Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2001-06-22
2002-05-07
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S042500, C521S044500, C521S045500, C521S046000, C521S046500, C521S047000, C521S048000, C521S049000, C521S049800
Reexamination Certificate
active
06384093
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the melt processing of crosslinked thermoplastic material, for example, for use in recycling such material.
The use of a thermoplastic material to form an article may facilitate the later recycling of that article. This is because a thermoplastic material by its nature may be repeatedly softened by heat and hardened by cooling. Thus, it is relatively straightforward to recycle a thermoplastic material simply by softening it to the point that is may be processed or blended with virgin plastic material. The use of a thermoplastic material may be contrasted with the use of a thermoset plastic material—which is generally recognized as difficult to recycle. A thermoset material is cured by heat, catalysis, or other chemical means to form an extensive crosslinked network. Because a thermoset generally may not be melted or softened by reheating, it is difficult to blend a thermoset plastic with a virgin plastic material simply by reheating the thermoset plastic.
After a thermoplastic material has been thermoformed, its performance characteristics may be enhanced by crosslinking its polymeric structure to a desired level. Crosslinking of thermoplastic materials is used, for example, in the manufacture of extruded thermoplastic films for food and non-food packaging, thermoplastic insulation for electrical wire and cable, and injection- or blow-molded thermoplastic articles. Chemical crosslinking may be performed through the use of one or more crosslinking agents (e.g., organic peroxides), which may or may not require irradiation for activation. Also crosslinking may also occur by irradiation without the use of a crosslinking agent to facilitate the crosslinking (i.e., “radiation induced crosslinking”).
The greater degree to which a thermoplastic material has been modified by crosslinking, the more the crosslinked thermoplastic resin will behave as if it were a thermoset material. Thus, recycling a thermoplastic material that has been crosslinked may be problematic.
SUMMARY OF THE INVENTION
The present invention addresses one or more of the aforementioned problems. A method of recycling plastic comprises forming a mixture comprising: (i) 100 weight parts of crosslinked thermoplastic resin having a given melt flow index of at most about 0.5 g/10 minutes; (ii) from about 0.1 to about 150 weight parts of polymeric resin having an weight-average molecular weight of at least about 2,000 and a melt flow index of at least about 10 times the given melt flow index of the crosslinked thermoplastic resin and a melt flow index of at least about 1.5 g/10 minutes; and (iii) optionally, a given amount of non-crosslinked thermoplastic resin having a melt flow index of less than the melt flow index of the polymeric resin. The mixture is exposed to mechanical shearing energy to create a processed mixture having a melt flow index of at least about 0.8 times 10
X
, where:
X=(WF
1
)log
10
(MFI
1
)+(WF
2
)log
10
(MFI
2
)+(WF
3
)log
10
(MFI
3
);
WF
1
=(weight of the crosslinked thermoplastic resin)/(weight of the mixture);
WF
2
=(weight of the polymeric resin)/(weight of the mixture);
WF
3
=(weight of the non-crosslinked thermoplastic resin)/(weight of the mixture);
MFI
1
=the melt flow index of the crosslinked thermoplastic resin;
MFI
2
=the melt flow index of the polymeric resin; and
MFI
3
=the melt flow index of the non-crosslinked polymeric resin.
The processed mixture is subsequently mixed with thermoplastic polymer.
A method of enhancing the melt-processibility of crosslinked plastic comprises forming a mixture comprising: (i) 100 weight parts of crosslinked thermoplastic resin having a given melt flow index of at most about 0.5 g/10 minutes; (ii) from about 0.1 to about 150 weight parts of polymeric resin having a weight-average molecular weight of at least about 2,000 and a melt flow index of at least about 10 times the given melt flow index of the crosslinked thermoplastic resin and a melt flow index of at least about 4 g/10 minutes; and (iii) optionally, a given amount of non-crosslinked thermoplastic resin having a melt flow index of less than the melt flow index of the polymeric resin. The mixture is exposed to to mechanical shearing energy to create a processed mixture having a melt flow index of at least about 0.8 times 10
X
, where “x” is as stated in the preceding paragraph.
Other advantages and features of the invention will be more readily understood and appreciated by reference to the detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The melt processibility of a crosslinked thermoplastic resin may be enhanced by mixing it with a low viscosity polymeric resin (“diluent resin”) having a specified melt flow index (“MFI”) relative to the melt flow index of the crosslinked thermoplastic resin, and exposing the mixture to mechanical shearing energy to produce a processed mixture having enhanced melt flow characteristics.
Crosslinked Thermoplastic Resin
“Crosslinked thermoplastic resin” is thermoplastic resin (i.e., one or more thermoplastic polymers) that has crosslinks formed by subjection to a crosslinking treatment or reaction, which may reduce or eliminate the ability of the thermoplastic resin to soften or melt upon reheating and harden or freeze upon cooling, and thus render these characteristics more like those of a thermoset resin than those of the thermoplastic resin before the crosslinking treatment or reaction. Thermoplastic resin that may be crosslinked include that comprising one or more thermoplastic polymers such as polyolefins, polystyrenes, polyurethanes, polyamides, and polyesters.
Polyolefins include ethylene homo- and co-polymers. Ethylene homopolymers include high density polyethylene (“HDPE”) and low density polyethylene (“LDPE”). Ethylene copolymers include ethylene/alpha-olefin copolymers (“EAOs”), ethylene/unsaturated ester copolymers, and ethylene/(meth)acrylic acid. (“Copolymer” as used in this application means a polymer derived from two or more types of monomers, and includes terpolymers, etc.)
EAOs are copolymers of ethylene and one or more alpha-olefins, the copolymer having ethylene as the majority mole-percentage content. Preferably, the comonomer includes one or more C
3
-C
20
&agr;-olefins, more preferably one or more C
4
-C
12
&agr;-olefins, and most preferably one or more C
4
-C
8
&agr;-olefins. Particularly preferred &agr;-olefins include 1-butene, 1-hexene, 1-octene, and mixtures thereof.
EAOs include one or more of the following: 1) medium density polyethylene (“MDPE”), for example having a density of from 0.93 to 0.94 g/cm3; 2) linear medium density polyethylene (“LMDPE”), for example having a density of from 0.926 to 0.94 g/cm3; 3) linear low density polyethylene (“LLDPE”), for example having a density of from 0.915 to 0.930 g/cm3; 4) very-low or ultra-low density polyethylene (“VLDPE” and “ULDPE”), for example having density below 0.915 g/cm3, and 5) homogeneous EAOs. EAOs may have a density of less than about any of the following: 0.925, 0.922, 0.92, 0.917, 0.915, 0.912, 0.91, 0.907, 0.905, 0.903, 0.9, and 0.898 grams/cubic centimeter. Unless otherwise indicated, all densities herein are measured according to ASTM D1505 and expressed in units of g/cc.
The polyethylene polymers may be either heterogeneous or homogeneous. As is known in the art, heterogeneous polymers have a relatively wide variation in molecular weight and composition distribution. Heterogeneous polymers may be prepared with, for example, conventional Ziegler Natta catalysts.
On the other hand, homogeneous polymers are typically prepared using metallocene or other single site-type catalysts. Such single-site catalysts typically have only one type of catalytic site, which is believed to be the basis for the homogeneity of the polymers resulting from the polymerization. Homogeneous polymers are structurally different from heterogeneous polymers in that homogeneous polymers exhibit a relatively even sequencing of comonomers within a chain, a
Bourland Larry
Freundlich Richard A.
Herran Vincent W.
Nwana Rudolph G.
Cryovac Inc.
Foelak Morton
Ruble Daniel B.
LandOfFree
Method of melt processing crosslinked thermoplastic material does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of melt processing crosslinked thermoplastic material, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of melt processing crosslinked thermoplastic material will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2828725