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
2002-08-16
2004-04-06
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S301000, C525S064000, C525S074000, C525S078000, C525S193000, C525S242000
Reexamination Certificate
active
06716928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to grafted propylene copolymer products and adhesive blends containing same. More particularly, the invention relates to impact propylene-ethylene copolymer grafted with carboxylic acids and derivatives thereof having high graft concentrations at significantly lower melt flow rates (MFRs).
2. Description of the Prior Art
Propylene-based polymers grafted with ethylenically unsaturated carboxylic acids or derivatives are well-known and widely used as adhesive blends for adhesion to one or more polypropylene substrates.
Typically such adhesive blends include the grafted propylene copolymer blended with a propylene homopolymer or an ethylene/propylene copolymer and, optionally, a third component such as a linear low density polyethylene (LLDPE), a hydrocarbon rubber such as ethylene-propylene-diene monomer (EPDM) rubber or ethylene-propylene rubber (EPR), a poly(1-olefin) such as poly(butene-1), or an ethylene polymer such as high molecular weight low density polyethylene (HMW LDPE).
Prior polypropylene-based graft copolymers have been limited in terms of their maximum attainable functionality, i.e., the concentration of grafted acid or derivative, and/or have exhibited unacceptably low viscosity, i.e., high melt flow rates (MFRs). High acid or acid derivative functionalities are desirable in order to obtain acceptable levels of adhesion at desirably low graft copolymer concentrations with the adhesive blends. Furthermore, high MFR propylene copolymers grafts are difficult to process and, if the MFR is sufficiently high, will adversely affect the processing characteristics of the resulting adhesive blend and its adhesion properties.
Due to the inherently difficult process of grafting ethylenically unsaturated acids or acid derivatives to propylene polymers, prior attempts to graft propylene polymers by high temperature thermal grafting techniques in extruders has resulted in maximum grafted acid or derivative concentrations of no more than about 1 to about 1.2 wt. %. Using peroxide or other free radical generating catalysts in the extruder/reactor makes it possible to achieve higher graft contents but results in chain scission, often referred to as “visbreaking,” and the production of relatively low molecular weight grafted and ungrafted fragments. The presence of these low molecular weight species produces a corresponding undesirable increase in MFR. While the low molecular weight species can be removed from the grafted reaction product, such as by solvent extraction, such procedures are costly and they result in loss of desired functionality.
The aforementioned problems are well recognized and described in the prior art. For example, U.S. Pat. No. 5,367,022 points out that when polypropylene homopolymer is grafted with maleic anhydride using peroxide to a target grafted anhydride concentration of 2% by weight, the resulting reaction product exiting the extruder reactor contains about 1.5 to 2.2 wt. % grafted monomer. After refining by solvent extraction to remove low molecular weight polymer fragments, the product only contains about 0.6 to about 1.2 wt. % grafted monomer. The reference also states that grafting graft polypropylene backbones with acid or derivative monomers resulted in unacceptably large increases in the melt flow rate of the product as compared to that of the ungrafted polypropylene, principally due to chain scission. It goes on to indicate that polypropylene homopolymer backbones having an initial melt flow rate (MFR) of about 2 to about 5 g/10 min before grafting typically exhibit MFR values on the order of about 1500 g/10 min after grafting with 1wt. % maleic anhydride and concludes that such MFRs are far too high for economical pelletizing operations.
While it is an object of U.S. Pat. No. 5,367,022 to provide propylene polymers and adhesive blends based thereon having high grafting monomer functionality and relatively low MFRs, the maximum level of maleic anhydride grafted onto the impact copolymer was 2 wt. %. Moreover, at that graft level the MFR of the grafted product was 398 g/10 min, a level generally considered to be unacceptable for commercial processes. In commercial processing operations for adhesive applications it is generally preferred that the grafted product have a MFR less than 300 g/10 min and, more preferably, 250 g/10 min or lower. It is further observed in the examples of the patent that efforts to increase the amount of maleic grafted anhydride by increasing the amount of peroxide catalyst used, had the opposite effect. Not only was the amount of maleic anhydride grafted reduced, the MFR of the product was increased to even higher and more unacceptable levels.
Other references report the use of various coagents in efforts to increase the amount of graft monomer reacted to propylene polymers and increase graft efficiency during the grafting process. Such processes are disclosed in U.S. Pat. Nos. 5,344,886 and 5,344,888. While graft monomer (maleic anhydride) levels as high as 3.47 wt. % are reported using vinyl acetate as a coagent, there is no mention of the MFR of the resulting functionalized products. Furthermore, the reactive nature of the coagents being used virtually assures that all or at least a substantial portion of the coagent is also reacted with the propylene polymer so that the resulting product would have a significantly different structure than functionalized products produced using the graft monomer by itself.
SUMMARY OF THE INVENTION
It is an object of the present invention to produce functionalized propylene polymer products having higher amounts of acid or acid derivative grafted, i.e., reacted to the polymer backbone. It is a further objective to obtain grafted propylene polymers having higher graft contents while maintaining relatively low MFRs. A still further object is to provide improved adhesive blends formulated with the grafted propylene polymers.
These and other objectives are achieved with the present invention wherein it has unexpectedly been found that a select group of propylene impact copolymers can be grafted with olefinically unsaturated carboxylic acid and derivative monomers to produce functionalized products characterized by high grafting monomer functionality and relatively low MFR.
Specifically, the improved grafted propylene copolymers of the invention are grafted impact copolymers comprising a propylene-ethylene impact copolymer characterized by having a relatively narrow molecular weight distribution and comprising a reactor-made intimate mixture of propylene homopolymer and 20 wt. % or more ethylene-propylene copolymer and having at least 1 wt. % grafting monomer selected from the group consisting of ethylenically unsaturated carboxylic acid or acid derivative grafted thereto. Preferably, said grafted impact copolymer having a graft to melt flow rate ratio of 1 or more.
Especially useful products are obtained using maleic anhydride as the graft monomer. Highly useful grafted products have MWDs of 7 or less and, more preferably, 6 or less. Rubber, i.e., ethylene-propylene copolymer, contents are most advantageously 25 wt. % or greater. The grafted products preferably have MFRs less than 300 g/10 min even at graft levels of 2 to 3 wt. %. The ability to achieve graft to melt flow rate ratios of 1 and above at high graft levels is highly advantageous and unexpected.
Adhesive blends comprised of 0.1 to 25 wt. % of the grafted impact copolymer and up to 99.9 ungrafted polyolefin blending resin are also disclosed. Highly useful adhesive blends contain up to 40 wt. % elastomeric polyolefin. In an especially preferred embodiment of the invention, the adhesive blends contain 0.25 to 15 wt. % grafted impact copolymer and 10 to 30 wt. % ungrafted elastomeric polyolefin with the balance of the composition being an ungrafted propylene polymer.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides grafted, i.e., functionalized, propylene impact copolymer products characterized by having high graft monomer functionali
Asinovsky Olga
Baracka Gerald A.
Equistar Chemicals LP
Heidrich William A.
Seidleck James J.
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