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
2000-08-30
2001-04-10
Cain, Edward J. (Department: 1714)
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
active
06214924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polyethylene compositions. In particular, the present invention relates to highly mineral filled polyethylene compositions.
BACKGROUND OF THE INVENTION
Heretofore, polyvinylchloride resin (a.k.a. PVC) has been commonly used as a base resin for resin compositions containing mineral filler, due to its ability to accept higher levels of such filler. For example, compositions comprising PVC and a mineral filler such as SiO
2
, BaSO
4
, and CaCO
3
has been used in floor tile and sheeting applications, due to the high impact strength, abrasion resistance and flexibility of PVC, coupled with the lost cost associated with increased filler loadings.
However, PVC has come under increased scrutiny for several reasons. For example, the presence of chloride atom in the backbone structure of PVC renders it difficult to re-melt, re-extrude, and recycle, and leads to poor heat stability. In addition, when combusted, PVC tends to disadvantageously release noxious substances, such as hydrochloric acid. Further, PVC typically contains a plasticizer to improve flexibility, which plasticizer may leach from landfilled PVC and cause soil and/or water pollution. PVC is further disadvantageous in that it is thermally sensitive, and thus requires tighter temperature control in molding processes than non-halogen containing polymers.
In view of the above deficiencies, industry would find advantage in a halogen-free PVC replacement which is more easily recyclable, but which does not sacrifice physical properties.
U.S. Pat. No. 4,847,317 (Dokurno et al.) discloses filled thermoplastic compositions comprising: (a) 30-90 parts ethylene polymer, (b) 10-70 parts graft modified ethylene polymer, and (c) 20-70 weight percent filler, based upon the amount of (a) and (b). Those in industry would find advantage in compositions which tolerate filler levels greater than 70 weight percent. Those in industry would further find advantage in compositions which achieve the desired performance, but which utilize less than 10 weight percent functionalized polyethylene, more preferably less than 3 weight percent functionalized polyethylene.
U.S. Pat. No. 4,379,190 (Schenck I) teaches filled thermoplastic compositions comprising: (a) 5-60 weight percent of a mixture of at least two copolymers of ethylene, having specified polar comonomer contents, (b) 40-90 weight percent filler, and (c) 0-15 weight percent plasticizer. When the filler is present in an amount exceeding 75 weight percent, Schenck requires that the plasticizer be present in an amount of at least 1 weight percent, with plasticizer levels between 3 and 10 weight percent being preferred, and with plasticizer levels between 4 and 8 weight percent being most preferred.
U.S. Pat. No. 4,403,007 (Coughlin) describes filled thermoplastic composition comprising: 5-55 weight percent of a copolymer of ethylene with a functionalized comonomer, 1-15 weight percent plasticizer, and 40-90 weight percent filler.
U.S. Pat. No. 4,438,228 (Schenck II) discloses a filled thermoplastic composition useful, e.g., as sound-deadening sheeting for automotive carpet, comprising: (a) 5-55 weight percent of an ethylene/a-olefin copolymer, (b) 2-12 weight percent plasticizer, and (c) 40-90 weight percent filler.
PCT Publication WO 96/04419 discloses the use of substantially linear ethylene polymers in sheet materials for flooring. While the PCT Publication recognizes the potential use of substantially linear ethylene polymers in sheet materials comprising up to 85 weight percent filler, it does not utilize greater than 65 weight percent filler in the Examples.
In contrast to the teaching of Schenck I, Schenck II, and Coughline, those in industry would further find advantage in a filled plasticizer-free thermoplastic composition, i.e., a thermoplastic composition containing less than 3 weight percent, especially less than 1 weight percent plasticizer.
However, the compositions of above references do not teach or disclose substantially halogen-free, highly filled, plasticizer-free polyethylene-based compositions achieving high flexibility.
SUMMARY OF THE INVENTION
One aspect of the present invention is a plasticizer-free polyethylene composition comprising:
(A) from about 5 weight percent to about 70 weight percent of at least one homogeneous ethylene/&agr;-olefin interpolymer having:
(i) a density from about 0.85 g/cm
3
to about 0.92 g/cm
3
,
(ii) a molecular weight distribution (M
w
/M
n
) of less than about 3.5,
(iii) a melt index (I
2
) of from about 0.1 grams/10 minutes to about 175 grams/10 minutes,
(iv) a CDBI of greater than about 50 percent;
(B) from about 30 weight percent to about 95 weight percent of at least one filler; and
(C) from about 0.1 weight percent to less than about 10 weight percent of at least one functionalized polyethylene. All percentages used herein are by weight based on the total formulation weight.
Preferably, the homogeneous ethylene/&agr;-olefin interpolymer used in the polyethylene compositions of the present invention is a substantially linear ethylene polymer, more preferably a substantially linear interpolymer of ethylene and C
3
-C
20
&agr;-olefin.
The polyethylene compositions of the present invention may be usefully employed in floor tile and sheeting applications, due to their good abrasion resistance, indentation resistance, flexibility, impact strength and filler holding capability. Furthermore, the polyethylene compositions of the present invention are substantially halogen-free, and do not require the presence of plasticizer to achieve the stated advantages.
DETAILED DESCRIPTION OF THE INVENTION
The homogeneous ethylene/&agr;-olefin useful in forming the polyethylene compositions of the present invention is a homogeneously branched interpolymer. That is, the &agr;-olefin comonomer of the interpolymer is randomly distributed within each given interpolymer molecule such that substantially all of the interpolymer molecules have the same ethylene/comonomer ratio. The homogeneous ethylene/&agr;-olefin interpolymers used for forming the polyethylene compositions of the present invention essentially lack a non-short chain branched polymer fraction which is measurable as “high density” fraction by the TREF technique.
The homogeneity of ethylene/&agr;-olefin interpolymers is typically described by the SCBDI (Short Chain Branching Distribution Index) or CDBI (Composition Distribution Branch/Breadth Index) and is defined as the weight percent of the polymer molecules having a comonomer content with 50 percent of the median total molar comonomer content. The CDBI of a polymer is readily calculated form data obtained from techniques known in the art, such as, for example, temperature rising elution fractionation (abbreviated herein as “TREF”) as described, for example, in Wild et al,
Journal of Polymer Science, Poly. Phys. Ed
., Vol. 20, p 41 (1982), in U.S. Pat. No. 4,798,081 (Hazlitt et al.), in U.S. Pat. No. 5,008,204 (Stehling), in U.S. Pat. No. 5,246,783 (Spenadel et al.), in U.S. Pat. No. 5,322,728 (Davey et al.), in U.S. Pat. No. 4,798,081 (Hazlitt et al.), or in U.S. Pat. No. 5,089,321 (Chum et al.), the disclosures of all of which are incorporated herein by reference. The SCBDI or CDBI for the homogeneous ethylene/&agr;-olefin interpolymers used for the polyethylene composition of the present invention is greater than about 50 percent, preferably greater than about 70 percent, especially greater than about 90 percent.
The density of the homogeneous ethylene/&agr;-olefin interpolymer used for forming the composition of the present invention (as measured in accordance with ASTM D-792) is generally at least about 0.85 g/cm
3
, preferably at least about 0.86 g/cm
3
. The density of the homogeneous ethylene/&agr;-olefin interpolymer is likewise typically less than about 0.95 g/cm
3
, preferably less than about 0.92 g/cm
3
, more preferably less than about 0.91 g/cm
3
, and most preferably less than about 0.905 g/cm
3
.
The molecular weight of homogeneous ethylene/&agr;-olefin interpolymer useful i
Bethea James R.
Bieser John O.
Feig Edwin R.
Turley Robert R.
Cain Edward J.
The Dow Chemical Company
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