Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-03-12
2003-12-02
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S582000, C524S570000, C524S236000, C523S333000
Reexamination Certificate
active
06656995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for producing olefin polymer composites having improved melt strength. The process is a solution process whereby an organoclay is incorporated into an olefin polymer base resin. Utilizing the process of the invention, it is possible to produce olefin polymer composites with improved melt strengths using low levels of organoclays and without the use of compatibilizing agents.
2. Description of the Prior Art
Olefin polymers are widely used for the production of film and sheet goods, fibers, molded goods, etc., utilizing a variety of known processes, such as extrusion and coextrusion, blow molding, injection molding, thermoforming and the like.
In extrusion processes, such as those used for the production of films, fibers and molded goods, the olefin polymer resins must have sufficiently low melt viscosity under the high shear conditions encountered in the extruder in order to have acceptable processability and achieve the high throughputs necessary for commercial operation. On the other hand, the resins must have sufficient melt strength after extrusion to prevent sagging/distortion of the extrudate before it is cooled below the resin melt point. High melt strength resins are therefore highly advantageous in these operations. They are particularly advantageous for the production of large thermoformed and blow molded articles. For example, blow molding resins suitable for production of small shampoo bottles may not have sufficient melt strength for the production of one-gallon milk jugs where the parison is substantially larger and heavier. High melt strength olefin polymer resins are also highly desirable for extrusion coating and foamed and sheet extrusion processes.
Whereas some types of olefin polymers, such as low density polyethylene (LDPE) and ethylene-vinyl acetate (EVA) copolymers, are generally regarded to have sufficient melt strength for most of the aforementioned applications, other olefin polymer resins, most notably polypropylene (PP), high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) resins, are deficient in this regard. In fact, these latter types of resins are frequently subjected to post-reactor treatments, such as oxidation treatments during finishing, in order to raise the melt strength of the resins to acceptable levels. While such treatments are capable of increasing the melt strength of certain of these resins, it is often at the expense of other physical properties, e.g., environmental stress crack resistance.
It would be highly advantageous if the melt strength of polyolefin resins could be improved without the use of such post-reactor oxidation treatments. The goal of the present invention is to provide polyolefin composites which exhibit increased melt strength using a straightforward solution technique. It is a further objective to accomplish this using low levels of ammonium-modified clays and without the use of costly compatibilizing agents.
The use of organically modified clays, sometimes referred to as intercalates or organoclays, produced by a cation exchange reaction between the clay and an alkylammonium salt, is known in the prior art. Alkylammonium cations exchanged into and between the clay platelets increase the interlayer spacing between adjacent platelets and render the hydrophilic clays organophilic and thus more easily dispersed in polyolefin resins. Compared to conventional filled polyolefin compositions, polyolefins filled with the intercalated organoclays have improved physical properties at similar loading levels.
Compatibilizing agents are commonly employed to facilitate incorporation of modified clays into non-polar polymers, such as polyolefins, during melt compounding. Compatibilizers are generally maleic anhydride grafted polymers employed at a weight ratio of 3:1 (compatibilizer:organoclay). While polyolefin, composites have been prepared using ratios of compatibilizer to organoclay as low as 1:1, the lower ratios are generally considered to be less desirable and, therefore, are typically avoided. For example, Hasegawa, et al., in an article entitled “
Preparation and Mechanical Properties of Polypropylene
-
Clay Hybrids Using a Maleic Anhydride Modified Polypropylene Oligomer
,” JAPS 67, 87 (1998), observe that as the ratio of compatibilizer to organically modified clay is increased, the particles of the silicate layers become smaller and are dispersed more uniformly so that the reinforcement effect of the clays is increased.
Lim, et al., in their article “
Phase Morphology and Rheological Behavior of Polymer/Layered Silicate Nanocomposites
,” Rheol Acta 4: 220-229 (2001), report the fabrication of nanocomposites with organophilic modified clays and polyethylene base resins grafted with 0.8 weight percent maleic anyhydride. The nanocomposites are formed by melt-mixing.
Nitrile copolymer and HDPE nanocomposites containing modified silicate fillers are disclosed by Jeon, et al., in “
Morphology of Polymer/Silicate Nanocomposites
,” Polymer Bulletin 41: 107-113 (1998). The HDPE polymer composites contain 20% dodecylamine-modified montmorillonite clay and are obtained by dissolving the HDPE and the modified clay in a co-solvent of xylene and benzonitrile and precipitating in tetrahydrofuran.
In copending application Ser. Nos. 09/947,836 and 10/027,742 propylene polymer composites and ethylene polymer composites having improved melt strength are obtained by incorporating, by melt blending, specific modified organoclays and compatibilizing agents at low compatibilizer levels and at low ratios of compatibilizer to modified clay. Certain ethylene-vinyl acetate copolymer (EVA) composites are obtained without the use of compatibilizing agents.
SUMMARY OF THE INVENTION
We have now discovered a solution process whereby it is possible to significantly improve the melt strength and other physical characteristics of olefin polymers by intimately incorporating 0.5 to 10 weight percent of an organically modified clay therein. The process comprises contacting an olefin polymer base resin, said olefin polymer base resin dissolved in an aromatic solvent and selected from the group consisting of ethylene homopolymers, propylene homopolymers, ethylene-propylene copolymers, ethylene-C
4-8
&agr;-olefin copolymers, propylene-C
4-8
&agr;-olefin copolymers, ethylene-vinyl C
2-4
carboxylate copolymers and ethylene-C
1-4
alkyl methacrylate copolymers, and an organically modified clay, said organically modified clay dissolved in an aromatic solvent and consisting of a smectite clay that has been ion-exchanged and intercalated with a quaternary ammonium ion of the formula
(
R
)(
R
1
)(
R
2
)(
R
3
)
N
+
where R represents a C
18
alkyl substituent or mixture of alkyl substituents wherein C
18
alkyl moieties constitute 50 percent or more of the mixture and R
1
, R
2
, and R
3
are independently selected from the group consisting of R, H and C
1-22
hydrocarbyl; and evaporating said aromatic solvent to obtain an olefin polymer composite. The resulting olefin polymer composites preferably have from 1 to 7 weight percent, based on the total weight of the composite, of the organically modified clay intimately dispersed therein. Organically modified clays are preferably montmorillonite clays ion exchanged and intercalated with quaternary ammonium ions wherein the R group is comprised of at least 60 percent C
18
alkyl groups. Most preferably, the montmorillonite clay is modified with dimethyl dihydrogenated tallow ammonium ion.
Xylene and toluene are highly useful aromatic solvents. In one embodiment of the invention contacting the olefin polymer and organically modified clay is carried out at a temperature of 40° C. up to the boiling point of the solvent. Another aspect of the invention utilizes agitation during the contacting step.
Dissolution of the olefin polymer and organically modified clay may be accomplished in the same operation or as separate operations. High shear mixing may be advantageously utilized for dissolution of the orga
Klendworth Douglas D.
Mehta Sameer D.
Reinking Mark K.
Baracka Gerald A.
Equistar Chemicals LP
Heidrich William A.
Lee Rip A
Wu David W.
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