U.S. patent application number 10/301140 was filed with the patent office on 2003-07-03 for multilayer structures of poly(1,3-propylene 2,6-naphthalate and poly ethylene terephthalate).
Invention is credited to Lee, Ross A., Ng, Howard Chung-Ho, Subramanian, Pallatheri M..
Application Number | 20030124280 10/301140 |
Document ID | / |
Family ID | 22512168 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030124280 |
Kind Code |
A1 |
Subramanian, Pallatheri M. ;
et al. |
July 3, 2003 |
Multilayer structures of poly(1,3-propylene 2,6-naphthalate and
poly ethylene terephthalate)
Abstract
Multilayer shaped articles, including films, preforms and
containers, and method for forming the same, having at least one
layer of poly(1,3-propylene 2,6-naphthalate) and at least one layer
of poly(ethylene terephthalate). Poly(1,3-propylene
2,6-naphthalate) can be co-stretched with poly(ethylene
terephthalate) to form oriented multilayer structures which have
superior barrier properties. The poly(1,3-propylene
2,6-naphthalate) and poly(ethylene terephthalate) layers have good
adhesion and do not require an adhesive tie layer.
Inventors: |
Subramanian, Pallatheri M.;
(Hockessin, DE) ; Ng, Howard Chung-Ho; (Kingston,
CA) ; Lee, Ross A.; (Chesapeake City, MD) |
Correspondence
Address: |
E. I. du Pont de Nemours & Company
Legal - Patent
1007 Marker Street
Wilmington
DE
19894
US
|
Family ID: |
22512168 |
Appl. No.: |
10/301140 |
Filed: |
November 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10301140 |
Nov 21, 2002 |
|
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09145230 |
Sep 1, 1998 |
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Current U.S.
Class: |
428/35.7 ;
264/173.16; 264/235.8; 264/290.2; 264/515 |
Current CPC
Class: |
B29C 2949/303 20220501;
B32B 37/153 20130101; B29C 2949/3028 20220501; B29K 2067/00
20130101; B29C 2949/3008 20220501; B29C 2949/3034 20220501; B32B
1/02 20130101; B29K 2995/004 20130101; B32B 27/08 20130101; B29C
2949/3038 20220501; B29C 49/0005 20130101; B29C 2949/22 20220501;
B29C 2949/3014 20220501; Y10T 428/31797 20150401; Y10T 428/1352
20150115; B29C 2949/3012 20220501; B29C 2949/3016 20220501; B29C
2949/3036 20220501; B32B 27/36 20130101; B29C 49/22 20130101; B29C
2949/0872 20220501; B29C 2949/0829 20220501; B29C 2949/24 20220501;
B29C 2949/3026 20220501; B29K 2023/12 20130101; Y10T 428/31938
20150401; B29C 2949/0811 20220501; B29C 2949/0819 20220501; B29C
2949/302 20220501; B32B 2439/70 20130101; B32B 2439/60 20130101;
B32B 2038/0028 20130101 |
Class at
Publication: |
428/35.7 ;
264/173.16; 264/235.8; 264/290.2; 264/515 |
International
Class: |
B32B 001/02; B29C
047/06; B29C 049/04; B29C 049/22; B29C 055/12 |
Claims
What is claimed is:
1. A multilayer film or preform comprising at least a first resin
layer and a second resin layer wherein the first resin layer
comprises poly(1,3-propylene 2,6-naphthalate) and the second resin
layer comprises poly(ethylene terephthalate).
2. A multilayer film according to claim 1 wherein the film is
oriented in at least one direction.
3. The multilayer film of claim 2 wherein the film is biaxially
oriented.
4. A multilayer hollow structure having a sidewall with an inner
surface and an outer surface, the sidewall comprising at least a
first resin layer and a second resin layer wherein the first resin
layer comprises poly(1,3-propylene 2,6-naphthalate) and the second
resin layer comprises poly(ethylene terephthalate), and at least a
portion of the sidewall is oriented in at least one direction.
5. The multilayer hollow structure of claim 4 wherein at least a
portion of the sidewall is biaxially oriented.
6. The multilayer hollow structure of claim 5 wherein the inner
surface comprises the poly(ethylene terephthalate) layer and the
outer surface comprises the poly(1,3-propylene 2,6-naphthalate)
layer.
7. The multilayer hollow structure of claim 4 further comprising a
third resin layer comprising poly(ethylene terephthalate) wherein
the inner and outer surfaces comprise the poly(ethylene
terephthalate) layers and the poly(1,3-propylene 2,6-naphthalate)
forms a core layer between the inner and outer poly(ethylene
terephthalate) layers.
8. A process for forming a biaxially oriented multilayer film
comprising the steps of: co-extruding at least first and second
resin layers wherein the first resin layer comprises substantially
amorphous poly(1,3-propylene 2,6-naphthalate) and the second resin
layer comprises substantially amorphous poly(ethylene
terephthalate); and biaxially stretching the co-extruded film at a
temperature of from about 90.degree. C. to about 115.degree. C.
9. The process of claim 8 wherein the film is biaxially stretched
at a temperature of from about 100.degree. C. to about 110.degree.
C.
10. The process of claim 9 further comprising the step of
heatsetting the film at a temperature of from about 160.degree. C.
to about 180.degree. C. after the step of biaxial stretching.
11. A process for forming a hollow container comprising the steps
of: forming a multilayer preform comprising at least a first resin
layer and a second resin layer wherein the first resin layer
comprises substantially amorphous poly(1,3-propylene
2,6-naphthalate) and the second resin layer comprises substantially
amorphous poly(ethylene terephthalate); and blow molding the
preform at a temperature of from about 90.degree. C. to about
115.degree. C.
Description
CROSS REFERENCED TO RELATED APPLICATION
[0001] This application is a continuation of co-pending application
Ser. No. 09/145,230, filed Sep. 1, 1998, which is hereby
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to multilayer shaped articles
including films, preforms and structures made therefrom, comprising
at least one layer of poly(1,3-propylene 2,6-naphthalate) and at
least one layer of poly(ethylene terephthalate). Multilayer
biaxially oriented films and containers are useful in food
packaging end uses.
[0004] 2. Description of Related Art
[0005] Polyethylene terephthalate (PET) is widely used in the
production of containers, especially beverage bottles, due to its
excellent impact resistance, rigidity, gas barrier properties,
light weight, and transparency. However, further improvements in
gas barrier properties are desirable to increase the shelf life of
products packaged in polyester bottles and films.
[0006] It has been proposed in the art to use containers composed
of laminated layers for improved barrier properties. For example,
multilayer bottles comprising inner and outer layers of
polyethylene terephthalate, an intermediate layer of an
oxygen-barrier resin, and adhesive layers interposed between
adjacent layers are disclosed in Nohara et al, U.S. Pat. No.
4,741,936. Anderson U.S. Pat. No. 5,324,467 discloses oriented
multilayer laminated films having at least three layers comprising
polypropylene, an adhesive of a polar modified polyolefin, and a
copolyester. Hosoi, et al. Japanese Kokai published patent
application 5-131602 discloses laminated films comprising two resin
layers, wherein each resin layer comprises a different polyester
composition, and further including an intermediate tie layer
comprising a copolymer of the two different polyester compositions.
Preferred polyesters are poly(ethylene terephthalate),
poly(ethylene 2,6-naphthalate) (PEN), and
poly(1,3-cyclohexylenedimethylene terephthalate). The films are
useful for high-density magnetic recording media. Use of the
intermediate copolymer layer overcomes the problems of interlayer
delamination and curling which can occur in certain multilayer
structures, especially in flat films. The absence of this tie layer
in PET/PEN multilayer films results in a lack of a adhesion between
the PET and PEN layers, which leads to delamination and
curling.
[0007] Matsubayashi et al. Japanese granted patent Kokoku 1-26940
discloses a polyester multilayer hollow molding made from a
laminate of at least two layers where one of the layers is PET and
another is PEN. The hollow moldings are obtained by blow expansion
of a multilayer preform at a temperature above the glass transition
temperature (T.sub.g) of the poly(ethylene naphthalate) but below
the crystallization temperature (T.sub.c) of the poly(ethylene
terephthalate). In the Examples, blow molding was conducted at
temperatures between 120 and 140.degree. C. Because of the higher
T.sub.g of PEN (between about 113.degree. C. and 125.degree. C.)
relative to the T.sub.g of PET (between about 70.degree. C. and
80.degree. C.), the process described in the Matsubayashi et al.
application requires the blow molding to be done at a temperature
that is higher than the optimum processing temperature for PET,
which is between about 90.degree. C. and 115.degree. C. Processing
at the higher temperatures required by Matsubayashi et al. results
in a reduction in strain orientation in the PET layer and a
corresponding reduction in physical properties such as tensile
strength. If the molding temperature was below the T.sub.g of PEN,
poor transparency and gas barrier properties resulted, as shown by
Comparative Example 2. Comparative Example 3 demonstrates that when
blow-molding was done at 100.degree. C. that there was significant
thickness variation in the bottle body sidewall making blow molding
impossible.
[0008] Collette et al. U.S. Pat. No. 5,628,957 teaches that in the
presence of a PEN-rich layer that PET cannot be used as a co-layer
in blow molding because the orientation temperature of PET is much
lower than that for PEN (minimum of 127.degree. C.). At this
temperature or above, the PET would begin to crystallize and no
longer undergo strain hardening, and the resulting container would
be opaque and have insufficient strength. Collette et al. overcomes
the problem of the different processing requirements of PEN and PET
by providing a multilayer preform and container having at least one
layer of PEN which may be a homopolymer, copolymer, or blend and a
core layer which comprises a non-strain-hardenable polyester such
as a low-copolymer PET. The core layer can be blow molded at
temperatures and stretch ratios required for enhancing the physical
properties of PEN by strain orientation and crystallization.
Suitable core layers disclosed in this patent include copolymers of
PET and cyclohexane dimethanol (PETG), and blends of PETG and
PEN.
[0009] Multilayer structures which comprise layers which can be
co-stretched, for example during blow molding or film stretching
processes, at temperatures that provide improved mechanical and
barrier properties, and which do not require an intermediate
adhesive tie layer, would represent an improvement over those
disclosed in the art.
SUMMARY OF THE INVENTION
[0010] The present invention overcomes the problems described above
by providing improved multilayer shaped articles such as films,
preforms, and hollow containers comprising at least a first resin
layer and a second resin layer wherein the first resin layer
comprises poly(1,3-propylene 2,6-naphthalate) (3GN) and the second
resin layer comprises poly(ethylene terephthalate).
[0011] Multilayer films and preforms of the current invention can
be biaxially stretched at optimum PET processing temperatures
(90-115.degree. C.) to provide oriented films and other structures
such as bottles having excellent mechanical, optical, and barrier
properties. In addition, the multilayer films have excellent
adhesion between the 3GN and PET layers, without problems of
delamination and curling and do not require an adhesive tie layer
between the 3GN and PET layers.
[0012] One or more additional resin layers can be present wherein
the additional layers comprise 3GN or PET or other polymeric
compositions which can be co-stretched with 3GN and PET at
temperatures between about 90.degree. C. and about 115.degree.
C.
[0013] In a process for forming oriented films, a substantially
amorphous multilayer 3GN/PET film is formed, for example by
coextrusion of the 3GN and PET layers, followed by stretching
uniaxially or preferably biaxially at a temperature between about
90.degree. C. and 115.degree. C.
[0014] The films are generally heat set at a temperature of about
160.degree. C. to about 180.degree. C. after stretching.
[0015] Hollow containers, such as bottles, can be formed by first
forming a multilayer 3GN/PET preform followed by blow molding at a
temperature of from about 90.degree. C. to about 115.degree. C.
Other methods known in the art which do not require formation of a
preform to form multilayer shaped articles can also be used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a sectional view showing an injection molded
multilayer preform used in the current invention.
[0017] FIG. 2 is a sectional view showing a bottle made by blow
molding the multilayer preform of FIG. 1.
[0018] FIG. 3 is an enlarged fragmentary view taken along the
section line 3-3 of FIG. 2 showing the inner layer of PET and the
outer layer of 3GN.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] The current invention is a multilayer shaped article such as
a film, hollow container, preform or article formed therefrom
wherein at least one layer is formed from poly(1,3-propylene
2,6-naphthalate) and at least one other layer is formed from
poly(ethylene terephthalate).
[0020] Poly(1,3-propylene 2,6-naphthalate) contains repeating units
of the formula 1
[0021] and can be prepared using methods known in the art including
transesterification of a dialkyl ester of 2,6-naphthalene
dicarboxylic acid and 1,3-propanediol or direct esterification of
2,6-naphthalene dicarboxylic acid and 1,3-propanediol followed by
polycondensation. For example, in a batch process, a
C.sub.1-C.sub.4 dialkyl ester of 2,6-naphthalene dicarboxylic acid
and 1,3-propanediol are reacted in an inert atmosphere such as
nitrogen in a mole ratio of about 1:1.2 to about 1:3.0 in the
presence of a transesterification catalyst at a temperature between
about 170.degree. C. and 245.degree. C. at atmospheric pressure to
form a monomer and a C.sub.1-C.sub.4 alkanol corresponding to the
C.sub.1-C.sub.4 alkanol components of the dialkyl ester of
2,6-naphthalene dicarboxylic acid. The C.sub.1-C.sub.4 alkanol is
removed as it is formed during the reaction. Examples of
transesterification catalysts include compounds of manganese, zinc,
calcium, cobalt, titanium, and antimony such as Mn(acetate).sub.2,
Zn(acetate).sub.2, Co (acetate).sub.2, tetrabutyl titanate,
tetraisopropyl titanate, and antimony trioxide. The resulting
reaction product, comprising bis(3-hydroxypropyl) 2,6-naphthalate
monomer and oligomers thereof, is then polymerized at temperatures
between about 240.degree. C. and 280.degree. C. under a reduced
pressure of below about 30 mm Hg in the presence of a
polycondensation catalyst, with removal of excess 1,3-propanediol,
to form 3GN having an inherent viscosity in the range of 0.2-0.8
deciliter/gram (dL/g). Examples of suitable polycondensation
catalysts include compounds of antimony, titanium, and germanium
such as antimony trioxide, tetrabutyl titanate, tetraisopropyl
titanate. A titanium catalyst can be added prior to
transesterification as both the transesterification and
polycondensation catalyst. The transesterification and
polycondensation reactions can also be carried out in continuous
processes.
[0022] The inherent viscosity of the 3GN can be further increased
using conventional solid phase polymerization methods. Particles of
3GN having an inherent viscosity of about 0.2-0.7 dL/g can
generally be solid phased to an inherent viscosity of 0.7-2.0 dL/g
by first crystallizing at a temperature of between about
165.degree. C. and 190.degree. C. for at least about 6 hours,
preferably about 12-18 hours, followed by solid phase polymerizing
under an inert atmosphere, such as a nitrogen purge, at a
temperature of between about 190.degree. C. to 220.degree. C.,
preferably between about 195.degree. C. to 205.degree. C., for at
least about 12 hours, preferably 16-48 hours. The solid phase
polymerization of the 3GN particles may also be conducted under a
vacumm of about 0.5-2.0 mm Hg.
[0023] Other comonomers can be included during the preparation of
the 3GN. For example, one or more other diol (other than
1,3-propanediol), preferably in an amount up to about 10 mole %
based on total diol (including 1,3-propanediol and the other diol),
and/or one or more other dicarboxylic acid or C.sub.1-C4 dialkyl
ester of a dicarboxylic acid (other than 2,6-naphthalene
dicarboxylic acid and C.sub.1-C.sub.4 diesters thereof), preferably
in an amount up to about 10 mole % based on the total diacid or
dialkyl ester (including the 2,6-naphthalene dicarboxylic acid or
C.sub.1-C.sub.4 diakyl ester thereof and the other dicarboxylic
acid or C.sub.1-C.sub.4 dialkyl ester thereof) can be added before
or during the esterification or transesterification reaction.
Examples of comonomers which can be used include terephthalic acid
or isophthalic acid and C.sub.1-C.sub.4 diesters thereof, and
C.sub.1-C.sub.10 glycols such as ethylene glycol, 1,4-butanediol,
and 1,4-cyclohexane dimethanol. Blends of 3GN with up to about 5
mole % other polymers, including other polyesters can also be used
so long as the blends formed provide transparent blow molded
structures and films.
[0024] Polyethylene terephthalate suitable for use in the current
invention is available from a number of commercial sources
including E. I. du Pont de Nemours and Company, of Wilmington, Del.
and can be prepared from ethylene glycol and dimethyl terephthalate
or terephthalic acid using methods known in the art. Post-consumer
PET can also be used. Polyethylene terephthalate containing up to
about 10 mole % of other comonomers can also be used. For example,
up to 10 mole % isophthalic acid or a C1-C4 diester thereof (based
on total diacid or diester) and/or up to 10 mole % 1,4-cyclohexane
dimethanol (based on total diol) can be added during the
polymerization. Blends of PET with up to about 5 mole % of other
polymers, including other polyesters can also be used so long as
the blends formed provide transparent blow molded structures and
films.
[0025] Poly(1,3-propylene 2,6-naphthalate) has a unique combination
of properties that provides a number of advantages over
poly(ethylene 2,6-naphthalate) when used in multilayer films which
include at least one layer of poly(ethylene terephthalate). 3GN has
a lower melting point (between about 181-213.degree. C.) than PEN
(between about 264-267.degree. C.) and PET (between about
250-256.degree. C.) but its glass transition temperature (about
79.degree. C. for unstretched films and about 94.degree. C. for
fully oriented films) is similar to that for PET (about 70.degree.
C. for unstretched films and about 80.degree. C. for fully oriented
films). The preferred orientation temperature for 3GN and 3GN rich
copolymers and blends is between about 90.degree. C.-135.degree.
C., compared to a preferred orientation temperature for PET of
between about 90.degree. C.-115.degree. C., thus allowing 3GN to be
biaxially oriented under optimum thermal stretching conditions for
PET, e.g. between about 90.degree. C.-115.degree. C. On the other
hand, PEN has a significantly higher glass transition temperature
(about 113-125.degree. C. for unstretched films and up to about
140.degree. C. for fully oriented films) and requires higher
orientation temperatures, e.g. about 120-150.degree. C. In PEN/PET
multilayer laminates, this results in uneven thickness, opaqueness,
and poor strength for the oriented PET layer due to a reduction in
strain hardening during stretching of PET at the higher
temperatures.
[0026] In addition to the advantage of the lower Tg of 3GN, which
allows the processing of 3GN/PET structures at temperatures at
which the PET layer does not crystallize and has good transparency,
3GN also has a slow crystallization rate, which is slower than the
crystallization rate of PEN. This results in the 3GN layer being
more amorphous and translates into improved transparency of the 3GN
layer in blow molded and extruded articles and may also account for
the improved adhesion with PET in the multilayer structures versus
PEN. In addition, 3GN has excellent barrier properties and is
therefore useful as a barrier layer in PET films and
containers.
[0027] Unoriented multilayer films of the current invention can be
formed using methods known in the art including coextrusion of the
one or more layers of 3GN and PET as described in the Encyclopedia
of Polymer Science and Engineering, 2nd Edition, Vol. 6, John Wiley
and Sons, N.Y. (1986) pages 608-613. Alternatively, the multilayer
films can be formed in a continuous lamination process, either
in-line with the film-forming process (e.g. extrusion) or in a
separate off-line process using heat or optionally adhesive layers
to bond the separate layers. Press lamination can also be used to
form multilayer films by pressing layers of individual films at
elevated temperature and pressure. Lamination methods are described
in the Encyclopedia of Polymer Science and Engineering, 2nd
Edition, Vol. 15, John Wiley and Sons, N.Y. (1986), page 15.
[0028] The 3GN and PET used to form the multilayer films have an
inherent viscosity in the film-forming range, generally between
about 0.2-1.0 dL/g, more preferably 0.5-0.9 dL/g, most preferably
0.55-0.85 dL/g. The polymers are generally dried prior to film
formation by heating to a temperature that is at least about
5.degree. C. below the crystallization temperature of the polymer.
The polymers are preferably dried under vacuum or inert atmosphere,
but may also be dried in air. Preferably the moisture content in
the polymer prior to forming films is less than about 0.1 wt %,
more preferably less than about 0.01 wt %. Generally, the molten
polymer is blanketed with an inert gas prior to extrusion, but the
films can be extruded in air.
[0029] The unoriented multilayer films are primarily amorphous,
with the degree of crystallinity depending on the conditions used
to form the films. For example, the films can be rapidly cooled
(generally to about 60.degree. C. or less) after extrusion to
inhibit crystallization. The unoriented multilayer films are useful
in a number of end uses, including in thermoforming processes, such
as the method described in Slat et al. U.S. Pat. No. 5,651,933, to
form shaped articles such as bottles or they can be stretched to
form oriented flat films. For example, a film having a thickness of
10 mils is suitable for thermoforming into cups having a wall
thickness of 1 mil or a 100 mil film can be thermoformed into a
tray having a thickness of 10 mil.
[0030] Oriented multilayer films are prepared by stretching heated
unoriented films in at least one direction using methods known in
the art. The film can be stretched in the direction coincident with
the direction of casting of the film (machine direction) or the
direction perpendicular to the machine direction (transverse
direction) to obtain a uniaxially oriented film. Preferably, the
films are stretched in the machine direction as well as in the
transverse direction to obtain a biaxially oriented film. Biaxial
stretching may be done sequentially by drawing first in the machine
direction followed by stretching in the transverse direction.
Alternately, the stretching in two directions can take place
simultaneously. Prior to stretching, the films are preheated to the
stretching temperature of about 90.degree. C.-115.degree. C., for
example in an air heated oven, followed by stretching at about
90.degree. C.-115.degree. C., preferably about 100-110.degree.
C.
[0031] Stretching methods which can be used to make the oriented
multilayer films of the current invention include the tubular-film
process and tenting-frame process, as described in the Encyclopedia
of Polymer Science and Engineering, 2nd Edition, Vol. 10, John
Wiley and Sons, N.Y. (1986), pages 619-636. In the tubular-film
process, the co-extrudate consisting of layers of 3GN and PET is
extruded through a narrow die to form a tube. Pressurized air of
controlled temperature is blown into the tube which is then
inflated to a larger diameter bubble. Biaxial orientation is
induced in the film while it is being stretched in the machine and
transverse directions. Alternatively, in the tenting-frame process,
the multilayer film containing one or more layers of 3GN and PET is
heated to an optimum orientation temperature and stretched in the
tenting frame. During stretching, strain orientation and
crystallization occurs which results in improved physical
properties. The oriented films of the current invention are
especially useful in end uses requiring good oxygen barrier
resistance, such as food packaging applications. Preferably, the
films are biaxially stretched to about 2 to 4 times the original
length of the unstretched film in each direction to provide
oriented films having good barrier and physical properties.
[0032] Preferably, the stretched films are heat set at a
temperature above the crystallization temperature of the polymers
to stabilize the films, using methods known in the art. The
heatsetting may be done in air. During heatsetting, the oriented
film is heated and annealed while the film is dimensionally
constrained. This stabilizes the structure of the polymers in the
multilayer film by increasing the crystallinity, which reduces
shrinkage. Heatsetting temperatures of 160.degree. C.-180.degree.
C. are preferred. More preferably, the oriented films are heated at
temperatures of about 170.degree. C.-180.degree. C. for about 2-5
minutes. The heat set oriented films have excellent clarity, e.g. a
light transmission of greater than about 50%, preferably greater
than about 80%.
[0033] The multilayer films of the current invention can include
more than one layer of 3GN and/or PET. For example, the 3GN layer
can be used as a core layer between inner and outer layers of PET
in a 3-layer structure or in a 5-layer structure where the layers
alternate as PET-3GN-PET-3GN-PET. In addition to the at least one
layer of 3GN and the at least one layer of PET, the multilayer
films of the current invention can also include additional layers
of other polymers which are co-stretchable with 3GN and PET.
Polymers used in the additional layers should have a T.sub.g that
is lower than the stretch temperature of the multilayer films,
preferably less than about 90.degree. C., more preferably in the
range of about 10-80.degree. C., so that the layers can be
co-stretched with the PET and 3GN layers at temperatures between
about 90.degree. C.-115.degree. C. In addition, the crystallization
temperature of polymers used in any additional layers should be
higher than the stretch temperature, preferably greater than about
120.degree. C., more preferably in the range of about 130.degree.
C. to 170.degree. C., so that crystallization of the polymer does
not interfere with strain hardening during orientation. Non-strain
hardenable layers, comprising polymers or copolymers with a T.sub.g
less than about 90.degree. C., such as copolymers of poly(ethylene
terephthalate) and cyclohexane dimethanol, disclosed in Collette et
al. U.S. Pat. No. 5,628,957 can also be used. Examples of polymers
that can be used in other layers of the multilayer laminates of the
current invention include ethylene vinyl alcohol and copolymers
thereof, aliphatic polyamides and copolyamides, partially aromatic
polyamide copolymers such as poly(1,3-xylylene adipamide), and
polyolefins and copolymers thereof such as polypropylene and
polystyrene. Polyester copolymers can also be used in additional
layers, for example 3GN copolymers with poly(ethylene
terephthalate), poly(1,3-propylene terephthalate), and
poly(ethylene naphthalate); or copolymers of poly(ethylene
terephthalate) with poly(ethylene naphthalate) or
poly(1,3-propylene terephthalate); or copolymers of
poly(1,3-propylene terephthalate) with poly(ethylene naphthalate)
can be used. For example, polyolefins provide improved moisture
barrier properties and polyamides generally provide good odor
barrier properties.
[0034] The oriented films exhibit excellent adhesion between the
3GN and PET layers, eliminating the need for an adhesive tie layer.
If additional polymer layers such as those described above are
used, an adhesive tie layer may be used to prevent delamination. If
desired, a tie layer can also be used between the 3GN and PET
layers although in general it is not required. Examples of suitable
adhesive tie layers include copolyesters such as copolymers of 3GN
and PET, or adhesion promoting polymers such as Bynel.RTM. modified
polyolefin (available from E. I. du Pont de Nemours and Company, of
Wilmington, Del.) or Elvamide.RTM. low melting polyamides
(available from E. I. du Pont de Nemours and Company, of
Wilmington, Del.).
[0035] Three-dimensional multilayer structures, including hollow
structures such as bottles, which include at least one layer of 3GN
and at least one layer of PET can be prepared from multilayer
preforms using methods known in the art such as sequential
coinjection of a multilayer preform followed by reheat stretch blow
molding as described in Collette et al. U.S. Pat. No. 5,628,957;
multilayer pipe co-extrusion followed by drawblow forming as
described in Nohara et al. U.S. Pat. No. 4,649,004; and injection
molding of sequential layers to form multilayer preforms followed
by blow molding as described in Bonis, et al. U.S. Pat. No.
3,878,282.
[0036] Multilayer hollow structures containing one or more layers
of 3GN and PET can also be prepared by other known methods that do
not require the formation of a preform such as co-extrusion
blow-molding and co-extrusion stretch blow-molding as described in
Plastic Blow Molding Handbook, Chapters 4 and 5, ed. By N.C. Lee,
Van Nostrand Reinhold, N.Y., NY, 1990.
[0037] The polymers are generally dried prior to injection molding
to form the preform. The preferred moisture content in the polymer
prior to injection molding is less than about 0.1 weight percent,
more preferably less than 0.01 weight percent. Preferably, the
polymers have an inherent viscosity in the range of 0.4 to 0.9
dL/g.
[0038] In preparing a multilayer preform to be used for blow
molding, the molten resin preform should be cooled in a way that
inhibits crystallization. The preform is preferably substantially
amorphous. If the % crystallinity in the preform is too high, the
blow formability is reduced and the final container can become
opaque.
[0039] The thicknesses of the individual layers in the multilayer
preforms is preferably between about 0.2-5 mm, more preferably
0.5-3.5 mm, and most preferably between 1.0-3.0 mm. In bottle
applications, the minimum thickness for a preform layer is
generally about 0.4 mm.sup.-1. The thicknesses of the individual
layers in the multilayer preforms are governed by the materials
used and the desired properties. Preforms used for bottles
generally range in an overall wall thickness of from 2 to 5 mm
where 2 mm preform thickness is suitable for very small bottles and
5 mm preform thickness is used for one gallon heavy juice bottles.
Generally preform wall thicknesses of 2.5 to 4.5 mm are used for
carbonated soft drink bottles.
[0040] Conventional stretch blow molding processes can be used to
form hollow containers from the multilayer preforms of the current
invention and are described in Chapter 4, "Stretch Blow Moldings by
S. L. Belcher--Plastic Blow Molding Handbook, edited by N. C. Lee,
published by Van Nostrand Reinhold, 1990). Stretch blow molding
provides biaxial orientation of the container sidewall for enhanced
strength. Blow molding temperatures known for PET can be used for
blow molding the laminated preforms of the current invention.
Preferably, the blow-molding temperature is between about
90-115.degree. C., more preferably about 100-110.degree. C. The
blow-molded articles of the current invention can be heat set, for
example when used for hot filling, using methods known in the art
such as those described in the Blow Molding Handbook, editted by
Rosato and Rosato, Hanser Publishers, 1987.
[0041] The multilayer preforms and containers of the current
invention can include more than one layer of 3GN and/or PET. For
example, the 3GN layer can be used as a core layer between inner
and outer layers of PET in a 3-layer structure or in a 5-layer
structure where the layers alternate as PET-3GN-PET-3GN-PET. In
addition to the at least one layer of 3GN and the at least one
layer of PET, the multilayer preforms and containers of the current
invention can include additional layers of other polymers which are
co-stretchable with 3GN and PET. Examples of polymers that are
useful as layers in multilayer containers include those listed
above for films. Adhesive tie layers can also be used if needed.
However, delamination is generally less of an issue in
three-dimensional shaped articles than in flat films. In food
packaging applications, for example in bottles for beverages such
as beer, juice or milk, it may be desirable for the inner layer to
comprise PET or another polymer such as poly(1,3-xylylene
adipamide) which has been approved by various regulatory agencies
for contact with food. For example, the 3GN layer can be used as an
outer barrier layer with an inner layer of PET or as a core barrier
layer between inner and outer layers of PET.
[0042] If desirable, the multilayer oriented films or containers of
the invention can be coated with a metal such as aluminum using
conventional metallization techniques such as vacuum
deposition.
[0043] The Examples below describe injection molding of sequential
layers to form multilayer preforms followed by stretch blow
molding. 3GN provides two injection molding advantages in the
preparation of multilayer preforms: (1) easy coverage over the
first layer which is a direct result of its low viscosity at
processing temperatures of 230-340.degree. C. and (2) slow rate of
crystallization resulting in a completely clear preform.
Test Methods
[0044] Inherent viscosity was measured in 60 wt % phenol/40 wt %
1,1,2,3-tetrachloroethane at 30.degree. C. at a polymer
concentration of 0.50% by weight, according to the procedure of
ASTM D-4603-91.
[0045] Melting point, crystallization temperature and glass
transition temperature were determined using the procedure of ASTM
D-3418 (1988) using a DuPont DSC Instrument Model 2100. The heating
and cooling rates were 10.degree. C./min.
[0046] Density was measured in grams per cubic centimeter (g/cc)
using the density-gradient method, according to ASTM D-1505-85.
[0047] Tensile properties of biaxially oriented films (Young's
modulus, break strength, and %elongation at break) were measured
using the procedure of ASTM D-882.
[0048] The oxygen permeability of biaxially oriented films was
measured at 50% relative humidity using the method of ASTM
D-3985-81. oxygen permeability of bilayer bottles was measured at
50% relative humidity using the same method and square panels-that
were cut out from the midbody of the bottles. Values are reported
in mil-cc/100 in.sup.2/day.
[0049] The carbon dioxide permeability of biaxially oriented films
was measured using the procedure of ASTM D1434-82. Values are
reported as the average of 12 measurements in units of mil cc/100
in.sup.2/day. Carbon dioxide permeability of bilayer bottles was
measured using square panels cut from the mid-body of the bottles
Using the same method.
[0050] Water transmission rates for biaxially oriented films were
measured according to ASTM F-1249-90.
[0051] Film clarity was measured as percent transmission at 550
nanometers (nM) using a Hewlett Packard 8451A diode array
spectrophotometer, following the procedure of ASTM D1746-92.
[0052] Interlayer adhesion for co-extruded films was measured using
a qualitative peeling test described in Japanese Kokai published
Patent Application 5-131602 (1993). The co-extruded films were
soaked in water at room temperature for an hour. The cut edges of
the film were then plied with fingers in an attempt to peel into
separate layers for inspection.
[0053] The maximum compressive load for blow-molded bottles was
determined using the vertical top load test of ASTM D 2659-89
(standard test method for column crush properties of blown
thermoplastic containers). Values reported for maximum compressive
load represent the average of six measurements.
EXAMPLE 1
[0054] This example describes the synthesis of poly (1,3-propylene
2,6-naphthalate) (3GN).
[0055] Dimethyl 2,6-naphthalenedicarboxylate (36.36 kg, 149 moles)
(purchased from Amoco Chemical Company, with offices in Chicago,
Ill.) and 1,3-propanediol (purchased from Degussa, with offices in
Ridgefield Park, N.J.) (24.91 kg, 327.8 moles) were reacted under
atmospheric pressure under nitrogen in the presence of 6.1 g of
Tyzor.RTM. titanium tetraisopropoxide catalyst (100 ppm catalyst
based on the total weight of ingredients and catalyst)
(commercially available from E. I. du Pont de Nemours and Company,
of Wilmington, Del.) in 300 ml 1,3-propanediol in an agitated
vessel heated with a hot oil system. The vessel was heated to
242.degree. C. over a period of about 330 minutes. When the
temperature of the reaction mixture reached 188.degree. C.,
methanol started to evolve and was removed as a condensate by
distillation as it was formed. Methanol evolution continued until
about 180 minutes after the start of the reaction, when the
temperature reached about 213.degree. C. Excess 1,3-propanediol
started to evolve, and was collected as a condensate by
distillation, when the temperature reached about 217.degree. C. and
continued to evolve for another 150 minutes as the mixture was
heated to 242.degree. C.
[0056] The pressure in the reaction vessel was then reduced from
about atmospheric to about 10 mm Hg while the temperature was
increased to about 275.degree. C. over a period of about 90
minutes. The pressure was then reduced further to 0.5 mm Hg while
the temperature was raised to 280.degree. C. The polymerization was
allowed to proceed an additional 30 minutes to obtain a polymer
having an inherent viscosity of 0.56 deciliter/gram (dL/g).
[0057] The polymer obtained was translucent white in color and was
identified as poly (1,3-propylene 2,6-naphthalate) by analyzing the
peaks in the C-13 NMR using hexafluoroisopropanol solvent. The
polymer had a melting point of 203.degree. C., a crystallization
temperature of 166.degree. C., and a glass transition temperature
of 79.degree. C.
EXAMPLE 2
[0058] This Example demonstrates the preparation of a multilayer
3GN/PET co-extruded film. 3GN prepared in Example 1 was dried
overnight at 120.degree. C. in air, packaged and sealed under
ambient conditions in a 3-ply seven layer multi-wall packaging bag
(CIP, Inc., Montreal, Canada) and then used directly from the
package within about 12 hours after packaging. Bottle grade
Melinar.RTM. Laserplus poly(ethylene terephthalate) having an
inherent viscosity of 0.82 dL/g (commercially available from E. I.
du Pont de Nemours and Company, of Wilmington, Del.), was dried at
170.degree. C. for 4-5 hours in air immediately prior to film
formation.
[0059] The 3GN and PET were melt extruded in separate extruders,
using a 1.25 inch (3.18 cm) single screw extruder (Polysystem,
Ontario, Canada, serial number 84-854) for the PET and a 0.65 inch
(1.65 cm) single screw extruder(Randcastle, Cedar Grove, N.J.,
Model No. RCP-0625) for the 3GN. The temperature profiles in the
extruder and other processing conditions are shown in Table 1.
[0060] The polymer melt streams were combined and arranged to flow
together in layers moving in laminar flow as they entered the die
body using the feedblock method described in Encyclopedia of
Polymer Science and Engineering, 2 Edition, Volume 6, pages
611-613. An 8 inch (20.3 cm) multilayer coextrusion film die
(5-layer Lab Vane Died available from Cloeren Company, Orange,
Tex.) was used with a normal operating die lip gap of 0.020 inch
(0.051 cm) and a normal total product thickness range of 2 mil
(0.051 mm) and higher, adjustable by polymer feed rate, with a web
width of 8 inches (20.3 cm) before trimming. The 2-ply 3GN/PET
laminate was transferred onto a chill roll maintained at 60.degree.
C. and cooled to obtain an unstretched film.
[0061] Co-extruded bilayer films having two different thicknesses,
20 mil (0.508 mm) and 4 mil (0.102 mm), were prepared by adjusting
the polymer feed rate to the extruders. The 20 mil films comprised
a 10 mil (0.254 mm) 3GN layer and a 10 mil (0.254 mm) PET layer.
The 4 mil films comprised a 2 mil (0.051 mm) 3GN layer and a 2 mil
(0.051 mm) PET layer. The bilayer films had good film uniformity
and clarity with no curling, delamination upon working by hand, or
distortion. The 4 mil (0.102 mm) film had an optical clarity of 74%
transmission.
[0062] The films showed no peeling or delamination when subjected
to the adhesion test described above for both thicknesses. When the
soaked films were notched, by introducing a straight cut with a
knife, and pulled vigorously, they exhibited a straight tear in the
notch direction, with no delamination. The peeling test was
repeated after the films were soaked in water at room temperature
overnight, with no evidence of delamination demonstrating that the
adhesion between the layers is excellent.
1TABLE 1 Extrusion Conditions for Bilayer PET/3GN Films PET layer
3GN layer Extrusion Temperature Profile (.degree. C.): Feed 240 226
Center 280 260 Front 280 260 Die 280 282 Melt 312 219 Layer
thickness: 10 mil 10 mil 2 mil 2 mil Chill Roll Temperature
(.degree. C.): 60 60
EXAMPLE 3
[0063] This example demonstrates the preparation of biaxially
oriented bilayer films from the unoriented 3GN/PET films prepared
in Example 2.
[0064] Samples (11 cm.times.11 cm) of the unstretched 3GN/PET
coextruded films prepared in Example 2 were biaxially stretched
using a 4.times.4 film stretcher manufactured by T. M. Long Company
(Sommerville, N.J.). Individual film samples were clamped in the
air pressure jaw of the film stretcher, heated by hot air on both
sides to a temperature of 105.degree. C., and conditioned for 2
minutes. The film was then stretched simultaneously in the
longitudinal and transverse directions at a stretch rate of 9000%
per minute for a total stretch ratio of 12.25 (3.5.times.3.5 in the
longitudinal and transverse directions) to obtain a biaxially
oriented 3GN/PET two-ply laminated film. The stretched film was
then constrained in a square sample holder which clamped all four
edges of the film and placed in a forced air oven at 175.degree. C.
for 3 minutes to heat set the film.
[0065] The final thicknesses of the films were 1.6 mil (0.041 mm)
and 0.3 mil (0.007 mm), for starting thicknesses of 20 mil (0.508
mm) and 4 mil (0.102 mm) respectively, with a laminate layer
thickness ratio of 1.0. The biaxially stretched 3GN/PET co-extruded
films were clear and transparent, without defects, and were
prepared with excellent reproducibility and high efficiency.
[0066] The tensile properties of the thin (0.3 mil, 0.007 mm)
biaxially oriented co-extruded 3GN/PET film are shown in Table 2.
This film had an optical clarity of 83% transmission. oxygen
permeabilities and water transmission rates for the biaxially
oriented films are summarized in Table 3. The carbon dioxide
permeability of the 1.6 mil co-extruded 3GN/PET biaxially oriented
film was 9.36 mil-cc/100 in.sup.2/day.
[0067] The biaxially-oriented films showed no peeling or
delamination when subjected to the adhesion test described above
for both thicknesses. When the soaked films were notched, by
introducing a straight cut with a knife, and pulled vigorously,
they exhibited a straight tear in the notch direction, with no
delamination. The peeling test was repeated after the films were
soaked in water at room temperature overnight, with no evidence of
delamination, demonstrating that the adhesion between the layers is
excellent, even in the absence of an adhesive tie layer.
2TABLE 2 Tensile Properties of 0.3 mil (0.007 mm) Biaxially
Oriented 3GN/PET Film Machine Transverse Direction Direction
Young's Modulus (psi) 22482 36396 Break strength (psi) 1018 1561 %
Elongation at Break 17% 12%
[0068]
3TABLE 3 Oxygen Permeability and Water Transmission Rate for
Biaxially Oriented 3GN/PET Co-extruded Films Film Oxygen
Permeability H.sub.2O Transmission Rate Thickness (mil) (mil-cc/100
in.sup.2/day) (gm-cc/100 in.sup.2/day) 0.3 1.26 0.95 0.3 1.32 0.95
1.6 1.50 0.97 1.6 1.47 0.96
EXAMPLE 4
[0069] This example illustrates the preparation of a multilayer
hollow structure useful as a beverage bottle or other packaging
container.
[0070] Two-layer PET/3GN preforms were formed by injection molding.
FIG. 1 illustrates the shape of-the multilayer preform 10 with an
opening 12 at the top end and also having a threaded portion 14
with a support ring 16 and a generally cylindrical sidewall-forming
section 18. The inner layer 20 of PET was inject molded first,
followed by injecting the outer layer 22 of 3GN on top of the first
layer. The first layer cooled sufficiently between injection steps
so that it was not eroded by application of the second layer. The
outer 3GN layer was not injected over the threaded portion 14.
Bottles were formed from the layered PET/3GN preforms by stretch
blow molding. FIG. 2 shows the shape of the multilayer bottles 24
that were formed. The bottles have a threaded small-diameter
threaded neck portion 14, a shoulder portion 26, a generally
cylindrical multilayer sidewall 28, and a base portion 30 unitary
with the cylindrical sidewall. The base portion includes a
plurality of downwardly projecting hollow legs 32 extending
radially from a central hub 34. The multilayer sidewall is not
specifically illustrated in FIG. 2, however FIG. 3 shows in cross
section the sidewall which comprises an inner layer of PET 20 and
an outer layer 22 of 3GN as illustrated in FIG. 3. Shoulder portion
26 and the base portion 30 are stretched less than the sidewall
portion 28, and therefore are thicker and less oriented than the
sidewall 28.
[0071] A two-layer 26 g preform was made by injection molding using
bottle grade Melinar.RTM. Laserplus poly(ethylene terephthalate)
having an inherent viscosity of 0.82 dL/g (commercially available
from E. I. du Pont de Nemours and Company, of Wilmington, Del.) as
the inner layer and the 3GN prepared in Example 1 as the outer
layer. Both resins were dried before injection molding using the
drying procedures described in Example 2. The resins were injection
molded on an Engel 200 (Engel Machinery Inc., York, Pa.) injection
molding machine capable of overmolding two different resins to form
a 26 gm threaded preform mold. The set-point temperatures were
270.degree. C. for the extruders and 337.degree. C. for the
manifold surrounding the gates for both resins. The measured
temperatures of the PET at both the nozzle and before entering the
mold cavity was 332.degree. C. The measured temperatures of the 3GN
at both the nozzle and before entering the mold cavity was
300.degree. C. The first injection was of PET which resulted in a 3
mm thick sidewall inner layer. This was immediately followed by a
second injection of 3GN resulting in a 1.5 mm thick sidewall outer
layer. The 3GN had a low viscosity at these setpoint temperatures
resulting in good flow characteristics over the first layer but
required higher hold pressures and additional delays in gate
closing to make an adequate gate. Attempts to injection mold at
screw setpoint temperatures less than 270.degree. C. which would
have eliminated the extra hold pressures and gate closing delays
resulted in a higher viscosity for 3GN which led to unacceptable
shear spreading and crystallization on the first stage injection
layer. The total height of the preform was about 98 mm with a total
sidewall thickness of 4.5 mm and a bottom wall thickness of about
3.4 mm. The top threaded part, which was comprised of 100% PET had
a length of about 21 mm. A control preform having two layers of PET
was prepared using the same conditions used to form the 3GN/PET
preform.
[0072] The bilayer preforms were stretch blow molded into 600 ml
bottles using methods known in the art for molding PET bottles. A
conventional blow molding machine, manufactured by Sidel (Le Havre
Cedex, France, Model No. SBO 1/1), was used to stretch blow mold
the 26 gram bilayer preforms into 600 ml bilayer bottles. The blow
molding conditions were determined as is usual and customary in the
trade and included some manipulation of the shoulder lamp profiles.
Only 6 of the 10 possible lamps were required due to the height of
the preform. The overall lamp output to the lamps used to blow mold
the bottles was 85-90%. In order to reduce the weight in the
shoulder, the V/V lamp was turned on 100% with lamp 1 turned to
20%.
[0073] The resulting 3GN/PET bilayer bottles were completely
transparent without pearlesence or haze and were free of visual
defects. In addition, the bottles had excellent color with no hint
of yellow or gray. The bottles made from the PET/PET preforms,
prepared under identical conditions were of similar quality.
[0074] The blow-molded bottles were subjected to the vertical top
load test which determines the maximum compressive load that the
bottle can withstand. The pass/fail requirement, commonly adopted
by the industry, is that an empty bottle should withstand a minimum
compressive load of 40 lb force (18.1 kg force) and a mean
compressive load of 45 lb force (20.4 kg force) before buckling.
Both the 3GN/PET and the control PET/PET bilayer bottles passed the
test, with the PET/PET control showing larger variability in the
data as shown in Table 4.
4TABLE 4 Mechanical Integrity of 3GN/PET and PET/PET Bilayer
Bottles Load at maximum Bottle (Force in lb) Status Location of
Buckle 3GN/PET.sup. 84.9 .+-. 2.0 pass shoulder PET/PET 95.4 .+-.
5.7 pass shoulder, mid-body and heel
[0075] The oxygen permeabilities of panels cut from the bilayer
bottles are reported in Table 5. The permeabilities reported for
3GN are for a single layer that was separated from a 3GN/PET
bilayer bottle panel. The layers were separated by carefully
peeling the layers apart with force. The oxygen permeability of the
3GN/PET panel is superior to (about 2.times.improvement) the
PET/PET control as shown in Table 5.
5TABLE 5 Oxygen Permeability of Bilayer Bottles Panel Oxygen
Permeability Bottle Thickness (mil) (mil-cc/100 in.sup.2/day)
3GN/PET.sup. 12.28 2.73 " 12.52 2.85 PET/PET 12.01 5.33 " 12.44
5.37 3GN 4.33 1.51 " 4.76 1.66
[0076] The carbon dioxide permeabilities of panels cut from the
bilayer bottles are reported in Table 6. The carbon dioxide
permeability of the 3GN/PET panel is superior to (greater than
2.times.improvement) the PET/PET control.
6TABLE 6 Carbon Dioxide Permeability of Bilayer Bottles Panel
CO.sub.2 Permeability Bottle Thickness (mil) (mil-cc/100
in.sup.2/day) PET/PET 13.90 21.57 (.+-.1.85) 3GN/PET.sup. 13.48
8.92 (.+-.1.40)
[0077] The optical clarifies of the films are shown in Table 7. The
optical clarifies reported for 3GN and PET are for a single layer
that was separated from a 3GN/PET bilayer bottle panel by carefully
peeling the layers apart with force.
7TABLE 7 Optical Clarity of 3GN/PET Bilayer Bottle Thickness
Optical Clarity Bottle (mil) (% transmission) 3GN/PET.sup. 12.4 86
PET/PET 12.2 88 3GN 4.3 88 PET 8.1 84
[0078] Densities of the polymer in the 3GN and PET layers were
measured for the preform and blow-molded bottle and are reported in
Table 8. The increased density in the blow-molded bottle reflects
the orientation and crystallization in the polymer after blow
molding.
8TABLE 8 Density OF 3GN And PET In Injection-Molded Preforms And
Blow-Molded Bottles Preform Blow-Molded Bottles Polymer (body wall)
(body panel) PET 1.3373 g/cc 1.3670 g/cc 3GN 1.3080 g/cc 1.3200
g/cc
* * * * *