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
1996-10-18
2001-10-02
Mullis, Jeffrey (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...
C525S309000, C525S242000, C525S069000
Reexamination Certificate
active
06297326
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to graft copolymers of polyolefins and alkyl acrylate and processes for preparing the copolymers. More particularly, the invention relates to melt grafting 2-hydroxyethyl methacrylate onto polyethylene and polypropylene resins and a process for preparing such polymers.
Polyolefins such as polyethylene and polypropylene are non-polar polymers that, in general, are resistant to polar moieties. These polyolefins are customarily used commercially for barrier film applications. Such applications include product packaging to such commodities as disposable personal products like, sanitary napkins, diapers, adult incontinence products and the like.
Used polymers are typically disposed of by recycling, incineration or land filling. Because of the increasing amount of material being sent to landfills it is becoming more important for the refuse to be biodegradable, compostable or both. In the area of disposable personal products, the outer polyethylene film layer has to be separated from the rest of the absorbent structure or the entire structure has to be comminuted.
Over the past decade or so interest has grown in modifying existing polymers to achieve commercially important copolymers having improved and, at times, specific properties. This has been particularly evident in the drive to modify commodity polymers such as polyolefins with polar functional monomers such as acrylic acid and alkyl acrylates. For example, linear low-density polyethylene has been modified by melt grafting up to about 5 weight percent (wt. %) t-butylaminoethyl methacrylate (t-BAEMA) to produce a copolymer having improved properties for co-extrusion as tie layers. These tie layers are commercially important in the packaging and film industry to economically produce packages meeting specific requirements and sometimes governmental regulations.
Polyolefins have also been modified using acrylate esters such as methyl acrylate, 2-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, octadecyl acrylate and corresponding esters of methacrylate.
Moreover, there is an increased emphasis on environmentally safe coatings for plastics. These coatings are reducing the use of solvent based coatings and relying, to an ever increasing degree, on polar coatings such as water based materials. The utility of the graft copolymer of the present invention includes, but would not be limited to, materials having a greater affinity for a polar coating. Other uses may include wire coatings, injected molded articles and barrier films having increased mechanical compatibility between the graft copolymer of the present invention and hydrophilic compositions.
The production of the compositions has generally been accomplished by blending all the constituents into a monomer-coated resin mixture. The heterogeneous mixture of resin coated with monomer is then extruded, in the presence of a reaction initiator, to form a graft copolymer. This method has been successful to produce graft copolymers having a comparatively low weight percent of grafted monomer. Moreover, the efficiency of grafted monomer to the polyolefin resin is low, with an efficiency of less than 50 percent. Due to the grafting limitations and process inefficiency, there is a need for graft copolymers having a greater amount of monomer grafted to the polyolefin and an efficient process that is capable of producing such copolymers.
SUMMARY OF THE INVENTION
Briefly, the present invention is a modified polyolefin copolymer having from 95 weight percent to about 70 weight percent of a polyolefin with the remaining portion of the composition an alkyl acrylate monomer grafted thereto, wherein the percent grafted monomer is based on the weight of the polyolefin and the weight of the grafted (meth)acrylate. More specifically, the composition of the present invention is an ethylene or propylene polymer composition having from 95 weight percent to about 70 weight percent of the polyolefin and from 5 weight percent to about 30 weight percent of 2-hydroxyethyl methacrylate (HEMA) monomer grafted thereto. As used herein 2-hydroxyethyl methacrylate and HEMA are the same compound.
Surprisingly, it has now been found that graft copolymers of polyethylene or polypropylene can be obtained by melt grafting high levels, 5 weight percent to about 30 weight percent, of 2-hydroxyethyl methacrylate onto the polyolefin backbone.
Another aspect of the invention is a method of making the graft copolymer described herein. The polyolefin copolymer of this invention can be made by adding to a suitable reaction vessel and under melt grafting conditions, a predetermined amount of polyolefin polymer, adding a predetermined amount of 2-hydroxyethyl methacrylate monomer and a sufficient amount of reaction initiator to the melt to graft from 5 weight percent to about 30 weight percent of the 2-hydroxyethyl methacrylate onto the polyolefin. Desirably, the polyolefin copolymer is cooled sufficiently to solidify the melt
It is a general object of the invention to provide a composition having a higher weight percent of grafted monomer to a polyolefin than previously known. A more specific object of the invention is to provide a graft copolymer polyolefin having greater than 5 weight percent monomer grafted thereto.
Another object of the invention is to provide a composition having from 95 weight percent to about 70 weight percent of polyethylene and from 5 weight percent to about 30 weight percent 2-hydroxyethyl methacrylate grafted thereto.
Another object of the invention is to provide a composition having from 95 weight percent to about 70 weight percent of polypropylene and from 5 weight percent to about 30 weight percent 2-hydroxyethyl methacrylate grafted thereto.
It is another object of the invention to provide a method of melt grafting 2-hydroxyethyl methacrylate onto a polyolefin resin under melt conditions.
DETAILED DESCRIPTION OF THE INVENTION
The saturated ethylene polymers useful in the practice of this invention are homopolymers or copolymer of ethylene and polypropylene and are essentially linear in structure. As used herein, the term “saturated” refers to polymers which are fully saturated, but also includes polymers containing up to about 5% unsaturation. The homopolymers of ethylene include those prepared under either low pressure, i.e., linear low density or high density polyethylene, or high pressure, i.e., branched or low density polyethylene. The high density polyethylenes are generally characterized by a density that is about equal to or greater than 0.94 grams per cubic centimeter (g/cc). Generally, the high density polyethylenes useful as the base resin in the present invention has a density ranging from about 0.94 g/cc to about 0.97 g/cc. The polyethylenes can have a melt index, as measured at 2.16 kg and 190° C., ranging from about 0.005 decigrams per minute (dg/min) to 100 dg/min. Desirably, the polyethylene has a melt index of 0.01 dg/min to about 50 dg/min and more desirably of 0.05 dg/min to about 25 dg/min. Alternatively, mixtures of polyethylene can be used as the base resin in producing the graft copolymer compositions, and such mixtures can have a melt index greater than 0.005 dg/min to less than about 100 dg/min.
The low density polyethylene has a density of less than 0.94 g/cc and are usually in the range of 0.91 g/cc to about 0.93 g/cc. The low density polyethylene polymer has a melt index ranging from about 0.05 dg/min to about 100 dg/min and desirably from 0.05 dg/min to about 20 dg/min. Ultra low density polyethylene can be used in accordance with the present invention. Generally, ultra low density polyethylene has a density of less than 0.90g/cc.
Generally, polypropylene has a semi-crystalline structure having a molecular weight of about 40,000 or more, a density of about 0.90 g/cc, a melting point of 168 to 171° C. for isotactic polypropylene and a tensile strength of 5000 psi. Polypropylene can also have other tacticities including syndiotactic and atactic.
Copolymers of ethylene which can be useful in the present i
Schertz David Michael
Wang James Hongxue
Kilpatrick & Stockton LLP
Kimberly-Clark Corporation
Mullis Jeffrey
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