CA2169068A1 - Polyolefin blends and their solid state processing - Google Patents
Polyolefin blends and their solid state processingInfo
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- CA2169068A1 CA2169068A1 CA002169068A CA2169068A CA2169068A1 CA 2169068 A1 CA2169068 A1 CA 2169068A1 CA 002169068 A CA002169068 A CA 002169068A CA 2169068 A CA2169068 A CA 2169068A CA 2169068 A1 CA2169068 A1 CA 2169068A1
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- Prior art keywords
- polyolefin
- blend
- temperature
- polyethylene
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
- C08L23/08—Copolymers of ethene
- C08L23/0807—Copolymers of ethene with unsaturated hydrocarbons only containing more than three carbon atoms
- C08L23/0815—Copolymers of ethene with aliphatic 1-olefins
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
- C08L23/06—Polyethene
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2205/00—Polymer mixtures characterised by other features
- C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
Abstract
Polyolefin blends characterized by melting and crystallization curves which exhibit either two distinct melt regions, or wherein one component of the blend has a low softening temperature relative to the individual components of the blend, provide an unusually wide window for solid state processing The solid state processing characteristics of these blends are independent of the manner in which the blends are formulated e.g. mechanical mixing, solvent dispersion and the like.
Description
W O 95105419 21 6 9 0 6 8 PCTrUS94/08943 PO~YO~EFIN BLENDS AND THEIR SOLID STATE PROCESSING
BAcKGRouNn OF TH~ INV~NTION
This invention relates to polyolefin blends. In one aspect, the invention relates to polyolefin blends suitable for solid state processing while in another aspect, the invention relates to particular blends of various polyethylenes. In still another aspect, the invention relates to polyolefin blends characterized by melting and crystallization curves exhibiting either two distinct melt regions, or wherein one component has a softening point lower than that of a conventional polyolefin, either technique of which provides an unusually wide window for solid state processing.
While the field of metal forming offers a wide variety of solid state processing, e.g. stamping, forging, rolling, extrusion, etc., the solid state processing of semicrystalline polymers is much more limited. To process a thermoplastic in the solid state, typically the processing temperature is maintained at just a few degrees below the melting point of the polymer. If the processing temperature is above the melting point of the polymer, then the processing is simply a melt extrusion. At temperatures considerably below the melting point of the polymer, the polymer is essentially a solid and its deformation requires a tremendous amount of pressure (often in excess of one million psi (7000 MPa)). Such enormous pressures make large deformations very difficult, and result in a relatively low production rate and a generally energy inefficient process. Moreover, since the processing temperature is the most critical parameter in solid state processing, this technique has been limited to those polymers and polymer blends with relatively wide (e.g. at least about 20 degrees on the Celsius scale) ranges between their softening and melting temperatures. Since this temperature range is relatively narrow for conventional polyolefins and their blends, these materials have not been the subject of extensive, commercial-scale solid state processing.
Despite their relatively narrow processing temperature window, the sheer commercial scale of the polyolefin market has generated considerable interest in applying this technique to polyolefins. The W O 95/05419 -~ PCTrUS9~/08943 2l6sn6~
potential benefits to be gained include energy efficiency, speed, and scrap reduction. Ciferri and Ward in ~Ultra High Modulus Polymers~, AnDlied Science Publication~, London (197g), teach that the extrusion of polymers below the melting point is a promising method of producing highly oriented materials. Krjutchkov, et al. in Poly~er Co~osite, Vol. 7, No. 6, pp. 4-13-420 ~1986), disclosed the detailed investigations of the dynamics of solid state extrusion, and they have also postulated a model to correlate the flow of instability in extrudate defects to the extrusion temperature and pressure.
o Chung in USP 5,028,663 teaches that certain blends of high density polyethylene (HDPE) and low density polyethylene (LDPE) prepared by solution mixing can achieve a broader operating window for certain solid state processing applications than would otherwise be achieved by mechanical mixing. The melting peak of each component in the blend is separated due to solution precipitation such that large deformation processing can be performed at a temperature between the melting peaks of the two components.
Pawloski, et al. in USP 4,352,766, 4,161,502 and 3,739,052 teach a unique process called Solid Phase Forming (SPF) to form polymers and composites at a pre-melt state. This unique fabrication process induces a biaxial orientation throughout the finished parts.
Enikolopow, et al. in USP 4,607,797 teach a process called Solid State Sheer Extrusion or Pulverization to perform polymer extrusion at a temperature below the peak melting temperature of the polymer.
However, Shutov has observed in a 1992 I.I.T. Research Report that certain polymers, such as HDPE, polypropylene (PP) and polycarbonate (PC) did not perform well in this process.
We have discovered a composition suitable for solid state processing, characterized as a blend comprising a first and a second polyolefin, wherein the first polyolefin is characterized as having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, the first polyolefin component comrpising at least 10 percent of the total weight of the polyolefin blend.
Preferably, the composition will be characterized as a blend comprising a polyolefin composition suitable for solid state W O95/05419 2 1 6 ~ 0 6 8 PCTrUS94/08943 processing, the composition characterized as a blend comprising: (a) a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to 0.910 g/cm3; and tb) a second polyolefin having a density from 0.940 g/cm3 to 0.965 g/cm3, s wherein the first polyolefin is characterized by a softening point of at least ten degrees on the Celsius scale lower than the softening point of the second polyolefin.
We have also discovered a process for shaping a solid polyolefin blend, the process characterized as comprising the following steps:
lo (a) heating a solid polyolefin blend which comprises at least a first and second polyolefin, the first polyolefin having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, the first polyolefin comprising at least 10 percent of the total weight of the polyolefin blend heated to a processing temperature above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin; (b) shaping the blend at the processing temperature; and (c) cooling the shaped blend of (b) to a temperature below the processing temperature.
Preferably, the process will be characterized as comprising the following steps: (a) heating to a processing temperature a solid polyolefin blend which comprises: (i) a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to0.910 g/cm3; and (ii) a second polyolefin having a density of 2s from 0.940 g/cm3 to 0.965 g/cm3; wherein the first polymer is characterized by a softening point of at least ten degrees on the Celsius scale lower than the softening point of the second polyolefin and wherein the processing temperature is above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin; (b) shaping the blend at the processing temperature; and (c) cooling the shaped blend of (b) to a temperature belowe the processing temperature.
According to this invention, polyolefin blends characterized by melting and crystallization curves which exhibit either two distinct melt regions, or a low softening point relative to the high melting component of the blend, provide an unusually wide window for solid W O95/05419 PCTrUS9~/08943 2l6sn6s state processing. These blends comprise at least 10 percent by weight of the low melting component, and the difference between the peak melting temperature of the low melting component and the high melting component is at least about twenty degrees on the Celsius scale. These blends are processed in their solid state at a temperature above about the peaK melting temperature of the low melting component and below the peak melting temperature of the high melting component. The solid state processing characteristics of the blends of this invention are independent of the manner in which the components are mixed, e.g.
o mechanical, solvent, etc.
DF~ CRTPTION OF THF~ PRF:FF~RRF~n F~MRoDTMF~NTs The polyolefin blends of this invention comprise two or more, typically two, polyolefin components. These blends are characterized by having a solid state processing temperature (Tp) defined by Tml < Tp < Tm2 in which the Tm2 is the peak melting temperature of the high melting component, and Tml is the peak melting temperature of the low melting component. Typically, the difference or range between Tm2 and Tml, i.e. Tm2-Tml, is greater than twenty, preferably greater than thirty, and most preferably greater than forty, degrees on the Celsius scale.
The components of the blends of this invention are polyolefins, e.g. polyethylenes, polypropylenes, dienes, styrene, etc. Preferred polyolefins are the various polyethylenes and polypropylenes, and preferred blends are those containing at least one polyethylene, 2s particularly a substantially linear ethylene polymer.
The polyethylenes can be divided into two broad classes, heterogeneously branched and homogeneously branched. The heterogeneously branched polyethylenes that can be used in the practice of this invention fall into two broad categories, those prepared with a free radical initiator at high temperature and high pressure, and those prepared with a coordination catalyst at high temperature and relatively low pressure. The former are generally known as low density polyethylenes (LDPE) and are characterized by branched chains of polymerized monomer units pendant from the polymer backbone. LDPE polymers generally have a density between 0.910 and 0.935 grams per cubic centimeter (g/cm3).
W O 95/05419 2 1 6 9 ~ 6 8 PCTrUS94/08943 Ethylene polymers and copolymers prepared by the use of a coordination catalyst, such as a Ziegler or Phillips catalyst, are generally known as linear polymers because of the substantial absence of branch chains of polymerized monomer units pendant from the s backbone. High density polyethylene (HDPE), generally having a density of 0.940 to 0.965 g/cm3, is typically a homopolymer of ethylene, and it contains relatively few branch chains relative to the various linear copolymers of ethylene and an a-olefin. HDPE is well known, commercially available in various grades, and is useful in this lo invention.
Linear copolymers of ethylene and at least one -olefin of 3 to 12 carbon atoms, preferably of 4 to 8 carbon atoms, are also well known, commercially available and useful in this invention. As is well known in the art, the density of a linear ethylene/-olefin copolymer is a function of both the length of the -olefin and the amount of such monomer in the copolymer relative to the amount o~f ethylene, the greater the length of the -olefin and the greater the amount of -olefin present, the lower the density of the copolymer.
Linear low density polyethylene (LLDPE) is typically a copolymer of ethylene and an -olefin of 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms (e.g., 1-butene, 1-octene, etc.), that has sufficient -olefin content to reduce the density of the copolymer to that of LDPE.
When the copolymer contains even more -olefin, the density will drop below 0.91 g/cm3 and these copolymers are known as ultra low density polyethylene (ULDPE) or very low density polyethylene (VLDPE). The densities of these linear polymers generally range from 0.87 to 0.91 g/cm3.
Both the materials made by the free radical catalysts and by the coordination catalysts are well known in the art, as are their methods of preparation. Relevant discussions of both of these classes of materials, and their methods of preparation, are found in USP
4,950,541 and the patents to which it refers.
The homogeneously branched polyethylenes that can be used in the practice of this invention also fall into two broad categories, the 3~ linear homogeneously branched and the substantially linear homogeneously branched. Both are known. The former and their method WO95/05419 - PCTrUS94108943 ~16906g , of preparation are described in USP 3,645,992 to Elston, and the latter and their method of preparation are fully described in U.S.
Patent 5,272,236 and 5,278,272. ~Examples of the former are the Tafmer~ polymer of Mitsui and the Exact~ polymer of Exxon, while an example of the latter are the polymers made by the Insite~ Technology of The Dow Chemical Company.
As here used, ~substantially linear~ means that the polymer backbone is substituted with 0.0l long-chain branches/l000 carbons to 3 long-chain branches/l000 carbons, preferably from 0.0l long-chain 0 branches/l000 carbons to l long-chain branch/l000 carbons, and more preferably from 0.05 long-chain branches/l000 carbons to l long-chain branch/l000 carbons. In contrast, simply ~linearR means that long chain branching is essentially absent from the polymer backbone.
Long-chain branching is here defined as a chain length of at least 6 carbon atoms, above which the length cannot be distinguished using l3C
nuclear magnetic resonance spectroscopy, yet the long-chain branch can be about the same length as the length of the polymer backbone.
These unique substantially linear homogeneously branched polymers ~subsequently referred to as ~substantially linear ethylene polymers~) are prepared by using constrained geometry catalysts (CGC), and are characterized by a narrow molecular weight distribution and if an interpolymer, by a narrow comonomer distribution. As here used, ~interpolymer~ means a polymer of two or more comonomers, e.g. a copolymer, terpolymer, etc. Other basic characteristics of these substantially linear ethylene polymers include a low residuals content (i.e. low concentrations in the substantially linear ethylene polymer of the catalyst used to prepare the polymer, unreacted comonomers, if any, and low molecular weight oligomers made during the course of the polymerization), and a controlled molecular architecture which provides good processability even though the molecular weight distribution is narrow relative to conventional olefin polymers.
While the substantially linear ethylene polymers used in the practice of this invention include substantially linear ethylene homopolymers, preferably these substantially linear ethylene polymers comprise between about 95 and 50 wt percent ethylene, and about 5 and 50 wt percent of at least one a-olefin comonomer, more preferably l0 W O 95/05419 2 1 6 9 0 6 8 PCTrUS94/08943 to 25 wt percent of at least one ~-olefin comonomer. Percent comonomer is measured by Infrared Spectroscopy according to ASTM
D-2238 Method B. Typically, the substantially linear ethylene polymers are copolymers of ethylene and an ~-olefin of 3 to about 20 carbon s atoms (e.g. propylene, l-butene, l-hexene, 4-methyl-1-pentene, 1-heptene, l-octene, styrene, etc.). Typical substantially linear ethylene polymers exhibit a density of at least 0.850 g/cm3, preferably at least 0.870 g/cm3. Typical substantially linear ethylene polymers exhibit a density of no more than 0.960 g/cm3, o preferably no more than O.910g/cm3. The melt flow ratio, measured as Ilo/I2 (ASTM D-1238), is greater than or equal to 5.63, and is preferably from about 6.5 to 15, more preferably from about 7 to 10.
The molecular weight distribution (MW/Mn), measured by gel permeation chromatography (GPC), is defined by the equation:
Mw/Mn _ (Ilo/I2) - 4.63, and is preferably between about 1.5 and 2.5. For the substantially linear ethylene polymers, the Ilo/I2 ratio indicates the degree of long-chain branching, i.e. the larger the Ilo/I2 ratio, the more long-chain branching in the polymer.
The ~rheological processing index~ (PI) is the apparent viscosity (in kpoise) of a polymer measured by a gas extrusion rheometer (GER). The gas extrusion rheometer is described by M.
Shida, R.N. Shroff and L.V. Cancio in Polymer ~naineerina Science, Vol. 17, No. 11, p. 770 (1977), and in ~Rheometers for Molten 2s Plastics~ by John Dealy, published by Van Nostrand Reinhold Co. (1982) on pp. 97-99. GER experiments are performed at a temperature of 190C, at nitrogen pressures between 250 to 5500 (1.8 to 38 MPa) psig using about a 7.54 cm diameter, 20:1 L/D die with an entrance angle of 180. For the substantially linear ethylene polymers described herein, the PI is the apparent viscosity (in kpoise) of a material measured by GER at an apparent shear stress of 2.15 x 106 dyne/cm2.
These substantially linear ethylene interpolymers and homopolymers preferably have a PI in the of about 0.01 kpoise to 50 kpoise, preferably 15 kpoise or less, which is less than or equal to 70 3s percent of the PI of a comparative linear ethylene polymer (either a Ziegler polymerized polymer or a linear uniformly branched polymer as 2169~6~ - -described by Elston in US Patent 3,645,992) at about the same I2 and MW/Mn .
An apparent shear stress versus apparent shear rate plot is used to identify the melt fracture phenomena. According to ~ rthy in the Journal of Rheoloav, 30(2~, 337-357, 1986, above a certain critical flow rate, the observed extrudate irregularities may be broadly classified into two main types: surface melt fracture and gross melt fracture.
Surface melt fracture occurs under apparently steady flow conditions and ranges in detail from loss of specular film gloss to the more severe form of ~sharkskin.U In this disclosure, the onset of surface melt fracture (OSMF) is characterized at the beginning of losing extrudate gloss at which the surface roughness of the extrudate can only be detected by 40x magnification. The critical shear rate at the onset of surface melt fracture for the substantially linear ethylene interpolymers and homopolymers is at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a comparative linear ethylene polymer (either a Ziegler polymerized polymer or a linear uniformly branched polymer as described by Elston in US Patent 3,645,992) having about the same I2 and MW/Mn.
Gross melt fracture occurs at unsteady extrusion flow conditions and ranges in detail from regular (alternating rough and smooth, helical, etc.) to random distortions. For commercial acceptability, (e.g., in blown films and bags therefrom), surface defects should be ini ~1, if not absent, for good film quality and properties. The critical shear stress at the onset of gross melt fracture for the substantially linear ethylene interpolymers and homopolymers used in making the biaxially oriented, heat-shrinkable film of the present invention is greater than 4 x 106 dynes/cm2. The critical shear rate at the onset of surface melt fracture (OSMF) and the onset of gross melt fracture (OGMF) will be used herein based on the changes of surface roughness and configurations of the extrudates extruded by a GER.
As here used, ~homogeneously branchedU means that the comonomer is randomly distributed within a given molecule and that substantially all of the copolymer molecules have the same W 095/05419 2 1 ~ g O ~ ~ PCTrUS94/08943 ethylene/comonomer ratio. The distribution or homogeneity of comonomer branches for the substantially linear ethylene interpolymers and homopolymers is characterized by its SCBDI (Short Chain Branch Distribution Index) or CDBI (Composition Distribution Branch Index), and it is defined as the weight percent of the polymer molecules having a comonomer content within 50 percent of the median total molar comonomer content. The CDBI of a polymer is readily calculated from data obtained from techniques known in the art, such as, for example, temperature rising elution fractionation (abbreviated herein as ~TREF~) as described, for example, by Wild et al., Journa] of PQ1VmSI
Sci~nce. Poly. Phvs. ~d., Vol. 20, p. 441 (1982), or in US Patent 4,798,081. The SCBDI or CDBI for the substantially linear homogeneously branched interpolymers and homopolymers of the present invention is preferably greater than about 30 percent, especially s greater than about 50 percent.
Both the linear homogeneously branched and the substantially linear homogeneously branched ethylene polymers used in this invention have a single melting peak, as measured using differential scanning calorimetry (DSC), in contrast to heterogeneously branched linear ethylene polymers, which have two or more melting peaks due to their broad branching distribution.
The unique characteristic of the homogeneously branched, substantially linear ethylene polymers is a highly unexpected flow property where the Ilo/I2 value of the polymer is essentially independent of the polydispersity index (i.e., MW/Mn) of the polymer.
This is contrasted with conventional linear homogeneously branched and linear heterogeneously branched polyethylene resins having rheological properties such that to increase the I1o/I2 value the polydispersity index must also be increased.
The preferred melt index, measured as I2 (ASTM D-1238, condition 190/2.16 (formerly condition E)), is from 0.5 g/10 min to 20 g/10 min, more preferably 1 to 5 g/10 min. Typically, the preferred substant-ially linear ethylene polymers used in the construction of the plastic films used in this practice of this invention are homogeneously branched and do not have any measurable high density fraction, (i.e. short chain branching distribution as measured by W O95/05419 ', ~ PCTrUS94/08943 2l~sn6s Temperature Rising Elution Fractionation which is described in USP
5,089,321, e.g. they do not contain any polymer fraction that has a degree of branching less than or equal to 2 methyl/1000 carbons.
These preferred substantially linear ethylene polymers have a single s differential scanning calorimetry (DSC) melting peak.
The polypropylene component of this invention, if present, is a homopolymer or one or more copolymers of propylene and up to about 20 mole percent ethylene or other a-olefin having up to about 12 carbon atoms. If a copolymer, it can be random, block or graft. The o polypropylene component of this has a typical melt flow rate (as determined by ASTM D-1238, Condition 230/2.16 (formerly Condition L)) of between 0.1 and 30 g/10 minutes, and preferably between 0.8 and 30 g/10 minutes.
The blends of this invention can also include polyolefins derived~from post-consumer recycle (PCR) sources. These materials will vary in composition, but include HDPE derived from milk bottle recycled resin and LLDPE derived from recycled grocery sacks. The PCR
resins used in this invention usually have a polyethylene content of at least about 70 wt percent, based on the weight of the resin, up to about 100 wt percent. The polyethylenes in the PCR resins usually have a melt index between 0.1 and 10 g/10 minutes, and a density between 0.86 and 0.97 g/cm3.
Typically, the polyolefin blends of this invention comprise at least 10 percent, preferably at least 20 percent and more preferably at least 30 percent, based on the weight of the blend, of the low melting component. In a preferred embodiment of this invention, the component with the low melting or softening temperature is at least one linear or substantially linear homogeneously branched polyethylene, e.g. at least one of a Tafmer~, Exact~ or a polymer made by Insite~ Technology, or an ethylene-propylene rubber, or an ethylene-propylene-diene monomer terpolymer. More preferably, the low melting temperature component of the blend is a substantially linear homogeneously branched polymer, e.g. a polymer made by Insite~. In these embodiments, the remainder of the blend comprises one or more, preferably one, heterogeneously branched polyethylene.
The solid state processing temperature of these blends is W O95/05419 2 1 69 0 6 8 PCTrUS94108943 usually at least 5, and preferably at least 10, degrees on the Celsius scale below the peak melting temperature of the blend component with the highest melting temperature, and it is usually at least 5, preferably at about 10, degrees on the Celsius scale above the melting s or softening temperature of the blend component with the lowest melting or softening temperature.
The polyolefin blends of this invention can be prepared by any one of a number of different methods that ensures a relatively homogenous blend, the particular method employed being a matter of lo convenience. Illustrative methods include roller milling, extrusion, solvent mixing, and the like. Similarly, the blends can be processed by any conventional solid state technique, e.g. stamping, forging, rolling, extrusion, etc.
The following examples are illustrative of certain specific s embodiments of this invention. All parts and percentages are by weight unless otherwise noted.
SP~CIFIC FMRODTM~NTS
e 1 Sample E-l was prepared from a 50/50 blend of CGC resin (a substantially linear ethylene/l-octene compolymer prepared in accordance with the teachings of US Patent Nos. 5,272,236 and 5,278,272 (Sample C-l)) and DOWLEX~ 12065 HDPE resin, available from The Dow Chemical Company (Sample C-2) using a Haake blender operated for 4 minutes at 180C. Sample C-5 was prepared in the same manner except that it was prepared from a 50/50 blend of conventional LLDPEs (Samples C-3 (DOWLEX~ 2045 LLDPE, available from The Dow Chemical Company)~ and C-4). All the samples except Sample C-l were subjected to solid state extrusion evaluation by using an Instron Capillary Rheometer (ICR) at 105C using a Number 8 die (0.0494 inches (1.255 mm) in diameter, length/diameter ratio of 5.10). Sample E-l (with a Tp of 50 (133-83)) was successfully extruded at a plunger speed of 0.1 inch (2.54 mm) per minute and at a pressure of 250 psi (1.72 MPa).
The other samples (including Sample C-5 with a Tp of 10 (122-132)) could not be extruded at these conditions, or even at the maximum safe extrusion pressure of the ICR of 4500 psi (31 MPa). These results are reported in Table I.
W O95/05419 PCTrUS94/08943 216gO6~
TABLE I
Sample Composition MI Density Mw/Mn Peak Solid Number (g/10 (g/cm3) Melt State min) Temp Extrudable (C) E-lCGC/HDPE* 1.33 0.926 -- Yes C-l CGC 1.33 0.893 2 83 NA+
C-2 HDPE 1.0 0.9593.98 133 No C-3 LLD-3 1.0 0.9203.8 122 No C-4 LLD-4 2.0 0.9303.7 122 No C-5LLD-3/LLD-4* 1.4 0.925 -- No * 50/50/Blend based on weight.
+ NA = Not applicable: above melting point F.xA~le 2 The procedures of Example 1 were repeated with different samples (although the composition of Sample C-6 was the same as the composition of Sample C-l). C7 was a high density polyethylene lo available from The Dow Chemical Company as DOWLEXTM 10062. Samples E-2 (a blend of C-6 and C-7) (with a Tp of 51) and E-3 (a blend of C-8 and C-9 (Fina 3824 polypropylene homopolymer)) (with a Tp of 79) were successfully extruded on the ICR at a plunger speed of 0.1 inch (2.54 mm) per minute, a pressure of about 2800 psi (19.3 MPa), a temperature of about 105C, and using a Number 2 die (0.030 inch (0.762 mm), length/ciameter ratio of 33.3). Neither the Tafmer~ A-4085 resin (available from Mitsui Petrochemical) nor the polypropylene resin could be extruded at these conditions, or even at the maximum safe extrusion pressure of 4500 psi (31 MPa). The results are reported in Table II.
W O95/05419 2 1 6 9 0 ~ 8 PCTrUS91,'0~91~
TABL: II
Sample CompositionMI Density Mw/Mn Peak Solid Number(g/10 min) (g/cm3)Melt State Temp Extrudable (C) E-2 CGC/HDPE* 2.33 0.926 -- Yes C-6 CGC 1.78 0.893 2 83 NA***
C-7 HDPE 10 0.962 2.73 134 NM+
E-3 TafmerTM/pp** 1.4 0.925 1.9 __ Yes C-8 TafmerTMA-4085 1.0 0.88 1.9 88 No C-9 PP 30**** -- 167 No * 50/50 Blend based on weight.
30/70 Blend based on weight.
+ NM = not measured.
*** NA = Not applicable: above melting point **** Melt index determined at 230C
F~m~le 3 The procedures of Example 1 were repeated with different 0 samples. The compositions of Samples C-10 and C-12 were the same, with both being a substantially linear ethylene/l-octene copolymer prepared in accordance with the teachings of U.S. Patent Nos.
5,272,236 and 5,278,272. The PCR resin of Sample C-13 was post-consumer recycled grocery sack resin from Advanced Environmental Recycling Technology of Little Rock, Arkansas, and the PCR resin of Sample C-11 was post-consumer recycled milk bottle resin FR-120 flake from Akron WTE Corp of Akron, Ohio. Both the resins of Samples E-4 (a blend of C-10 and C-11) and E-5 (a blend of C-12 and C-13) (with a Tp of 49) were successfully extruded under the same conditions as those used in Example 2. Neither the resin of C-ll nor the resin of C-13 were extruded under these conditions, and they could not be extruded under these conditions even at the maximum safe extrusion pressure of 4500 psi (31 MPa). The results are reported in Table III.
W O95/05419 PCTrUS94/08943 TABLE -II
Sample Composition MI Density Peak Solid Number (g/10 min) ~g/cm3) Melt State Temp Extrudable (C) E-4 CGC/PCR* -- 0.912 -- Yes C-10 CGC 1.0 0.882 86 NA**
C-ll PCR 0.75 0.955 132 No E-5 CGC/PCR* 1.4 0.935 -- Yes C-12 CGC 1.0 0.882 86 NA**
C-13 PCR 0.4 0.962 135 No * 30/70 Blend based on weight.
** NA = Not applicable: above melting point.
~x~rle 4 The procedures of Example 1 were repeated with different samples. Sample C-14 (which is the same as Sample C-3) was DOWLEXTM
2045 LLDPE (available from The Dow Chemical Company) with a similar lo melt index and density as Sample E-6 (a blend of C-16 (DOWLEXTM 12065 HDPE, available from The Dow Chemical Company) and C-15 (a substantially linear ethylene/l-octene copolymer having a Mw/Mn of 2 and prepared in accordance with the teachings of U.S. Patent Nos.
5,272,236 and 5,278,272)) (with a Tp of 107). Both Samples E-6 and C-14 were compression molded into a 125 mil (3.175 mm) thick plaque according to the procedures of ASTM-1238. The plaques were heated to 65C, and then compressed in a 40 ton (2075 psi (14.3 MPa)) solid phase forming machine for 3 minutes. The samples were then cooled under the same pressure, removed at room temperature, and the modulus and percent deformation determined. These results are reported in Table IV, and the modulus and percent deformation characteristics of Sample E-6 are clearly superior to those of Sample C-14.
W O 95tO5419 PCTrUS94/08943 216906~
TA-LE IV
Sample Composition MI Density Peak Percent Modulus Number (g/10 min) (g/cm3) Melt Deformed psi Temp (MPa) (C) E-6 HDPE/CGC 1.01 0.922 -- 203 39,900 (275) C-14 LLD-3 1.0 0.920 122 162 16,120 ( 1 11 ) C-15 CGC 1.01 0.856 26 NM+ NM+
C-16 HDPE 1.0 0.959 133 NM+ NM+
* 35/65 Blend based on weight.
+ NM = Not measured.
s Although the invention has been described in considerable detail through the preceding examples, this detail is for illustration purposes only, and it is not to be construed as a limitation on the spirit and scope of the invention as described in the following o claims.
BAcKGRouNn OF TH~ INV~NTION
This invention relates to polyolefin blends. In one aspect, the invention relates to polyolefin blends suitable for solid state processing while in another aspect, the invention relates to particular blends of various polyethylenes. In still another aspect, the invention relates to polyolefin blends characterized by melting and crystallization curves exhibiting either two distinct melt regions, or wherein one component has a softening point lower than that of a conventional polyolefin, either technique of which provides an unusually wide window for solid state processing.
While the field of metal forming offers a wide variety of solid state processing, e.g. stamping, forging, rolling, extrusion, etc., the solid state processing of semicrystalline polymers is much more limited. To process a thermoplastic in the solid state, typically the processing temperature is maintained at just a few degrees below the melting point of the polymer. If the processing temperature is above the melting point of the polymer, then the processing is simply a melt extrusion. At temperatures considerably below the melting point of the polymer, the polymer is essentially a solid and its deformation requires a tremendous amount of pressure (often in excess of one million psi (7000 MPa)). Such enormous pressures make large deformations very difficult, and result in a relatively low production rate and a generally energy inefficient process. Moreover, since the processing temperature is the most critical parameter in solid state processing, this technique has been limited to those polymers and polymer blends with relatively wide (e.g. at least about 20 degrees on the Celsius scale) ranges between their softening and melting temperatures. Since this temperature range is relatively narrow for conventional polyolefins and their blends, these materials have not been the subject of extensive, commercial-scale solid state processing.
Despite their relatively narrow processing temperature window, the sheer commercial scale of the polyolefin market has generated considerable interest in applying this technique to polyolefins. The W O 95/05419 -~ PCTrUS9~/08943 2l6sn6~
potential benefits to be gained include energy efficiency, speed, and scrap reduction. Ciferri and Ward in ~Ultra High Modulus Polymers~, AnDlied Science Publication~, London (197g), teach that the extrusion of polymers below the melting point is a promising method of producing highly oriented materials. Krjutchkov, et al. in Poly~er Co~osite, Vol. 7, No. 6, pp. 4-13-420 ~1986), disclosed the detailed investigations of the dynamics of solid state extrusion, and they have also postulated a model to correlate the flow of instability in extrudate defects to the extrusion temperature and pressure.
o Chung in USP 5,028,663 teaches that certain blends of high density polyethylene (HDPE) and low density polyethylene (LDPE) prepared by solution mixing can achieve a broader operating window for certain solid state processing applications than would otherwise be achieved by mechanical mixing. The melting peak of each component in the blend is separated due to solution precipitation such that large deformation processing can be performed at a temperature between the melting peaks of the two components.
Pawloski, et al. in USP 4,352,766, 4,161,502 and 3,739,052 teach a unique process called Solid Phase Forming (SPF) to form polymers and composites at a pre-melt state. This unique fabrication process induces a biaxial orientation throughout the finished parts.
Enikolopow, et al. in USP 4,607,797 teach a process called Solid State Sheer Extrusion or Pulverization to perform polymer extrusion at a temperature below the peak melting temperature of the polymer.
However, Shutov has observed in a 1992 I.I.T. Research Report that certain polymers, such as HDPE, polypropylene (PP) and polycarbonate (PC) did not perform well in this process.
We have discovered a composition suitable for solid state processing, characterized as a blend comprising a first and a second polyolefin, wherein the first polyolefin is characterized as having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, the first polyolefin component comrpising at least 10 percent of the total weight of the polyolefin blend.
Preferably, the composition will be characterized as a blend comprising a polyolefin composition suitable for solid state W O95/05419 2 1 6 ~ 0 6 8 PCTrUS94/08943 processing, the composition characterized as a blend comprising: (a) a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to 0.910 g/cm3; and tb) a second polyolefin having a density from 0.940 g/cm3 to 0.965 g/cm3, s wherein the first polyolefin is characterized by a softening point of at least ten degrees on the Celsius scale lower than the softening point of the second polyolefin.
We have also discovered a process for shaping a solid polyolefin blend, the process characterized as comprising the following steps:
lo (a) heating a solid polyolefin blend which comprises at least a first and second polyolefin, the first polyolefin having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, the first polyolefin comprising at least 10 percent of the total weight of the polyolefin blend heated to a processing temperature above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin; (b) shaping the blend at the processing temperature; and (c) cooling the shaped blend of (b) to a temperature below the processing temperature.
Preferably, the process will be characterized as comprising the following steps: (a) heating to a processing temperature a solid polyolefin blend which comprises: (i) a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to0.910 g/cm3; and (ii) a second polyolefin having a density of 2s from 0.940 g/cm3 to 0.965 g/cm3; wherein the first polymer is characterized by a softening point of at least ten degrees on the Celsius scale lower than the softening point of the second polyolefin and wherein the processing temperature is above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin; (b) shaping the blend at the processing temperature; and (c) cooling the shaped blend of (b) to a temperature belowe the processing temperature.
According to this invention, polyolefin blends characterized by melting and crystallization curves which exhibit either two distinct melt regions, or a low softening point relative to the high melting component of the blend, provide an unusually wide window for solid W O95/05419 PCTrUS9~/08943 2l6sn6s state processing. These blends comprise at least 10 percent by weight of the low melting component, and the difference between the peak melting temperature of the low melting component and the high melting component is at least about twenty degrees on the Celsius scale. These blends are processed in their solid state at a temperature above about the peaK melting temperature of the low melting component and below the peak melting temperature of the high melting component. The solid state processing characteristics of the blends of this invention are independent of the manner in which the components are mixed, e.g.
o mechanical, solvent, etc.
DF~ CRTPTION OF THF~ PRF:FF~RRF~n F~MRoDTMF~NTs The polyolefin blends of this invention comprise two or more, typically two, polyolefin components. These blends are characterized by having a solid state processing temperature (Tp) defined by Tml < Tp < Tm2 in which the Tm2 is the peak melting temperature of the high melting component, and Tml is the peak melting temperature of the low melting component. Typically, the difference or range between Tm2 and Tml, i.e. Tm2-Tml, is greater than twenty, preferably greater than thirty, and most preferably greater than forty, degrees on the Celsius scale.
The components of the blends of this invention are polyolefins, e.g. polyethylenes, polypropylenes, dienes, styrene, etc. Preferred polyolefins are the various polyethylenes and polypropylenes, and preferred blends are those containing at least one polyethylene, 2s particularly a substantially linear ethylene polymer.
The polyethylenes can be divided into two broad classes, heterogeneously branched and homogeneously branched. The heterogeneously branched polyethylenes that can be used in the practice of this invention fall into two broad categories, those prepared with a free radical initiator at high temperature and high pressure, and those prepared with a coordination catalyst at high temperature and relatively low pressure. The former are generally known as low density polyethylenes (LDPE) and are characterized by branched chains of polymerized monomer units pendant from the polymer backbone. LDPE polymers generally have a density between 0.910 and 0.935 grams per cubic centimeter (g/cm3).
W O 95/05419 2 1 6 9 ~ 6 8 PCTrUS94/08943 Ethylene polymers and copolymers prepared by the use of a coordination catalyst, such as a Ziegler or Phillips catalyst, are generally known as linear polymers because of the substantial absence of branch chains of polymerized monomer units pendant from the s backbone. High density polyethylene (HDPE), generally having a density of 0.940 to 0.965 g/cm3, is typically a homopolymer of ethylene, and it contains relatively few branch chains relative to the various linear copolymers of ethylene and an a-olefin. HDPE is well known, commercially available in various grades, and is useful in this lo invention.
Linear copolymers of ethylene and at least one -olefin of 3 to 12 carbon atoms, preferably of 4 to 8 carbon atoms, are also well known, commercially available and useful in this invention. As is well known in the art, the density of a linear ethylene/-olefin copolymer is a function of both the length of the -olefin and the amount of such monomer in the copolymer relative to the amount o~f ethylene, the greater the length of the -olefin and the greater the amount of -olefin present, the lower the density of the copolymer.
Linear low density polyethylene (LLDPE) is typically a copolymer of ethylene and an -olefin of 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms (e.g., 1-butene, 1-octene, etc.), that has sufficient -olefin content to reduce the density of the copolymer to that of LDPE.
When the copolymer contains even more -olefin, the density will drop below 0.91 g/cm3 and these copolymers are known as ultra low density polyethylene (ULDPE) or very low density polyethylene (VLDPE). The densities of these linear polymers generally range from 0.87 to 0.91 g/cm3.
Both the materials made by the free radical catalysts and by the coordination catalysts are well known in the art, as are their methods of preparation. Relevant discussions of both of these classes of materials, and their methods of preparation, are found in USP
4,950,541 and the patents to which it refers.
The homogeneously branched polyethylenes that can be used in the practice of this invention also fall into two broad categories, the 3~ linear homogeneously branched and the substantially linear homogeneously branched. Both are known. The former and their method WO95/05419 - PCTrUS94108943 ~16906g , of preparation are described in USP 3,645,992 to Elston, and the latter and their method of preparation are fully described in U.S.
Patent 5,272,236 and 5,278,272. ~Examples of the former are the Tafmer~ polymer of Mitsui and the Exact~ polymer of Exxon, while an example of the latter are the polymers made by the Insite~ Technology of The Dow Chemical Company.
As here used, ~substantially linear~ means that the polymer backbone is substituted with 0.0l long-chain branches/l000 carbons to 3 long-chain branches/l000 carbons, preferably from 0.0l long-chain 0 branches/l000 carbons to l long-chain branch/l000 carbons, and more preferably from 0.05 long-chain branches/l000 carbons to l long-chain branch/l000 carbons. In contrast, simply ~linearR means that long chain branching is essentially absent from the polymer backbone.
Long-chain branching is here defined as a chain length of at least 6 carbon atoms, above which the length cannot be distinguished using l3C
nuclear magnetic resonance spectroscopy, yet the long-chain branch can be about the same length as the length of the polymer backbone.
These unique substantially linear homogeneously branched polymers ~subsequently referred to as ~substantially linear ethylene polymers~) are prepared by using constrained geometry catalysts (CGC), and are characterized by a narrow molecular weight distribution and if an interpolymer, by a narrow comonomer distribution. As here used, ~interpolymer~ means a polymer of two or more comonomers, e.g. a copolymer, terpolymer, etc. Other basic characteristics of these substantially linear ethylene polymers include a low residuals content (i.e. low concentrations in the substantially linear ethylene polymer of the catalyst used to prepare the polymer, unreacted comonomers, if any, and low molecular weight oligomers made during the course of the polymerization), and a controlled molecular architecture which provides good processability even though the molecular weight distribution is narrow relative to conventional olefin polymers.
While the substantially linear ethylene polymers used in the practice of this invention include substantially linear ethylene homopolymers, preferably these substantially linear ethylene polymers comprise between about 95 and 50 wt percent ethylene, and about 5 and 50 wt percent of at least one a-olefin comonomer, more preferably l0 W O 95/05419 2 1 6 9 0 6 8 PCTrUS94/08943 to 25 wt percent of at least one ~-olefin comonomer. Percent comonomer is measured by Infrared Spectroscopy according to ASTM
D-2238 Method B. Typically, the substantially linear ethylene polymers are copolymers of ethylene and an ~-olefin of 3 to about 20 carbon s atoms (e.g. propylene, l-butene, l-hexene, 4-methyl-1-pentene, 1-heptene, l-octene, styrene, etc.). Typical substantially linear ethylene polymers exhibit a density of at least 0.850 g/cm3, preferably at least 0.870 g/cm3. Typical substantially linear ethylene polymers exhibit a density of no more than 0.960 g/cm3, o preferably no more than O.910g/cm3. The melt flow ratio, measured as Ilo/I2 (ASTM D-1238), is greater than or equal to 5.63, and is preferably from about 6.5 to 15, more preferably from about 7 to 10.
The molecular weight distribution (MW/Mn), measured by gel permeation chromatography (GPC), is defined by the equation:
Mw/Mn _ (Ilo/I2) - 4.63, and is preferably between about 1.5 and 2.5. For the substantially linear ethylene polymers, the Ilo/I2 ratio indicates the degree of long-chain branching, i.e. the larger the Ilo/I2 ratio, the more long-chain branching in the polymer.
The ~rheological processing index~ (PI) is the apparent viscosity (in kpoise) of a polymer measured by a gas extrusion rheometer (GER). The gas extrusion rheometer is described by M.
Shida, R.N. Shroff and L.V. Cancio in Polymer ~naineerina Science, Vol. 17, No. 11, p. 770 (1977), and in ~Rheometers for Molten 2s Plastics~ by John Dealy, published by Van Nostrand Reinhold Co. (1982) on pp. 97-99. GER experiments are performed at a temperature of 190C, at nitrogen pressures between 250 to 5500 (1.8 to 38 MPa) psig using about a 7.54 cm diameter, 20:1 L/D die with an entrance angle of 180. For the substantially linear ethylene polymers described herein, the PI is the apparent viscosity (in kpoise) of a material measured by GER at an apparent shear stress of 2.15 x 106 dyne/cm2.
These substantially linear ethylene interpolymers and homopolymers preferably have a PI in the of about 0.01 kpoise to 50 kpoise, preferably 15 kpoise or less, which is less than or equal to 70 3s percent of the PI of a comparative linear ethylene polymer (either a Ziegler polymerized polymer or a linear uniformly branched polymer as 2169~6~ - -described by Elston in US Patent 3,645,992) at about the same I2 and MW/Mn .
An apparent shear stress versus apparent shear rate plot is used to identify the melt fracture phenomena. According to ~ rthy in the Journal of Rheoloav, 30(2~, 337-357, 1986, above a certain critical flow rate, the observed extrudate irregularities may be broadly classified into two main types: surface melt fracture and gross melt fracture.
Surface melt fracture occurs under apparently steady flow conditions and ranges in detail from loss of specular film gloss to the more severe form of ~sharkskin.U In this disclosure, the onset of surface melt fracture (OSMF) is characterized at the beginning of losing extrudate gloss at which the surface roughness of the extrudate can only be detected by 40x magnification. The critical shear rate at the onset of surface melt fracture for the substantially linear ethylene interpolymers and homopolymers is at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a comparative linear ethylene polymer (either a Ziegler polymerized polymer or a linear uniformly branched polymer as described by Elston in US Patent 3,645,992) having about the same I2 and MW/Mn.
Gross melt fracture occurs at unsteady extrusion flow conditions and ranges in detail from regular (alternating rough and smooth, helical, etc.) to random distortions. For commercial acceptability, (e.g., in blown films and bags therefrom), surface defects should be ini ~1, if not absent, for good film quality and properties. The critical shear stress at the onset of gross melt fracture for the substantially linear ethylene interpolymers and homopolymers used in making the biaxially oriented, heat-shrinkable film of the present invention is greater than 4 x 106 dynes/cm2. The critical shear rate at the onset of surface melt fracture (OSMF) and the onset of gross melt fracture (OGMF) will be used herein based on the changes of surface roughness and configurations of the extrudates extruded by a GER.
As here used, ~homogeneously branchedU means that the comonomer is randomly distributed within a given molecule and that substantially all of the copolymer molecules have the same W 095/05419 2 1 ~ g O ~ ~ PCTrUS94/08943 ethylene/comonomer ratio. The distribution or homogeneity of comonomer branches for the substantially linear ethylene interpolymers and homopolymers is characterized by its SCBDI (Short Chain Branch Distribution Index) or CDBI (Composition Distribution Branch Index), and it is defined as the weight percent of the polymer molecules having a comonomer content within 50 percent of the median total molar comonomer content. The CDBI of a polymer is readily calculated from data obtained from techniques known in the art, such as, for example, temperature rising elution fractionation (abbreviated herein as ~TREF~) as described, for example, by Wild et al., Journa] of PQ1VmSI
Sci~nce. Poly. Phvs. ~d., Vol. 20, p. 441 (1982), or in US Patent 4,798,081. The SCBDI or CDBI for the substantially linear homogeneously branched interpolymers and homopolymers of the present invention is preferably greater than about 30 percent, especially s greater than about 50 percent.
Both the linear homogeneously branched and the substantially linear homogeneously branched ethylene polymers used in this invention have a single melting peak, as measured using differential scanning calorimetry (DSC), in contrast to heterogeneously branched linear ethylene polymers, which have two or more melting peaks due to their broad branching distribution.
The unique characteristic of the homogeneously branched, substantially linear ethylene polymers is a highly unexpected flow property where the Ilo/I2 value of the polymer is essentially independent of the polydispersity index (i.e., MW/Mn) of the polymer.
This is contrasted with conventional linear homogeneously branched and linear heterogeneously branched polyethylene resins having rheological properties such that to increase the I1o/I2 value the polydispersity index must also be increased.
The preferred melt index, measured as I2 (ASTM D-1238, condition 190/2.16 (formerly condition E)), is from 0.5 g/10 min to 20 g/10 min, more preferably 1 to 5 g/10 min. Typically, the preferred substant-ially linear ethylene polymers used in the construction of the plastic films used in this practice of this invention are homogeneously branched and do not have any measurable high density fraction, (i.e. short chain branching distribution as measured by W O95/05419 ', ~ PCTrUS94/08943 2l~sn6s Temperature Rising Elution Fractionation which is described in USP
5,089,321, e.g. they do not contain any polymer fraction that has a degree of branching less than or equal to 2 methyl/1000 carbons.
These preferred substantially linear ethylene polymers have a single s differential scanning calorimetry (DSC) melting peak.
The polypropylene component of this invention, if present, is a homopolymer or one or more copolymers of propylene and up to about 20 mole percent ethylene or other a-olefin having up to about 12 carbon atoms. If a copolymer, it can be random, block or graft. The o polypropylene component of this has a typical melt flow rate (as determined by ASTM D-1238, Condition 230/2.16 (formerly Condition L)) of between 0.1 and 30 g/10 minutes, and preferably between 0.8 and 30 g/10 minutes.
The blends of this invention can also include polyolefins derived~from post-consumer recycle (PCR) sources. These materials will vary in composition, but include HDPE derived from milk bottle recycled resin and LLDPE derived from recycled grocery sacks. The PCR
resins used in this invention usually have a polyethylene content of at least about 70 wt percent, based on the weight of the resin, up to about 100 wt percent. The polyethylenes in the PCR resins usually have a melt index between 0.1 and 10 g/10 minutes, and a density between 0.86 and 0.97 g/cm3.
Typically, the polyolefin blends of this invention comprise at least 10 percent, preferably at least 20 percent and more preferably at least 30 percent, based on the weight of the blend, of the low melting component. In a preferred embodiment of this invention, the component with the low melting or softening temperature is at least one linear or substantially linear homogeneously branched polyethylene, e.g. at least one of a Tafmer~, Exact~ or a polymer made by Insite~ Technology, or an ethylene-propylene rubber, or an ethylene-propylene-diene monomer terpolymer. More preferably, the low melting temperature component of the blend is a substantially linear homogeneously branched polymer, e.g. a polymer made by Insite~. In these embodiments, the remainder of the blend comprises one or more, preferably one, heterogeneously branched polyethylene.
The solid state processing temperature of these blends is W O95/05419 2 1 69 0 6 8 PCTrUS94108943 usually at least 5, and preferably at least 10, degrees on the Celsius scale below the peak melting temperature of the blend component with the highest melting temperature, and it is usually at least 5, preferably at about 10, degrees on the Celsius scale above the melting s or softening temperature of the blend component with the lowest melting or softening temperature.
The polyolefin blends of this invention can be prepared by any one of a number of different methods that ensures a relatively homogenous blend, the particular method employed being a matter of lo convenience. Illustrative methods include roller milling, extrusion, solvent mixing, and the like. Similarly, the blends can be processed by any conventional solid state technique, e.g. stamping, forging, rolling, extrusion, etc.
The following examples are illustrative of certain specific s embodiments of this invention. All parts and percentages are by weight unless otherwise noted.
SP~CIFIC FMRODTM~NTS
e 1 Sample E-l was prepared from a 50/50 blend of CGC resin (a substantially linear ethylene/l-octene compolymer prepared in accordance with the teachings of US Patent Nos. 5,272,236 and 5,278,272 (Sample C-l)) and DOWLEX~ 12065 HDPE resin, available from The Dow Chemical Company (Sample C-2) using a Haake blender operated for 4 minutes at 180C. Sample C-5 was prepared in the same manner except that it was prepared from a 50/50 blend of conventional LLDPEs (Samples C-3 (DOWLEX~ 2045 LLDPE, available from The Dow Chemical Company)~ and C-4). All the samples except Sample C-l were subjected to solid state extrusion evaluation by using an Instron Capillary Rheometer (ICR) at 105C using a Number 8 die (0.0494 inches (1.255 mm) in diameter, length/diameter ratio of 5.10). Sample E-l (with a Tp of 50 (133-83)) was successfully extruded at a plunger speed of 0.1 inch (2.54 mm) per minute and at a pressure of 250 psi (1.72 MPa).
The other samples (including Sample C-5 with a Tp of 10 (122-132)) could not be extruded at these conditions, or even at the maximum safe extrusion pressure of the ICR of 4500 psi (31 MPa). These results are reported in Table I.
W O95/05419 PCTrUS94/08943 216gO6~
TABLE I
Sample Composition MI Density Mw/Mn Peak Solid Number (g/10 (g/cm3) Melt State min) Temp Extrudable (C) E-lCGC/HDPE* 1.33 0.926 -- Yes C-l CGC 1.33 0.893 2 83 NA+
C-2 HDPE 1.0 0.9593.98 133 No C-3 LLD-3 1.0 0.9203.8 122 No C-4 LLD-4 2.0 0.9303.7 122 No C-5LLD-3/LLD-4* 1.4 0.925 -- No * 50/50/Blend based on weight.
+ NA = Not applicable: above melting point F.xA~le 2 The procedures of Example 1 were repeated with different samples (although the composition of Sample C-6 was the same as the composition of Sample C-l). C7 was a high density polyethylene lo available from The Dow Chemical Company as DOWLEXTM 10062. Samples E-2 (a blend of C-6 and C-7) (with a Tp of 51) and E-3 (a blend of C-8 and C-9 (Fina 3824 polypropylene homopolymer)) (with a Tp of 79) were successfully extruded on the ICR at a plunger speed of 0.1 inch (2.54 mm) per minute, a pressure of about 2800 psi (19.3 MPa), a temperature of about 105C, and using a Number 2 die (0.030 inch (0.762 mm), length/ciameter ratio of 33.3). Neither the Tafmer~ A-4085 resin (available from Mitsui Petrochemical) nor the polypropylene resin could be extruded at these conditions, or even at the maximum safe extrusion pressure of 4500 psi (31 MPa). The results are reported in Table II.
W O95/05419 2 1 6 9 0 ~ 8 PCTrUS91,'0~91~
TABL: II
Sample CompositionMI Density Mw/Mn Peak Solid Number(g/10 min) (g/cm3)Melt State Temp Extrudable (C) E-2 CGC/HDPE* 2.33 0.926 -- Yes C-6 CGC 1.78 0.893 2 83 NA***
C-7 HDPE 10 0.962 2.73 134 NM+
E-3 TafmerTM/pp** 1.4 0.925 1.9 __ Yes C-8 TafmerTMA-4085 1.0 0.88 1.9 88 No C-9 PP 30**** -- 167 No * 50/50 Blend based on weight.
30/70 Blend based on weight.
+ NM = not measured.
*** NA = Not applicable: above melting point **** Melt index determined at 230C
F~m~le 3 The procedures of Example 1 were repeated with different 0 samples. The compositions of Samples C-10 and C-12 were the same, with both being a substantially linear ethylene/l-octene copolymer prepared in accordance with the teachings of U.S. Patent Nos.
5,272,236 and 5,278,272. The PCR resin of Sample C-13 was post-consumer recycled grocery sack resin from Advanced Environmental Recycling Technology of Little Rock, Arkansas, and the PCR resin of Sample C-11 was post-consumer recycled milk bottle resin FR-120 flake from Akron WTE Corp of Akron, Ohio. Both the resins of Samples E-4 (a blend of C-10 and C-11) and E-5 (a blend of C-12 and C-13) (with a Tp of 49) were successfully extruded under the same conditions as those used in Example 2. Neither the resin of C-ll nor the resin of C-13 were extruded under these conditions, and they could not be extruded under these conditions even at the maximum safe extrusion pressure of 4500 psi (31 MPa). The results are reported in Table III.
W O95/05419 PCTrUS94/08943 TABLE -II
Sample Composition MI Density Peak Solid Number (g/10 min) ~g/cm3) Melt State Temp Extrudable (C) E-4 CGC/PCR* -- 0.912 -- Yes C-10 CGC 1.0 0.882 86 NA**
C-ll PCR 0.75 0.955 132 No E-5 CGC/PCR* 1.4 0.935 -- Yes C-12 CGC 1.0 0.882 86 NA**
C-13 PCR 0.4 0.962 135 No * 30/70 Blend based on weight.
** NA = Not applicable: above melting point.
~x~rle 4 The procedures of Example 1 were repeated with different samples. Sample C-14 (which is the same as Sample C-3) was DOWLEXTM
2045 LLDPE (available from The Dow Chemical Company) with a similar lo melt index and density as Sample E-6 (a blend of C-16 (DOWLEXTM 12065 HDPE, available from The Dow Chemical Company) and C-15 (a substantially linear ethylene/l-octene copolymer having a Mw/Mn of 2 and prepared in accordance with the teachings of U.S. Patent Nos.
5,272,236 and 5,278,272)) (with a Tp of 107). Both Samples E-6 and C-14 were compression molded into a 125 mil (3.175 mm) thick plaque according to the procedures of ASTM-1238. The plaques were heated to 65C, and then compressed in a 40 ton (2075 psi (14.3 MPa)) solid phase forming machine for 3 minutes. The samples were then cooled under the same pressure, removed at room temperature, and the modulus and percent deformation determined. These results are reported in Table IV, and the modulus and percent deformation characteristics of Sample E-6 are clearly superior to those of Sample C-14.
W O 95tO5419 PCTrUS94/08943 216906~
TA-LE IV
Sample Composition MI Density Peak Percent Modulus Number (g/10 min) (g/cm3) Melt Deformed psi Temp (MPa) (C) E-6 HDPE/CGC 1.01 0.922 -- 203 39,900 (275) C-14 LLD-3 1.0 0.920 122 162 16,120 ( 1 11 ) C-15 CGC 1.01 0.856 26 NM+ NM+
C-16 HDPE 1.0 0.959 133 NM+ NM+
* 35/65 Blend based on weight.
+ NM = Not measured.
s Although the invention has been described in considerable detail through the preceding examples, this detail is for illustration purposes only, and it is not to be construed as a limitation on the spirit and scope of the invention as described in the following o claims.
Claims (23)
1. A polyolefin composition suitable for solid state processing, the-composition characterized as a blend comprising a first and a second polyolefin, wherein the first polyolefin is characterized as having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, the first polyolefin component comprising at least 10 percent of the total weight of the polyolefin blend.
2. The blend of Claim 1 in which at least one of the first polyolefin and the second polyolefin is a polyethylene homopolymer or an ethylene/.alpha.-olefin copolymer.
3. The blend of Claim 2 in which the first polyolefin is a homogeneously branched linear polyethylene or a homogeneously branched substantially linear polyetheylene characterized as having:
a. a melt flow ratio, I10/I2 5.63 b. a molecular weight distribution, MW/MN, defined by the equation:
MW/MN (I10/I2)-4.63; and c. a critical shear stress at the onset of gross melt fracture of greater than about 4 x 106 dyne/cm2.
a. a melt flow ratio, I10/I2 5.63 b. a molecular weight distribution, MW/MN, defined by the equation:
MW/MN (I10/I2)-4.63; and c. a critical shear stress at the onset of gross melt fracture of greater than about 4 x 106 dyne/cm2.
4. The blend of Claim 3 in which the second polyolefin is a heterogeneously branched polyethylene.
5. The blend of any of the preceeding Claims wherein the second polyolefin is characterized as at least one of high density polyethylene, low density polyethylene, linear low density polyethylene, and ultra low linear low density polyethylene.
6. A polyolefin composition suitable for solid state processing, the composition characterized as a blend comprising:
a. a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to 0.910 g/cm3; and b. a second polyolefin having a density from 0.940 g/cm3 to 0.965 g/cm3;
wherein the first polyolefin is characterized by a softening point of at least 10 degrees on the Celsius scale lower than the softening point of the second polyolefin.
a. a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to 0.910 g/cm3; and b. a second polyolefin having a density from 0.940 g/cm3 to 0.965 g/cm3;
wherein the first polyolefin is characterized by a softening point of at least 10 degrees on the Celsius scale lower than the softening point of the second polyolefin.
7. The blend of any of the preceeding Claims in which the softening point of the first polyolefin is at least 20 degrees on the Celsius scale lower than the softening point of the second polyolefin.
8. The blend of any of the preceeding Claims in which the first polyolefin comprises at least 20 percent of the total weight of the polyolefin blend.
9. The blend of any of the preceeding Claims in which the second polyolefin comprises a post-consumer recycle polyethylene resin.
10. The blend of any of the preceeding Claims in which the second polyolefin is a polypropylene.
11. A process for shaping a solid polyolefin blend, the process characterized as comprising the following steps :
a. Heating a solid polyolefin blend which comprises at least a first and second polyolefin, the first polyolefin having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, the first polyolefin comprising at least 10 percent of the total weight of the polyolefin blend, to a processing temperature above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin;
b. Shaping the blend at the processing temperature; and c. Cooling the shaped blend of (B) to a temperature below the processing temperature.
a. Heating a solid polyolefin blend which comprises at least a first and second polyolefin, the first polyolefin having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, the first polyolefin comprising at least 10 percent of the total weight of the polyolefin blend, to a processing temperature above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin;
b. Shaping the blend at the processing temperature; and c. Cooling the shaped blend of (B) to a temperature below the processing temperature.
12. The process of Claim 11 in which the first polyolefin is a homogeneously branched linear polyethylene or a substantially linear homogeneously branched polyethylene characterized as having a. a melt flow ratio, I10/I2 5.63 b. a molecular weight distribution, MW/MN, defined by the equation:
MW/MN (I10/I2)-4.63; and c. a critical shear stress at the onset of gross melt fracture of greater than about 4 x 106 dyne/cm2.
MW/MN (I10/I2)-4.63; and c. a critical shear stress at the onset of gross melt fracture of greater than about 4 x 106 dyne/cm2.
13. The process of Claim 12 in which the second polyolefin is at least one of high density polyethylene, low density polyethylene, linear low density polyethylene, and ultra low density polyethylene.
14. A process for shaping a solid polyolefin blend, the process characterized as comprising the following steps:
a. heating to a processing temperature a solid polyolefin blend which comprises: (i) a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to 0.910 g/cm3; and (ii) a second polyolefin having a density of from 0.940 g/cm3 to 0.965 g/cm3; wherein the first polymer is characterized by a softening point of at least ten degrees on the Celsius scale lower than the softening point of the second polyolefin and wherein the processing temperature is above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin;
b. shaping the blend at the processing temperature; and c. cooling the shaped blend of (b) to a temperature below the processing temperature.
a. heating to a processing temperature a solid polyolefin blend which comprises: (i) a first homogeneously branched linear or substantially linear polyolefin having a density from 0.850 g/cm3 to 0.910 g/cm3; and (ii) a second polyolefin having a density of from 0.940 g/cm3 to 0.965 g/cm3; wherein the first polymer is characterized by a softening point of at least ten degrees on the Celsius scale lower than the softening point of the second polyolefin and wherein the processing temperature is above the softening temperature of the first polyolefin but below the softening temperature of the second polyolefin;
b. shaping the blend at the processing temperature; and c. cooling the shaped blend of (b) to a temperature below the processing temperature.
15. The process of any of Claims 11-14 in which the first polyolefin comprises at least 20 percent of the total weight of the polyolefin blend.
16. The process of Claim 15 in which the processing temperature is a temperature of at least 5 degrees on the Celsius scale lower than the softening temperature of the first polyolefin, and at least 5 degrees on the Celsius scale higher than the softening temperature of the second polyolefin.
17. The process of Claim 15 in which the processing temperature is at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, and at least 10 degrees higher than the softening temperature of the first polyolefin.
18. The process of any of Claims 11-14 in which the polyolefin blend is prepared by mechanically mixing the first and second polyolefins with one another.
19. An article prepared by the process of Claim 11.
20. The process of any of Claims 11-14 in which the second polyolefin is a polypropylene.
21. A polyolefin composition suitable for solid state processing, the composition characterized as a blend comprising a first and second polyolefin, wherein:
the first polyolefin is characterized as a homogeneously branched substantially linear polyethylene characterized as having:
a. a melt flow ratio, I10/I2 5.63 b. a molecular weight distribution, Mw/Mn, defined by the equation:
MW/Mn (I10/I2) - 4.63; and c. a critical shear stress at the onset of gross melt fracture of greater than about 4 x 106 dyne/cm2, the first polyolefin is further characterized as having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, and the first polyolefin component comprises at least 10 percent of the total weight of the polyolefin blend.
the first polyolefin is characterized as a homogeneously branched substantially linear polyethylene characterized as having:
a. a melt flow ratio, I10/I2 5.63 b. a molecular weight distribution, Mw/Mn, defined by the equation:
MW/Mn (I10/I2) - 4.63; and c. a critical shear stress at the onset of gross melt fracture of greater than about 4 x 106 dyne/cm2, the first polyolefin is further characterized as having a softening temperature of at least 10 degrees on the Celsius scale lower than the softening temperature of the second polyolefin, and the first polyolefin component comprises at least 10 percent of the total weight of the polyolefin blend.
22. The polyolefin composition of Claim 21, wherein the second polyolefin component is a homogeneously branched polyethylene homopolymer, homogeneously branched ethylene/.alpha.-olefin copolymer, heterogeneously branched polyethylene homopolymer, heterogeneously branched ethylene/.alpha.-olefin copolymer or a polypropylene.
23. The polyolefin composition of Claims 21 or Claim 22 further characterized as having melting and crystallization curves which exhibit two distinct melt regions.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/107,482 US5408004A (en) | 1993-08-17 | 1993-08-17 | Polyolefin blends and their solid state processing |
| US08/107,482 | 1993-08-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2169068A1 true CA2169068A1 (en) | 1995-02-23 |
Family
ID=22316849
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002169068A Abandoned CA2169068A1 (en) | 1993-08-17 | 1994-08-08 | Polyolefin blends and their solid state processing |
Country Status (8)
| Country | Link |
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| US (1) | US5408004A (en) |
| EP (1) | EP0722476A1 (en) |
| JP (1) | JPH09501717A (en) |
| KR (1) | KR960703983A (en) |
| AU (1) | AU7483094A (en) |
| CA (1) | CA2169068A1 (en) |
| FI (1) | FI960717A (en) |
| WO (1) | WO1995005419A1 (en) |
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| US6316549B1 (en) * | 1991-10-15 | 2001-11-13 | The Dow Chemical Company | Ethylene polymer fiber made from ethylene polymer blends |
| US5677383A (en) * | 1991-10-15 | 1997-10-14 | The Dow Chemical Company | Fabricated articles made from ethylene polymer blends |
| US5525659A (en) * | 1993-09-08 | 1996-06-11 | The Dow Chemical Company | Batch inclusion packages |
| US5631069A (en) * | 1994-05-09 | 1997-05-20 | The Dow Chemical Company | Medium modulus molded material comprising substantially linear polyethlene and fabrication method |
| US5932659A (en) | 1994-09-19 | 1999-08-03 | Sentinel Products Corp. | Polymer blend |
| US5883144A (en) | 1994-09-19 | 1999-03-16 | Sentinel Products Corp. | Silane-grafted materials for solid and foam applications |
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| US5792534A (en) | 1994-10-21 | 1998-08-11 | The Dow Chemical Company | Polyolefin film exhibiting heat resistivity, low hexane extractives and controlled modulus |
| US5858491A (en) * | 1994-11-02 | 1999-01-12 | Dow Belgium | Hollow molded articles and process for manufacturing them |
| US6506866B2 (en) | 1994-11-17 | 2003-01-14 | Dow Global Technologies Inc. | Ethylene copolymer compositions |
| CN1053610C (en) * | 1995-08-21 | 2000-06-21 | 财团法人工业技术研究院 | Article with net structure |
| US5795941A (en) * | 1995-10-03 | 1998-08-18 | The Dow Chemical Company | Crosslinkable bimodal polyolefin compositions |
| JP3840499B2 (en) * | 1996-01-22 | 2006-11-01 | ザ・ダウ・ケミカル・カンパニー | Polyolefin elastomer blends with improved properties |
| US5844009A (en) | 1996-04-26 | 1998-12-01 | Sentinel Products Corp. | Cross-linked low-density polymer foam |
| CA2203595A1 (en) | 1996-04-26 | 1997-10-26 | Robert F. Hurley | Cross-linked polyolefin tape |
| US5876813A (en) * | 1996-07-09 | 1999-03-02 | Senitnel Products Corp | Laminated foam structures with enhanced properties |
| US5882776A (en) | 1996-07-09 | 1999-03-16 | Sentinel Products Corp. | Laminated foam structures with enhanced properties |
| US5938878A (en) | 1996-08-16 | 1999-08-17 | Sentinel Products Corp. | Polymer structures with enhanced properties |
| WO1998059000A1 (en) * | 1997-06-20 | 1998-12-30 | The Dow Chemical Company | Ethylene polymer compositions and article fabricated from the same |
| US6458300B1 (en) | 1998-05-27 | 2002-10-01 | Kraton Polymers U.S. Llc | Conversion of sticky elastomeric polymer crumb into pellets without polymer degradation |
| US6403717B1 (en) | 2000-07-12 | 2002-06-11 | Univation Technologies, Llc | Ethylene inter-polymer blends |
| CN1982361B (en) * | 2001-08-17 | 2011-11-16 | 陶氏环球技术有限责任公司 | Bimodal polyethylene composition and articles made therefrom |
| WO2003020821A1 (en) | 2001-08-31 | 2003-03-13 | Dow Global Technologies Inc. | Multimodal polyethylene material |
| US20040096626A1 (en) * | 2002-11-14 | 2004-05-20 | Epoli-Espumas De Polietileno Sa | Layered structures with enhanced properties |
| ATE509983T1 (en) * | 2004-03-19 | 2011-06-15 | Dow Global Technologies Llc | FILM LAYERS MADE OF POLYMER FORMULATIONS |
| CN103374168B (en) * | 2012-04-27 | 2018-12-04 | 住友化学株式会社 | Polyethylene-based resin composition and formed body containing it |
| WO2016063205A2 (en) | 2014-10-21 | 2016-04-28 | Nova Chemicals (International) S.A. | Dilution index |
| CA2868640C (en) | 2014-10-21 | 2021-10-26 | Nova Chemicals Corporation | Solution polymerization process |
| US10329412B2 (en) | 2017-02-16 | 2019-06-25 | Nova Chemicals (International) S.A. | Caps and closures |
| US10442921B2 (en) | 2017-04-19 | 2019-10-15 | Nova Chemicals (International) S.A. | Means for increasing the molecular weight and decreasing the density employing mixed homogeneous catalyst formulations |
| US10442920B2 (en) | 2017-04-19 | 2019-10-15 | Nova Chemicals (International) S.A. | Means for increasing the molecular weight and decreasing the density of ethylene interpolymers employing homogeneous and heterogeneous catalyst formulations |
| US10683376B2 (en) | 2017-11-07 | 2020-06-16 | Nova Chemicals (International) S.A. | Manufacturing ethylene interpolymer products at higher production rate |
| US10995166B2 (en) | 2017-11-07 | 2021-05-04 | Nova Chemicals (International) S.A. | Ethylene interpolymer products and films |
| US10882987B2 (en) | 2019-01-09 | 2021-01-05 | Nova Chemicals (International) S.A. | Ethylene interpolymer products having intermediate branching |
| US11046843B2 (en) | 2019-07-29 | 2021-06-29 | Nova Chemicals (International) S.A. | Ethylene copolymers and films with excellent sealing properties |
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| US5210142A (en) * | 1992-02-13 | 1993-05-11 | The Dow Chemical Company | Reduction of melt fracture in linear polyethylene |
| EP0572034A2 (en) * | 1992-05-29 | 1993-12-01 | Idemitsu Kosan Company Limited | Ethylenic copolymer and ethylenic copolymer composition |
-
1993
- 1993-08-17 US US08/107,482 patent/US5408004A/en not_active Expired - Fee Related
-
1994
- 1994-08-08 CA CA002169068A patent/CA2169068A1/en not_active Abandoned
- 1994-08-08 WO PCT/US1994/008943 patent/WO1995005419A1/en not_active Application Discontinuation
- 1994-08-08 EP EP94924604A patent/EP0722476A1/en not_active Withdrawn
- 1994-08-08 JP JP7507040A patent/JPH09501717A/en active Pending
- 1994-08-08 KR KR1019960700798A patent/KR960703983A/en not_active Application Discontinuation
- 1994-08-08 AU AU74830/94A patent/AU7483094A/en not_active Abandoned
-
1996
- 1996-02-16 FI FI960717A patent/FI960717A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FI960717A (en) | 1996-04-15 |
| EP0722476A1 (en) | 1996-07-24 |
| WO1995005419A1 (en) | 1995-02-23 |
| US5408004A (en) | 1995-04-18 |
| AU7483094A (en) | 1995-03-14 |
| FI960717A0 (en) | 1996-02-16 |
| JPH09501717A (en) | 1997-02-18 |
| KR960703983A (en) | 1996-08-31 |
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