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
2001-09-06
2003-06-24
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...
C524S236000, C524S570000, C525S070000
Reexamination Certificate
active
06583209
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to improved propylene polymer composites and to masterbatch compositions utilized for their preparation. Propylene polymer composites produced in accordance with the invention having increased melt strength and other improved physical properties contain a clay modified with a hydrogenated tallow quaternary ammonium compound and a propylene polymer compatibilizing agent.
2. Description of the Prior Art
Propylene polymer resins have enjoyed significant growth in recent years in view of the diverse resin types which are available. In addition to propylene homopolymer, numerous copolymers of propylene with ethylene and other &agr;-olefins are now commercially produced. These include random copolymers, block copolymers and multi-phase polymer systems. This latter group of resins includes the so-called impact copolymers and thermoplastic elastomers (TPEs) which consist of a continuous phase of a crystalline polymer, e.g., highly isotactic propylene homopolymer, having a rubbery phase, e.g., ethylene-propylene copolymer, dispersed therein.
These resins are widely used in extrusion for the production of films, fibers and wide variety of molded goods, such as bottles, hose and tubing, auto parts and the like. While it is necessary that these resins have sufficiently low melt viscosity under conditions of high shear encountered in the extruder, in order to have acceptable processability and achieve the high throughputs necessary for commercial operations, the resin must also have sufficient melt strength after extrusion to prevent sagging/distortion of the extrudate before it is cooled below the melt point. High melt strength resins are particularly advantageous for the production of large thermoformed and blow molded articles, for extrusion coating and for foamed and sheet extrusions. For example, a blow molding resin suitable for the production of small shampoo bottles may not have sufficient melt strength for the production of one-gallon jugs where the parison is substantially larger and heavier.
The goal of the present invention is to provide propylene polymer composites which exhibit increased melt strength. It is a further objective to accomplish this through the use of a quaternary ammonium—modified clays, thereby achieving the enhanced physical and mechanical properties typically associated with these filled systems.
The use of organically modified clays, sometimes referred to as intercalates or organoclays, produced by a cation exchange reaction between the silicate and alkylammonium salts, especially quaternary ammonium compounds is known in the prior art. The alkyl cations exchanged into and between the clay platelets increase interlayer spacing between adjacent platelets and render the hydrophilic clay organophilic and thus more easily dispersed in thermoplastic resins. Compared to conventional filled thermoplastic compositions, thermoplastics filled with the intercalated organoclays have improved physical properties at similar loading levels.
With polymers which are nonpolar or have low polarity, such as polypropylene, it is generally considered to be necessary to include a compatibilizer resin for effective intercalation. The compatibilizers are most commonly maleic anhydride grafted polypropylene and are employed at a weight ratio of 3:1 (compatibilizer:organoclay). While propylene polymer composites have been prepared using ratios of compatibilizer to organoclay as low as 1:1, these lower ratios are generally considered to be less desirable and, therefore, typically avoided. Hasegawa, et al., in their article entitled “
Preparation and Mechanical Properties of Polypropylene
-
Clay Hybrids Using a Maleic Anhydride Modified Polypropylene Oligomer
,” JAPS 67, 87 (1998), observed that the particles of the silicate layers became smaller and were dispersed more uniformly as the ratio of the maleic anhydride grafted polypropylene compatibilizer was increased. They further concluded that as the dispersability of the clays was improved, the reinforcement effect of the clays increased.
We have now discovered that by utilizing certain organoclay/compatibilizer combinations, it is possible to significantly improve the melt strength of propylene polymer composites. Furthermore, this improvement is unexpectedly obtained at lower compatibilizer levels and lower ratios of compatibilizer to modified clay than was heretofore considered possible by the prior art.
SUMMARY OF THE INVENTION
The present invention relates to propylene polymer composites having improved melt strength. More specifically, the compositions of the invention comprise a thermoplastic resin composite having improved melt strength comprising: 76 to 99 weight percent, based on the total composition, of a thermoplastic propylene homopolymer, copolymer or blends thereof, 0.5 to 12 weight percent of an organically modified clay consisting of a smectite clay that has been ion-exchanged and intercalated with a quaternary ammonium compound of the formula:
(R)
n
(CH
3
)
m
N
+
Cl
−
where R represents a hydrogenated tallow moiety, n is 1 to 4, m is 0 to 3 and n+m=4; and 0.5 to 12 weight percent of a propylene polymer compatibilizing agent obtained by copolymerizing or grafting 0.1 to 8 weight percent ethylenically unsaturated carboxylic acid or derivative monomer with propylene. The weight ratio of organically modified clay to compatibilizer will range from 1:5 to 1:0.1.
In a preferred embodiment of the invention the organically modified clay is a montmorillonite clay modified with dimethyl dihydrogenated tallow ammonium chloride and the compatibilizing agent is a propylene homopolymer or copolymer of propylene or ethylene grafted with 0.2 to 2.5 weight percent maleic anhydride. It is especially useful if the modified clay has a modifier concentration of 95 to 140 meq/100 g and the compatibilizing agent has a melt flow from 40 to 400 g/10 min. Preferred composites contain 84 to 98.75 weight percent base resin, 1 to 8 weight percent modified clay and 1 to 8 weight percent comptabilizing agent with the modified clay and compatibilizer present at a weight ratio from 1:1 to 1:0.25.
Concentrates or masterbatches used to prepare the above-described compositions are also claimed herein. The concentrates comprise 20 to 60 weight percent propylene polymer carrier resin selected from the group consisting of propylene homopolymer, propylene copolymer and mixtures thereof and 40 to 80 weight percent additives comprising an organically modified smectite clay that has been ion-exchanged and intercalated with a quaternary ammonium compound of the formula:
(R)
n
(CH
3
)
m
N
+
Cl
−
where R represents a hydrogenated tallow moiety, n is 1 to 4, m is 0 to 3 with the proviso that n+m=4; and a propylene polymer compatibilizing agent obtained by copolymerizing or grafting 0.1 to 8 weight percent ethylenically unsaturated carboxylic acid or derivative monomer and 95 to 99.9 weight percent propylene, the weight ratio of organically modified clay to compatibilizing agent ranging from 1:5 to 1:0.1. Preferably, the carrier resin is polypropylene homopolymer. Especially useful concentrates contain 20 to 50 weight percent carrier resin and 50 to 80 weight percent organically modified clay and compatibilizing agent present at a weight ratio from 1:1 to 1:0.25 with up to 5 weight percent other conventional compounding additives.
DETAILED DESCRIPTION
In accordance with the present invention there is provided propylene polymer compositions, also referred to as composites, having increased melt strength as a result of using specific organoclay/compatibilizer combinations. Moreover, with the compositions of the invention it is possible to achieve the desired melt strength improvement and improve other physical properties utilizing significantly lower levels of compatibilizer and lower ratios of compatibilizer to organoclay than heretofore considered possible.
The increased melt strength or melt elasticity of the inventive compositions is eviden
Mavridis Harilaos
Mehta Sameer D.
Shankernarayanan Manivakkam J.
Baracka Gerald A.
Equistar Chemicals LP
Heidrich William A.
Lee Rip A
Wu David W.
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