Note: Descriptions are shown in the official language in which they were submitted.
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PHOSPHOROUS CONTAINING REPROCESSED POLYMER MATERIALS,
ARTICLES FORMED THEREOF, AND METHODS OF FORMING SUCH
ARTICLES
FIELD OF THE INVENTION
[0001]The present invention relates to the treatment and use of
polymer materials processed under elevated temperature and pressure in
1 o various molding (e.g., injection, extrusion) processes. In particular the
invention relates to the treatment of polymer materials that have been
previously melt formed and cooled, enabling their reuse in subsequent melt
processes without undue degradation in one or more aesthetic or functional
properties.
BACKGROUND OF THE INVENTION
[0002] Injection and extrusion molding are well known methods for
manufacturing plastic articles known as preforms which may subsequently be
expanded (e.g. blow molded) into bottles or other containers. In particular,
it
is desirable to produce clear and transparent articles from such materials.
[0003] When plastic materials are subjected to elevated temperatures
and pressures as are typically used in the referenced molding processes, the
plastic materials can be prone to molecular degradation, unwanted
polymerization and unwanted reaction with other materials that may be
present in the plastic material. This is particularly true in polymer
materials
that have been processed once and are processed a second time at elevated
temperature, i.e., subjected to a second melting and processing cycle as is
typical in reusing scrap or recycled plastic preforms or bottles as the raw
plastic material for new preforms and bottles. Such polymer reaction
processes can cause the plastic material to acquire undesirable coloring,
yellowing, blackening, haze or other degradation of transparency. Such
processes may also cause a reduction in melt strength, intrinsic viscosity
(IV)
or otherwise deleteriously effect their processability or layer compatibility
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during subsequent molding into a shaped article, or the physical or aesthetic
properties of such article during use.
SUMMARY OF THE INVENTION
[0004] In accordance with various embodiments of the invention, there
are provided phosphorous containing reprocessed polymer materials, articles
formed thereof, and methods of forming such articles. It has been found that
the addition of phosphorous facilitates the reuse of a previously melt formed
and cooled mixture of polymer materials, namely a mixture of two or more
different polymers that have previously been (separately or together) melt
formed and cooled (hereinafter "processed mixture"), such that the processed
mixture can be reused in forming an article in a subsequent melt process with
a reduced tendency to produce one or more of an undesirable coloring (e.g.,
yellowing), haze or other degradation of transparency, and/or a reduction in
melt viscosity. The addition of phosphorous thus enables or enhances the
reuse of such processed mixture in a subsequent melt formed article.
[0005] In one embodiment, the phosphorous material is a phosphite
and is added to the processed mixture (e.g., commingled post consumer
regrind or commingled plant scrap regrind), thus enabling the processed
mixture to be reused in a significantly higher amount (than is possible
without
the phosphorous material) in a subsequently melt formed article without
producing an undesirable amount of yellowing, haze and/or reduction in melt
viscosity. The subsequently formed article may comprise all or a portion of a
monolithic or a multilayer article, wherein the formed article is preferably
substantially clear and transparent, and/or exhibits improved delamination
resistance or layer compatibility. Other materials, polymer and/or non-
polymer, which may or may not have been previously melt formed and cooled,
may be present in the melt in addition to the reprocessed mixture and
included in the subsequently melt formed article.
[0006] In one example, the processed mixture may comprise as its
principal component an ester containing polymer, such as an aromatic
polyester, and more specifically polyethylene terephthalate (PET). It may
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further comprise a polyamide material such as, for example, a meta-xylylene
polyamide such as MXD6, and optionally a transition metal (e.g., cobalt) in an
amount which provides active gas barrier performance. This processed
mixture of polymer materials that have previously been subjected to a melt
process (i.e., polymer that has previously been melted from a polymer in its
solid form at room temperature and then cooled), is then subsequently melt
processed in combination with phosphorous and the reprocessed mixture
used to form at least a portion of an article. As used herein, an article
includes all or a portion of an article, which may take the form of, for
example,
1o a package, container, preform, closure, liner, sheet or film. For example,
the
article may be a multilayer preform including one or more layers of an ester
containing polymer, such as PET, and one or more layers of the reprocessed
mixture, of which the principal component is PET. The invention enables the
use of such reprocessed mixtures in greater amounts and/or applications
where such reprocessed mixture, without the addition of phosphorous, would
not provide the desired aesthetic and/or functional performance
characteristics. Reuse of the processed mixture may thus provide a
significant reduction in cost of the subsequently formed article.
[0007] In alternative embodiments, the processed mixture may
comprise any structural or matrix polymer, typically as a principal (greater
than 50% by total weight) component, and one or more barrier materials such
a polyalcohol, polyamide, polyolefin, polyalkyldiene, polyglycolic acid (PGA),
acrylonitrile copolymer, cyclic olefin copolymer, and copolymers and blends
thereof. More specific examples of barrier materials include ethylene vinyl
alcohol copolymer (EVOH), nylon, such as nylon-6 or a meta-xylylenediamine
(MXD6), polyester/polyolefin copolymers (e.g. a polybutadiene/polyester
copolymer in the presence of a transition metal, such as Amosorb , available
from BP p.l.c., London UK), and polyvinylidene chloride (PVDC). Suitable
ester containing matrix polymers include polyethylene terephthalate (PET),
polybutylene terephthalate (PBT), polypropylene terephthalate (PPT),
polyethylene naphthalate (PEN), poly(lactic acid) (a.k.a. polylactide) (PLA),
and polytrimethylene naphthalate (PTN). Other suitable matrix polymers
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include polyacrylates, such as polymethyl methacrylate (PMMA) and
polyethylene methacrylate (PEMA), polyolefins, polyamides, and
polycarbonate. The matrix polymer is preferably an aromatic polyester, such
as PET. The gas barrier material and/or the structural polymer material may
further include a layer adhesion promoting material, e.g., an amine polymer,
such as polyethyleneimine (PEI) polymer. Alternatively, a layer adhesion
promoting additive is not required.
[0008] In various applications, phosphorous is added (to the
reprocess melt) in an amount sufficient to substantially prevent or reduce the
1o amount of yellowing, reduction in melt strength, formation of haze, or
other
loss of thermal stability of the processed mixture when subsequently used in a
melt process to form an article. In various embodiments, plant scrap and/or
previously used articles are ground (e.g., into flake) and the reground
material
can either be compounded (e.g., melt extruded and pelletized) with the
addition of the phosphorous material, or provided as regrind flake and
together with the phosphorous material processed directly by addition/mixing
of the phosphorous material via the feed throat of the injection molding
machine. Yet another approach is production of a masterbatch concentrate
material, such as a pellet formed with a high concentration of phosphorous
material, that is later blended/mixed with the processed mixture. The
processed mixture may optionally be crystallized and dried for ease of
processing. Still further, some or all of the phosphorous may be provided in
the polymer material(s) prior to, during or after the previous melt forming
and
cooling. For example, some or all of the phosphorous may be incorporated in
the material used to make the prior melt formed and cooled article, in
anticipation of the article being reprocessed as a blended material (and thus
at a higher level than may be present for the melt forming of virgin polymer).
[0009] In one embodiment, a method is provided which includes the
steps of providing a processed mixture of polymer material that has been
previously melt formed and cooled, subjecting the processed mixture to an
elevated temperature sufficient to melt the processed mixture, and providing
an amount of a phosphorous material in the melt to enhance a desired
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aesthetic or functional property of the reprocessed mixture in forming an
article from the melt. The method may further include the step of forming the
article.
[0010] In various embodiments, the phosphorous material comprises
a phosphorous atom bound to one or more oxygen atoms. The one or more
oxygen atoms may be bound to an organic substituent, which organic
substituent may include an aromatic moiety. Two or more aromatic moieties
may be bound to the phosphorous atom. The phosphorous material may
comprise one or more of a phosphite, a phosphonite and a phosphate. In one
1 o embodiment, the phosphorous material is a phosphite material having one or
more oxygen atoms bound to an organic substituent, wherein the organic
substituent may include an aromatic moiety.
[0011] In various embodiments, the processed mixture includes a gas
barrier polymer subject to degradation in an aesthetic or functional property
during melt processing. The gas barrier polymer may comprise one or more
of an active barrier and a passive barrier. The processed mixture may include
a structural polymer along with the gas barrier polymer. The structural
polymer may comprise one or more of polyester, polyolefin, polyamide,
polyacrylate, poly(lactic acid), polycarbonate, and copolymers and blends
thereof. The gas barrier polymer may comprise one or more of polyalcohol,
polyamide, polyglycolic acid, acrylonitrile copolymer, cycle olefin copolymer,
polyvinylidiene chloride, and copolymers and blends thereof. More
specifically, the gas barrier polymer may comprise one or more of
polyethylene vinyl alcohol copolymer (EVOH), polyamide in the presence of a
transition metal, and polybutadiene/polyester copolymer in the presence of a
transition metal. In one example the nylon includes meta-xylylene groups.
[0012] In a more specific embodiment, the processed mixture
includes:
= an ester containing polymer and a gas barrier polymer,
= the ester containing polymer comprising one or more of
polyethyleneterephthalate (PET), polyethylenenaptha late (PEN),
polypropylene terephthalate (PPT), poly(lactic acid) (PLA),
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polytrimethylene naphthalate (PTN), and copolymers and blends
thereof, and
= the gas barrier polymer polymer comprising one or more of
polyalcohol, polyamide, polyglycolic acid (PGA), acrylonitrile
copolymer, cyclic olefin copolymer, polybutadiene/polyester
copolymer, polylvinyldine chloride, and copolymers and blends
thereof.
[0013] In various embodiments the article that is melt formed from the
reprocessed mixture is one or more of a package, container, preform, closure,
liner, sheet or film. The article may be a multilayer article that includes
one or
more layers of the reprocessed mixture. It may be a substantially transparent
article and/or a substantially clear article.
[0014] In one embodiment, the processed mixture comprises an ester
containing polymer and a gas barrier polymer, and the article comprises a
multilayer article including at least one layer of the reprocessed mixture and
an adjacent layer of an ester containing polymer. The ester containing
polymer may be an aromatic polyester and the gas barrier polymer a nylon
including meta-xylylene groups.
[0015] In yet another embodiment, the processed mixture includes
polyethyleneimine (PEI). The processed mixture may include PEI and
polyethylene vinyl alcohol (EVOH).
[0016] The processed mixture may comprise regrind, such as flake or
pellet. The regrind and phosphorous material may be melt processed and
pelletized. The melt processing may be performed in a molding machine,
such as an injection or extrusion molding machine. The phosphorous
containing pellets may be melt processed in a molding machine along with
nonphosphorous containing pellets of the processed mixture.
[0017] In various embodiments, the phosphorous material is present
in the melt in an amount sufficient to:
= reduce or eliminate coloring of the reprocessed mixture in the article;
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= reduce or eliminate yellowing of the reprocessed mixture in the
article;
= reduce or eliminate a reduction in melt viscosity of the reprocessed
mixture;
= reduce or eliminate haze in the reprocessed mixture in the article;
= enhance material distribution of the reprocessed mixture in forming a
multilayer article;
= thermally stabilize the reprocessed mixture.
[0018] In various embodiments, the processed mixture includes a
1o structural polymer and a gas barrier polymer, and the reprocessed mixture
forms at least one layer of a multilayer article adjacent to another layer of
the
structural polymer. The amount of structural polymer in the reprocessed
mixture may be sufficient to provide delamination resistance with the adjacent
layer, in the absence of adhesive. The reprocessed mixture in the article is
preferably clear and transparent. The reprocessed mixture may include a
nylon and a structural polymer comprising an aromatic polyester. The
reprocessed mixture may further include a transition metal.
[0019] In another embodiment, an article is formed from a melt
mixture, the melt mixture including a reprocessed mixture of polymer
materials that have been previously melt formed and cooled, and a
phosphorous material is present in an amount sufficient to enhance a desired
aesthetic and/or functional property of the reprocessed mixture in the artice.
[0020] In another embodiment, a composition is provided comprising
a processed mixture of polymer materials that have been melt formed and
cooled, and a phosphorous material is present in an amount sufficient to
enhance a desired aesthetic and/or functional property of the processed
mixture in subsequent melt forming of an article from the processed mixture.
[0021] These and other advantages of several embodiments of the
invention may be better understood by referring to the following detailed
3o description in conjunction with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Fig. 1A is a schematic view of a multilayer preform which
includes reprocessed polymer material according to one embodiment of the
present invention, and Fig. 1 B ia an expanded partial cross-sectional view of
a
multilayer sidewall of the preform;
[0023] Fig. 2A is a schematic view of a blow molded container made
from the preform of Fig. 1 A, and Fig. 2B is an enlarged partial cross-
sectional
view of a multilayer sidewall of the container;
[0024] Fig. 3 is a flow chart illustrating alternative method
embodiments for producing an article having a layer of reprocessed polymer
material according to the present invention;
[0025] Figs. 4A-4D are a series of sequential schematic illustrations
of a method for injection molding a multilayer preform, which includes the
reprocessed material of the present invention;
[0026] Fig. 5A is a graph of "b" value versus thickness (mm),
comparing a degree of yellow color in plaques made from various
reprocessed polymer materials;
[0027] Fig. 5B is a graph of "b" value versus elemental phosphorous
weight percent, comparing two different phosphorous addidtives;
[0028] Fig. 6 shows the melt rheology, a plot of shear viscosity (Pa.s)
versus corrected shear rate (s'), for various reprocessed polymer materials to
illustrate the effect of phosphorous on melt viscosity;
[0029] Fig. 7 is a schematic illustration of another embodiment of a
multilayer preform; and
[0030] Fig. 8 is a chart of haze measurements on plaques made of
various reprocessed polymer materials.
DETAILED DESCRIPTION
[0031] It has been found that adding a phosphorous material to a
mixture of previously melt processed polymer materials, herein the processed
mixture, enables the processed mixture to be reused in a subsequent melt
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process without suffering an undue degradation in one or more aesthetic or
functional properties of the processed mixture either during the subsequent
melt processing or in a subsequently formed article. The phosphorous
containing reprocessed mixture may provide one or more of improved
transparency, melt strength, lack of or reduced color and/or layer
compatibility
in the article formed. Various aspects of the invention, as described in the
embodiments described below, may be used independently and/or in various
combinations to provide compositions, methods and articles in accordance
with the invention.
Processed Mixture of Polymer Materials
[0032] A processed mixture of polymer materials includes two or
more polymers having different chemical structures. For example, an
aromatic polyester (e.g., PET or PEN) and a polyamide (e.g., nylon). Another
example of different polymers would be an aromatic polyester and an aliphatic
polyester (e.g., PGA). Another example is PET and EVOH. Yet another
example is PET and a polybutadiene/polyester based copolymer.
[0033] Polymer material that has been melt formed and cooled as
used herein refers to a polymer material that has been previously melted from
a polymer in its solid form at room temperature, formed (e.g., into a three-
dimensional object or sheet) and then cooled into a formed article.
[0034] The previously melt processed and cooled polymer materials
are typically cleaned/washed, ground up into a bulk flake, or extruded and
formed into pellets or other readily transportable form and then used in a
new,
subsequent forming cycle, such as injection molding, where a mixture
including such polymer material is subjected to a new, subsequent heat
treatment that melts the polymer materials.
[0035] The starting (previously melt processed and cooled) polymer
materials may or may not have previously been mixed with substantial
amounts of other polymer or non-polymer materials, which other materials
may or may not have been subjected to previous melt processing. The
starting polymer material may come from previously formed articles, such as
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preforms, bottles, containers and the like, or manufacturing scrap from making
such articles, and may contain one or more inorganic atoms (such as cobalt,
magnesium, iron, chromium, copper and the like) that were added to the
polymer material for other purposes, such as oxygen scavenging or reduced
gas permeability and the like.
[0036] The starting polymer material may come from a monolithic
article or from one or more layers of a multilayer article, and may include: a
structural polymer material such as polyethylene terephthalate (PET),
polyethylene naphthalate, polycarbonate, poly(lactic acid) (PLA), polystyrene,
lo a polyacrylate (e.g. polymethyl or polyethyl methacrylate), polypropylene,
polyethylene; and one or more layers of another polymer material used as a
functional layer, e.g., oxygen or gas barrier or scavenging polymer layer
containing polyamide (e.g., nylon or meta-xylylenediamine (MXD)),
polybutadiene/polyester based copolymers (e.g., Amosorb ), EVOH or other
material, which may optionally contain a transition metal (e.g. cobalt).
[0037] A "barrier material" as used herein is any material that exhibits
a reduced rate of permeation for a particular substance, such as oxygen or
carbon dioxide, in comparison to another material. A "passive barrier
material" is generally understood to reduce the rate of permeation by blocking
passage of the particular substance, e.g., oxygen or carbon dioxide. An
"active barrier material" is commonly understood to refer to a material having
the ability to consume a particular substance through chemical and/or
physical means. In the context of a closed environment with the active barrier
material present, the consumption of for example molecular oxygen may
eliminate or substantially reduce the net ingress of oxygen into the closed
environment. Moreover, the consumption of molecular oxygen may reduce
the total enclosed amount of molecular oxygen.
[0038] Polymer material as used herein means a homopolymer but
also copolymers thereof, including random copolymers, block copolymers,
graft copolymers, etc. A polymer material may be of a single polymer or a
mixture or blend of multiple polymers; it may further include nonpolymer
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materials added for any of various processing, performance or aesthetic
characteristics.
Aesthetic or Functional Propert
y
[0039] Aesthetic or functional property of a polymer material as used
herein refers to any of various physical properties (e.g., tensile strength,
impact resistance, tear strength), thermal properties (e.g., melt strength,
rate
of crystallization) and/or aesthetic properties (e.g., transparency, color,
gloss).
[0040] Transparent as used herein refers to a polymer material that is
substantially transparent such that the amount of haze (opacity) is not
significantly detectable by unaided human vision. A suitable measure of
transparency is the percent haze for transmitted light through the wall (HT)
which is given by the formula:
HT=[Yd(1'd+YS)1X100
where Yd is the diffuse light transmitted by the specimen, and YS is the
specular light transmitted by the specimen. The diffuse and specular light
transmission values are measured in accordance with ASTM Method D 1003,
using any standard color difference meter such as the UltraScan XE
manufactured by HunterLab Inc. (www.HunterLab.com). Preferably, a
substantially transparent article, such as a beverage container, would have a
percent haze through the sidewall of less than about 15%, and more
preferably less than about 10%.
[0041]Clear as used herein refers to a polymer material that is
substantially lacking in color (e.g., yellow) such that the amount of color is
not
sufficiently detectable by unaided human vision. Preferably, the phosphorous
material is added to the processed polymer materials in an amount sufficient
to reduce the standard HunterLab yellow "b value" of the material to less than
about 5 as measured in a plaque having a thickness of between about 0.5
and about 3.0 mm. A convention for measurement of such "b values" is
3o described in HunterLab application Note, Insight on Color, Vol. 8, No. 9,
pp. 1-
4 (Aug. 1-15, 1996), (available at www.HunterLab.com).
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Phosphorous Material
[0042] One or more phosphorous containing materials having the
following formula can be used as an additive to the starting polymer material
(e.g., regrind) according to various embodiments of the invention: P-(O-R)3 or
Ri-P-(O-R)2 or P-(O-R)4 or Ri-P-(O-R)3 or (Rl)2-P-(O-R)2, where R and R, are
H or an organic substituent, most preferably containing an aromatic moiety.
Specific examples of suitable phosphorous containing compounds are:
CC3 ~ ~ OPO-CHz,C'CHz-O% P-~ P7, CCJ CH CH~ `t7-CHz~ .CHz O/ CH3.I~
s ' C CH3
CH3 ~ ~ 0--"CH3
{It) _ C (CH3~ 3
[(CH~}3C- ~ ~ -a-]3P
C (CH3} 3 O - CHz = ,CH z -- , C (CHO 3
(CH3) C6 0- P C P- a 6 C(CH3)
3
O-CHz CH7--Q
(Iu) C H C?-~O-CHi~C~CH2 - U P-OC~e H3~
,8 37 O- O..~z CH2 - 0 C(CH3) 3 C (CHO 3
(CH3) 3 C o . _ 10 0 C (CH3) 3
tr') _ P P
(CH3~ 3 C ~ ~ O / 0 Q C (CH3) 3
C(CH3} C (CHO 3
[0043] In select embodiments, the phosphorous is added an amount
sufficient to reduce or eliminate discoloration. However, in other
embodiments the phosphorous is added in an amount sufficient to reduce or
eliminate the formation of haze, to reduce or eliminate a loss of melt
viscosity
(or other indicator of melt processability), or otherwise thermally stabilize
(reduce or avoid one or more of the problems identified in paragraph 3 herein)
the previously melt formed and cooled polymer material.
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[0044] Preferred phosphorous containing materials are those having
a phosphorous atom bound to one or more oxygen atoms, one or more of
which are in turn bound to an organic substituent, most preferably an organic
substituent that contains one or more aromatic moieties. The phosphorous
atom is most preferably bound to two or more aromatic moieties either
through an oxygen atom or directly. The phosphorous containing material is
preferably a phosphite, phosphonite or phosphate, most preferably a
phosphite.
[0045] The following phosphorous containing compounds are suitable
examples:
CH3 O-H2. CHz O CH~
~~~t ~ 4PZCc = i. .i'-O v ~ ~ = ~
CH~ ,C=CH3 O-CHZ CHz- CH3, CH
3
CH3 V ~.I CH3
\ f
bis (2,4-dicumylphenyl) pentaerythritol diphosphite, CAS Registry No.
154862-43-8, available as Doverphos S-9228 (7.3 weight percent
phosphorous) from Dover Chemical Corporation, 3676 Davis Road, N.W.,
P.O. Box 40, Dover, OH 44622-0040, USA;
C {CH~} 3
ci~> _
[(CH3)3C- ~ ~ -O-]3P
tris (2,4-di-t-butylphenyl) phosphite, available as Doverphos S-480 from
Dover Chemical Corp., or as Irgafos 168 (4.8 weight percent phosphorous)
from Ciba Specialty Chemicals, Basel, CH;
C(CH3) 3 " O- CHz .. CH2` O. C(CH3) 3
(CH3) C - O- P C P- O b C(CH3) 3
o-CH2 CH2-0
bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite available as Doverphos
S-9432 from Dover Chemical Corp.;
C18 H370-I-,-0 -CH2~CCH2 - Or'P - OCH"
~O-CHz'' ~CH2 - O~,s
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distearyl pentaerythritol diphosphite available as Doverphos S-682 from
Dover Chemical Corp.; and
C(CH3) 3 C (CH3) 3
(CH3) 3 C , , 0 \ _ ~ ~ 0 C (CH3) 3
f ~7 p \L
(CH3) 3C Q~ 0 , O C(CH3) 3
C(CH3) Y C (CH3) 3
tetrakis (2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphonite available as P-
4
from Dover Chemical Corp.
[0046] The phosphorous material, when present in the melt of the
reprocessed mixture, may (without being bound or limited to this theory)
interfere with or reduce degradation between the different polymer materials
and/or other materials that are present in the reprocessed mixture. Thus the
1o phosphorous material can prevent or lessen: a darkening, yellowing or other
color formation; a reduction in viscosity; and/or a formation of haze in the
previously melt processed and cooled polymer materials when subjected to
another heat history in a subsequent melt processing (e.g., extrusion or
injection molding) process.
[0047] Phosphorous is typically added to the processed mixture of
polymer materials as a phosphorous containing additive, and the
phosphorous containing mixture is then reprocessed (the reprocessed
mixture) by melt forming back into subsequently molded articles. Other
polymer or nonpolymer materials may be added to the reprocessed mixture,
before, during and/or after, the melt forming step. In all embodiments
described herein, the amount of elemental phosphorous provided in the
reprocessing melt is based on the weight percentage of the processed
mixture polymer materials (which have been previously melt formed and
cooled, either separately or together).
[0048] The phosphorous would most typically be added to the
processed mixture after the prior melt forming and cooling. It is however also
within the scope of the present invention to provide some or all of the
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phosphorous desired for use in the reprocessed mixture, in the polymer
materials prior to or during the prior melt forming and cooling.
[0049] When phosphorous is provided as part of a phosphorous
containing additive, the mathematical relationship of the weight percentage
elemental phosphorous to the weight of additive can be determined as
follows, where the weight of processed mixture is the amount in the
reprocessing melt:
% elemental phosphorous = Ct' ``d`"Ve X % Paddir,ve
(t)additrve + (t)processedmixhve
w,d;;ve = weight of additive
wprocessedm;.zt,re = weight of processed mixture
% Padd,t,ve = % elemental phosphorous content of the additive.
[0050] Preferably, the phosphorous containing material is added to
the reprocessed mixture in an amount such that the elemental phosphorous
content of the mixture is in a range of from about 0.01 % to about 0.5% by
weight of the processed mixture, and more preferably in a range of from 0.05
to 0.25%. Providing more than the minimum amount of phosphorous required
to achieve a desired aesthetic or functional property is contemplated as being
within the scope of the present invention.
Reuse of Processed Mixture
[0051] In one embodiment of the invention, the processed mixture
comprises a supply of plant scrap or otherwise recycled or previously used
preforms and/or bottles of multilayered or blended polymer materials which
are collected, cleaned, dried and ground up and provided in pellet or flake
form, sometimes referred to herein as "regrind" material. Such multilayered
scrap or previously used articles may typically comprise, for example, one or
more layers of structural polymer material and one or more layers of a
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functional polymer material, e.g. passive gas barrier or active gas barrier
(scavenging) material. Alternatively they may comprise a mixture, blend or
copolymer of such structural and/or functional materials. The weight ratio of
structural (the principal component) to other polymer materials in such
objects
typically ranges from about 60% to about 99% of the structural polymer(s),
more typically from about 80% to about 99%. The functional polymer material
comprises some or all of the remaining weight percent and may comprise a
gas barrier (active or passive) composition, which optionally includes a
transition metal such as cobalt, magnesium, iron, chromium, copper and the
1o like.
[0052] Preferably, the phosphorous material is mixed with the regrind
material (prior to or during melting) and the mixture is melted and cooled to
form a monolithic article or one or more layers or portions of an article,
such
as a preform, bottle, package or other article that packages, contains, houses
or encloses for example a food or beverage. It is noted that the U.S. Food
and Drug Administration has approved the use of phosphorous materials at
weight percentages useful in the present invention. Thus, the phosphorous
and regrind mixture can be provided in direct food contact, e.g., as a
monolithic article or outer layer made from a blend of MXD6, PET and
phosphorous.
[0053] Fig. 1 A shows a multilayer preform 5 having a five-layer
sidewall, namely exterior inner and outer layers 6 and 7, central core layer
8,
and interior intermediate layers 9 and 10 (see the expanded view of Fig. 1 B).
Fig. 2A shows a container 25 blown from the preform 5 having the same five-
layer sidewall with corresponding layers 26-30 (see the expanded view of Fig.
2B). In one such embodiment, the phosphorous containing layer is disposed
among the multiple layers of the bottle or package such that the phosphorous
containing layer does not make physical contact with the food or drink
material that is ultimately packaged or enclosed within the interior space of
the bottle, package or article, e.g., provided as an "interior" layer of the
multilayered preform (layers 8, 9 and/or 10), bottle (layers 28, 29 and/or
30),
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package or other object. An interior layer is any layer that is positioned
between two other layers of polymer materials.
[0054] Fig. 3 shows various method embodiments for forming a
molded article from the processed mixture. In a first step 51, a collection is
made of the previously melt processed articles or scrap. This material is
ground into flake in step 52, and subsequently extruded to form pellets in
step
54. The extruding step may include mixing, extruding and cooling in order to
pelletize the ground flake and make it easier for subsequent handling.
Phosphorous material is added to the extruder in accordance with one
method embodiment (step 53); alternatively, the phosphorus material and
flake may be premixed before introduction to the extruder. The phosphorous
material may be provided in a relatively high or a relatively low
concentration.
In one embodiment, high phosphorous concentration pellets from the extruder
are provided in step 56, along with nonphosphorous containing pellets (step
57), to an injection molding machine (step 58) and used to produce a molded
article (step 59). In alternative embodiments, low phosphorous concentration
pellets (step 60) are added alone to an injection molding machine (step 61) to
form a molded article (step 59). In another alternative embodiment, the
pelletizing/extrusion step 54 may be eliminated, and instead phosphorous
material (step 62) and regrind flake (step 52) are added directly to the
injection molding machine (step 63), in order to injection mold an article
(step
59).
[0055] In a further alternative embodiment, the pellets are first
crystallized and dried before being introduced into the injection molding
machine. In some cases, amorphous polymer material which is capable of
being crystallized is more difficult to process because as it approaches the
glass transition temperature it enters a rubber-like or glue-like state which
makes it difficult to handle. One solution is to first crystallize the pellets
to
make them easier to handle during injection molding.
[0056] A monolithic or multilayer article may be made which includes
the processed mixture according to any of various known melt forming
methods, such as injection or extrusion. The article may take any form, such
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as a sheet, film, closure (e.g., cap) or other shaped article. A multilayer
article
which includes one or more layers of the phosphorous containing mixture may
be made according to any of various known injection or extrusion methods
which include sequential, simultaneous and/or combinations thereof. Other
materials may be added to the processed mixture and included in the
subsequently formed article.
[0057] One exemplary multilayer injection molding process, which
may be used to form a five-layer preform such as shown in Fig. 1A, is shown
schematically in Figs. 4A-4D. A preform is formed in a mold cavity 15
between an outer mold and core (not shown) of a conventional injection mold.
A first shot of first polymer material 18 is injected into the lower end
(gate) of
the mold cavity and as it flows through the mold cavity, due to the relatively
cool temperatures of the outer mold and inner core, there will be
solidification
of the first polymer material both externally and internally of the mold
cavity to
define exterior inner and outer layers (layers 6 and 7 in Fig. 1 B) of the
first
material. In Fig. 4A, the relatively large volume of first material has
progressed part way (roughly half way) up the mold cavity walls. As shown in
Fig. 4B, a second shot of a second polymer material, e.g., a barrier material,
is injected into the bottom of the mold cavity. The relatively small amount of
barrier material 20 may pool at the lower end of the cavity. A relatively
large
third shot of a third polymer material 22 is then injected into the gate at a
pressure which causes the second shot material 20 to be pushed up the mold
cavity and form inner and outer intermediate layers (9, 10 in Fig. 1 B) of the
preform, while the third material 22 forms a central core layer (layer 8 in
Fig.
1 B). The tunnel flow of the second and third shots, between the exterior
layers 6 and 7, enables the formation of relatively uniform and thin interior
layers 9 and 10 of the barrier material 20, and a thicker layer of material 22
in
the core layer 8. Finally, the advancing layers reach the end of the mold
cavity, producing the five-layer preform structure having interior
intermediate
3o and core layers extending up into the neck finish (as shown in Fig. 4D).
Alternatively, the interior layers 8, 9 and 10 may extend only partially up
the
preform wall and terminate, for example, below the preform neck finish 4.
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This process is described by way of example only, and it not meant to be
limiting; many other processes may be used to form multilayer articles,
including articles other than preforms. Typical examples of multilayered
preforms, bottles and packages, the compositions of the various layers of
such multilayer objects, and methods of making such objects are disclosed in
U.S. Patent Nos. 4,781,954; 4,863,046; 5,599,496; and 6,090,460,
disclosures of all of the foregoing of which are incorporated herein by
reference.
[0058] Several more specific embodiments of the invention will now
1o be described for enhancing one or more aesthetic or functional properties
of
the reprocessed mixture for use in a subsequently melt formed article.
Enhancing Regrind Color
[0059] Plastic containers and preforms comprising multiple polymer
materials are now in widespread commercial use for the packaging of food
and beverages. For packaging of oxygen-sensitive products, such as juice,
ketchup and beer, a polyamide, such as meta-xylylenediamine (MXD) or
2o nylon-6, is often used as an oxygen barrier either alone or in combination
with
a transition metal; other barrier materials/mixtures include ethylene vinyl
alcohol copolymer (EVOH), and copolymers of polyester and polybutadiene in
the presence of a transition metal (e.g., Amosorb ).
[0060] During commercial production there is typically generated a
certain amount of scrap material which would be desirable to reuse.
However, the reuse of such materials in large quantities has not been
possible due in part to excessive yellowing that occurs when the previously
melt processed and formed (e.g., injection molded) material is subjected to a
second heat history, i.e., subsequent melting and cooling to form another
article. It would be desirable to recycle both scrap material and previously
used containers, if not for this problem of excessive yellowing during
subsequent melt processing.
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[0061] In accordance with the present invention, this problem can be
solved by incorporating phosphorous material into the polymer reprocessing
stream, which eliminates or substantially reduces yellowing and brings the
properties of the reprocessed material to values approaching that of virgin
polymer material (as supplied by the polymer resin manufacturer with defined
thermal and physical properties). The reprocessed polymer material thus
treated with the addition of phosphorous can for example be used in a
monolithic or one or more layers of a subsequent injection melt processed
article alone or as a mixture or blend with other polymers and materials.
[0062] In one embodiment, the (previously) processed mixture of
polymer materials is plant scrap and/or previously used monolayer blend
and/or multilayer containers which include as a principal component an ester
containing polymer, a polyamide and optionally a transition metal. In this
example, the previously melt processed mixture is a pelletized regrind made
from multilayer container and preform articles comprising 97 weight percent
by total weight of the article of polyethylene terephthalate (PET), 3 weight
percent MXD6, and cobalt added as 0.25 weight percent cobalt neodecanoate
based on the weight of the MXD6 (hereinafter the "PET/3%MXD6/Co
regrind"). Virgin 8006 PET resin from M&G of Tortona, Italy was used to
make the original preforms/containers. The phosphorous material in this
example is Doverphos S-9228, comprising bis(2,4-dicumylphenyl)
pentaerythritol diphosphite, CAS Registry No. 154862-43-8, having the
structural formula:
CCH2Q,
n~ CC3 CH3
P-
~ r C! C
~ T
~CH 0' '~
r ~ CH ~O-CH "
CH3 C~ 3 2 2 C31C CH3
CH3 ~ 'CH3
1 ! ~
available from Dover Chemical Corporation, 3676 Davis Road, N.W., P.O.B.
40, Dover, OH 44622-0040, USA. Phosphorous is added to the
PET/3%MXD6/Co regrind and the phosphorous containing regrind is
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reprocessed (the reprocessed mixture) by melt forming back into
subsequently molded articles (e.g., preforms and containers).
[0063] In similar embodiments, the original barrier preforms and
containers (used to form the regrind) may comprise from up to 15%, and more
typically 1% to 2% by weight of one or more barrier polymer(s), and the
remaining 80-99% of one or more structural polymer(s). The subsequently
formed preform/container may include the reprocessed mixture in one or more
layers, with for example 1 to 50 weight percent of the article being of the
reprocessed mixture, and more preferably 5 to 40 weight percent.
1o Alternatively the reprocessed mixture is provided in a blend at a weight
percent in a range of 10 to 30 of the article weight, more preferably 15 to 25
weight percent.
[0064] The phosphorous material is preferably added to the
processed mixture (e.g., PET/3%MXD6/Co regrind) in an amount sufficient to
reduce the standard HunterLab yellow "b value" of the material to less than
about 5 as measured in a plaque having a thickness of between about 0.5
and about 3.0 millimeter (mm). A convention for measurement of such "b
values" is described in the HunterLab Color Scale Applications Note of August
1-15, 1996, Vol. 8, No. 9, available from Hunter Associates Laboratory, Inc.,
11491 Sunset Hills Road, Reston, VA 22090, USA.
[0065] Fig. 5 shows the effect on the b value of varying amounts of
phosphorous material, for plaque samples having a thickness ranging from 1
to 3.5 mm. The graph provides a comparison of b values (across the plaque
thickness range set forth on the horizontal scale) for:
a) virgin 8006 PET (70);
b) processed 8006 PET (previously melt formed and cooled, before
being melt processed (injection molded) to form a plaque) (71);
c) pelletized PET/3%MXD6/Co regrind (previously melt formed articles
of PET, 3% MXD6 and 0.25% cobalt neodecanoate as previously described
were subjected to two subsequent heat histories, namely a first melt
processing comprising twin-screw extrusion and pelletizing and a second melt
processing comprising melting of the pellets and injection molding to form a
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plaque) (72);
d) pelletized PET/3%MXD6/Co regrind (same as c) but with 0.1 %
Doverphos S-9228 (7.3% P by weight) added as the phosphorous material to
the melt during plaque formation (73);
e) pelletized PET/3%MXD6/Co regrind (same as d) but with 0.25% S-
9228 (74); and
f) pelletized PET/3%MXD6/Co regrind (same as d) but with 0.5% S-
9228 (75).
As shown in Fig. 5, the virgin 8006 PET (70) has the lowest b value. It would
1 o be desirable to attempt to match the b value of the regrind with the low b
value of the virgin PET, so that a subsequently formed article of, for
example,
the virgin 8006 PET and regrind has substantially the same non-yellow (low b
value) as would an article processed from virgin 8006 PET. The regrind
without phosphorous (72) having been (subsequently) melt processed twice,
has the highest b value (least desirable), higher than the processed 8006 PET
(71) (subsequently melt processed once). All three samples of regrind
(subsequently melt processed twice) with varying amounts of phosphorous
(73, 74, 75) have lower values than both the processed 8006 (71), and the
regrind without phosphorous (72). Here, the b value improves (approaches
that of virgin 8006 PET) with increasing amounts of phosphorous (0.1, 0.25
and 0.5% S-9228).
[0066] This example shows that it is possible to reduce or
substantially eliminate the undesirable yellowing which occurs during
subsequent melt processing of the processed mixture.
[0067] Fig. 5B compares the "b" value results for two phosphorous
additives compounded into the regrind at different levels and normalized to
their elemental phosphorus content. Additive I is Doverphos S-9228 (7.3% P
by weight), and Additive II is Irgafos 168 (4.8% P by weight). The regrind is
the same PET/3%MXD6/Co regrind previously described. The b value was
measured on the actual pellets as compounded, as compared to measuring
the b value on plaques molded from the pellets. The regrind was dried to
about 50ppm residual moisture content prior to melt compounding, as is
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typical in the art. The regrind was formed into pellets utilizing a Coperion
ZSK
25mm co-rotating intermeshing twin screw extruder, made by Coperion
Wemer & Pfleiderer GmbH & Co KG, Theodorstrasse 10, 70469 Stuttgart,
Germany. The melt temperature in the extruder was 280 C. The b value was
measured with HunterLab equipment according to the HunterLab process
previously described.
[0068] Fig.5B shows substantially similar behavior regardless of the
phosphorous source.
Layer Compatibility
[0069] According to another embodiment of the invention, the
phosphorous containing mixture (reprocessed mixture) can be provided in one
or more layers of a multilayer article having a desired layer integrity and
layer
adherence for a given application. Layer adherence and integrity is generally
a function of the melt viscosity of a polymer material. Melt viscosity can be
represented by a melt rheology curve, namely a plot of shear viscosity versus
shear rate as shown in Fig. 6 (discussed further below).
[0070] Measurement of the melt viscosity of polymers is generally
well known in the art and a number of standardized tests are in use, such as
those detailed in ASTM D3835 and ISO 11443. In the results presented in
Fig. 6, the melt viscosity of the examples was measured at a variety of shear
rates spanning the range of about 1,000 sec 1 to about 12,000 sec"' at a
280 C melt temperature on a Rosand RH 2000 series capillary melt
rheometer, utilizing a 1 mm x 16mm capillary die (Bohlin Instruments, East
Brunswick, NJ, USA, www.bohlinusa.com). As is typical practice in the art,
the well known Rabinowitsch corrections were applied to the apparent shear
rates and the corrected shear rates are utilized on the horizonal-axis in Fig.
6.
The following reference can be consulted for further information: Macosko,
C.W. "Rheology: Principles, Measurements, and Applications," VCH
Publishers (1994) pp. 242-244.
[0071] The polymers as used herein are generally high molecular
weight polymers, having a molecular weight of at least 20,000 Daltons, for
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which the melt viscosity is an important process parameter. Generally, as the
molecular weight of the polymer increases, the melt viscosity increases. For
multilayer applications, those skilled in the art can determine an appropriate
combination of melt viscosity and melt strength for a layer of the reprocessed
mixture (phosphorous containing mixture) positioned adjacent to one or more
layers of other polymer materials.
[0072] Where one or more layers are positioned adjacent a layer of
the reprocessed mixture in the absence of an adhesive (e.g., an additive for
promoting layer adherence, provided either as a separate layer or within one
or more of the adjacent layers), it is preferred that the two layers "be
compatible." Compatibility implies that the multilayer article have the
structural integrity to withstand delamination, observable deformation from a
desired shape or other degradation of a layer caused by a chemical or other
process initiated by an adjacent layer during the article forming process
and/or in the final article during respective use. Compatibility can be
enhanced by selecting melt viscosities, melt indices, and/or solubility
parameters that allow one of ordinary skill in the art to achieve a desired
package characteristic.
[0073] In accordance with one embodiment, a phosphorous material
is added to the previously melt processed polymer materials to avoid an
undesired change in melt viscosity during subsequent melt processing.
Generally, it is desired to approach (a perfect match is not required) a melt
viscosity of an adjacent layer, whereby the reprocessed polymer mixture has
sufficient melt strength to spread the reprocessed mixture substantially
evenly
in a layer of a multilayer article.
[0074] Fig. 6 shows the beneficial effect on melt viscosity by the
addition of the phosphorous material. Fig. 6 is a graph of shear viscosity
(Pa.s) versus corrected shear rate (s') for each of the following examples:
a) virgin 8006 PET (80);
b) PET/3%MXD6/Co regrind (one subsequent heat history) without
phosphorous added (81); and
c) PET/3%MXD6/Co regrind (same as b) but with 1 % Doverphos S-
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9228 (7.3% P by weight) added as the phosphorous material (82).
The PET/3%MXD6/Co regrind is the same regrind previously described and
was subjected to an additional heat history - melt processing in a twin
extruder, cooling and pelletizing followed by measurement in the melt
rheometer. As shown in Fig. 6, the virgin 8006 PET (80) has the highest
shear viscosity. There is a drop in shear viscosity when the previously
processed regrind is melt processed without the phosphorous material (81).
Adding the phosphorous material (82) improved (increased) the shear
viscosity to approach that of the virgin polymer (80). Thus, addition of the
1o phosphorous material can be used to obtain a desired layer compatibility
with
an adjacent layer in a subsequently melt processed multilayer article.
[0075] Preferably, the amount of phosphorous added is sufficient to
raise or maintain the shear viscosity value of the reprocessed mixture to a
value that is not less than 40% of the shear viscosity value of an adjacent
layer polymer material (e.g., virgin PET, which has not been previously melt
formed and cooled), when measured at a Rabinowitsch corrected shear rate
of 2000 sec' and at a melt temperature of 280 C by capillary melt rheometry
(as previously described).
2o Enhanced Transparency (Decreased Haze)
[0076] In yet another embodiment, it has been found that the addition
of the phosphorous material enables reuse of a mixture of previously melt
formed and cooled polymer materials with a significant reduction in the
amount of haze (opacity) that would otherwise form during the subsequent
melt processing.
[0077] In this embodiment, the invention is directed to eliminating or
reducing haze when the regrind is used to form a subsequently melt
processed article (e.g., to form injection molded preforms), thus subjecting
the
regrind polymer material to one or more additional heat histories. The
phosphorous material is added in an amount so as to decrease the rate of
crystallization of the regrind polymer material, thus enabling the regrind to
be
formed into a subsequently melt processed article with decreased formation of
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haze. This is particularly useful with relatively thick articles, which
because of
their increased thickness have a tendency to cool more slowly and thus are
more likely to have a problem with haze formation; also, interior layers in a
multilayer article are more likely to have a problem with haze due to slower
cooling. By way of example, the reprocessed mixture may be used in a two-
material three-layer (2M, 3L) preform 40 (see Fig. 7), where the reprocessed
mixture forms a core layer 42 of about 20-60 weight percent of the preform
(more specifically 40%), and the exterior inner and outer layers 44 and 46
form the remaining 40-80% of the preform weight.
[0078] Fig. 8 shows the results of haze measurements as percent
haze in a 1 mm thickness plaque, for the following four samples:
a) PET/3%MXD6/Co regrind (same as previously described);
b) same regrind as in a) but with 0.25% Doverphos S-9228 (7.3% P by
weight) added as the phosphorous material to the melt during plaque
formation;
c) same regrind as b) but with 0.5% S-9228; and
d) same regrind as b) but with 0.75% S-9228.
The results show decreasing haze with increasing phosphorous content.
[0079] These and other modifications would be readily apparent to
the skilled person as included within the scope of the following claims.
26
