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Claims  |
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We claim:
1. A container for holding a pressurized product, said container having a
substantially transparent sidewall formed of a molecularly oriented
polymeric material comprising
a polymer containing moieties derived from a conjugated diene monomer and
a polymer containing moieties derived from an alpha, beta-olefinically
unsaturated mononitrile having the formula
##EQU1##
where R is selected from the group consisting of hydrogen, an alkyl group
having from 1 to 4 carbon atoms, and a halogen,
said sidewall having an average circumferential orientation release stress
between about 500 and about 2500 p.s.i. as measured for total sidewall
thickness.
2. The container of claim 1 wherein the conjugated diene monomer is
selected from the group consisting of butadiene and isoprene.
3. The container of claim 1 wherein the said polymeric material is a
composition containing 100 parts by weight of the nitrile-containing
polymer and from about 1 to about 20 additional parts by weight of said
polymer containing moieties derived from a conjugated diene monomer.
4. The container of claim 3 wherein said nitrile-containing polymer is a
polymer containing a major proportion of moieties derived from said
mononitrile.
5. The container of claim 4 wherein said moieties derived from conjugated
diene monomer comprise a major proportion of the polymer containing said
moieties.
6. The container of claim 4 wherein the said orientation release stress is
between about 500 and about 1600 p.s.i. and wherein the amount of the said
polymer containing moieties derived from a conjugated diene monomer is
from about 10 to about 20 parts by weight.
7. The container of claim 5 wherein the said orientation release stress is
between about 500 and 1600 p.s.i., and wherein the amount of the said
polymer containing moieties derived from a conjugated diene monomer is
from about 10 to about 20 parts by weight.
8. The container of claim 3 wherein the amount of the said polymer
containing moieties derived from a conjugated diene monomer is from about
8 to about 20 parts by weight.
9. The container of claim 4 wherein the amount of said polymer containing
moieties derived from a conjugated diene monomer is from about 8 to about
20 parts by weight.
10. The container of claim 5 wherein the amount of the said polymer
containing moieties derived from a conjugated diene monomer is from about
8 to about 20 parts by weight.
11. The container of claim 4 wherein said sidewall has a creep strain in
the circumferential direction of less than 3% under a wall stress of 3000
p.s.i. in the circumferential direction at 100 hours at 98.degree. F at
50% relative humidity.
12. The container of claim 11 wherein the amount of the said polymer
containing moieties derived from a conjugated diene monomer is from about
8 to about 20 parts by weight.
13. The container of claim 4 wherein the nitrile is selected from the group
consisting of acrylonitrile and methacrylonitrile.
14. The container of claim 13 wherein the amount of the said polymer
containing moieties derived from a conjugated diene monomer is from about
8 to about 20 parts by weight.
15. The container of claim 5 wherein the nitrile is selected from the group
consisting of acrylonitrile and methacrylonitrile.
16. The container of claim 1 wherein the said polymeric material is a
composition resulting from the polymerization of a major portion of said
olefinically unsaturated nitrile and a minor portion of an ester of an
olefinically unsaturated nitrile and a minor portion of an ester of an
olefinically unsaturated carboxylic acid in the presence of a copolymer
having a major proportion of moieties derived from conjugated diene
monomer and a minor proportion of moieties derived from olefinically
unsaturated nitrile.
17. The container of claim 1 wherein the said polymeric material is a
composition resulting from the polymerization of 100 parts by weight of
A. a major portion of said olefinically unsaturated nitrile and
B. a minor portion of an ester of an olefinically unsaturated carboxylic
acid in the presence of from about 1 to about 20 additional parts by
weight of
C. a copolymer having a major proportion of moieties derived from
conjugated diene monomer and a minor proportion of moieties derived from
olefinically unsaturated nitrile.
18. The container of claim 17 wherein the conjugated diene monomer is
selected from the group consisting of butadiene and isoprene.
19. The container of claim 18 wherein there is employed at least 60% by
weight of (A), based on the combined weight of (A) and (B).
20. The container of claim 19 wherein the (B) component is an ester of an
alpha, beta-olefinically unsaturated carboxylic acid having the formula
##STR3##
where R.sub.1 is selected from the group consisting of hydrogen, an alkyl
group having from 1 to 4 carbon atoms and a halogen, and R.sub.2 is an
alkyl group having from 1 to 6 carbon atoms and wherein there is employed
up to 40% by weight of (B), based on the combined weight of (A) and (B).
21. The container of claim 1 wherein said sidewall has a creep strain in
the circumferential direction of less than 3% under a wall stress of 3000
p.s.i. in the circumferential direction at 100 hours at 98.degree. F at
50% relative humidity.
22. The container of claim 2 wherein said sidewall has a creep strain in
the circumferential direction of less than 3% under a wall stress of 3000
p.s.i. in the circumferential direction at 100 hours at 98.degree. F at
50% relative humidity.
23. The container of claim 17 wherein said sidewall has a creep strain in
the circumferential direction of less than 3% under a wall stress of 3000
p.s.i. in the circumferential direction at 100 hours at 98.degree. F at
50% relative humidity.
24. The container of claim 20 wherein said sidewall has a creep strain in
the circumferential direction of less than 3% under a wall stress of 3000
p.s.i. in the circumferential direction at 100 hours at 98.degree. F at
50% relative humidity.
25. The container of claim 1 wherein the nitrile is selected from the group
consisting of acrylonitrile and methacrylonitrile.
26. The container of claim 2 wherein the nitrile is selected from the group
consisting of acrylonitrile and methacrylonitrile.
27. The container of claim 20 wherein the nitrile is selected from the
group consisting of acrylonitrile and methacrylonitrile.
28. The container of claim 17 wherein the ester is selected from the group
consisting of methyl acrylate, ethyl acrylate and methyl methacrylate.
29. The container of claim 27 wherein the ester is selected from the group
consisting of methyl acrylate, ethyl acrylate and methyl methacrylate.
30. The container of claim 4 wherein the said nitrile-containing polymer is
a copolymer resulting from the polymerization of a major portion of said
mononitrile and a minor portion of an ester selected from the group
consisting of methyl acrylate, ethyl acrylate and methyl methacrylate.
31. The container of claim 1 wherein the said polymeric material is derived
from 73 to 77 parts by weight acrylonitrile and 27 to 23 parts by weight
methyl acrylate, polymerized in the presence of 8 to 10 additional parts
by weight of a nitrile rubber containing about 70 percent by weight
butadiene moieties and about 30 percent by weight acrylonitrile moieties.
32. The container of claim 21 wherein the said polymeric material is
derived from 73 to 77 parts by weight acrylonitrile and 27 to 23 parts by
weight methyl acrylate, polymerized in the presence of 8 to 10 additional
parts by weight of a nitrile rubber containing about 70 percent by weight
butadiene moieties and about 30 percent by weight acrylonitrile moieties.
33. The container of claim 3 wherein the nitrile is selected from the group
consisting of acrylonitrile and methacrylonitrile, the container has a
weight of from 0.03 to 0.13 gram per cubic centimeter of internal volume,
and said sidewall has a creep strain in the circumferential direction of
less than 3 percent under a wall stress of 3000 p.s.i. in the
circumferential direction at 100 hours at 98.degree. F at 50 percent
relative humidity.
34. The container of claim 1 weighing 0.03 to 0.13 gram per cubic
centimeter of internal volume blown from a thermoplastic polymer having an
oxygen permeability between 0.3 and 6.0 cubic centimeters per 100 square
inches per mil thickness and a carbon dioxide permeability between 0.5 and
10.0 cubic centimeters per 100 square inches per mil thickness, each
permeability being measured at a differential pressure of 1 atmosphere at
73.degree. F and zero percent relative humidity per 24 hours, said bottle
having a sidewall creep strain in the circumferential direction of less
than 3 percent under a wall stress of 3000 p.s.i. in the circumferential
direction at 100 hours at 98.degree. F at 50 percent relative humidity and
able to withstand a free fall of at least 3 feet onto a steel surface when
dropped on its bottom when enclosed and filled with water carbonated with
3.7 volumes of carbon dioxide per 1 volume of water.
35. The container of claim 1 weighing 0.03 to 0.13 gram per cubic
centimeter of internal volume blown from a polymer derived from about 60
to 90 parts by weight of acrylonitrile or methacrylonitrile and about 40
to 10 parts by weight respectively of an ester selected from the group
consisting of methyl acrylate, ethyl acrylate and methyl methacrylate,
polymerized in the presence of about 1 to 20 parts by weight of a nitrile
rubber containing about 60 to 80 percent by weight butatdiene or isoprene
moieties and about 40 to 20 percent by weight acrylonitrile or
methacrylonitrile moieties, said bottle having a sidewall creep strain in
the circumferentail direction of 0.25 to 3.0 percent under a wall stress
of 4000 p.s.i. in the circumferential direction at 100 hours at 98.degree.
F at 50 percent relative humidity and able to withstand a free fall on a
steel surface when dropped on its bottom between 8 and 20 feet when
enclosed and filled with water carbonated with 3.7 volumes of carbon
dioxide per 1 volume of water.
36. The container of claim 1 wherein the said polymeric material is a
composition resulting from the polymerization of a major proportion of
said olefinically unsaturated mononitrile and a minor proportion of an
aromatic olefin in the presence of said polymer containing moieties
derived from a conjugated diene monomer.
37. The container of claim 36 wherein the said polymer comprises a major
proportion of said moieties derived from a conjugated diene monomer and a
minor proportion of an aromatic olefin.
38. The container of claim 37 wherein both of said minor proportions of an
aromatic olefin are the same 0lefin.
39. The container of claim 1 wherein the said polymeric material is a
composition resulting from the polymerization of 100 parts by weight of
A. a major portion of said olefinically unsaturated mononitrile and
B. a minor portion of an aromatic olefin in the presence of from about 1 to
about 20 additional parts by weight of
C. a polymer having a major proportion of moieties derived from conjugated
diene monomer and a minor proportion of moieties derived from an aromatic
olefin.
40. The container of claim 39 wherein the conjugated diene monomer is
selected from the group consisting of butadiene and isoprene.
41. The container of claim 40 wherein there is employed at least 60% by
weight of (A), based on the combined weight of (A) and (B).
42. The container of claim 39 wherein the aromatic olefin contains 8-14
carbon atoms.
43. The container of claim 39 wherein the aromatic olefin is selected from
the group consisting of styrene, alpha-methyl styrene, and vinyl toluene.
44. The container of claim 39 wherein the amount of (C) is up to 11 parts
by weight.
45. The container of claim 39 wherein the amount of (C) is about 3 parts by
weight.
46. The container of claim 39 wherein the amount of is about 6 parts by
weight.
47. The container of claim 39 wherein the amount of (C) is about 11 parts
by weight.
48. A container for holding a pressurized product, said container having a
substantially transparent sidewall formed of a molecularly oriented
polymeric material comprising
a polymer containing a major proportion of moieties derived from a
conjugated diene and a minor proportion of a polymerizable aromatic
olefin, and
a polymer containing a major proportion of moieties derived from an alpha,
beta-olefinically unsaturated mononitrile having the formula
##STR4##
where R is selected from the group consisting of hydrogen, an alkyl group
having from 1 to 4 carbon atoms, and a halogen, and a minor proportion of
said aromatic olefin,
said sidewall having an average circumferential orientation release stress
between about 500 and about 2500 p.s.i. as measured for total sidewall
thickness.
49. The container of claim 48 wherein said aromatic olefin is styrene.
50. The container of claim 4 wherein the said nitrile-containing polymer is
a copolymer resulting from the polymerization of a major portion of said
mononitrile and a minor portion of an aromatic olefin. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to thermoplastic bottles and more particularly to
thermoplastic beer and carbonated beverage bottles having a unique
combination of physical properties and is a continuation-in-part of Ser.
No. 248,495 filed Apr. 28, 1972, now abandoned.
There are polymeric materials available today which have high impact
strength and low gas permeability but none of these possesses the property
of excellent resistance to creep strain under tensile load, which is so
necessary to the manufacture of commercially acceptable plastic bottles
for beer and carbonated beverage. Creep strain is undesirable for two
reasons: it results in a change of bottle shape whereby the liquid level
is lowered, and it results in a loss of carbonation of the liquid owing to
the expanded volume of the bottle.
The instant invention therefore provides a thermoplastic bottle having the
following unique combination of physical properties: high impact strength,
excellent resistance to creep strain under tensile road, and extremely low
gas permeability. Existing thermoplastic bottles possess one or two of
these properties, but the combination of all three in the required degree
is unknown in the prior art.
This unique combination of physical properties is desired for the packaging
of fluids under a high internal pressure, i.e. beer, carbonated beverages,
and aerosol container products. A high level of molecular orientation, as
characterized by orientation release stree (ASTM D 1504), is utilized to
obtain the physical properties specified above.
It is known that the physical properties of thermoplastic polymers can be
improved by uncoiling and straightening the molecules of the polymeric
material by a stretching operation while the polymeric material is at a
temperature at which such molecular orientation can be imparted thereto
(orientation temperature), i.e, while the polymeric material is in the
so-called "leathery" state, and thereafter cooling the material so that
the molecules of the polymer are set in the direction or directions in
which the stretch is applied.
SUMMARY OF THE INVENTION
It has not been known until the present invention that very high levels of
orientation can result in surprisingly dramatic improvements in the creep
strain resistance of thermoplastic, polymeric materials. Accordingly, the
instant invention provides a method of substantially improving resistance
to creep strain in thermoplastic polymers which comprises molecularly
orienting the polymer to an orientation release stress between 350 and
2500 p.s.i.
The instant invention also provides a bottle weighing 0.03 to 0.13 grams
per cubic centimeter of internal volume blown from a thermoplastic polymer
having an oxygen permeability between 0.3 and 6.0 cm.sup.3. mil/100
in.sup.2.day.atm carbon dioxide permeability between 0.5 and 10.0
cm.sup.3.mil/100 in.sup.2.day.atm. The test is conducted at 73.degree.F.
and 0 per cent relative humidity. The bottle has a sidewall creep strain
in the circumferential direction of 0 to 3.0 per cent under a wall stress
in the circumferential direction of 3000 p.s.i. at 100 hours at 98.degree.
F. at 50 per cent relative humidity, said bottle, when enclosed and filled
with water carbonated with 3.7 volumes of carbon dioxide per 1 volume of
water, able to withstand a free fall of at least 3 feet when dropped on
its bottom onto a steel surface.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a central vertical sectional view of a parison used to form the
bottle of the instant invention.
FIG. 2 is a central vertical sectional view of a bottle blow molded from
the parison of FIG. 1.
FIG. 3 is a graph of the creep strain in the sidewall of an oriented and
unoriented bottle at 98.degree.F. and 50 per cent relative humidity.
FIG. 4 is a graph showing three kinds of strain in an oriented bottle.
FIG. 5 and 6 are graphs showing the relationship between ORS and % haze as
a function of rubber content.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The instant invention is best practiced according to the parameters set
forth hereinbelow. In forming a parison 11 (FIG. 1) from which a bottle 13
having a sidewall 15 (FIG. 2) is blown, it is necessary to select a
thermoplastic polymer having low permeability to gases, so that the bottle
13 may act as a barrier to gases. The barrier properties of a polymer are
determined in large part by the characteristics of the monomers from which
said polymers are made. Monomers having high dipole moments are
particularly suited for making barrier resins because their high dipole
moments result in strong intermolecular forces between the polymer chains,
reducing the diffusion and permeation rates of gases through the polymer.
Since permeability is reduced as the concentration of highly polar monomer
is increased, at least 50% by weight of the final polymer should result
from inclusion of highly polar monomers in the polymerization reaction.
The polymers suited for use in the instant invention should have an oxygen
permeability between 0.5 and 3.0 cm..sup.3 per 100 square inches per mil
thickness and a carbon dioxide permeability between 0.8 and 5.0 cm..sup.3
per 100 square inches per mil thickness when tested for 24 hours at a
differential pressure of 1 atmosphere at 73.degree. F. and 0 per cent
relative humidity. Preferably, the oxygen permeability is less than 0.8
cm.sup.3.mil/100 in.sup.2.day.atm and the carbon dioxide permeability is
less than 2.0 cm.sup.3. mil/100 in.sup.2.day.atm.
The polymers most suited for the present invention are prepared by
polymerizing a major portion of an olefinically unsaturated nitrile, such
as acrylonitrile, and a minor portion of an ester of an olefinically
unsaturated carboxylic acid, such as ethyl acrylate, methyacrylate or an
aromatic olefin such as styrene, in the presence of an unsaturated rubber.
Such a rubber might comprise a major proportion of a conjugated diene
monomer, such as butadiene, and a minor proportion of olefinically
unsaturated nitrile, such as acrylonitrile or an aromatic olefin such as
styrene.
The conjugated diene monomers useful in the present invention include
1,3-butadiene, isoprene, and others such as chloroprene,
2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,
2,3-diethyl-1,3-butadiene.
The olefinically unsaturated nitriles useful in the present invention are
the alpha,beta-olefinically unsaturated mononitriles having the structure
##STR1##
wherein R is hydrogen, a lower alkyl group having from 1 to 4 carbon
atoms, or a halogen. Such compounds include acrylonitrile,
methacrylonitrile, alphachloroacrylonitrile, alpha-fluoroacrylonitrile,
ethacrylonitrile and others.
The esters of olefinically unsaturated carboxylic acids useful in the
present invention are preferably the lower alky esters of
alpha,beta-olefinically unsaturated carboxylic acids and more preferred
are the esters having the structure
##STR2##
wherein R.sub.1 is hydrogen, an alkyl group having from 1 to 4 carbon
atoms, or a halogen and R.sub.2 is an alkyl group having from 1 to 6
carbon atoms. Compounds of this type include methyl acrylate, ethyl
acrylate, other acrylates and methacralates, and the like.
The aromatic olefins useful in the present invention include styrene,
alpha-methyl styrene, vinyl toluene, and others containing 8-14 carbon
atoms.
Preferred polymers for the present invention are derived from (A) about 60
to 90 parts by weight of an alpha,beta-olefinically unsaturated
mononitrile having the structure CH.sub.2 =C(--R.sub.1)--CN where
--R.sub.1 is selected from the group consisting of hydrogen, halogen, and
the lower alkyl groups, (B) about 40 to 10 parts by weight of an ester of
an olefinically unsaturated carboxylic acid having the structure CH.sub.2
=C(--R.sub.1)--C(0)0--R.sub.2 where --R.sub.1 is as defined above and
--R.sub.2 is an alkyl group having from 1 to 6 carbon atoms, (A) and (B)
together comprising 100 parts by weight, polymerized in the presence of
(C) about 1 to 20 parts by weight of a nitrile rubber containing about 60
to 80 per cent by weight of moieties derived from a conjugated diene
monomer and about 40 to 20 per cent by weight of moieties derived from a
monomitrile having said CH.sub.2 =C(--R.sub.1 )--CN structure.
The more preferred polymers for the present invention are derived from
about 60 to 90 parts by weight of acrylonitrile or methacrylonitrile and
about 40 to 10 parts by weight of an ester selected from the group
consisting of methyl acrylate, ethyl acrylate and methyl methacrylate,
polymerized in the presence of about 1 to 20 additional parts by weight of
a nitrile rubber containing about 60 to 80 per cent by weight butadiene or
isoprene moieties and about 40 to 20 per cent by weight of acrylonitrile
or methacrylonitrile moieties.
More specifically, the preferred polymers are derived from about 73 to 77
parts by weight acrylonitrile and 27 to 23 parts by weight methyl
acrylate, polymerized in the presence of 8 to 10 additional parts by
weight of a nitrile rubber containing about 70 per cent by weight
butadiene moieties and about 30 per cent by weight acrylonitrile moieties.
Examples of the polymers suited for use in the instant invention may be
found in U.S. Pat. No. 3,426,102, the entirety of which is hereby
incorporated into the instant specification by reference.
Examples of other preferred polymers suited for use in the present
invention may be found in U.S. Pat. No. 3,819,762, the entirety of which
is incorporated into the instant specification by reference. Therein is
disclosed as an example a composition consisting essentially of a
copolymer of acrylonitrile and styrene blended with polymer comprising a
rubber component polymerized from styrene and butadiene or isoprene onto
which a copolymer of styrene and acrylonitrile is grafted. Typically, the
composition would be about 70% by weight acrylonitrile, about 20% by
weight styrene and about 10% by weight butadiene.
Forming the parison may be achieved by any one of several techniques. In
one method, a hollow cylinder is extruded from an annular die. The bottom
end of the parison is formed by closing one end of the cylinder by
pinching, swaging, compression molding, or some other mechanical means
either immediately after extrusion when the cylinder is still hot, or
after the cylinder (or at least one end thereof) has been reheated. The
other end of the cylinder is left open for subsequent blowing. The desired
neck finish can be formed either by a mechanical forming of the open end
of the cylinder (such as compression molding) or by blowing into a neck
mold of the proper dimensions. The forming of the neck finish can be
accomplished either immediately after extrusion when the cylinder is still
hot or after the cylinder (or at lest this end thereof) is reheated.
The continuous extruded cylinder can be cut to the proper length by a
separate cutting operation or by mechanical means such as the pinching
used to close the cylinder end, or by a combination of these methods. (See
U.S. Pat. No. 3,599,280).
Extrusion blow molding is another parison forming technique that may be
employed. In this method, the starting parison for the orientation blowing
step is formed by blowing a hollow cylinder, extruded as described above,
at a high temperature.
If it is found desirable in forming bottles of the desired material and
orientation distribution to start with a parison of non-uniform thickness
and/or diameter, as seen in FIG. 1, injection molding the parison is
recommended, as well as any of several "programmed parison" methods when
the parison is extruded, such as variable extrusion rates, a movable core
mandrel, mechanical stretching of the cylinder as it is extruded, or
mechanical stretching of a cylinder of non-uniform axial temperature
distribution. Mechanical means such as compression molding, swaging or
machining also enable one to begin bottle blowing with a non-uniformly
thick parisons.
The next step in providing a plastic bottle according to the present
invention comprises blow molding the parison in the leathery state into
the desired bottle shape using high pressure fluid, at which time the
polymer is oriented. Generally, the bottle is blown to a sidewall
thickness between 5 and 50 mils at the maximum diameter, and preferably
between 15 and 35 mils. Since resistance to creep is proportional to the
amount of molecular orientation, it is desirable that the molecular
orientation level be as high as possible, as determined by orientation
release stress. The level of orientation achieved is dependent upon
variations in conditions under which the bottle is oriented. Higher levels
of orientation result from greater stretching rates, greater amounts of
stretch, and/or lower stretching temperatures. It is thus desirable to
blow slightly above the glass transition temperature. Once the bottle is
blown, the orientation is locked in by cooling the bottle below the glass
transition temperature. For the present invention, an average orientation
release stress in the circumferential direction between 350 and 2500
p.s.i. as measured for total sidewall thickness may be imparted to the
polymer comprising the bottle. Preferably the orientation release stress
will fall between 500 and 1600 p.s.i., since within this range it is easy
to avoid stress whitening of the polymer which so often accompanies higher
levels of orientation, thus enabling the formation of a transparent bottle
having high molecular orientation. Most preferably, the orientation
release stress will fall between 800 and 1000 p.s.i.
For purposes of this specification, creep strain is defined to be the net
total strain of the bottle when subjected to internal pressure creating a
wall stress in the circumferential direction. For molecularly oriented
bottles this strain is the resultant of a tendency for the bottle to
expand under the effect of the internal pressure and an opposing tendency
for the bottle to contract as a result of the locked-in orientation
stresses. It can be shown that the net effect of these two tendencies
could be substantially 0 per cent creep strain which might even be a
small, negative, resultant amount of creep strain (contraction).
Unoriented bottles subjected to tensile forces (such as those resulting
from internal pressure) respond with a rapid elastic extension followed by
a viscous extension which takes place over a long period of time. The
behavior of oriented bottles is more complex. They too exhibit elastic and
viscous extensions in response to tensile forces; however, these
extensions are opposed by the tendency to contract which is inherent in
all molecularly oriented plastics. It is well known that oriented plastics
shrink when heated above their glass transition temperature. Shrinkage
also occurs below the glass transition temperature but at a greatly
reduced rate. This shrinkage results from the molecules attempting to
return to the random coil configuration from the extended network
structure produced during the orientation process. The net amount of creep
strain is therefore due to a balance which exists between these tensile
and retractive tendencies. Where the retractive tendency is very strong
and the tensile forces are moderate, there is the very real possibility of
achieveing 0 per cent strain or of having a net contraction (a negative
extension).
Bottles made according to the instant invention exhibit sidewall creep
strains in the circumferential direction between 0 and 2.0 per cent when
tested at a wall stress of 3000 p.s.i. in the circumferential direction
after 100 hours at 98.degree. F. at 50 per cent relative humidity. The
wall stress, in test conditions, is generated by pressurized water. More
specifically, under the same conditions, the bottles made according to the
instant invention exhibit creep strains between 1.0 and 2.0 per cent. When
tested at 4000 p.s.i., bottles of the present invention exhibit sidewall
creep strains between 0.25 and 3.0 per cent.
Bottles of the present invention, i.e. weighing between 0.03 and 0.13 grams
per cubic centimeter of internal volume, exhibit superior impact strength.
They are able to withstand a free fall onto a steel surface when dropped
on their bottoms of preferably at least about 6 and even as high as about
25 feet when enclosed and filled with water carbonated with 3.7 volumes of
carbon dioxide per 1 volume of water. More specifically, they are able to
withstand free falls between about 9 and 11 feet particularly when the
bottles weigh between 0.06 and 0.1 grams per cubic centimeter of internal
volume. Naturally, heavier bottles having thicker walls can be dropped
from great heights without breaking. For purposes of this specification
and the claims that follow, the drop heights indicated would be those as
determined by ASTM D-2463. The data set forth in Table I, although not
tested as per ASTM D-2463, clearly supports the range set forth above.
Another method of determining impact properties, independent of bottle
geometry, consists of measuring the amount of energy absorbed in a
flexural test conducted at high rates of loading. Test specimens are
pieces of plastic cut from the walls of the bottle, and the results are
reported in inch-lbs/square inch. This test is similar in many respects to
the well known Charpy Impact Test ASTM-D 256-56 (1961), Method B,
Unnotched, the primary difference being a smaller test specimen. Test
conditions are as follows:
______________________________________
SPECIMEN DIMENSIONS:
______________________________________
Width 0.125 inch
Thickness 0.015-.035 inch
Length 0.5 inch
Distance between end supports
0.160, 0.240 inch
Test speeds (in./sec.)
2.5, 110, 260
______________________________________
Specimens tested according to the above conditions demonstrate flexural
impact values in excess of 3000 inch-lbs./square inch in the
circumferential direction.
At the facilities of American Can Company's Laboratory in Princeton, NJ,
unoriented compression molded plaques and molecularly oriented bottles
were fabricated from various polymeric materials, described below, and
measurements were made of the percent haze in the plaques and in the
material of the sidewall of the bottles at different levels of molecular
orientation. The degree of orientation of the polymeric material was
determined by measurement of the orientation release stress (ORS) in
accordance with ASTM D1504 on 1/8 inch .times. 1 inch samples taken from
the sidewall of the bottles formed from that material. The percent haze
was measured in accordance with ASTM D1003 and was observed with a Gardner
Haze Meter Model UX-10 with a PG5500 digital readout.
Polymeric material No. 1 was a polymer containing about 74 weight percent
acrylonitrile, about 23 weight percent styrene and no rubber component.
Polymeric material No. 2 was a polymer containing about 74 weight percent
acrylonitrile, about 23 weight percent styrene and about 6 additional
parts per hundred of resin (phr) of a rubbery polymer containing about 49
weight percent butadiene. The ORS and percent haze values for samples
taken from bottles and plaques fabricated from these materials are given
in Table II and plotted in FIG. 5.
TABLE II
______________________________________
Polymeric Material No. 1
Polymeric Material No. 2
ORS % Haze ORS % Haze
______________________________________
0 3 0 4
0 4 0 6
360 7 380 6
360 8 410 8
370 6 470 8
380 8 490 9
540 22 720 15
580 25 760 18
760 31 780 18
870 38 860 18
1090 57 1020 26
1150 64 1280 32
1200 69 1380 33
1520 30
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Polymeric material No. 3 was a polymer containing about 80 weight percent
acrylonitrile, about 20 weight percent styrene and no rubbery component.
Polymeric material No. 4 was the same as No. 3, but, in addition,
contained about 3 phr of a rubbery polymer of butadiene and styrene.
Polymeric material No. 5 was the same as No. 3, but, in addition,
contained about 11 phr of a rubbery polymer of butadiene and styrene. The
ORS and percent haze values for samples taken from bottles and plaques
fabricated from these materials are given in Table III and plotted in FIG.
6.
TABLE III
______________________________________
Polymeric Polymeric Polymeric
Material No. 3
Material No. 4
Material No. 5
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ORS % Haze ORS % Haze
ORS % Haze
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0 19 0 6 0 2
0 19 0 7 0 2
480 9 290 11 290 2
650 6 320 20 290 4
720 8 340 23 390 3
720 10 390 18 720 4
740 21 400 2 770 3
780 5 450 7 820 4
800 24 470 8 870 5
810 17 480 7 910 2
820 23 480 9 960 3
830 17 510 3 960 4
850 35 560 3 960 6
870 9 520 7 990 5
980 47 700 6 1040 6
1310 71 720 15 1150 3
720 15 1200 26
790 21 1460 8
810 31 1530 4
830 22 2020 16
860 30
870 27
1080 46
1160 43
1200 61
1280 47
1280 57
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In the examples that follow, the blown bottles all have the shape shown in
FIG. 2, and the polymer used was derived from 75 parts by weight
acrylonitrile and 25 parts by weight methyl acrylate polymerized in the
presence of 9 additional parts by weight of a nitrile rubber containing
about 70 per cent by weight 1,3-butadiene and about 30 per cent by weight
acrylonitrile. This polymer has a glass transition temperature of about
180.degree.F. All bottles discussed in the examples below were blown to
produce a transparent bottle.
The difference in creep behavior between unoriented and oriented bottles is
shown in FIG. 3. The unoriented bottle was made by extrusion blow molding.
It has an internal volume of 12.4 fluid ounces, weighs 44 grams and has a
wall thickness of 40 mils. The oriented bottle was blown from a 51/2 inch
long extrusion blow molded parison into a bottle 7 inches high having a
wall thickness of 25 mils, weighing 26.8 grams, having a 21/4 inch
diameter and an internal volume of 10.3 fluid ounces. The oriented bottle
had an orientation release stress in the circumferential direction of 900
p.s.i. The two bottles exhibit completely different behavior patterns
under the conditions of the creep strain test: 98.degree. F., 50 per cent
relative humidity and a 3000 p.s.i. wall stress. The oriented bottle has a
total strain in the circumferential direction of 1.6 per cent after 1000
hours. By contrast, the unoriented bottle shows a creep strain of 9 per
cent after only 20 hours at the same conditions.
Other tests indicate that resistance to creep strain improves as the amount
of molecular orientation is increased. Unoriented bottles were made by
conventional extrusion blow molding while the oriented bottles were made
by blowing at low temperatures, between 190.degree. and 218.degree. F. The
following results indicate the per cent creep strain at 3300 p.s.i. at 100
hours at 98.degree. F., at 50 per cent relative humidity in the
circumferential direction:
TABLE IV
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CIRCUMFERENTIAL ORIENTATION
RELEASE STRESS (p.s.i.)
STRAIN (%)
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0 6.2 (30 hours)
540 3.6
640 2.0
850 1.7
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As seen above, unoriented bottles creep more in 30 hours than do any of the
oriented bottles at 100 hours.
The graph shown in FIg. 4 illustrates how zero or negative creep strain can
be attained. The bottle was blown from an extrusion blow molded parison
51/2 inches long. The parison had a three-fourths inch outer diameter with
a 0.130 inch thick wall.
The parison was heated in a 550.degree. F. radiant over for 49 seconds and
cooled for 85 seconds prior to blowing. The bottle was blown at a maximum
pressure of 500 p.s.i. with a 43 second blowing time. The bottle developed
an orientation release stress of 800 p.s.i. in the circumferential
direction. The bottle was tested for creep strain in the circumferential
direction at 98.degree. F. at 50 per cent relative humidity at a wall
stress of 2000 p.s.i.
Elastic strain is the strain which occurs immediately on stressing the
bottle. Because it is impossible to make accurate measurements of strain
at extremely short periods of time, the elastic strain is defined as "the
strain which occurs in the first 36 seconds of the test". This is the
strain at Point A on the graph of FIG. 4. The strain at longer time
periods represents a balance between viscous extension and "orientation
contraction". During the time represented by the interval A-B viscous
extension dominated and the specimen extended. During the time period B-C
"orientation contraction" was the dominant effect and the sample
contracted. If the specimen had been more highly oriented there would have
been even more orientation contraction and the net strain could have been
zero or even a negative percentage.
The following tables (V and VI) described bottles blown from extrusion blow
molded parisons 5, 51/2 and 6 inches long, having a three-fourths inch
outer diameter and a 0.130 inch thick wall. The closed end of the parisons
were formed in the extrusion blow molding step. The parisons were heated
in a radiant oven having a temperature of 550.degree.F. After removal from
the oven the parisons were conditioned for blowing by holding them in the
air.
TABLE V
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Parison length (inches)
5" 5 1/2"
6"
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Time in oven (seconds)
50-51
50 50
Thermal conditioning (seconds)
68 68-78
65-75
Max. blowing pressure (p.s.i.)
120 120 120
Blowing time (seconds)
27-32
27-30
20-35
Bottle height (inches)
7 7 7
Bottle wall thickness (inches)
.023 .025 .027
Bottle weight (grams)
24.4 26.8 29.3
Bottle diameter (inches)
2 1/4
2 1/4
2 1/4
Bottle internal volume (fl. oz.)
10.3 10.3 10.3
Orientation release stress,
circumferential direction (p.s.i.)
790 900 950
% creep strain at 100 hours.,
50% R. H. 98.degree.F.
Wall stress (p.s.i.):
3000
.80 1.2 1.05
4000
-- 2.0-2.1
2.6
5000
2.9 3.3 3.6
% creep strain at 1000 hrs.
50% R. H. 98.degree.F.
Wall stress (p.s.i.):
3000
1.04 1.6 1.30
4000
-- 2.6-2.8
4.1
5000
4.0 4.6 4.7
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