30, the solid-gas separator 31 and the separator discharge pipe 34.
The active oxygen content of the environment or atmosphere in the rest of the system containing
Establish and keep below 140ppm. After irradiation, the polyethylene is removed from the end of the conveyor belt 21 by a belt discharge recovery device.
28 to the transfer pipe 30 through the rotary valve 29. After separation of the gas from the irradiated polymer, the polymer is fed through a separator discharge line 34 into a bag purged with nitrogen. The irradiated polyethylene is kept for 30 minutes at room temperature in the absence of oxygen. The material was introduced into a nitrogen-purged extruder feed hopper and then heated in a 2.5 inch single screw extruder.
Extrude at ° C. The properties of the gel-free final product of Example 1 are summarized in Table 1.

[0032] Examples 2-4 absorbed dose obtained is respectively 0.6, except were 0.9 and 1.0 megarads, performs Examples 2-4 Using the method and ingredients of Example 1. The oxygen amount is controlled by the closed radiation chamber 22, the irradiation polyethylene transfer pipe 30, the solid gas separator 31, and the separator discharge pipe.
Keep below 60ppm in 34. The properties of the gel-free final products of Examples 2-4 are summarized in Table 1. Dow in pellet form with MI of Examples 5 to 84 and a density of 0.952 (D
Examples 5-8 are carried out using the methods and ingredients of Example 1 except that ow) 04052N polyethylene was used and the absorbed doses obtained were 0.5, 0.7, 0.8, and 1.0 megarads, respectively. The amount of oxygen is set to 100 p in the closed radiation chamber 22, the irradiation polyethylene transfer pipe 30, the solid gas separator 31 and the separator discharge pipe 34.
Keep below pm. The properties of the gel-free final products of Examples 5-8 are summarized in Table 1 below. Control Examples 1 and 2 Controls 1 and 2 are Soltex T50-200 and Dow 0405, respectively.
It is a non-irradiated sample of 2N.

[0033]

[Table 1]

Example 9 and Comparative Examples 3 to 8 Irradiation atmosphere (referred to as IA) corresponding to the irradiation step (1) of this method, and an oxygen content of less than 15% corresponding to the second step (2) of this method. Aging of free-radical intermediates in regulated environments (R
IA), as well as the free radical intermediate deactivation step (designated RID) corresponding to the final step of the method of the present invention, using the method of Example 1 with the following exceptions: Example 9 and Controls 4-8 are performed. -Highmont Italy instead of the Soltex T50-200
6.90 MI in spherical granular form from (HIMONT Italia) Srl
High density polyethylene having -The absorbed dose obtained is 1.1 megarads. -Changing the processing environment of Controls 3-8 as reported in Table 2,
And-removing the free radicals by about 26 in a 3/4 inch Brabender extruder.
Perform at 0 ° C. The results are shown in Table 2 below.

[0035]

TABLE 2 Example IA RIA RID 1 Day I ₂ 2 Day I ₂ 13 Day _{I 2 C-3 - - -} 6.90 - - C-4 N 2 air air 3.56 3.13 3.23 C-5 N ₂ --2.44 3.67 4.58 C-6 Air Air Air 4.62 4.30 4.51 C-7 Air N ₂ N ₂ 4.39 4.14 4.13 C-8 Air--4.56 5.90 8.40 9 N ₂ N ₂ N ₂ 2.86 2.63 2.60

Insufficient melt flow stability for 13 days compared to Example 9 of the present invention was demonstrated by Controls 5 and 8. Controls 4, 6 and 7 showed better melt flow stability than Controls 5 and 8, but the melt flow is not as low as Example 9 of the present invention. Examples 10-15 and Controls 9 and 10 The ethylene polymer used was fed through separator discharge tube 34 to the nitrogen purged hopper of a 210 ° C 3/4 inch Brabender extruder in the first zone. , In the second band 215
Example 10 using the method of Example 1 except that it was fed at 0.degree. C., 220.degree.
Repeat steps 15 and 15. The pellets are then made into Maddoch
Re-extrude with 0.1% Irganox 1010 stabilizer at 100 rpm in a 1-1 / 4 inch Killian single screw extruder equipped with a mixer at a flat profile of 420 ^° F. The holding time between irradiation and extrusion averages about 15 minutes. The properties of the final products of Examples 10-15 are shown in Table 3.
And Table 4, summarized in Examples 10, 12 and 14 and Control Example 9.
And elongational viscosities of 10 (180 ° C at strain rates between 0.05 and 2.0 sec- ¹
(Measured using a Rheometrics RER9000 Elongation Rheometer at.) Are shown in Figures 2 and 3.

[0037]

[Table 3] Example Polymer type Dose Melt tension ⁽¹⁾ Melt elongation ⁽¹⁾ (Megarad) (cm-Newton) (cm) C-9 Dow 4352N ⁽⁵⁾ 0 0.9 19.6 10 0.5 2.8 19.5 11 1.0 4.1 22.0 12 1.5 4.6 22.5 C-10 LLDPE 1E10 / A ⁽⁶⁾ 0 0.4 20.1 13 0.5 0.8 22.6 14 1.5 1.5 21.1 15 3.0 ----

[0038]

[Table 4] Example 190 to 190 ° C I ₁₀ / I ₂ IV ⁽²⁾ Mw ⁽³⁾ BI ⁽⁴⁾ I _{2 at} I ₁₀ C-9 3.9 27.4 7.0 1.57 150000 1.0 10 1.5 15.8 10.1 1.65 211000 0.83 11 0.8 12.0 13.5 1.72 370000 0.57 12 0.7 10.3 15.1 1.79 633000 0.40 C-10 7.9 58.4 --1.3 ---- 13 --51.6 --1.29 ---- 14 --39.7 ------ -15 --27 --1.40 ----

(1) Measured by measuring the tension (centimeters-Newton) of the strands of molten ethylene polymer as follows using a Gottfeld Rheotens melt tension device from Gottfeld. 180 the polymer to be tested through a 20 mm long, 2 mm diameter capillary
Extrude at ° C. The strands are then subjected to drawing using the drawing system with a constant acceleration of 0.3 cm / sec ² . The higher the tension, the better the viscoelasticity and therefore the better the processability of the polymer in the molten state. (2) Intrinsic viscosity measured in decalin at 135 ° C. (3) Weight average molecular weight measured by laser light scattering with a Wyatt Down Laser light scattering device from Wyatt Technology Inc. in trichlorobenzene at 135 ° C. (4) Branching index; [IV] _Lin = 2.77x10 ^-4 Mw ^0.725 (5) Melt index of 3.9 from Dow Chemical Company.
High density polyethylene containing 0.5% propylene monomer units in pellet form with (MI). (6) LL containing 6.1% butene-1 monomer units mixed with 200 ppm Irganox 1076 stabilizer in pellet form with MI of 7.9 from Himont Italia Srl.
DPE.

The results shown in the above table show that the ethylene polymers of the present invention increased the melt index ratio, which shows an increase in the molecular weight distribution, an increase in the melt strength as well as an increase in the melt tension. The branching index indicating the formation of chain branching is shown. The results shown in Figures 2 and 3 show that the ethylene polymers of the present invention have extensional viscosities indicative of the strain hardening ability of the material. As the branching index decreases, ie, the degree of long chain branching increases, the tendency of strain hardening elongational viscosity increases. The free-ended long-chain branched ethylene polymer materials of the present invention are melt processed to form useful products such as foamed and thermoformed products such as foamed sheet materials and thermoformed sheet materials, extrusion coated products and fibers. It has practicality in operation. In fact, the strain-hardening ethylene polymer materials of the present invention are useful in all melt processing operations where high melt molecular weight ethylene polymer materials are desired.

Other features, advantages and embodiments of the invention disclosed herein will be immediately apparent to those skilled in the art after reading the above disclosure. In this regard, although particular embodiments of the present invention have been described in considerable detail, modifications and improvements of these embodiments can be made without departing from the spirit and scope of the invention described and claimed. As used herein, the term “consisting essentially of” excludes an undescribed substance at a concentration sufficient to significantly adversely affect the essential properties and characteristics of the composition of matter identified. , The presence of one or more unlisted substances in concentrations that are insufficient to significantly adversely affect the essential properties and characteristics described above.

[Brief description of drawings]

FIG. 1 is a flowsheet of a preferred embodiment of a continuous process for converting, for example, normally solid polyethylene into normally solid, gel-free polyethylene having strain hardening properties.

FIG. 2 is a graph showing elongational viscosity versus elongational time of two samples, a free-end long chain branched high density polyethylene and a high density polyethylene control, obtained by the method of the present invention.

FIG. 3 is a graph showing elongational viscosity versus elongational time of free end long chain branched low density polyethylene and LLDPE control samples obtained by the method of the present invention.

[Explanation of symbols]

 10-Fluidized bed unit 11,13,15-Conduit 16-Solid flow controller 20-Conveyor belt supply hopper 21-Endless conveyor belt 22-Radiation chamber 25-Electron beam generator 28-Solid collector 29,32-Star type Vehicle 31-Gas-solid separator 33-Gas discharge pipe 34-Solid discharge pipe 35-Extruder hopper 36-Extruder 37-Pelletizing and cooling unit 38-Solid transport pipe

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor John W. Mayfield Delaware, United States 19803 Wilmington Stafford Road 406 (72) Inventor Thomas F McCrawlin, Delaware, United States 19808 Wilmington Glenbury Drive 6 (72) Inventor James Arlveran United States Pennsylvania 19803 West Chester McKenzie Drive 288

Claims (16)

[Claims] 1. A normally solid, high molecular weight, gel-free, irradiated ethylene polymer material characterized by a branching index of less than 1 and having a strain hardening elongational viscosity. 2. The branching index is less than 1 and 0.89.
A normally solid, high molecular weight, gel-free, irradiated ethylene polymer material having a density of ˜0.97 g / cc and a strain hardening elongational viscosity. 3. The ethylene polymer material of claim 2 consisting essentially of a high molecular weight ethylene polymer having a density greater than 0.94 g / cc and a branching index less than about 0.9. 4. The ethylene polymer material of claim 3 having a branching index of about 0.2-0.8. 5. The ethylene polymer material of claim 2 consisting essentially of a high molecular weight ethylene polymer having a density less than 0.94 g / cc and a branching index less than about 0.9. 6. The ethylene polymer material of claim 5 having a branching index of about 0.2-0.8. 7. The ethylene polymer material of claim 2, wherein the ethylene polymer is in particulate form. 8. Strain hardening elongation 0.89-0.97 without having elongation viscosity
a normal solid with a density of g / cc, a high molecular weight, normal solid with a strain hardening extensional viscosity from an ethylene polymer material,
A method for producing a high molecular weight, gel-free, irradiated ethylene polymer material, wherein (1) (a) the active oxygen concentration is established and maintained below about 15% by volume of the environment, b) Sufficient to provide exposure to up to 2.0 megarads of radiation, but about 1 to about 1x10 per minute for a period of time insufficient to cause gelation of the substance.
Irradiating the ethylene polymer material with high-energy ionizing radiation at a dose rate in the range of ⁴ megarads, and (2) exposing the material thus irradiated for a period sufficient to form a significant amount of long chain branching. Maintaining in such an environment, and then (3) treating the irradiated material while in such environment to deactivate substantially all of the free radicals present in the irradiated material. A method of making an irradiated ethylene polymer material as described above. 9. The method of claim 8 wherein said ethylene polymer material is created and maintained in said reduced active oxygen environment prior to irradiation. 10. The active oxygen content of the environment is about 0.004.
9. The method of claim 8, which is less than volume%. 11. The method of claim 8 wherein the absorbed dose of high energy ionizing radiation is 1 to 12 megarads. 12. The method of claim 8, wherein the period of step (2) ranges from about 1 minute to about 1 hour. 13. A normal solid, high molecular weight, gel-free, irradiated ethylene polymer material having a density of 0.89 to 0.97 g / cc and a branching index of less than 1, which material has a strain hardening elongational viscosity. A film-forming composition consisting essentially of: 14. A normally solid, high molecular weight, gel-free, irradiated ethylene polymer material having a density of 0.89 to 0.97 g / cc and a branching index of less than 1, which material has a strain hardening elongational viscosity. ) Consisting essentially of a film. 15. Extruding the ethylene composition into a tube,
Then, in a method for producing a blown film in which this is blow-molded into a bubble, the composition has a density of 0.89 to 0.97 g / cc, a normal solid having a branching index of less than 1, a high molecular weight A method of making a blown film, which consists essentially of a gel-free, irradiated ethylene polymer material, which material has a strain hardening extensional viscosity. 16. A normal solid, high molecular weight, gel-free, irradiated ethylene polymer material having a density of 0.89 to 0.97 g / cc and a branching index of less than 1, which material has a strain hardening elongational viscosity. A useful article characterized in that it comprises an ethylene polymer composition comprising a substantial amount of