Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD OF. BLOW MOLDING A BOTTLE FROM BIORESIN
FIELD OF THE INVENTION
[0001] The present invention relates to a bottle made from a biodegradable
bioresin and in particular to a renewable biodegradable bioresin bottle made
from
plants, not crude oil, comprising polylactic acid or polylactide.
BACKGROUND OF THE INVENTION
[0002] Virtually all "single-serve" or "convenience-size" beverage. bottles
sold in the United States are made from polyethylene terephthalate ("PET").
PET has
become the material of choice for bottled beverages because, among other
reasons, of
its lightweight and shatter resistance and because PET bottle inanufacturing
techniques are widely known. A 2007 study by the Container Recycling Institute
("CRI") estimates that 37 billion of the 5.8 billion non-carbonated, non-
alcoholic
beverages purchased in the United States in 2005 were packaged in PET bottles,
of
which over, 27 billion were plastic water bottles having a size of I liter or
less. CRI
also estimates that 96% of bottled water sold in the U.S. in 2005 was sold in
PET
bottles.
[0003] Notwithstanding the wide-spread use and popularity of PET
beverage bottles, there are at least four significant disadvantages associated
with using
PET for making beverage bottles. First, PET is a petroleum-based product. CRI
estimates that approxitnately 18 billion barrels of crude oil equivalent were
consumed
in 2005 to replace the 2 million tons of PET bottles that were wasted and not
recycled.
Second, single-serve PET beverage bottles are prone to being littered and have
a
lower recycle rate than any of the most common beverage packaging materials.
CRI
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estimates that only about 23% of PET beverage bottles sold in the U.S. in 2005
were
recycled and that 52 billion plastic bottles and jugs were wasted - i.e., not
recycled --
in that year. This is problematic because PET is not readily biodegradable and
thus
littered PET bottles or PET bottles ending up in landfills remain in bottle
form
indefmitely. Third, production of PET creates a significant amount of green
house
gases. According to one study, 4 tons of greenhouse gases as COz equivalents
are
generated for every ton of virgin (i.e., non-recycled) PET produced. Fourth,
even
when PET is recycled, the chemical properties of PET degrade each time that
PET is
recycled and thus it is not possible to make an acceptable PET 'beverage
bottle using
100% recycled PET. Rather, recycled. PET must be mixed with virgin PET to make
acceptable PET beverage bottles. Even if every PET beverage bottle was
recycled,
there would still be a need for production of virgin PET, with the associated
petroleum dependence and green house gas production.
[0004] In light of the significant disadvantages associated with PET
beverage containers, attention has been given in recent years to the
possibility of
creating acceptable beverage containers from resins made from renewable, plant-
based- materials, with the additional benefit of being biodegradable. One such
biodegradable bioresin is polylactic acid or polylactide ("PLA"). PLA is a
biodegradable, thermoplastic, aliphatic polyester that is derived from
renewable
resources, such as corn, starch or sugarcanes, and thus is not a petroleum-
based
product. PLA provides several different landfill waste diversion options as
compared
to PET because PLA can be physically recycled, industrially composted,
incinerated
or chemically converted back to lactic acid through hydrolysis. In addition,
unlike
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= ' ,
PET, PLA is 100% recyclable and can be recycled into virgin PLA and then used
to
make PLA bottles without the need to add additional non-recycled PLA.
[0005] Unfortunately, the advantages of using PLA instead of PET -in the
manufacture of beverage bottles have not yet been fully realized because the
chemical
properties of PLA differ from those of PET in several significant ways and
these
differences present challenges to the successful manufacture and use of PLA
for
single serve beverage bottles. With respect to the manufacture of PLA beverage
bottles, factors such as the lower density of PLA as compared to PET, the
greater risk
of inadvertent occurrence of thermal crystallization in PLA as compared to
PET, the
lower mechanical strength of PLA as compared to PET, and lower melt
temperature
of PLA as. compared with PET. all make successful manufacture and.
commercialization of acceptable PLA beverage bottles very, very difficult.
[0006] With respect to the use of PLA for beverage bottles, the thermal
properties of PLA currently present significant challenges to the use of PLA
bottles
for hot or warm fill applications. Because the barrier properties of PLA are
relatively
poor compared to PET, PLA is not currently considered a viable material
candidate-
for bottle applications requiring barrier to oxygen ingress or carbon dioxide
permeation. Thus, PLA is not currently regarded as a suitable material from
which to
manufacture bottles for use with carbonated beverages.
[0007] One beverage bottle application in which PLA has been attempted,
although with only limited success, is for the manufacture of non-carbonated
drinking
water bottles. But known PLA drinking water bottles have. a significant
disadvantage.
The water vapor transmission rate (` WVTR") of PLA is significantly higher
thaii that
of PET. As a result, after drinking water is filled into a known PLA bottle
and the
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bottle is capped, over time a vacuum is created within the bottle as the water
product
escapes by permeation through the bottle sidewall faster than N2 or 02 can
permeate
into the bottle. As . a result, the sidewall of known PLA drinking water
bottles
significantly deforms into the bottle. This inward deformation of the bottle
side wall
in response to vacuum created within the bottle is known as "paneling." While
this
phenomenon has been observed in PET drinking water bottles as well, it occurs
much
quicker in PLA bottles than it does in PET bottles because of the higher water
vapor
transmission rate of PLA.
[0008] Figs. 1 and 2 illustrate paneling observed in known PLA drinking
water bottles. After being filled and capped, as shown in Fig. 1, the body
portion of
the known PLA bottle has a hollow cylindrical shape with a substantially
circular
cross section as shown in Fig. IA. Over time, permeation of water vapor
outwardly
from the bottle through the PLA bottle material creates a vacuum inside the
bottle. As
illustrated in Figs. 2 and 2A, this vacuum causes the walls of the body
portion to
deform inwardly into the bottle, thereby significantly transforming the shape
and
overall appearance of the known PLA bottle. It has even been observed that,
given
enough time, such deformation of known PLA drinking water bottles can result
in
failure of the PLA walls of the body portion of the bottle, thereby causing
water to
leak out from the known PLA bottle.
[0009] Paneling of known PLA beverage bottles is a significant problem
for at least three reasons. First, there is a belief that some consumers may
interpret a
"paneled" bottle as being of poor quality, and therefore delay or forego their
purchase
of water in such a paneled bottled. Second, in addition to not presenting a
desirable
appearance, many consumers are likely to believe that a paneled beverage
bottle has
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been opened and will therefore not purchase drinking water in such a bottle.
Third,
because product labels on beverage bottles are often printed or affixed on the
bottle
circumference, paneling often renders the product label difficult or
impossible to
easily read or to adhere to the bottle.
[0010] What is needed in the art is a new beverage bottle that not only
overcomes the adverse environmental consequences associated with known PET
beverage bottles but also addresses the adverse problems associated with
paneling in
known PLA beverage bottles. What is also needed in the art is a new method of
manufacturing PLA beverage bottles that overcomes the difficulties associated
with
known methods of manufacturing PLA drinking water bottles.
SUMMARY OF THE INVENTION
[0011] The present invention overcomes problems associated with known
PLA beverage bottles by providing a bioresin bottle with a neck having a
finish with
an opening, an adjacent shoulder, a base capable of supporting the bottle
upright, and
a main body between the shoulder and base. The main body has a first portion
that is
substantially circular in cross-section and a second portion that is
substantially
elliptical In cross-section at a predetermined location. The hoop stiffness of
the first
portion is greater than the hoop stiffness of the second portion such that
when a
vacuum is created inside the bottle by the outward permeation of water vapor
through
the bottle walls, the second portion deforms inwardly to decrease the length
of the
minor axis and deforms outwardly to increase the length of the major axis. In
this
way, the shape of the bottle after vacuum-induced deformation is controlled
and the
resulting bottle after such defocmation maintains a shape that is attractive
to
consumers.
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[0012] In an embodiment of the present invention, the second portion is
capable of deforming outwardly to a point at which the length of the major
axis of the
substantially elliptical cross section of the second portion is greater than
the length. of
the diameter of the substantially circular cross section of the first portion.
In another
embodiment, a circumferential rib separates the base from the second portion
of the
main body and a circumferential rib separates the first portion of the main
body from
the second portion of the main body. The circumferential rib separating the
base
from the second portion of the main body and the circumferential rib
separating the
first portion of said main body from the second portion of said main body may
not be
parallel.
[0013] The first portion of the main body further may have at least one
circumferential rib and, advantageously, the second portion of the main body
may be
free from circumferential ribs. At least one circumferential rib may be a wave-
like
circumferential rib.
[0014] A plurality of longitudinally spaced arcuate projections may extend
outwardly from the second portion of the main body to provide localized
stiffness at
predetennined locations. Advantageously, the second portion of the main body
of the
bottle may include a first plurality of outwardly extending longitudinally
spaced
arcuate projections and a second plurality of outwardly extending
longitudinally
spaced arcuate projections, the second plurality of arcuate projections being
separated
from the first plurality of arcuate projection by the minor axis of the
substantially
elliptical cross section of the second portion.
[0015] The present invention also provides and advantageous method of
making a preform comprising a biodegradable bioresin. The method of making the
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preform comprises obtaining a bioresin comprising polylactide or polylactic
acid,
drying the bioresin, injection molding the bioresin in a mold to form a
preform having
a weight in a range of from 21 g to 23.5 g, preferably 22 g to 23 g. In
accordance
with the method, the injection pressure is in a range of from about 350 to
about 700
bar. The resulting preform is suitable for blow molding a biodegradable
bioresin
bottle having a main body comprising a substantially circular cross-section
and a
substantially elliptical cross-section in the main body of the bottle.
[0016] In another embodiment of the present invention, the. injectio.n
molded prefonn comprises a fmish portion, a transition portion, a body
portion, and a
closed end cap portion for making a blow molded biodegradable bioresin bottle
having a body comprising a substantially circular cross-section and a
substantially
elliptical cross-section in the body of the bottle. The preform comprises
polylactic
acid or polylactide. The prefortn, in accordance with the present invention,
has a
weight in a.range of from 21 g to 23.5 g, preferably 22 g to 23 g.
[0017] In another embodiment of the present invention, the preform is
used to make a biodegradable bioresin bottle comprising polylactic acid or
polylactide. The method comprises stretch blow molding a preform comprising
polylactic acid or polylactide into a biodegradable bioresin bottle having a
main body
comprising a substantially circular cross-section and a substantially
elliptical cross-
section in the main body of the bottle. The preform -is suitable to use to
make a 500
mL biodegradable bioresin bottle.
[0018] In another aspect of the present invention, a method of making a
biodegradable bioresin bottle having a finish with a finish ledge and a main
body
having first and second portions with bottle side walls is provided. In
accordance
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with the method of the present invention, a preform is obtained comprising
polylactic
acid or polylactide, the preform is heated to a temperature in a range of
about 80 C to
95 C as measured on the preform above the finish ledge of the preform, and
the
preform is stretch blow molded in a ratio of preform to bottle such that the
side walls
of the bottle are molecularly oriented in a portion of the main body of the
bottle so as
=to produce a bottle that deforms in a predetermined location.
[0019] Further areas of applicability of the present invention will become
apparent from the detailed description provided hereinafter. It should be
understood
that the detailed, description and specific examples, while indicating. the
preferred
embodiment of the invention, are intended for purposes of illustration only
and are not
intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will become more fully understood from the
detailed description and the -accompanying drawings, which are not necessarily
to
scale, and in which:
[0021] FIG. I is a perspective view of a known PLA drinking water bottle;
[0022] FIG lA. is a sectional view of the known PLA drinking water
bottle of FIG. 1 taken along the line IA-lA in FIG. 1;
[0023] FIG. 2 is a perspective view of the known PLA drinking water
bottle of FIG. 1 that has undergone paneling as a result of vacuum creation
inside the
bottle;
[0024] FIG 2A. is a sectional view of the known PLA drinking water
bottle of FIG. 2 taken along the line 2A-2A in FIG. 1;
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[0025] FIG. 3 illustrates a typical stress-strain curve for materials that
undergo strain hardening;
[0026] FIG. 4 is a perspective view of a preform having heat induced
deformation in the finish region;
[0027] FIG. 5 illustrates an infrared (IR) absorption spectra for PET and
PLA materials;
[0028] FIG. 6A is a plan view of the base of a bottle in accordance with
the present invention;
[0029] FIG. 6B is a sectional view of the base illustrated in FIG. 6A taken
along the line 6B-6B in FIG. 6A;
[0030] FIG. 7 depicts the sensitivity of bottle base weight to preform
temperature for PLA and PET bottles;
[0031] FIG. 8A is a perspective view of a preform in accordance with the
present invention;
[0032] FIG. 8B is a longitudinal sectional view of the preform of FIG. 8A;
[0033] FIG. 9 is a drawing of a mold suitable for blow molding the
preform of FIG. 8A into a biodegradable bioresin bottle;
[0034] FIG. 10 is a perspective view of a biodegradable bioresin bottle in
accordance with the present invention;
[0035] FIG. 11 is a perspective view of a biodegradable bioresin bottle in
accordance with the present invention;
[0036] FIG. 11A is a perspective view of the bottle of FIG. l i rotated 90
degrees counterclockwise about its longitudinal axis;
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[0037] FIG. 11B is a perspective view of the bottle of FIG. 11 rotated 90
degrees clockwise about its longitudinal axis;
[0038] FIG: 12A is a sectional view of the bottle of FIG. 10 taken along
the line 12A-12A in FIG. 10;
[0039] FIG. 12B is a sectional view of the bottle of FIG. 10 taken along
the line 12B-12B in FIG. 10; and
[0040] FIG. 13 is a sectional view of the bottle of FIG. 10 taken along the
line 12B-12B in FIG. 10 after the occurrence of bottle wall deformation in
response to
vacuum creation inside the bottle.
DETAILED DESCRIPTION OF TIIE INVENTION
[0041] . The following detailed description of the embodiment(s) is merely
exemplary in nature and is in no way intended to limit the invention, its
application, or
uses.
[0042] A biodegradable material is a material that can be broken down
into carbon dioxide (COZ) and water (Ii20), by microorganisms, such as
bacteria and
fungi. Such materials undergo a significant change in chemical structure
during this
process, resulting in loss of properties including, but not limited to,
molecular weight,
structure, strength, and integrity. A compostable material is a biodegradable
material
that satisfies one or more of the various standards regarding
biodegradability, such as
rate biodegradation, maximum residue of material left at a specific point in
time and a
requirement for the material to have no harmful impact on the final compost or
the
composting process. Commonly used standards for compostable plastic materials
are
the American standard ASTM D 6400-99, the European standard EN-13432 and DIN
V-54900. As set forth in ASTM D 6400-99, such a material is "capable of
CA 02651391 2009-01-28
undergoing biological decomposition in a compost site as part of an available
program, such that the plastic is not visually distinguishable and breaks down
to
carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent
with
known compostable materials (e.g. cellulose) and leaves no toxic residue." In
accordance with the present invention, a biodegradable and compostable bottle
may
be created using bioresin material.
[0043] Biodegradable materials suitable for use as a bioresin in the
present invention include, but are not limited to, polylactic acid or.
polylactide.
Several forms of PLA include, but are not limited to, poly-L-lactide, poly-D-
lactide;
poly-D, L-lactide, and a combination thereof.
[0044] Table 1 below lists PLA's physical and chemical properties, with
PET for comparison, to understand the behavior of PLA. Each of these is
discussed
herein.
[0045] Table 1
PROPERTY PLA PET
Density (g/cm )
Amorphous 1.248 1.335
C stalline 1.290 1.450
Resin Bulk Density 0.79 cc 0.76 cc
Yellowness Index 20-60 -1-3
Melt Temperature ( C) 155-175 245
(165 - 173
for
bottle grade
PLA)
Glass Transition Temperature ( C) 55-60 70-79
Crystallization Temperature C 100-120 120-155
Thermal Conductivity (cal / cm-sec C)
Arrmorphous 3.1 x 10-4 3.6 x 10-4
Crystalline 4.5 x 10' 9.5 x 10-4
Specific Heat (caUg C)
Below Tg 0.29 0.29
Above Tg 0.51 0.32
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CO2 Transmission cc-miV100in /da 200 19.6
02 Transmission (cm -25p/m /24hr) 600 140
WVTR k da -atm 0.301 0.010-0.020
Mechanical Strength - Young's Modulus on Oriented
Film
Tensile Yield Stress (MPa)
Machine Direction 72 275
Cross Direction 65
[0046] In one aspect of the present invention, the present invention relates
to preform designs and the preforms resulting therefrom.
[0047] A preform is a polymeric pre-shaped part that is used to make 'a
specific product, which for purposes of the present invention is a
biodegradable
bioresin bottle. As illustrated in FIGS. 4, 8A and 8B, the preform 20 is a
tube-like
piece of plastic having a generally cylindrical outer wall 21 connecting a
closed end
22 to an open end 23 having an opening 24- through which compressed high
pressure
gas such as air can pass. The preform. 20 comprises a finish portion 25, a
transition
portion 26, a body 27, and an end cap 29.
[0048] In accordance with the present invention, the preform is formed by
injection molding. After being formed by-injection molding, the preform is
quickly
quenched in the mold in order to keep the preform amorphous. After manufacture
the
preform may be packaged for later use or fed into a blow molding machine.
[0049] Blow molding is a process by which hollow plastic articles are
formed. In the present invention, the method is directed to a blow molding
process
for manufacturing biodegradable bioresin bottles, more particularly
biodegradable
bioresin bottles comprising PLA suitable for containing non-carbonated
beverages
such as water. More particularly, the method of the present invention is
directed to
what is generally referred to as a "two-stage" or "reheat stretch" blow
molding
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process. In the two-stage blow molding process, the preform is heated above
its glass
transition temperature, then blown into a bottle using high pressure air using
a blow
mold. The preform is usually stretched with a core rod as part of the process.
[0050] With respect to the preform heating, the preform is typically heated
by infrared heaters or lamps. The preforms are passed in front of lamps that
emit
light in the infrared (IR) region while being cooled with airflow on the outer
surface.
The lamps are designed to heat the preform from the outside to the inside as
the
energy emitted penetrates through the preform wall and is absorbed. The ovens
in
standard blow molding equipment have typically been optimized to heat
polyethylene
terepthalate (PET) resins as opposed to polylactic acid (PLA) resins.
Variances in the
IR absorption from that of PET may cause less efficient preform heating.
Therefore,
reheat rate enhancing additives are often added to the PLA. Examples of reheat
rate
enhancing additives include, but are not limited to, activated carbon, carbon
black,
phthalocyanines, 2,3-napthalocyanines, squaraines (squaric acid derivatives),
croconic
acid derivatives, substituted indanthrones and certain highly substituted
anthraquinones, near infrared absorbing dyes or combinations of these with
carbon
black, antimony metal, tiny,copper, silver, gold, palladium platinucn, black
iron oxide,
and the like. Further reheat rate enhancing additives are described in U.S.
Patent No.
6,197,851 and U.S. Patent 7,189,777.
[0051] Since PLA is a crystallizable thermoplastic, two different densities
are reported - an amorphous density and crystalline density. The amorphous
density
represents the PLA density in its amorphous state, such as preforms or the un-
oriented
bottle fmish area. The crystalline density shown represents the density of a
100%
crystalline PLA. PLA has a density lower than PET; thus, if using existing PET
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tooling, the ratio of the densities should be multiplied by the PET preform
weight to
estimate the PLA preform weight: The degree of crystallinity.impacts the
material
properties and perfonnance. In the preform molding, the PLA material is cooled
quickly to prevent thermal crystallization from occuning. Thus, if molded
properly,
PLA preforms are highly amorphous and' clear. Crystals formed through thermal
crystallization are larger than the wavelength of light, thus when present can
cause
visible light to scatter producing haze in the molded part. In addition,
thermal
crystallinity results in more rigid or brittle areas in the preform which,
when reheated
during blow molding, further crystallize causing blow-outs.
(0052] Similar to PET, stretch orientation in PLA causes strain-induced
crystalliriity to occur which creates oriented and transparent crystals with
significantly
improved mechanical properties. In bottle blow molding, the fmal bottle
sidewall
crystallinity is in the 35-45% range. FIG. 3 illustrates a typical stress-
strain curve for
materials which undergo strain hardening. There are three distinct regions of
such
curve - an initial region in which the material easily stretches as force is
applied but is
recoverable; a plateau region where permanent stretching, chain deformation
and
crystal growth occurs and then a strain hardening region, shown as the
triangles, in
which the material is over-stretched. During the stretching process, the
material will
yield to the forces applied as the preform expands. However, it will reach a
point at
which the force required to further move the material increases dramatically.
As the
PLA stretches, the strain induced crystallinity increases within the amorphous
regions
of the polymer and improves the polymer's mechanical properties. For PET, the
mechanical strength of the oriented material prevents it from further stretch
if force is
continually applied after complete strain-hardening occurs. PLA, however, has
lower
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mechanical strength and continues to yield until the bottle sidewall becomes
too thin
and ruptures.
[0053] PLA crystallinity is evaluated using a first heat only Differential
Scanning Calorimetry (DSC) method. The level of crystallinity is determined by
the
ratio of the sample heat of fusion to the 100% crystalline PLA heat of fusion
(DHm),
937/g. A well-oriented PLA bottle has a OHm of 35-45 J/g. Through X-ray
diffraction
studies, it is believed that 45% quiescent crystallization is the maximum that
can be
achieved. As a bottle development and quality tool, crystallinity measurements
ensure
that blow molding orientation is sufficient to
maxunize bottle properties and aid in the understanding of preform processing
and
quality issues.
[00541 Resin bulk density for PLA is comparable to PET, which would
indicate that bulk handling systems such as air transfer lines should handle
both
materials. PLA resin pellets typically appear slightly yellow in color and
spherical
with smooth, rounded edges from the under-water pelletization through which
they
are formed. The pellet diameter typically ranges from about 3 mm to about 3.5
mm.
The difference in pellet geometry from PET pellets, which are smaller in
diameter and
strand-cut with sharp edges, may require slight adjustments to conveying lines
when
changing from one pellet geometry to another. For dedicated PLA systems,
however,
this difference would not be of concern. The melt temperature for PLA is about
155
C to 175 C, depending upon the copolymer content and molecular weight. When
running on existing PET equipment, all transfer lines, dryers, hoppers, and
any
equipment in contact with the PLA resin should be thoroughly cleaned to remove
all
PET. Any PET remaining that enters the injection feed throat becomes an un-
melted
CA 02651391 2009-01-28
contaminant in the PLA molding, PLA preforms containing PET that are blow
molded
results in blowouts as PET's Tg is significantly higher. Regarding permeation
characteristics, PLA has increased permeation to non-polar gases and water
when
compared to oriented PET. Since the barrier properties of PLA are relatively
poor
compared to PET, PLA is not currently considered a suitable material candidate
for
applications requiring barrier to oxygen ingress or carbon dioxide permeation.
The
bottle of the present invention takes into consideration the vacuum that
occurs as the
water product escapes by permeation through the bottle sidewall faster than N2
or 02
can permeate into the bottle. PLA improves in mechanical properties through
stretch
orientation due to. the strain hardening that occurs. The PLA bottles,
however, have
lower Young's modulus when compared to PET, and are not able to withstand
pressurization even when blown producing high levels of strain induced
crystallization without excessive creep. The thermal, barrier and mechanical
properties of PLA are currently thought to limit commercial applications for
PLA
requiring significant pressuriaed containers and certain hot fill bottle
applications.
[0055] Blow molding PLA preforms into a warm or hotter mold can help
relieve molded-in stresses caused by the bottle blow molding process; but does
not
build sufficient thermal stability for hot filling or elevated bottle storage
temperatures.
It has been reported that both preforms and bottles deform under elevated
temperatures. When stored in hot and humid warehousing conditions of 120 F and
at
least 50% RH for 1 week, PLA preforms, especially those exposed to.the weight
of
other preforms above within the gaylord, distort in the thinner finish area.
FIG. 4
illustrates an example of a preform 20 tested under these conditions, with the
resulting
finish deformation indicated at reference numeral 28. Due to the severity of
the finish
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distortion, such preforms can no longer be blow molded as they no longer fit
on blow
molding spindles. Proper management of prefonxi storage and shipping
conditions
can reduce or eliminate this problem. PLA bottles shrink similarly to PET
bottles
when exposed to 100 F temperatures, but such shrinkage increases dramatically
as the
temperature increases beyond about 120 F to about 140 F.due to PLA's lower
Tg.
[0056] In drop impact testing, PLA bottles have been shown to perform
adequately when the material is well-oriented within the base area. Another
characteristic of PLA that is relevant for two stage bottle blow molding is
the IR
absorption spectra. During the preform heating in the blow molding process,
the PLA
preforms are passed in front of lanips that emit light in the IR region while
being
cooled,with airflow on the outer surface. The lamps ate designed to heat the
preform
from the outside to the inside as the energy emitted penetrates through the
preform
wall and is absorbed. The ovens in standard blow molding equipment have been
optimized to heat PET resins efficiently. Variances in the IR absorption from
that of
PET may cause less efficient preform heating, unless this Is compensated for
by the
addition of reheat additives to the PLA. The IR absorption spectra for
standard PET
and PLA materials are sbown in FIG. 5 and show slight differences in the IR
absorption in the 1400 to 5000 (1/cm) wavenumber region. Since the reheating
rate is
important for PLA preforms to maintain high blow molding rates, several reheat
additives have been manufactured to allow for better infrared absorption
resulting in
more efficient IR heating as discussed previously herein. They are commonly
used for
two-stage PLA bottle manufacturing, as opposed to re-designing the blow
molding
oven to achieve preform heating, so that PLA bottles can be. produced on
existing,
standard equipment.
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[0057] While PLA may not have the physical attributes that PET has for
many rigid container applications, PLA continues to see high interest as a
replacement
material for PET in some applications. As a material, it offers superb
clarity. In stark
contrast to PET, it provides great definifion when blown into bottles with
decorations
such as logos or features that have sharp radii. Some of the properties that
may have
limited widespread commercial adoption of PLA as a replacement material for
PET in
the market are PLA's poorer gas barrier characteristics, impact properties and
lower
thermal deformation temperature.
[0058] There are design considerations associated with PLA with both the
molded article and tooling design. The preform is an integral part of
acttieving
acceptable bottle clarity, performance, and consistency. As with PET preform
design,
there is a range of stretch ratios that achieve an acceptable bottle
distribution and are
discussed in more detail herein. Preforms and bottle combinations below the
lower
end of both axial and radial stretch ratio tend to form bands of thicker
material in the
bottle sidewall that cannot be eIiminated through blow molding processing.
Above
the upper end of the stretch ratio limits, the preform becomes overstretched
during the
blow molding process and creates stress whitening or pearlescence in the final
bottle.
Other preform design considerations are the neck diameter and neck to bottle
opening.
[0059] PLA preforms shrink slightly during the reheating process, causing
the preform diameter to increase and theoverall length to decrease. As a
result, if
employed, the blow mold top plate is designed with higher clearance between
the as-
molded PLA preform and top plate diameter to ensure sufficient clearance
between
the preform neck and mold during blow molding. Checking preforms for their
shrinkage levels during injection molding can be used as a quality tool.
18
CA 02651391 2009-01-28
[0060] The preform end cap thickness is generally thinner than the
preform wall thickness to prevent excess material in the base area during blow
molding. For the inside dimensions, preform shrinkages of 0.005 inch/1 inch on
preform diameters-and 0.008 inch/1 inch on preform lengths are applied to the
plastic
print to design the injection mold tooling. On the outer dimensions,
shrinkages of
0.011 inch/I inch and 0.008 inch/1 inch are applied to the preform diameter
and
length, respectively. For example, to produce the plastic dimension of 1 mm, -
the
tooling is manufactured to a dimension of 1 mm x 1.005 mm/mm. Another
consideration for PLA preform design is to avoid sharp transitions from thick
to thin
sections as this may produce stress-whitening in the bottle blow molding.
[0061] From an injection molding tooling standpoint, injection mold
tooling should be polished on both the core and cavity to prevent drag lines
or marks
in the preform that create visual bottle defects. Hardened stainless steel is
commonly
used in production tooling. PLA has successfully been molded on hot-runner
systems
designed for PET, though as discussed below, care must be taken to eliminate
all PET
from the hot runner system. In the preform tooling design, consideration
should be
given to allow maximum water cooling to the core rod and cavity because PLA's
higher heat capacity and lower thermal conductivity impede heat transfer from
the
plastic to the mold. Preforms ejected from the mold should be sufficiently
cooled to,
prevent defonnation as they are transferred into a gaylord.
[006,2] In addition to the preform/bottle relationship, other important
characteristics for making the bottle of the present invention include the
mold venting
and base design. For blow molding design, it has been established that PLA
blows
into contours and details very well giving better definition than PET would
allow.
19
CA 02651391 2009-01-28
From a mold design standpoint, the air vents and mold parting lines should be
minimized so these areas are not accentuated due to the flowing nature of this
material. The air vent diameters generally used for PLA are half the size of
those
found in a typical PET mold.
[0063] The blow molds used in accordance with the present invention
have smaller pin vents in the base area to prevent the material from flowing
into the
pin vent area. The bottle face vents for a bottle mold to produce a bottle
having
substantially circular and substantially elliptical cross-sections in the main
body of the
bottle as in the present invention were vented through a parting line with a
face vent
that was 0.003 inches to prevent material from flowing into this vent. Pin
vents are
not required in the base or bottle sidewall for the bottle having an oval and
round =
cross-sections. A bottle mold with no pin vents in either the base or bottle
sidewall is
not uncommon for polypropylene or PLA containers as these materials tend to
flow
into any mold details and would be aesthetically unacceptable with pin. vents
or on
bottle designs that do not need the venting in order to fnlly blow into the
botde mold.
[0064] As discussed above, PLA resin is typically supplied as a
crystallized pellet. Since the material degrades at melt temperatures in the
presence of
moisture, PLA pellets should be stored utader conditions that minimize
temperature
and humidity exposure and prevent moisture. absorption. PLA resin is typically
supplied in gaylord cartons or super sacks which are sealed to prevent
moisture
absorption. Once transferred into bulk handling systems, such as silos or
hoppers, the
PLA resin may be purged with dry air or nitrogen to minimize moisture gain.
Unopened containers are often allowed to equilibrate prior to opening when
transferring material from a cold environment to prevent condensation of
moisture on
CA 02651391 2009-01-28
the pellets. As PLA is a hygroscopic material, it should be dried prior to
melt
processing to minimize degradation and loss in molecular weight. If not
properly
dried, PLA may produce hazy, poor quality preforms or unacceptable bottles.
The
material should be dried to a moisWre level below 100 ppm moisture to prevent
adverse effects on the PLA. Karl Fischer method or a gravimetric moisture
analyzer
may be used to confirm that the moisture level is acceptable. For processing
with
unusually long melt residence time or melt temperatures above 240 C, PLA is
often
dried further to a moisture level below 50 ppm to ensure molecular weight
retention
and stability. After opening, any PLA resin containers are typically sealed to
prevent
moisture gain.
[0065] The PLA resin can be dried in standard desiccant bed dryers
commonly used for PET drying. In dryers with a regeneration cycle between
desiccant
beds, care must be taken to ensure that the resin pellets do not experience a
spike in
temperature as the dryer cycles from one desiccant bed to the other. If a
spike in
temperature in excess of 150 C is experienced, the PLA resin pellets may melt
due to
the excessive heat causing bridging or blocking air flow around the dryer
cone. The
drying conditions set forth in Table 2 below may suitably be used with the
present
invention.
[0066] Table 2
Drying Parameter Recommended Settings
Residence Time (hours) 4
Air Temperature F ( C) 212 (100)
Air Dew Point F ( C) -30 (-35)
Air Flow Rate, CFM/]b resin (m /hr-kg >0.5 (1.85)
resin)
21
CA 02651391 2009-01-28
[0067] Once dried, the resin should be transferred to the injection molding
system through sealed transfer lines. Jacketing or nitrogen purging of
transfer lines is
recommended, but not necessary. Dedica.ted transfer lines for PLA are
preferred to
prevent cross-contamination with PET fines that can accumulate in the transfer
lines
or dryer. As mentioned above, when running on existing PET equipment, the
dryer
and all transfer lines are thoroughly cleaned to remove PET pellets, angel
hair, and
fines. Any PET that transfers into the injection molding equipment may create
an un-
melted contaminant when molded into the preforms.
[0068] A suitable PET purging process may be accomplished by running a
compound such as polypropylene or- polyethylene through the entire injection
system,
at the current resin's operating temperatures for at least 30 minutes.
Advantageously,
higher viscosity polypropylene may be initially used in the purge process and
then
followed by use of a lower viscosity.polypropylene as the temperature is
decreased to
improve purging effectiveness. System temperature is then decreased to PLA
melt
temperature and PLA is then introduced into the molder at its recommended
operating
temperatures until. the PLA purge becomes clear. If polypropylene is not
available a
typical purging compound may also produce satisfactory results.. Molding
machines
with shooting pots may take longer to purge then conventional molding machines
because of the increased areas in which resin can "hang up" or accumulate.
Upon
shutdown or changeover to another material, the molding equipment should again
be
purged with polypropylene to remove any residual PLA.
[0069] To augment preform heating during the blow molding process, IR
reheat additives may be incorporated into the preform in the injection molding
step.
22
CA 02651391 2009-01-28
Color concentrates or liquid colorants can be incorporated into the PLA resin
preforms at a letdown ratio. In such production systems, the liquid colorant
is fed into
the throat of the injection molding press using a liquid color pump that is
calibrated to
deliver at the desired let-down ratio. PLA is typically melt processed with
general
purpose or barrier-type screws to produce preforms suitable for blow molding.
Injection molding problems encountered in the past have included the hot
runner tips
pulling off, splay, swirl in the endcap, and preform shrinkage upon reheat.
[0070] Table 3 below lists the injection molding conditions used as a
starting point for process optimization. Similar conditions were used to
injection
mold a 22.4g preform with a finish that is referred to in the industry by the
Closure
1Vlanufacturers Association as a PCF-26P=1, Voluntary Standard Flat Water
Finish
("26P") fmish, in accordance with the present invention. If the unit cavity
prototype
tool has only in-mold cooling, the cycle time is significantly longer than
would be
expected on production equipment.
[0071] Table 3
Barrel Tem eratures C 210-220
Mold Temperature C 23-25
Nozzle Temperature ( C) 210-220
Injection Pressure (bar) 350-700
In'ection S eed (ccm/s) 12.0
Circumferential Screw Speed m/min 10.0-25.0
Back Pressure (bar) 10-25
Cycle Time sec 27.0-27.5
[0072] PLA preforms should be clear, with no haze or visible
contaminants. Good preform concentricity less than 0.005 inches is important
to
produce even radial material distribution in the bottle. PLA can also be
analyzed for
23
CA 02651391 2009-01-28
molded-in stresses using the cross-polarized lights. It is important to
minimize
molded-in stress as the preforms shrink during the reheating process to
relieve any
molded-in stress. This shrinking causes dimensional changes in the PLA preform
that
impacts its fit into the blow mold neck plate and affects the stretch ratio
between
preform and bottle. PLA preforms may also craze as they shrink upon reheating
and
form waves or ridges that will blow out in the well-oriented sections, but
show as
visual defects in the un-oriented sections. For this reason, injection molding
conditions should be optimized as much as possible to minimize molded-in
stress. A
quick quality tool used to evaluate the molded-in stresses is to evaluate the
preform
appearance under cross-polarized lighting. The process can be adjusted to
minimize
the. appearance of differential stress patterns that appear under cross-
polarized lights.
Another tool for measuring preform molded-in stress is to measure the preform
before
and after immersing the preform in 180 C to 185 C water for one minute. The
preform shrinkage under this condition should.not exceed 4%. During extended
runs,
plate-out of lactide may occur in the form of a very fine powder deposit on
the
tooling. This can be removed with a soft cloth routinely during the injection
molding.
Plate-out may also occur if injection speeds are tbo low, and or mold
temperature is
too cold, or machine shut-down causes excessively long melt residence
time.
[0073] The second step in producing a bottle through two-stage blow
molding after the step of heating the preform is to inflate the preform into a
mold.
The manner in which the prefonns are heated impacts bottle clarity and
material
distribution. The preform heating should be optimized to achieve an even
sidewall
distribution of material and highly oriented base. Preform temperatures for
PLA
24
CA 02651391 2009-01-28
preforms after heating range from 85 C to 95 C, depending upon the point of
measurement and preform to bottle matchup. Unlike PET which can generally be
processed over a rainge of 15 C to 20 C, the processing window for PLA for a
given
preform and bottle combination is typically significantly smaller in the 5 C
range. As
the preform temperature increases, the bottle base weight will increase
significantly
similarly to PET. At the lower end of the preform temperature, the bottle has
pearlescence or blow out during the blow molding process. For a given preform
and
bottle combination, the blow. molding window is determined by varying the
overall
oven power input to determine the upper and lower limits. FIG. 7 illustrates
the
sensitivity of bottle base weight to preform temperature for PET and PLA. As
illustrated, for PLA a slight change in preform temperature can result in a
significant
change in the base weight of the resulting bottle. As discussed above, the
preforms
are heated in the blow molding oven using infrared heaters. Thus, the outside
wall is
heated first and as the energy penetrates through the wall, the inside of the
preform
becomes heated. As the inside of the preform must stretch significantly
farther during
the blow molding process, this must be sufficiently heated to avoid blowouts
or haze
in the bottle. The soak time for the preforms between ovens is important to
allow the
heat to equilibrate throughout the prefonn wall. This soak time is dependent
upon
wall thickness of the preform. Ariother consideration during PLA blow molding
is to
liinit the time between preform transfer from the oven into the blow mold and
where
possible, ensure that .this time is consistent among all blow. molding
cavities.
Differences in this dwell time between oven and, blow molding can lead to
inconsistent bottle material distribution and quality.
CA 02651391 2009-01-28
[0074] The air pressures required to blow mold PLA are typically lower
than those used for PET, but must be optimized for a given preform and bottle
combination.
Because PLA strain hardens earlier than PET, stretching speeds and timing are
slightly
different with earlier stretching used for PLA. Stretching speeds of 1.2 m/s
to 2.0 m/s
have been successfully used to produce acceptable PLA bottles. The bottle mold
temperature is generally warm while the base mold is cooled to 40 F to
quickly cool
that area. Due to the lower Tg of PLA, the bottle cooling should be optimized
to
ensure that the bottle dimensions meet specifications. Excess amorphous materi
al
remaining in the base will remain pliable after exiting the blow mold. This
material
-may deform because the material remains above Tg after exiting the blow mold.
Additional mold cooling, such as air jets, may be.incorporated to quickly cool
and
harden this center base area. As discussed above, the base design can also be
adjusted
to facilitate more stretch orientation in the base area and prevent excessive
material
there. As the bottle is removed from the blow mold, if the base is too
pliable, it will
snap back causing the base to bulge outwardly or can stick onto the base mold
carrier
and prevent the bottle from being removed from the blow mold. Thus, the base
mold
design and cooling are important considerations. Blow molding considerations
are
listed in Table 4 below to assist in the optimization process.
[0075] Table 4: Parameter Setting
Parameter Setting
Low Pressure Minimize
Hi h Pressure Minimum that produces acceptable bottle
Mold Temp 70-100
Base Mold Temp. ( F 40
Prefonn Temp. C 80-95
26
CA 02651391 2009-01-28
[0076] Exposure to high temperatures and humidity during shipping
adversely affect bottle dimensional stability and permeation. The reconunended
storage temperature of the bottle is below about 105 F. However, this is not
always
possible given the high temperatures experienced during shipping and warehouse
storage.
[0077] Preform
[0078] FIG. 8A illustrates a preform 20 in accordance with the present
-invention. FIG. 8B illustrates a longitudinal sectional view of the preform
20 of FIG.
8A in accordance with the present invention.
[0079] As shown in FIG. 8A, a preform 20 comprises a finish portion 25, a
transition portion 26, a body 27, and an end cap 29. The finish portion 25 of
the
preform 20 comprises threads, referred to as the -"finish," and what is
referred to as the
"finish ledge" 30: The transition portion 26 of the preform 20 comprises the
portion
between the finish ledge 30 of the finish portion 25 and the body 27 of the
preform
20. The body 27 of the preform 20 comprises the portion of the preform between
the
transition portion 26 of the preform 20 and the end cap 29 of the preform 20.
The end
cap 29 of the preform 20 is positioned at the closed end 22 of the preform 20.
[0080] A preform 20 suitable for blow molding a 500 mL biodegradable
bioresin bottle in accordance with the present invention has a preform weight
in the
range of 21 to 23.5 g, preferably 22 g to 23 g. Inventors of the present
application
believe that it may be possible with continued further effort to create a
suitable PLA
preform having a lower weight than 21g but still be within the scope of the
present
invention.
27
CA 02651391 2009-01-28
[0081] In accordance with the present invention, the finish portion 25 of
a 22 g to 23 g preform preferably has.an inside diameter of between about 21
mm and
about 22.5 mm, more preferably about 21.5 mm to about 22 mm. The finish ledge
30
of a 22 g to 23 g preform preferably has an external diameter of about 31 nun
to about
32.5 mm, more preferably about 31.5 mm to about 32 mm. The finish portion 25
of a
22 g to 23 g preform to the fmish ledge 30 preferably has a length of about
16.5 mm
to about 17.5 mm, more preferably between about 16.9 mm to 17.2 mm.
Preferably,
the finish is a 26P (Standard Flat Water Finish) as is known in the industry.
[0082] The transition portion 26 of the preform 20 also has a preform wall
thickness that varies along its length. For a preform 20 having a weight range
of 22 g
to 23 g, the wall thickness in the transition portion 26 of the preform 20
ranges from
about 1.5 mm to about 3.5 mm, more preferably from about 2 mm to about 3 mm,
with the thinnest wall thickness of the transition portion 26 being adjacent
the finish
ledge 30.
[0083] The transition portion 26 of the preform 20 also has an inner
.diameter that varies across its length. In accordance with the present
invention, the
inner diameter of the transition portion 26 of a 22 g to 23 g preform
preferably ranges
from about 21 mm to about 22 mm, more preferably 21.5 mm to 22 mm, at its
widest
diameter to about 18 to about 19 mm, more preferably 18 nim to 18.5 mm, at its
narrowest diameter. The larger inner diameter is nearer. the fmish. The length
of the
transition portion 26 of a 22 g to 23 g preform is preferably about 13.5 to
about 14.5
mm. The transition portion 26 of a 22 g to 23 g preform preferably has an
external
diameter that varies aloing its length ranging from about 25 mm to about 26 mm
at its
widest diameter, to about 23.5 mm to 24.5 mm at its narrowest diameter.
28
CA 02651391 2009-01-28
[0084] In accordance with the present invention, the body 27 of a 22 g to
23 g preform 20 preferably has an inner diameter of about 18 mm to about 19
mm,
more preferably about 18 mm to about 18.5 mm. The length of the body 27 of a
22 g
to 23 g preform is from about 57 mm to about 58 mm. The body 27 of a 22 g to
23 g
preform preferably has an external diameter that ranges from about 23.5 mm to
about
24.5 mm. The body 27 of a 22 g to 23 g preform has a wall thickness in a range
of
from about 2 mm to about 3 mm, more preferably from about 2.5 mm to about 3
mm.
[0085] The end cap 29 of an.a 22 g to 23 g preform preferably has an inner
diaineter of about 17 mm to about 18 mm, more preferably about 17.5 mm to
about 18
mm. The end cap 29 of the preform preferably has a length of from about 11 mm
to
about 12 mm. The end cap 29 of a 22 g to 23 g preform has an external diameter
in
the range of from about 23 mm to 24 mm. The end cap 29 has a wall thickness at
the
closed portion of the end cap in a range of about 2 mm to about 3 mm, more
preferably from about 2 mm to about 2.5 mm. In the preform 20 of the present
invention, the preform end cap thickness is generally thinner than the prefqrm
body
wall thickness to prevent excess material in the base area during blow
molding. For a
22 g to 23 g preform, the ratio of the wall thickness of the body 27 of the
prefonn 20
to the wall thickness of the closed end cap 29 is in a ratio of from about 1:
0.70 to
about 1 : 0.80.
[0086] In the present invention, the preform 20 is injection molded and
subsequently blow molded into a biodegradable bioresin bottle having a desired
configuration and polymeric material weight distribution. The biodegradable
bioresin
bottle of the present invention is particularly suited for non-carbonated
beverages such
as water.
29
CA 02651391 2009-01-28
[0087] A feature of the preform 20 of the present invention is that it is
configured to avoid sharp transitions from thick to thin wall sections as this
may
produce stress-whitening in the bottle blow molding process. These preform
features
are particularly important to achieve bottle clarity, performance, and
consistency,
which is especially difficult to achieve in a biodegradable resin bottle,
particularly a
biodegradable resin bottle comprising PLA.
[0088] Another feature that is an improvement over existing biodegradable
rosin.preforms is that the preform designs. of the present invention account
for the
shrinkage factor associated with PLA. PLA prefonns shrink slightly during the
reheating process, causing the preform diameter to increase and the overall
length to
decrease. For the inside dimensions, prefonm shrinkages of 0.005 inch/1 inch
on
preform inner diameter and 0.008 inch/1 inch on preform length are applied to
the
plastic print to design the injection mold tooling. For example, to produce
the plastic
-dimension of 1 mm tooling is manufactured to a dimension of 1 mm x 1.005
mmlmm.
On the outer dimensions, shrinkages of 0.011 inch/1 inch are applied to the
preform
outer diameter and 0.008 inch/1 inch are, applied to the preform length.
[0089] From an injection molding tooling standpoint, injection mold
tooling is polished on both the core and the cavity to prevent drag lines or
marks in
the preform as to prevent visual bottle defects.
[0090] Blow moldin~
[0091] Referring to the figures, FIG. 9 illustrates a suitable blow mold 40
for blow molding a biodegradable bioresin bottle in accordance with the
present
invention. The blow mold 40 generally comprises a blow mold mandrel 41, a
finish
CA 02651391 2009-01-28
protection insert 42, a blow mold cavity 43, a mold carrier 44, a locking ring
45, a
base insert 46, a preform 20, and a base adapter 47.
[0092] To address the problem associated with shrinkage, if a blow mold
top plate is used (not shown in FIG. 9), it is designed to have enough
clearance
between the PLA preform after it is heated in the oven and the top plate
diameter to
ensure sufficient clearance between the preform neck and the mold during the
blow
molding.
[0093] Blowouts of PLA material refer to small spikes coming out of the
bottle sidewall with a hole in the center. To avoid problems associated with
blow outs
of the PLA material, pin vents, mold seams and/or parting lines must be
minimized so
that these areas are not accentuated due to the flowing nature of PLA. The
molds to
produce a biodegradable bioresin bottle in accordance with the present
invention have
face vents at the parting lines of the bottle mold. For example, the bottle
face vents,
the molds are vented through the parting line with a face vent that is about
0.003
inches to prevent material from flowing into this vent. Pin vents are not
required in
the base or the bottle sidewall for the biodegradable bioresin bottle of the
present
invention.
[0094] In another aspect of the method of the present invention, the
preform is stretch blow molded to molecularly orient the side walls of the
bottle. The
side walls of the bottle are preferably stretch blow molded to molecularly
orient a
predetermined location of the bottle, more preferably the second. portion of
the main
body to be discussed herein. The oriented side walls of the bottle are
generally
thinner than the molecularly unoriented regions of the walls. The desired
orientation
31
CA 02651391 2009-01-28
is achieved by stretching the preform during blow molding in a ratio of
preform to
bottle so as to provide a bottle that deforms in a predetermined location.
[0095] Biodegradable Bioresin Bottle
[0096] The various portions of a container such as a plastic drinking water
bottle may generally be described using the following terminology. The "base"
is the
bottom portion of a bottle. When a bottle is placed upright on a surface, the
base is
that portion of the bottle in contact with the surface. The body or "main
body" of a
bottle is the principal portion of the bottle, usually the largest portion of
a bottle. The
"shoulder" is the portion of a bottle in which the cross section area of the
body
decreases to join. the neck. In other words, the shoulder is the sloped area
of a bottle
between the main body and the neck. The "neck" is that portion of a bottle
where the
shoulder cross section area decreases to form the "finish." The "finish"
refers to a
configuration or opening of a bottle that is shaped to accommodate a specific
closure.
The finish is the portion of the neck having threads, lugs or friction fit
members to
which a closure is applied. A bottle, therefore, may generally be described
from top
:to bottom as having a finish (which is part of the neck), a shoulder, a main
body and a
base.
[0097] With respect to terminology used herein, the "longitudinal axis" of
a bottle refers to. an imaginary axis connecting the center of the opening of
the fiiiish
and the center of the base of the bottle. Thus, when the bottle is positioned
upright on
its base on a horizontal surface, the longitudinal axis of the bottle is
oriented generally
vertically. "Inward" as used herein refers to a direction of travel or path
toward the
inside of a bottle; "outward" as used herein refers to a direction of travel
or path away
from the inside of the bottle. A "rib" is a continuous indentation toward the
inside of
32
CA 02651391 2009-01-28
a bottle. As used herein, a "circumferential rib" is a rib that is continuous
around the
entire circumference of a bottle.
[0098] The present invention provides a biodegradable bioresin bottle that
overcomes the problem of unacceptably significant paneling in known PLA
beverage
bottles caused by the high water vapor transmission rate of PLA. Tuming now to
FIG. 10, a biodegradable bioresin bottle 50 in accordance with an embodiment
of the
present invention includes a finish 51, a shoulder 52, a main body 53 and a
base 54.
Advantageously, the finish 51 may be a 26P ("Standard Flat Water Finish").
[0099] The main body 53 comprises a first portion 55 and a second portion
56. Advantageously, the cross sectional shape of the first portion 55 of the
main body
53 may differ from the cross sectional. shape of the second portion 56 of the
main
body 53. For example, as illustrated in FIGS. 12A and 12B, the cross sectional
shape
of the first portion 55 of the main body 53 may be substantially circular (as
shown in
FIG. 12A) and the cross sectional shape of the second portion 56 of the main
body 53
may be substantially elliptical (as shown in FIG. 12B). The cross sectional
shape of
the first portion 55 of the main body 53 thus has a diameter d and the cross
sectional
shape of the second portion 56 of the main body 53 has a major axis Al and a
minor
axis A2.
[00100] .. It has been found that a bottle having a base above zero to about
22 mm, a second portion of the main body height of from about 22 nmm to about
100
nun, a first portion of the main body a height of from about 100 mm to about
150 mm
and a shoulder height of from about 150 mm to the location of the ledge of the
fmish
may be suitably used in accordance with the present invention. The height of
the
finish depends upon the dimensions of the finish selected.
33
CA 02651391 2009-01-28
[00101] It has 'been found that a bottle having a shoulder 52 of largest width
at the position where it meets the first portion 55 of the main body may be
advantageously used in accordance with the present invention. From that
location,
the width of the bottle decreases between the shoulder 52 and the first
portion 55 of
the main body by a ratio of about 1: 0.96. The width then increases where the
first
portion 55 meets the second portion 56 of the main body by a ratio of about
1:1.04.
Preferably, the width of the bottle where the shoulder 52 meets the first
portion 55 is
the same as the width where the, first portion 55 meets the second portion 56.
In the
case of a circular cross-section, the width is the diameter.
[00102] , In the second portion 56, the cross-sectional area of the elliptical
cross section decreases until reaching its narrowest point, typically near the
longitudinal midpoint of the second portion 56, and then increases until
meeting the
base. The cross-section of the bottle at the pinch point. is substantially
elliptical as
opposed to circular. The ratio of the minimum diameter of the second portion
to the
maximum diameter of the second portion is about 0.8: 1. Preferably, the width
of the
base (which is the diameter since the base has a substantially circular cross-
section) is
the same as the width of the shoulder of the bottle and the first portion of
the bottle at
their respective widest points.
[00103] In accordance with the present invention, for an about 22 g to 23 g
preform, the diameter of the base at its widest point is from about 67.5 mm to
about
68.5 mm. The .length of the major axis Al of the second portion of the main
body at
its widest point is from about 67.5 mm to about 68.5 mm. The diameter of the
shoulder of the bottle at its widest point is from about 67.5 mm to about 68.5
mm.
The diameter of the first portion varies between about 67.5 mm to about 68.5
mm, to
34
CA 02651391 2009-01-28
about 65 mm to about 66 mm along the height of the bottle. The length of the
minor
axis A2 of the second potion at its narrowest point in the second portion is
in a range
from about 53.5 mm to about 54.5 mm.
[00104] In a preferred embodiment, one or more circumferential ribs 60 are
located on the first portion 55 of the main body 53 and no circumferential
ribs are
located on the second portion 56 of the * main body 53. Advantageously,
circumferential ribs 60 located on the first portion 55 of the main body 53
may be
"wave-like circumferential ribs," meaning that the height of the rib above the
lowest
portion of the base varies at different circumferential positions between a
maximum
height and a minimum height. For example, in FIG. 11A the uppermost
circumferential rib is a wave-like circumferential rib that varies in height
along the
circumference of the bottle between a maximum height Hm. and a minimum height
~~.
[00105] The diameter of the shoulder 52 at the position 62 where . the
shoulder meets the first portion of the main body 55 may be substantially
equal to the
diameter of the second portion of the main body 56 at the position, 63 where
the
second portion of the main bctdy meets the first portion of the main body; and
both of
these diameters may be greater than the diameter of the first portion of the
main body.
In this way, a label placed circumferentially around the first portion of the
main body
will be prevented from rubbing against adjacent bottles or surfaces.
[00106] As illustrated in FIGS. 11, 11A and 11B, one or more arcuate
projections 61 may extend outwardly from the second portion 56 of the main
body 53.
Groups of spaced arcuate projections may be positioned at opposite ends of the
minor
CA 02651391 2009-01-28
axis A2 (as best illustrated in FIG. 11, and "face" concave upwardly (as
illustrated in
FIG. 11A) or concave downwardly (as illustrated in FIG. 11B) or both.
[00107] It has been found that PLA bottles have a tendency to deflect in the
amorphous base region if the PLA material is not adequately stretched or
cooled
during bottle production. Base sagging or deflection can result in a
peiformance and
aesthetic concern and in addition could cause volumetric fluctuations during
the bottle
filling.
[00108] Turning to FIGS. 6A and 6B, the present invention addresses this
tendency by providing a base design in which a first generally semicircular
"pushup"
region 65 extends into the bottle, a second, smaller generally semicircular
region 66
extends further into the bottle from the center of the first semicircular
region, and a
plurality of ribs 67 extending radially outward from the second semicircular
region
66. It should be noted that a small portion 68 of resin in the center of the
second
semicircular region 66 will often sag, thus making the second semicircular
region 66
not completely semicircular in shape. It has been found that a base pushup
depth
greater than about 10 mm, and preferably about I 1 mm to about 13 mm, and a
pushup
diameter in the range of about 49 mm to 50.5 mm, and preferably 50 mm to 50.5
mm,
may be suitably used in accordance with the present invention.
[00109] The bottle of the present invention addresses the paneling problem
created by PLA's relatively high water vapor transmission rate by utilizing a
second
portion 56 of the main body 53 of the bottle that has a different cross
sectional shape
than the 'fust portion 55 of the main body 53 and a lower hoop stiffness than
the first
portion 55 of the main body 53.
36
CA 02651391 2009-01-28
[00110] As illustrated in FIGS. 10, 12A and 12B, the cross sectional shape
of the first portion 55 of the main body 53 is substantially circular and the
cross
sectional shape of the second portion 56 of the main body 53 is substantially
elliptical.
A plurality of circumferential ribs 60 are. used to add hoop stiffness to the
first
portion 55 of the main body 53 and no circumferential ribs are used on the
second
portion 56 of the main. body 53. A- plurality of longitudinally spaced arcuate
projections 61 are positioned on the second portion 56 of the main body 53 at
the ends
of the minor axis A2 of the elliptical cross sectional shape to add localized
stiffness at
these locations.
[00111] Deformation of the bottle of the present invention in response to
vacuum creation inside the bottle is illustrated in FIGS. 12A, 12B and 13.
FIGS. 12A
and 12B illustrate, respectively, the cross sectional shapes of the first
portion 55 of
the main body 53 is substantially circular and the cross sectional shape of
the second
portion 56 of the main body 53 as such shapes exist before vacuum has been
created -
inside the bottle. As water vapor permeates outwardly through the bottle, a
vacuum is
created inside the bottle. In response, the second portion 56 of the main body
53
deforms inwardly in a direction that is generally parallel to the minor axis
A2 of such
portion and deforms outwardly in a direction that is generally parallel to the
major
axis Al of such portion. The resulting deforrnation is illustrated in FIG. 13,
in which
the length of the minor axis A2' after deformation is less than the length of
the minor
axis A2 before such deformation and the length of the major axis Al` after
deformation is greater than the length of the major axis Ai before such
deformation.
In this way, hoop stiffness, localized stiffness and cross sectional body
geometry are
utilized to control the resulting shape of the bottle after vacuum-induced
paneling.
37
CA 02651391 2009-01-28
= ' ,
After such deform-ation the cross sectional shape of the first portion of the
main body
is substantially circular, just as before such deformation. Similarly, the
cross section
shape of the second portion of the main body after such deformation is
substantially
elliptical, just as before such deformation, but after such deformation the
major axis
thereof is longer and the minor axis thereof is shorter than before such
deformation.
[00112] Prefonn stretch ratios are used to =blow mold the biodegradable
resin bottle of the present invention having round and oval cross-sectional
areas. The
term "preform stretch ratio" is well known to one of ordinary skill in the art
and is
typically defmed by the following defmitions.
[00113] The term "hoop stretch ratio," as used herein, is defined as the ratio
of the largest inner diameter (Dl) of the blown article to the inner diameter
(132) of
the body of the preform, or D1/D2.
[00114] The tenn "axial stretch ratio," as used herein, is defined as the
ratio
of the height of the blown article below the threaded neck finish (AS 1) to
the height
of the preform below the threaded neck fmish (AS2), or AS1/AS2.
[00115] The term "overall stretch ratio," as used herein, refers to the
product of the hoop stretch ratio and the axial stretch ratio.
[00116] . The axial stretch ratio is in a range of about 2 to about 3.2,
preferably about 2.4 for a PLA bottle having been blow molded from a preform
having a weight in the range of 21 g to 23.5 g, preferably about 22 g to 23 g.
The
hoop stretch ratio is in a range of about 3 to about 4, preferably about 3.5
to about 3.8
for a PLA bottle having been blow molded from a preform having a weight in the
range of 21 g to 23.5 g, preferably about 22 g to 23 g. The overall stretch
ratio is in a
range of about 6 to 13, more preferably about 8 to 10 for a PLA bottle having
been
38
CA 02651391 2009-01-28
blow molded from a preform having a weight in the range of 21 g to 23.5 g,
preferably about 22 g to 23 g.
[00117] EXAMPLES
[00118] Injection Mold Example
[00119] In this trial, PLA preforms were injection molded on, the unit cavity
Arburg injection molding press after the resin was dried for hours to a
moisture level
below 250 ppm. Preforms were made with ColorMatrix colorant #85-3243-5 at a
0.06% letdown ratio (LDR). The injection molding machine was prepared to run
PLA
by removing and cleaning the injection screw and barrel until free of PET. The
injection molding conditions were optimized to produce a clear part with no
visual
defects and minimal molded-in stress. The injection molding conditions used
are
shown in the below tables.
[00120] Table 5: General'Information
Variable Description 22.4 g PLA Preform with (85-3243-5 at
0.06%)
Machine #6 Arburg 420 M
(manufactured by ARBURG GmbH + Co
KG)
Preform Weight 22.7
Relative -Humidi 30%
Dew Point F 34.9
Mold Temperature F 60
Ambient Temperature F 67
Dryer Temperature ( F 175
[00121] Table 6: Barrel Temperatures
Feed C 216
Zone 2 C 216.
Zone 3 C) 215
Zone 4 C 215
Nozzle C 212
39
CA 02651391 2009-01-28
[00122] Table 7: Injection
Injection Pressure 1 (bar) 500
Injection Pressure 2 (bar) N/A
Injection Pressure 3 (bar) N/A
In'ection tinie sec 2.1
15 Injection Speed ccm/sec 12.0
2" In'ection Speed ccm/sec 10.0
3` Injection Speed ccm/sec 0.0
[00123] Table 8: Holding Pressure
Switch-Over Point ccm 10.0
ls Hold Pressure (bar) 350.0
2 Hold Pressure (bar) 275.0
3 Hold Pressure (bar) 200.0
4 Hold Pressure ar N/A
1 Hold Pressure Time (sec) 2.0
2 Hold Pressure Time sec 2.5
3 Hold Pressure Time sec 2.0
4 Hold Pressure Time sec 0.0
Remain Cool Time sec 10.0
[00124] Table 9: Dosage
Circumference Speed m/min 12.0
Back Pressure (bar) 25.0
Dosage Volume ccrn 27.0
Measured Dosage Time sec 3.0
Cushion ccm 5.4
[00125] Table 10: Adjustment Data
C cle Time sec 23.7
[00126] Blow molding Example
[00127] A polylactic acid (PLA) preform having a weight of 22.7 g with a
"26P" (standard flat water) finish was used.
CA 02651391 2009-01-28
[00128] This preform was to be used to blow mold a 500 mL PLA water
bottle having substantially circular and substantially elliptical cross-
sections in the
main body of the bottle. The bottle had the following section weights:
[00129] Table 11
Section Section Weight (g) Cuts Height (mm)
Descri tion
Shoulder 6.7 150-top
1S Portion of 4.1 100-150
Main Bod
2" Portion of 6.3 22-100
Main Body
Base 5.6 0-22
[00130] At room temperature a preform was provided and turned upside
down on a spindle, passed over a bank of ovens, and was heated with infrared
(IR)
heat lamps. The actual preform temperature was measured after the preform
exited
the oven. The actual preform temperature was measured as 83 C. The location
on
the preform where the temperature was measured was 30 mm above the support
ledge
or "finish" of the preform just prior to blow molding the preform. The heated
preform
subsequently was sent to a Sidel SBO2/3 blow molding machine. The body and
base
of the blow mold setpoint temperature was 45 F.
[00131] The preforms were heated in the oven with equilibration between
oven banks and after exiting the oven before being blown. The blow molding
speed
was 'set at 2000 bottles per hour. The cam angle was 45 degrees. The stretch
speed
was 898.8 mm/s.
[00132] With respect to the heating of the preform prior to blow molding,
the preform was heated using ten (10) lamps as "zones" within an oven banlc.
The
percentage power refers to a percentage of power delivered to an individual
lamp
41
CA 02651391 2009-01-28
based upon the available power input. The percentage power that the bulb
produced
was set forth as a percentage. The position of the lamp was also indicated as
"In" or
"Out" whereby the "In" position was closer to the preform and the "Out"
position was
further away from the preform. For example, Zone 1 was nearer the support
ledge or
fuush of the preform.
[00133] Each oven was set at the same overall power setting unless
individual lamps were "off' or "on" in one oven. There was no ability to have
different lamp settings in the same zone between ovens.
[00134] Table 12 : Lamp Settings
Lamp Location Percentage Oven I Oven 2 Oven 3 Position
Power (%)
Zone 10 Off Off Off
Zone 9 - Off Off Off
Zone 8' Off Off Off
Zone 7 57.0 On On Off In
Zone 6 45.0 On On Off In
Zone 5 63.0 On On Off Out
Zone 4 40.0 On On Off Out
Zone 3 35.0 On On . Off Out
Zone 2 45.0 On On Off Out
Zone 1 87.0 On On On In
[00135] The entire ovens were moved as close to the preform as possible
during the blow molding setup to most effectively heat the preform.
[00136] In addition to the ten (10) individual lamp settings; there was an
overall power input that was used to adjust preform reheating. The overall
power
input to the ovens was represented as AL1 (standby) and AL2 (startup). The AL1
(standby) was set at 74%and the AL2 (startup) was set at 74%. Oven ventilation
was
used to cool the outside of the preform while heating it in the oven in order
to get the
heat to penetrate through the wall of the preform. The venting was set at
100%.
42
CA 02651391 2009-01-28
[00137] The preform was used to blow mold the PLA bottle. The preforms
were placed into the blow mold and the stretch rod pushed the preform axially
down
into the bottom of the mold as preblow pressure air was applied to begin
stretching.
The stretch rod size was 10 mmf. The stop length was 12 inches.
[00138] "High blow" referned to the position where the very high pressure
was applied to fully orient the preform into the bottle mold.
[00139] With respect to the blow pressures used for blow molding, the
"low" blow was measured at 4 bar and the low blow flow was measured at 7.5
turns
open. The low blow position was 37 The "high" blow came on later and was
measured at 32 bar and fully blew the bottle. The high blow position was 80 .
[00140] EXAMPLE - BOTTLE MATERIAL DiSTRIBUTION
(SIDEWALL THICKNESS) PROFILE
[00141] Material distribution data was obtained for a 22.4g PLA bottle with
a 26P finish having substantially circular and substantially elliptical cross-
sections in
the main body of the bottle.
[00142] A Top Wave GAWIS-STD was used to measure the wall thickness
of twelve such bottles. Measurements were taken at 56 locations on the bottle,
as
shown in the following results table. Each bottle was measured at 16 height
locations
and four locations around the surface of the bottle. The data below is
reported as the
average of the bottle samples tested.
[00143] Table 13
Location Height Height Subgroup Averages (inches) Standard
(as measured (inches Deviation
in inches) converted
to mm)
00 90 180 270
Shoulder 7.288 185.1 0.018 0.020 0.018 0.020 0.001
43
CA 02651391 2009-01-28
Shoulder 6.788 172.4 0.012 0.012 0.012 0.013 0.000
Shoulder 6288 159.7 0.012 0.012 0.013 0.012 0.000
First
Portion of
Main
Body 5.788 147.0 0.012 0.013 0.013 0.014 0.001
First
Portion of
Main
Body 5.288 134.3 0.013 0.013 0.014 0.014 0.001
First
Portion of
Main
Body 4.788 121.6 0.012 0.013 0.000
First
Portion of
Main
Body 4.668 119.1 0.012 0.013 0.001
First
Portion of
Main
Body 4.400 111.8 0.010 0.011 0.000
First
Portion of
Main
Body 4.380 111.3 0.011 0.012 0.000
Second
Portion of
Main
Body 3.788 96.22 0.011 0.011 0.012 0.011 0.000
Second -
Portion of
Main
Body 3.288 83.52 0.013 0.013 0.014 0.013 0.001
Second -
Portion of
Main
Body 2.500 63.50 0.015 0.013 0.017 0.013 0.002
Second
Portion of
Main
Body 1.788 45.42 0.013 0.015 0.017 0.015 0.002
Second
Portion of 1.288 32.72 0.014 0.015 0.016 0.016 0.001
44
CA 02651391 2009-01-28
Main
Body
Base 0.669 0.012 0.011 0.013 0.012 0.000
Base 0.321 0.013 0.013 0.015 0.013 0.001
(00144] It will therefore be readily understood by those persons skilled in
the art that the present invention is susceptible of broad utility and
application. Many
embodiments and adaptations of the present invention other than those herein
described, as well as many variations, modifications and equivalent
arrangements,
will be apparent from or reasonably suggested by the present invention and the
foregoing description thereof, without departing from the substance or scope
of the
present invention. Accordingly, while the present invention has been described
herein
in detail in relation to 'its preferred embodiment, it is to be understood
that this
disclosure is only illustrative and exemplary of the present invention and is
made
merely'for purposes of providing a full and enabling disclosure of the
invention. The
foregoing disclosure is not intended or to be construed to limit the present
invention
or otherwise to exclude any such other embodiments, adaptations, variations,
modifications and equivalent arrangements.
