Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-07-28
2003-02-11
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S301000
Reexamination Certificate
active
06518365
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polymeric compositions, particularly partially neutralized acid copolymers with enhanced melt swell and, thus, improved processing characteristics. It also relates to a process for covalently crosslinking polar and non-polar alpha olefin polymers employing metal acrylates.
2. Description of Related Art
Ionomers (metal salts of acid copolymers) are prepared by methods well known in the art (see U.S. Pat. No. 3,264,272 (Rees) which is hereby incorporated by reference). Likewise, acid copolymers on which the ionomers are based are prepared by methods well known in the art (see U.S. Pat. No. 4,351,931, which is also incorporated by reference).
The acid copolymers typically used are direct acid copolymers. By “direct copolymer”, it is meant that the copolymer is made by polymerization of monomers together at the same time, as distinct from a “graft copolymer” where a monomer is attached or polymerized onto an existing polymer chain. They typically are alpha olefin, particularly ethylene/C
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&agr;,&bgr; ethylenically unsaturated carboxylic acid, particularly acrylic and methacrylic acid, copolymers. They may also contain a third softening monomer such as an alkyl acrylate or methacrylate.
The ethylene acid copolymers can be described as an E/X/Y copolymers where E is ethylene, X is the &agr;,&bgr; ethylenically unsaturated carboxylic acid, particularly acrylic and methacrylic acid, and Y is a softening comonomer such as acrylate or methacrylate ester.
Ionomers are produced by reacting an ion source with the acid copolymers. Typical ion sources include sodium hydroxide, sodium carbonate, zinc oxide, zinc acetate, magnesium hydroxide, and lithium hydroxide. Other ion sources are well known. In addition to the preferred sodium, zinc, magnesium and lithium cations, other alkali metal or alkaline earth metal cations are useful. Such other cations include potassium, calcium, barium, lead, and tin.
This ionic crosslinking produces a thermoplastic polymer that does not exhibit appreciable increase in the elastic component of flow and, therefore, produces a thermoplastic resin with low melt swell. Processing characteristics are thus adversely effected. By increasing melt swell, ionomers with improved Theological characteristics at a given viscosity useful in extrusion coating, blown film and molding applications could be made.
BRIEF SUMMARY OF THE INVENTION
It has now been discovered that, by including minor amounts (preferably about 0.05 to about 10 weight percent (wt. %) of the polymer being modified) of certain metal acrylates, particularly zinc acrylate and sodium acrylate, in a high temperature melt of ionomers, covalent crosslinks are formed and melt swell is significantly increased. Resulting high melt swell polymers are ones that exhibit melt swells at least 10 percent higher to as much as 100, 200, 300, or 400 percent higher than a similar melt index polymer which has not been exposed in the melt to a metal acrylate. This is particularly surprising in light of the finding that metal methacrylates similar to the metal acrylates do not form covalent crosslinks and do not increase melt swell. Also, metal acetates, propionates, benzoates and the like do not form covalent crosslinks and do not increase melt swell. It has also been found that the metal acrylate salt, not the acrylic acid itself, does the crosslinking.
Including minor amounts of metal acrylate in a high temperature polymer melt can be accomplished in a number of ways. The metal acrylate may be made in situ or added to the polymer. Examples of possible processes are: 1) acrylic acid may be added to an ionomer melt, thus making the metal acrylate in situ; 2) a non-acrylate ion source such as sodium hydroxide or zinc acetate may be added to a polyethylene or an acid copolymer melt that contains acrylic acid monomer, thus making the metal acrylate in situ; and 3) metal acrylates such as sodium acrylate and zinc acrylate may be melt mixed with the polymer to be crosslinked.
It has also been found that polar alpha olefin copolymers including non-neutralized copolymers functionalized by C
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&agr;,&bgr; ethylenically unsaturated carboxylic acid (acid copolymers) and non-polar alpha olefin polymers can be covalently crosslinked to significantly decrease melt index by the method discovered. Polar alpha olefin copolymers other than acid copolymers include polymers such as ethylene acrylate copolymers and ethylene acetate coploymers. Non-polar alpha olefin polymers include polymers such as polyethylene (particularly low density polyethylene and linear low density polyethylene). It has been found that these polymers can be covalently crosslinked by the method discovered, resulting in at least a 10 percent to several fold (up to 100, 200, 300 or more percent) decrease in Melt Index.
When crosslinking polymers in which the metal acrylates are not soluble (wherein solubility is too low to achieve the minimum level of metal acrylate required by the invention), sufficient acrylic acid which is soluble must be melt blended with the polymer followed by addition of sufficient cation source to produce the desired level of metal acrylate in situ. Non-polar polyolefins and non-acid polar alpha olefin polymers are examples of polymers in which the metal acrylates are not soluble. Order is not important with ionomers and other acid copolymers because the metal salts are soluable and will react with the polymer.
Thus, the present invention is a high melt swell polymer consisting essentially of a partially neutralized alpha olefin copolymer having polar functionality provided by C
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&agr;,&bgr; ethylenically unsaturated carboxylic acid. Preferably the alpha olefin copolymer is an ethylene copolymer, particularly a partially neutralized ethylene/C
3-8
&agr;,&bgr; ethylenically unsaturated carboxylic acid copolymer, and a minor amount of metal acrylate, particularly sodium or zinc acrylate. Preferably, about 0.05 to about 10 wt. %, more preferably about 0.1 to about 2 wt. %, and most preferably about 0.2 to about 0.8 wt. % metal acrylate is melt blended with the ethylene polymer (wt. % based on weight of ethylene polymer).
It also is a process for covalently crosslinking all alpha olefin polymers, with the proviso that in the case of non-polar alpha olefin polymers and polar alpha olefin copolymers other than acid copolymers, the metal acrylate is made in situ. The in situ process consists essentially of melt blending sufficient acrylic acid with the alpha olefin polymer and then adding a sufficient amount of a non-acrylate source of metal ion to convert the acrylic acid into about 0.05 parts to about 10 parts by weight of a metal salt of acrylic acid with 100 parts by weight of he alpha olefin polymer.
DETAILED DESCRIPTION
Various terms used in this disclosure are defined as follows:
1. “Copolymer” means polymers containing two or more monomers. The terms “bipolymer” and “terpolymer” mean polymers containing only two and three monomers respectively. The phrase “copolymer of various monomers” means a copolymer whose units are derived from the various monomers.
2. “(Meth) acrylic acid” means acrylic acid and methacrylic acid, and the term “(meth) acrylate” means acrylate and methacrylate.
3. “Consisting essentially of” means that the recited components are essential, while smaller amounts of other components may be present to the extent that they do not detract from the operability of the present invention.
It has been discovered that, by including minor amounts of certain metal acrylates in a high temperature melt of polar alpha olefin copolymers, particularly alpha olefin/C
3-8
&agr;,&bgr; ethylenically unsaturated carboxylic acid copolymers (acid copolymers) or ionomers thereof, covalent crosslinks are formed and melt swell is significantly increased and/or melt index is significantly decreased (the metal acrylates, the acid copolymers and ionomers made from the acid copolymers are as discussed below). Particularly in the case of ionomers of acid copolymers,
Chou Richard T.
Powell Richard James
Prejean George W.
E. I. du Pont de Nemours and Company
Evans Craig H.
Wilson D. R.
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