Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-09-06
2003-09-16
Harlan, Robert D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S172000, C525S240000, C502S155000, C428S513000
Reexamination Certificate
active
06620897
ABSTRACT:
FIELD OF THE INVENTION
Polyolefins, preferably polyethylene, having a density of about 0.86 to about 0.93 g/mL, and having methyl branches and at least 2 other different lengths of branches of 6 carbon atoms and less, form heat seals at exceptionally low temperatures, thereby allowing good seals to be formed rapidly. This is advantageous when heat sealing so-called flexible packaging made from single or multilayer films.
TECHNICAL BACKGROUND
Polyolefins such as polyethylene and polypropylene have been used in many applications, for example in packaging such as bags and cartons. In many instances in order to form the package it is necessary to effect a seal between two different pieces or two different parts made of the same polyolefin. This may be done using adhesives, but is more commonly done by applying heat to the surfaces to be joined to soften or melt them while applying some pressure to the place where they are to be joined to form a single piece of thermoplastic. This operation is called heat sealing, and is commonly used to join thermoplastic parts. See for instance K. R. Osborn, et al.,
Plastic Films
, Technomic Publishing Co., Inc., Lancaster, Pa., U.S.A., 1992, especially p. 152-153 and 173-175; H. Mark, et al., Ed.,
Encyclopedia of Polymer Science and Engineering
, Vol. 1, McGraw Hill Book Co., New York, 1985, p. 527; and
ibid
., Vol. 7, 1987, p.117.
Most commonly the heating is carried out by contacting the surfaces opposite those to be joined with a hot object such as a hot bar, or heating the surfaces with hot air or infrared radiation. In any event the speed at which one can heat the surfaces to be joined to the proper temperature for joining often determines the speed at which one can heat seal the surfaces. This is particularly true for thermoplastics such as polyolefins, because they often have relatively low thermal conductivities. High speed heat sealing is important because many such operations are high volume continuous operations where slow heat sealing speeds significantly increase costs.
One way to increase heat sealing speeds is to lower the temperature at which the seal may be formed. This is typically done by lowering the melting point of the polymer being sealed, but has its limits since if the melting point of the polymer is lowered too much the seal itself may be too weak or the polymer characteristics may be detrimentally affected. Therefore ways of forming satisfactory seals at lower temperatures are constantly being sought.
Numerous attempts have been made to find polymers with improved heat sealing properties, see for instance U.S. Pat. No. 5,358,792, U.S. Pat. No. 5,372,882, U.S. Pat. No. 5,427,807, U.S. Pat. No. 5,462,807, U.S. Pat. No. 5,530,065, U.S. Pat. No. 5,587,247, U.S. Pat. No. 5,741,861, U.S. Pat. No. 5,770,318, U.S. Pat. No. 5,773,106, U.S. Pat. No. 5,773,129, U.S. Pat. No. 5,792,549, WO9303093, WO9532235 and WO9728960. None of these references uses the polymers described herein.
WO9827124, WO9847934, WO9905189, U.S. Pat. No. 5,714,556 and U.S. Pat. No. 5,866,663 and U.S. Pat. No. 6,060,569 (all of which are incorporated by reference herein for all purposes as if fully set forth) describe generally certain branched polyolefins, and their uses. The specific polymers used herein are not particularly noted in these publications for use in heat sealing applications.
SUMMARY OF THE INVENTION
This invention concerns a process for lowering the heat sealing temperature of a polyolefin-based thermoplastic, comprising the step of replacing at least a portion of the polyolefin in the thermoplastic with a branched polyolefin having a density of about 0.86 to about 0.93 g/mL, and having methyl branches and at least branches of two other different lengths of six carbon atoms or less, provided that said methyl branches are at least 10 mole percent of total branching in said branched polyolefin.
This invention further concerns a first article having a first thermoplastic surface suitable for heat sealing to a second thermoplastic surface of the same or another article, wherein said first thermoplastic surface comprises a branched polyolefin having a density of about 0.86 to about 0.93 g/mL, having methyl branches and at least branches of two other different lengths of six carbon atoms or less, provided that said methyl branches are at least 10 mole percent of total branching in said branched polyolefin.
The invention still further concerns a process for preparing an article comprising the step of heat sealing a first thermoplastic surface to a second thermoplastic surface, wherein the first thermoplastic surface and the second thermoplastic surface comprise a branched polyolefin having a density of about 0.86 to about 0.93 g/mL, having methyl branches and at least branches of two other different lengths of six carbon atoms or less, provided that said methyl branches are at least 10 mole percent of total branching in said branched polyolefin.
This invention also concerns an article made at least in part from a first thermoplastic surface and a second thermoplastic surface joined together by heat sealing, wherein the first thermoplastic surface and a second thermoplastic surface comprise a branched polyolefin having a density of about 0.86 to about 0.93 g/mL, having methyl branches and at least branches of two other different lengths of six carbon atoms or less, provided that said methyl branches are at least 10 mole percent of total branching in said polyolefin.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polymers used herein are hydrocarbon polyolefins, that is polymers made by the addition polymerization of olefinic bonds of one or more hydrocarbon olefins. Preferably the polymers are made from one or more monomers (olefins) of the formula R
1
HC═CHR
2
, wherein R
1
and R
2
are each independently hydrogen or alkyl; more preferably wherein one of R
1
or R
2
is hydrogen, and the other is hydrogen or n-alkyl, and especially wherein both R
1
and R
2
are hydrogen (the olefin is ethylene). A specific preferred polymer is polyethylene, that is a polymer containing about 80 mole percent or more of repeat units derived from ethylene, and another specifically preferred polymer is homopolyethylene, which contains about 98 mole percent or more of repeat units derived from ethylene.
The polymers useful herein are obtainable (and preferably obtained) by polymerizing olefins in the presence of a catalyst component comprising a late transition metal catalyst such as, for example, disclosed in previously incorporated WO9827124, WO9847934, WO9905189, U.S. Pat. No. 5,714,556, U.S. Pat. No. 5,866,663 and U.S. Pat. No. 6,060,569, as well as U.S. Pat. No. 5,852,145, U.S. Pat. No. 5,880,241, U.S. Pat. No. 5,932,670, U.S. Pat. No. 5,942,461, WO98/30612, WO98/37110, WO98/40374, WO98/40420, WO98/42664, WO98/42665, WO98/47933, WO98/47934, WO99/30609, WO99/49969, WO99/41290 and WO99/62968 (all of which are also incorporated by reference herein for all purposes as if fully set forth). Preferably, the polymers are made by polymerizing an olefin component comprising a predominant amount of ethylene, in the presence of a catalyst component comprising a late transition metal complex (more preferably wherein the late transition metal is Ni or Pd) of a diimine ligand. One such preferred late transition metal complex is set forth in the examples appended hereto. The catalyst component may also optionally contain various suitable catalyst activators and co-catalysts. Further details regarding the catalyst component may be had by reference to the previously incorporated publications.
Although any type of polymerization process, gas phase, slurry, or solution, continuous, batch or semibatch, may be used to prepare the branched polyolefins suitable for use herein, because of the relatively low melting point of these polyolefins, it is preferred to make them in a solution or slurry process, more preferably a solution process.
The branched polyolefins have a density of about 0.86 to about 0.93 g/mL, preferably about 0.86 to about 0.91 g/mL, and especially abou
E. I. du Pont de Nemours and Company
Harlan Robert D.
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