U.S. patent application number 09/745482 was filed with the patent office on 2001-06-21 for inline solid state polymerization of pet flakes for manufacturing plastic strap by removing non-crystalline materials from recycled pet.
This patent application is currently assigned to ILLINOIS TOOL WORKS INC.. Invention is credited to Robinson, William Donald, Vadnais, Gary L..
Application Number | 20010004645 09/745482 |
Document ID | / |
Family ID | 22621340 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004645 |
Kind Code |
A1 |
Robinson, William Donald ;
et al. |
June 21, 2001 |
Inline solid state polymerization of PET flakes for manufacturing
plastic strap by removing non-crystalline materials from recycled
PET
Abstract
A process for preparing a PET flake mixture for use in
connection with the fabrication of high-performance plastic
strapping comprises the steps of initially collecting post-consumer
and non-post-consumer PET materials having an initially wide range
of relatively low intrinsic viscosity (IV) values with a relatively
low average intrinsic viscosity (IV) value, and processing the same
through solid state polymerization (SSP) so as to obtain a wide
range of relatively high intrinsic viscosity (IV) values with a
relatively high average intrinsic viscosity (IV) value. The
initially collected materials are chopped into flakes and chunks,
and the chunks are removed by a suitable destoner so as to render
the remaining mixture comprised substantially entirely of flake
materials or segments. This is advantageous because the flake
segments, as opposed to the chunk segments, are able to be
substantially increased in intrinsic viscosity (IV) values and
within a relatively short period of time, and in addition, the
flake segments are essentially crystalline while the chunk segments
are essentially non-crystalline which would otherwise undergo rapid
crystallization and generate a substantial amount of heat of
crystallization. Such heat of crystallization undesirably raises
the temperature of the polymerization process whereby the materials
tend to become sticky and agglomerate thereby impeding the flow of
the materials being processed as well as tending to clog components
of the processing apparatus.
Inventors: |
Robinson, William Donald;
(Walton, KY) ; Vadnais, Gary L.; (Grayslake,
IL) |
Correspondence
Address: |
Steven W. Weinrieb
SCHWARTZ & WEINRIEB
2001 Jefferson Davis Highway
Crystal Plaza One, Suite 1109
Arlington
VA
22202
US
|
Assignee: |
ILLINOIS TOOL WORKS INC.
|
Family ID: |
22621340 |
Appl. No.: |
09/745482 |
Filed: |
December 26, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09745482 |
Dec 26, 2000 |
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09170808 |
Oct 13, 1998 |
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09170808 |
Oct 13, 1998 |
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08794538 |
Feb 3, 1997 |
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5886058 |
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Current U.S.
Class: |
521/48 |
Current CPC
Class: |
B29C 48/04 20190201;
C08J 2367/00 20130101; C08J 2367/02 20130101; B29C 48/287 20190201;
C08J 11/06 20130101; Y02W 30/62 20150501; Y02W 30/701 20150501;
C08G 63/80 20130101 |
Class at
Publication: |
521/48 |
International
Class: |
C08J 011/04 |
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States of America, is:
1. A process of forming a polyethylene terephthalate (PET) material
mixture which is suitable for subsequent processing, comprising the
steps of; collecting diverse PET materials having a relatively wide
distribution of intrinsic viscosity (IV) values; co-mingling said
collected PET materials and reforming said co-mingled PET materials
into a heterogeneous mixture of PET materials comprising
substantially crystalline flake segments and non-crystalline chunk
segments; and removing said substantially non-crystalline chunk
segments from said heterogeneous mixture of PET materials so as to
leave substantially only said substantially crystalline flake
segments within said heterogeneous mixture of PET materials such
that when said heterogeneous mixture of PET materials comprising
substantially only said substantially crystalline flake segments is
processed further so as to increase said intrinsic viscosity (IV)
values of said PET materials, the generation of a substantial
amount of heat of crystallization within said processed mixture of
said PET materials will be effectively prevented.
2. The process as set forth in claim 1, wherein: said intrinsic
viscosity (IV) values of said collected PET materials are within
the range of 0.60 g/dl to 0.80 g/dl.
3. A process for making a polyethylene terephthalate (PET)
material, comprising the steps of: collecting diverse PET materials
having a relatively wide distribution of intrinsic viscosity (IV)
values; co-mingling said collected PET materials and reforming said
co-mingled PET materials into a heterogeneous mixture of PET
materials comprising substantially crystalline flake segments and
non-crystalline chunk segments; removing said substantially
non-crystalline chunk segments from said heterogeneous mixture of
PET materials so as to leave substantially only said substantially
crystalline flake segments within said heterogeneous mixture of PET
materials such that when said heterogeneous mixture of PET
materials comprising substantially only said substantially
crystalline flake segments is processed further so as to increase
said intrinsic viscosity (IV) values of said PET materials, the
generation of a substantial amount of heat of crystallization
within said processed mixture of said PET materials will be
effectively prevented; and subjecting said heterogeneous mixture of
PET material, comprising substantially only said substantially
crystalline flake segments, to a solid state polymerization (SSP)
process so as to form a heterogeneous PET material having an
enhanced intrinsic viscosity (IV) value.
4. The process as set forth in claim 3, wherein: said intrinsic
viscosity (IV) values of said collected PET materials are within
the range of 0.60 g/dl to 0.80 g/dl.
5. The process as set forth in claim 3, wherein: said formed
heterogeneous PET material has an average intrinsic viscosity (IV)
value of at least 0.90 g/dl.
6. The process as set forth in claim 3, wherein: said formed
heterogeneous PET material has an intrinsic viscosity (IV) value
range of 0.90 g/dl to 1.5 g/dl.
7. The process as set forth in claim 3, further comprising the
steps of: identifying any PVC impurities found within said
collected diverse PET materials; and removing said identified PVC
impurities prior to said reforming of said PET materials into said
heterogeneous mixture of substantially crystalline flake segments
and non-crystalline chunk segments.
8. The process as set forth in claim 3, wherein said solid state
polymerization step comprises the steps of: incorporating a
nitrogen cycle within said solid state polymerization; and removing
a majority of HCl contaminants, forming during said nitrogen cycle
portion of said solid state polymerization step, by passing the
nitrogen present within said nitrogen cycle, and including said HCl
contaminants, through a guard bed of basic material.
9. A process for forming a polyethylene terephthalate (PET)
material, suitable for use in making high-performance plastic
strapping, comprising the steps of: collecting diverse PET
materials having a relatively wide distribution of intrinsic
viscosity (IV) values; co-mingling said collected PET materials and
reforming said co-mingled PET materials into a heterogeneous
mixture of PET materials comprising substantially crystalline flake
segments and non-crystalline chunk segments; and removing said
substantially non-crystalline chunk segments from said
heterogeneous mixture of PET materials so as to leave substantially
only said substantially crystalline flake segments within said
heterogeneous mixture of PET materials such that when said
heterogeneous mixture of PET materials comprising substantially
only said substantially crystalline flake segments is processed
further so as to increase said intrinsic viscosity (IV) values of
said PET materials, the generation of a substantial amount of heat
of crystallization within said processed mixture of said PET
materials will be effectively prevented; and subjecting said
heterogeneous mixture of PET materials, comprising substantially
only said substantially crystalline flake segments, to a solid
state polymerization (SSP) process so as to form a heterogeneous
PET material having an enhanced intrinsic viscosity (IV) value.
10. The process as set forth in claim 9, wherein: said intrinsic
viscosity (IV) values of said collected PET materials are within
the range of 0.60 g/dl to 0.80 g/dl.
11. The process as set forth in claim 9, wherein: said formed
heterogeneous PET material has an average intrinsic viscosity (IV)
value of at least 0.90 g/dl.
12. The process as set forth in claim 9, wherein: said formed
heterogeneous PET material has an intrinsic viscosity (IV) value
range of 0.90 g/dl to 1.5 g/dl.
13. The process as set forth in claim 9, further comprising the
steps of: identifying any PVC impurities found within said
collected diverse PET materials; and removing said identified PVC
impurities prior to said reforming of said PET materials into said
heterogeneous mixture of substantially crystalline flake segments
and non-crystalline chunk segments.
14. The process as set forth in claim 9, wherein said solid state
polymerization step comprises the steps of: incorporating a
nitrogen cycle within said solid state polymerization; and removing
a majority of HCl contaminants, formed during said nitrogen cycle
portion of said solid state polymerization step, by passing the
nitrogen present within said nitrogen cycle, and including said HCl
contaminants, through a guard bed of basic material.
15. The process as set forth in claim 9, further comprising the
step of: extruding said solid stated PET material so as to
fabricate a high-performance plastic strap.
16. A heterogeneous mixture of polyethylene terephthalate (PET)
material which is suitable for subsequent processing, comprising: a
mixture of heterogeneous PET material having a relatively wide
distribution of intrinsic viscosity (IV) values and derived from an
initial mixture comprising substantially crystalline flake segments
and substantially non-crystalline chunk segments from which said
substantially non-crystalline chunk segments have been removed such
that said mixture comprises substantially only said substantially
crystalline flake segments, whereby when said heterogeneous mixture
of said PET materials comprising substantially only said
substantially crystalline flake segments is processed further so as
to increase said intrinsic viscosity (IV) values of said PET
materials, the generation of a substantial amount of heat of
crystallization within said processed mixture of said PET materials
will be effectively prevented.
17. A mixture as set forth in claim 16, wherein: said intrinsic
viscosity (IV) values of said mixture of PET materials are within
the range of 0.60 g/dl to 0.80 g/dl.
18. A heterogeneous solid stated polyethylene terephthalate (PET)
material for use in making high-performance strapping, comprising:
a mixture of heterogeneous PET material having a relatively wide
distribution of intrinsic viscosity (IV) values, derived from an
initial mixture comprising substantially crystalline flake segments
and substantially non-crystalline chunk segments from which said
substantially non-crystalline chunk segments have been removed such
that said mixture comprises substantially only said substantially
crystalline flake segments, and solid stated directly while in said
heterogeneous mixture state so as to increase said intrinsic
viscosity (IV) values without generating a substantial amount of
heat of crystallization.
19. A heterogeneous solid stated polyethylene terephthalate (PET)
materials as set forth in claim 18, wherein: said solid stated PET
material has an intrinsic viscosity (IV) value range of 0.90 g/dl
to 1.5 g/dl.
20. A high-performance plastic strap, comprising: a polyethylene
terephthalate (PET) material which has been solid stated directly
from a heterogeneous mixture of PET material, having a relatively
wide distribution of intrinsic viscosity (IV) values and derived
from an initial mixture comprising substantially crystalline flake
segments and substantially non-crystalline chunk segments from
which said substantially non-crystalline chunk segments have been
removed such that said initial mixture comprises substantially only
said substantially crystalline flake segments, so as to increase
said intrinsic viscosity (IV) values without generating a
substantial amount of heat of crystallization.
21. A high-performance plastic strap as set forth in claim 20,
wherein: said solid stated polyethylene terephthalate (PET)
material has an intrinsic viscosity (IV) value range of 0.90 g/dl
to 1.5 g/dl.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This patent application is a Continuation-In-Part (CIP)
Patent Application of U.S. patent application Ser. No. 08/794,538
filed on Feb. 3, 1997 in the name of Donald Van Erden et al. and
entitled INLINE SOLID STATE POLYMERIZATION OF PET FLAKES FOR
MANUFACTURING PLASTIC STRAP, and is being filed herewith under 37
CFR 1.53(b).
FIELD OF THE INVENTION
[0002] The present invention relates generally to the solid state
polymerization (SSP) processing of polyethylene terephthalate (PET)
material, as well as the material produced by such process, and
more particularly to the solid state polymerization (SSP)
processing of post-consumer and non-post-consumer polyethylene
terephthalate (PET) material, especially for use in connection with
the fabrication or manufacture of high-performance strapping, as
well as the high-performance strapping produced by such
process.
BACKGROUND OF THE INVENTION
[0003] Post-consumer polyethylene terephthalate (PET), which is
primarily provided by or derived from plastic soft drink bottles,
can be readily obtained from material recovery facilities. Such
material exhibits relatively low and heterogeneous intrinsic
viscosity (IV) values, and in the past, this characteristic has
prevented PET from being directly used to produce products, such
as, for example, high-performance plastic strapping, which in fact
require relatively high and homogeneous intrinsic viscosity (IV)
values. It was one of the discoveries of the invention disclosed
within the aforenoted related U.S. patent application Ser. No.
08/794,538 that such heterogeneity of the intrinsic viscosity (IV)
values of the PET material did not in fact adversely affect the
production of high-performance strapping, and the present invention
comprises a further improvement upon the processing of such PET
material.
[0004] In accordance with prior art processing techniques, the PET
material, whether post-consumer and/or non-post consumer material,
was initially chopped into flakes and chunks, and the flakes and
chunks were extruded into pellets. The chopped PET material had a
relatively low and wide range of IV values because the various soft
drink bottles, for example, were manufactured by different
companies using different materials exhibiting different IV values.
The IV values were typically within the range of 0.65-0.80 g/dl. In
accordance with such prior art processing techniques, it was
further believed that in order to make a high-performance product,
such as, for example, high-performance plastic strapping, from such
post-consumer PET materials, it was necessary that the materials
exhibit or achieve a relatively high and narrow range of IV values
after the solid state processing which therefore required, as an
initial step, the pelletizing of the flakes before commencement of
the solid state polymerization. When the PET pellets are then
subjected to solid state polymerization (SSP), the pellets would
have their IV values raised and exhibit a relatively high and
narrow range of IV values whereby such enhanced pellets could then
be used to produce high-performance products, such as, for example,
high-performance strapping.
[0005] As noted hereinabove, in accordance with the noted prior art
processing techniques, the prior art solid state polymerization
(SSP) of the PET materials commenced with pellets of uniform
geometry. Such prior art solid state polymerization (SSP) of the
pellets, however, required an inordinate amount of time, that is,
approximately twelve to nineteen hours, to complete in order to
produce the desired strapping, and it was not appreciated, until
the invention disclosed within the aforenoted U.S. patent
application Ser. No. 08/794,538, that a heterogeneous mixture of
flakes and chunk-like PET materials could undergo direct solid
state polymerization, without necessarily being initially
pelletized, to the same or higher average IV values as those of the
prior art pellets, and in a significantly faster manner, that is,
upon the order of one-quarter the time required for the solid state
polymerization of the pellet materials.
[0006] More specifically, while the resulting prior art strapping
exhibited average IV values which were not greater than 0.90 g/dl,
high-performance plastic strapping fabricated in accordance with
the processing techniques disclosed within the aforenoted U.S.
patent application Ser. No. 08/794,538 exhibited average IV values
which were greater than 0.90 g/dl. Therefore, in accordance with
the teachings of the invention embodied within the aforenoted U.S.
patent application Ser. No. 08/794,538, high-performance plastic
strapping could be commercially manufactured in an economical
manner using PET materials, having a relatively wide distribution
of IV values, and as a result of undergoing solid state
polymerization directly from flaked materials which do not have to
be initially pelletized.
[0007] While the solid state polymerization processing of PET flake
materials, and the production of the resulting high-performance
plastic strapping, as disclosed within the aforenoted U.S. patent
application, having Ser. No. 08/794,538, has been quite successful
and has resulted in the production of highly suitable plastic
strapping, it has been discovered that the process can be further
improved from an efficiency and material flow-through production
basis with decreased production downtime. For example, when the PET
materials, which are to be used in accordance with the processing
techniques of the aforenoted invention disclosed within U.S. patent
application Ser. No. 08/794,538, are in fact derived from plastic
soft drink bottles, it has been discovered that as a result of the
blow-molding manufacturing techniques attendant the fabrication or
manufacture of soft drink bottles, the recycled PET bottles
comprise essentially two different types of materials, that is,
substantially crystalline wall sections and substantially
non-crystalline neck sections, and accordingly, such different
materials must be handled or processed differently. More
particularly, the wall sections are preferably to be retained and
utilized within the solid state polymerization (SSP) process, while
the neck sections are preferably to be discarded from the solid
state polymerization (SSP) process in accordance with the
following.
[0008] It is known, for example, that temperature control of the
solid state polymerization (SSP) process is critical if the
temperature level of the solid state polymerization process is too
low, the polymerization reaction will be too slow, while if the
temperature level of the polymerization process is too high, the
chips will melt or soften and thereby form clumps which will clog
or jam the feeders or other components of the processing equipment.
Since the wall portions of the recycled soft drink bottles are
essentially crystalline, they react quickly within the solid state
polymerization unit so as to desirably increase the molecular
weight or intrinsic viscosity (IV) of the PET batch or charge,
however, since the neck portions of the recycled soft drink bottles
are substantially non-crystalline, they react quite slowly, if at
all, within the solid state polymerization process in connection
with the build-up or enhancement of the molecular weight or
intrinsic viscosity properties of the PET materials being
processed. Consequently, it is desirable from a processing
efficiency point of view to have the batch or charge of PET
materials within the solid state polymerization vessel to comprise
more of the crystalline wall sections of the recycled PET materials
than the non-crystalline neck sections of the recycled PET
materials. In addition, and even more importantly, such
non-crystalline neck portions or segments of the PET materials will
crystallize rapidly within the polymerization processing vessel
thereby emitting a significant amount of heat of crystallization.
This heat of crystallization can be large enough to undesirably
raise the temperature level of the process within the solid state
polymerization vessel such that the PET materials tend to become
sticky and agglomerate thereby forming clumps or chunks which will
impede the flow of the materials within the polymerization vessel
as well as clog or jam the various vessel components.
[0009] A need therefore exists in the art for effectively dealing
with non-crystalline portions of recycled PET materials whereby,
for example, such non-crystalline portions or segments of the
recycled PET materials can be effectively removed from the batch or
charge of PET materials to be fed into the solid state
polymerization vessel such that processing or flow-through problems
of the materials attendant temperature excursions, which would
otherwise develop as a result of the rapid crystallization of such
non-crystalline materials within the polymerization vessel and the
consequent generation of a significant amount of heat of
crystallization, would be obviated, and in addition, the processing
efficiency of such recycled PET materials, and the resulting
fabrication of high-performance strapping from such PET materials,
can be effectively enhanced.
OBJECTS OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to
provide a new and improved inline solid state polymerization (SSP)
process for processing PET flakes for subsequent processing of the
same into high-performance plastic strapping.
[0011] Another object of the present invention is to provide a new
and improved solid state polymerization (SSP) process, for
processing PET flakes into high-performance plastic strapping,
which obviates any operational or flow-through problems of the
batch or charge of the PET materials attendant the processing of
the PET materials within the solid state polymerization vessel.
[0012] Still another object of the present invention is to provide
a new and improved solid state polymerization (SSP) process, for
processing PET flakes into high-performance plastic strapping,
which enhances the operational efficiency of the process by only
using the more desirable crystalline flake components derived from
the wall sections of the recycled PET materials whereby the solid
state polymerization vessel facilities are optimally utilized so as
to produce solid state polymerized materials which exhibit
desirably high IV values, and the temperature level of the process
is properly controlled so as to eliminate agglomeration and
clumping of the materials which would otherwise cause flow-through
problems of the batch or charge materials as well as clogging and
jamming of the equipment components which would therefore result in
production downtime of the equipment and increased maintenance
costs.
SUMMARY OF THE INVENTION
[0013] The foregoing and other objectives are achieved in
accordance with the teachings of the present invention through the
provision of a process of directly converting post-consumer PET
flake materials to materials having relatively high average
intrinsic viscosity (IV) values whereby such resulting materials
are useful in connection with the fabrication of particularly
desirable products, such as, for example, high-performance
strapping. High performance strapping exhibits increased weld
strength. Weld strength is critically important in view of the fact
that weld strength is often the weak link in strapping products. A
weld strength value which is equal to 50% of the tensile strength
of the strapping is considered normal for conventional or prior art
high-performance strapping. As a result of the processing
techniques of the present invention, however, the tensile strength,
and accordingly the weld strength, of the strapping produced has
been able to be increased approximately 30% with respect to the
conventional or prior art high-performance strapping.
[0014] In accordance with the process of the present invention, the
inventive process begins by obtaining post-consumer and
non-post-consumer material containing PET. These materials may be
obtained, for example, from strapping or material recovery
facilities, and the materials have a relatively wide range of
initial IV values, such as, for example, from 0.70 g/dl to 0.81
g/dl. The PET materials usually contain a variety of impurities,
such as, for example, PVC, aluminum, polyethylene, polypropylene,
and paper.
[0015] The PVC and aluminum materials are initially removed from
the PET materials, and the PET materials are chopped into a
heterogeneous mixture of flakes and chunks. As noted hereinabove,
the material chunks are undesirable from the points of view of not
being especially useful in enhancing the IV values of the PET
materials, as well as adversely affecting the temperature level of
the solid state polymerization process. In accordance with the
specific teachings of the present invention, it is therefore
desirable to remove such material chunks from the batch or charge
of PET materials and such a process step is achieved by using a
suitable destoner or sorter which effectively removes or sorts all
or a large percentage of the chunk or neck portions of the PET
materials from the flake or wall portions of the PET materials as a
result of the different thickness and density properties of the
chunk or neck portions of the PET materials as compared to similar
properties characteristic of the flake or wall portions of the PET
materials. As a result, essentially only desirable flakes or wall
portions of the PET materials are further utilized within the solid
state polymerization process so as to permit an enhanced volume of
favorable or desirable PET materials to be processed, enhanced IV
values of the processed PET materials is readily achieved, and the
processing equipment is readily permitted to operate with a reduced
amount of production downtime or production run interruptions as a
result of the elimination of any agglomeration or clumping of the
PET materials due to the desirably proper control of the operative
processing temperatures.
[0016] After separation of the undesirable chunk or neck portions
of the PET materials from the batch or charge of PET materials
which now contains or comprises essentially only flake or wall
portions of the PET materials, the PET materials are preheated
within a fluid bed type dryer or preheater so as to undergo a
preheating stage at a temperature level of approximately
315.degree.F. and a time period of approximately 20-25 minutes. As
a result of such preheating process step, the PET materials are
dried in view of molecular water having been removed therefrom.
Subsequently, the PET flakes are now ready to enter the first stage
of solid state polymerization, and accordingly, the PET flakes are
placed into a hopper and heated in the absence of oxygen and in the
presence of nitrogen until they reach a temperature level of
between 390.degree.F. and 430.degree. F.
[0017] After undergoing the first stage of solid state
polymerization for approximately one hour or more, the flakes are
ready to enter the second stage of solid state polymerization, and
accordingly, the heated flake mixture is removed from the hopper
and placed within a bin in the absence of oxygen and in the
presence of nitrogen. The flakes are heated to a temperature level
of approximately 425.degree.F. and remain in the bin for a time
period of approximately four hours.
[0018] Once the flakes have completed the first and second stages
of solid state polymerization, the IV value of the resulting PET
material has been increased to at least 0.90 g/dl, and to as high
as 1.50 g/dl, withe the average IV value being approximately 0.95
g/dl. The PET flakes, having the enhanced IV values, can then be
extruded through a suitable extruder so as to produce
high-performance strapping. The strapping produced by means of the
process of the present invention, that is, utilizing PET flakes
which have been directly subjected to solid state polymerization,
which have not necessarily been subjected to intermediate
pelletization, and which have resulted in material having an
enhanced average IV value of approximately 0.95 g/dl and a wide
distribution of IV values within the range of 0.90 g/dl to 1.50
g/dl, is therefore able to comprise high-performance strapping
which exhibits good tensile strength, weld strength, and joint
strength characteristics. In addition, the solid state
polymerization process to which the flakes of the present invention
are subjected only requires a fractional amount of time that was
previously required in connection with the prior art processing of
the PET material pellets. As a result, in addition to the
elimination of the substantially non-crystalline chunk segments or
portions of the PET materials which enhances the flow-through
processing of the materials and operational efficiency of the
equipment without undergoing or experiencing operational
interruptions or production downtime, the economical processing
efficiency of PET materials, that is, the amount of time to process
a particular batch or charge of PET material, is enhanced still
further.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Various other objects, features, and attendant advantages of
the present invention will be more fully appreciated from the
following detailed description when considered in connection with
the accompanying drawings in which like reference characters
designate like or corresponding parts throughout the several views,
and wherein:
[0020] FIGS. 1A-1C comprise a flow chart showing the various steps
of the PET flake process of the present invention;
[0021] FIG. 2 is a flow chart of a nitrogen cycle portion, of the
solid state polymerization (SSP) stage of the process of the
present invention, including the use of a guard bed for HCl
removal; and
[0022] FIG. 3 is a graph showing the relationship between the
amount of PET material and the intrinsic viscosity (IV) for a
starting material and various resulting materials produced under
different conditions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Referring now to the drawings, and more particularly to FIG.
1A thereof, post-consumer and non-post-consumer polyethylene
terephthalate (PET) materials are collected from any one or more of
various different sources, including, for example, material
recovery facilities, and the materials are co-mingled into a
heterogeneous mixture. In addition to containing or comprising
polyethylene terephthalate (PET) materials, the mixture also
usually contains various other materials, such as, for example,
PVC, polypropylene, polyethylene, aluminum, and the like, which are
not desirable for use within the solid state polymerization (SSP)
processing of the PET materials in accordance with the present
invention. Accordingly, the PVC materials and aluminum cans, for
example, are initially removed from the PET materials by several
means, such as, for example, appropriate or suitable cameras or
sensors which can detect or distinguish, for example, PVC
containers or bottles from PET containers or bottles, and in
addition, operator personnel are also used to physically separate,
for example, the aluminum cans and the like.
[0024] The residual PET materials are then chopped into flakes and
chunks so as to render such constituents or components suitable for
further processing in accordance with the subsequent processing
steps characteristic of the present invention. The flakes and
chunks are respectively derived, for example, from wall portions
and neck portions of plastic soft drink bottles, with the neck or
chunk portions being thicker and denser than the wall or flake
portions. The materials are then subjected to a flotation
segregation process which serves to separate the polyethylene,
polypropylene, and any paper material from the PET materials as a
result of bulk density techniques whereby the polyethylene,
polypropylene, and paper material components float to the top of
the flotation apparatus while the PET materials sink to the bottom
of the flotation apparatus.
[0025] Subsequent to the flotation segregation processing step, the
PET flake and chunk materials are subjected to a wash cycle within
a suitable caustic solution so as to remove any dirt, grime, paper
labels, liquid syrups, and the like from the materials. After
completion of the wash cycle, the chopped materials are subjected
to another flotation segregation or separation process whereby
fines, or any residual papers which were not in fact removed as a
result of the first flotation segregation process but which have
been separated from the PET materials as a result of the caustic
solution, are removed from the cleansed PET materials. The cleansed
materials are then deposited within a suitable dryer whereby the
materials undergo a spin cycle not unlike that of a clothes washing
machine, and subsequently, the materials discharged from the spin
dryer are passed through a metal separation stage or phase whereby
suitable metal detectors are utilized to separate, for example, any
chopped portions of aluminum cans, aluminum caps, or the like,
which may have been initially co-mingled with the PET materials.
The resulting PET materials are then boxed for shipping or
deposited within suitable storage silos so that the same will be
available when needed for actual processing in accordance with the
solid state polymerization (SSP) processing of the present
invention.
[0026] The PET materials prepared in accordance with the foregoing
process steps initially have a substantially wide intrinsic
viscosity (IV) value range which in fact extends from a relatively
low IV value of approximately 0.60 g/dl to a relatively high IV
value of approximately 0.80 g/dl, with the average initial IV value
being approximately 0.70 g/dl as shown by curve A in FIG. 3. The
reason for this range of IV values is due, for example, to the fact
that different plastic soft drink bottles art manufactured by
different bottle manufacturers using different plastic materials.
It is also to be appreciated still further that the initial mixture
of PET materials can have IV values which may differ from those
noted hereinabove depending upon the particular source of the
materials. It is possible, for example, to use recycled materials,
other than plastic soft drink bottles, which are characterized by
relatively low IV values, or alternatively, to use recycled high
performance strapping made either by prior art processes or by the
process of the present invention whereby such strapping may exhibit
average IV values of 0.90 g/dl or higher. In any case, in
accordance with the various teachings of the present invention, it
is possible to produce, from a heterogeneous mixture having a
relatively wide or broad distribution of IV values of, for example,
0.60-0.80 g/dl and characterized by a relatively low average IV
value of, for example, 0.70 g/dl, resultant materials which have a
relatively wide or broad distribution of IV values of, for example
0.70 g/dl to 1.50 g/dl and characterized by a relatively high
average IV value of, for example, 0.95 g/dl as illustrated by means
of curve B shown in FIG. 3.
[0027] The precise curves and material results or characteristics
will of course depend upon the initial input material
characteristics and the particular processing parameters, and
accordingly, curves C and D of FIG. 3 illustrate other resultant
materials having relatively wide distributions of IV values with,
however, different average IV values, the different materials being
produced as a result of different process residence times. It is
therefore to be appreciated that in accordance with the processing
techniques and parameters characteristic of the present invention,
resulting solid state polymerized (SSP) material, having an average
IV value of, for example, approximately 0.80-0.85 g/dl and useful
or suitable for fabricating high-performance strapping exhibiting
currently or conventionally acceptable quality and performance
characteristics, can in fact be fabricated merely by reducing the
residence time of the materials within the process. Accordingly,
still further, and quite advantageously, high-performance strapping
exhibiting conventionally acceptable average IV values, and tensile
strength and weld strength characteristics, can be manufactured
faster and more economically when ultra-high-performance strapping,
which can also be manufactured in accordance with the various
processing techniques characteristic of the present invention and
having an average IV value of, for example, 1.15 g/dl, are not in
fact required for particular applications.
[0028] As was noted hereinabove, the initial material comprising
the charge or batch of material to be processed is comprised of a
heterogeneous mixture of flakes and chunks from which, at this
stage of the process of the present invention, undesirable PVC,
polypropylene, polyethylene, paper, and aluminum impurities have
been segregated. It has been additionally determined or discovered,
however, that from an economical and processing efficiency point of
view, that the material chunk portions or segments of the batch or
charge materials are equally undesirable and should likewise be
segregated and discarded from the solid state polymerization (SSP)
process and the processing equipment. The reasons for this are
several.
[0029] Firstly, as has been noted hereinabove, the material chunk
portions or segments of the batch or charge materials comprise
essentially or substantially non-crystalline PET materials which
react quite slowly, if at all, within the solid state
polymerization (SSP) process in connection with the enhancement or
build-up of the molecular weight or intrinsic viscosity (IV) values
or properties of the PET materials being processed. Consequently,
in order to in fact achieve the enhanced molecular weight or IV
values of the resulting or processed materials, it is desirable to
maximize the percentage amount of crystalline PET materials, and to
concomitantly minimize the percentage amount of non-crystalline PET
materials, within the batch or charge PET materials undergoing the
solid state polymerization process.
[0030] Secondly, in view of the fact that the chunk material
portions are essentially or substantially non-crystalline PET
materials, such materials will rapidly crystallize within the
polymerization processing vessel thereby generating a significant
amount of heat of crystallization. Such generated heat of
crystallization can be large enough to undesirably raise the
temperature level of the process within the solid state
polymerization vessel such that the PET materials disposed therein
tend to become sticky and agglomerate together thereby forming
clumps or material chunks which will tend to impede the flow of the
materials within the polymerization vessel as well as to clog or
jam the feeder or other operational components of the processing
apparatus.
[0031] In view of the foregoing, and in accordance with the
specific teachings of the present invention, it has been discovered
that the relatively thick and dense non-crystalline bottle neck or
chunk portions or segments of the charge or batch PET materials can
be effectively removed from the heterogeneous mixture of materials
prior to entry of the mixture of materials into the solid state
polymerization processing stages, and this step of the process can
be achieved with a commercially available "destoner".
Conventionally, such apparatus is currently used or designed to
remove dense stones from low density grains or powders. The
apparatus works upon vibrational and fluidization principles
whereby the dense stones are effectively separated from the less
dense grains or powders.
[0032] However, it has been discovered that such apparatus is also
useful in separating the thicker and denser bottle neck or chunk
portions or segments of the PET materials from the thinner and less
dense wall or flake portions or segments of the PET materials. An
exemplary destoner machine or apparatus that may be utilized within
the process of the present invention is the FORSBERG G-4 Sorter or
the FORSBERG P-6R Vacuum Destoner, both of which are manufactured
by the FORSBERG CORPORATION, MINNESOTA, although of course, it is
to be readily appreciated that other similar types of apparatus,
which operate upon similar separating principles or techniques, can
of course be utilized.
[0033] Accordingly, with continued reference being made to FIG. 1A,
after the PVC, polypropylene, polyethylene, paper, and aluminum
impurities have been segregated from the charge or batch materials,
and after the remaining charge or batch materials have been
destoned so as to remove the PET material chunks or bottle neck
portions therefrom, the flake materials are placed within a
suitable fluid bed type preheater or dryer so as to undergo a
pre-heating stage. In the preheater or dryer, the PET flake
materials are heated to a temperature level of approximately
315.degree.F. and for a time period of approximately 20-25 minutes.
The purpose of the pre-heating stage is essentially to dry the
flake materials so as to remove molecular water therefrom.
[0034] The PET flakes are now ready for the first stage of the
solid state polymerization process. It is known that the different
thickness characteristics of dimensions of different products or
materials affects the time required to solid state the materials to
a predetermined IV value, and as noted in the aforenoted related
parent patent application, the relatively thicker neck or chunk
portions were slower to solid state than the relatively thinner
wall or flake portions. The first stage of solid state
polymerization comprises increasing the temperature of the charge
or batch of PET materials, and in view of the fact that the chunk
portions or materials have been previously removed from the flake
portions or materials, the time required for processing the wall or
flake portions or materials is relatively short whereby enhanced
processing efficiency, comprising the processing flow-through of
the flake or wall portions of the materials, is able to be
achieved. More particularly, the PET flakes are deposited within a
hopper which comprises an oxygen-free environment within which
nitrogen is disbursed. The temperature of the materials is elevated
to approximately 390.degree.F.-430.degree. F., and the flakes are
continuously deposited into the hopper, and they continuously move
through the hopper from the top of the hopper to the bottom of the
hopper, during which time the materials experience a slight
increase in their IV values. In accordance with one embodiment or
example of practicing the present invention process, this first
stage of solid state polymerization took approximately one
hour.
[0035] The heated PET flakes are now ready for the second stage of
solid state polymerization. Accordingly, the flakes are removed
from the preheating hopper and are continuously deposited into a
bin. The heated PET flakes are retained within the bin for a
processing time period of approximately four hours during which
time the flakes travel from the top of the bin to the bottom of the
bin, and the temperature level within the bin is in the range of
380.degree.F. to 425.degree.F. in accordance with a nitrogen cycle
which will be explained more fully hereinafter. As a result of such
processing, the intrinsic viscosity (IV) value of the PET flakes,
which was initially within the range of approximately 0.60 g/dl to
0.80 g/dl, increases substantially to an average IV value of
approximately 0.95 g/dl and with a wide distribution of IV values
ranging from approximately 0.70 g/dl to 1.5 g/dl as shown, for
example, by means of curve B in FIG. 3. The heated, high intrinsic
viscosity flakes may then be removed from the bin and fed directly
to an extruder from which high-performance strapping, having an IV
value within the range of 0.80-1.0 g/dl, may be manufactured.
[0036] The nitrogen cycle utilized within the second stage of solid
state polymerization is more fully illustrated in FIG. 2 and
comprises supplying pure nitrogen to the bottom of the bin and
aspirating contaminants from the top of the bin. The nitrogen
travels upwardly through the bin and through the flakes, and in so
doing, the nitrogen reacts with the flakes so as to extract
acelhyde, ethylene glycol, and hydrochloric acid (HCl). The
nitrogen supplied or used within the nitrogen cycle may either be
continuously supplied pure nitrogen or nitrogen which has been
derived from the cycle and purified of the contaminants. If the
latter option is chosen, the same nitrogen can of course be reused
which renders the process somewhat more economical.
[0037] The contaminants can be removed from the nitrogen in
accordance with any one of several different techniques or
processes. One way is through the desiccant process formulated by
BEPEX .sup.R. Another means is through removal of waste products by
the catalytic oxygen process developed by BUHLER .sup.R. A still
further manner for removing hydrochloric acid (HCl) from the
nitrogen cycle is through the use of a lime bag filter apparatus
which eliminates the HCl from the flow of gas. Yet another manner
in which to remove the HCl from the nitrogen cycle is to conduct
the gas through a water spray whereby the HCl is absorbed in the
water slurry. A further endeavor may comprise the use of a guard
bed of basic material as will be discussed more fully
hereinafter.
[0038] The removal of the contaminants, and in particular, the
removal of the HCl, is important for several reasons. During the
second stage of the solid state polymerization, the amount of HCl
that is emitted is relatively small, however, the presence of the
HCl may nevertheless cause problems within at least two areas or
regions of the apparatus and process of the present invention, that
is, in connection with catalytic activity, and also in connection
with corrosion, especially when liquid water is or may also be
present. HCl is known to deactivate a platinum catalyst, although
the amount of such deactivation, as might be encountered during
practice of the present invention process, is not precisely known.
Increased temperature can offset some of the catalyst deactivation
but at an increased risk of sintering, that is, permanent
deactivation, of the catalyst. Increasing the size of the catalyst
bed is also an option for offsetting lower catalyst activity,
however, this option increases catalyst costs, drops the pressure
within the system, and may require additional blower capacity. In
connection with the corrosion problems, liquid water tends to
absorb HCl from the passing gas stream and concentrate the same to
levels where corrosion rates become problematic. This condition
appears to exist at a location after the condenser which cools the
process stream and before the absorbent bed.
[0039] In accordance then with various embodiments envisioned by
the teachings of the present invention, as more specifically
illustrated in FIG. 2, and as noted briefly hereinbefore, the
problems of catalytic deactivation and corrosion due to HCl
reactions may be eliminated by removing the HCl from the process of
the present invention as soon as possible by utilizing a guard bed
of basic material. Such a guard bed may be added to the BUHLER
.sup.R line just before the catalyst bed, or alternatively, may be
incorporated within the bag house filter assembly just after the
solid state fluidized bed. In accordance with another embodiment,
the guard bed may be placed after the bag house filter assembly so
as to avoid plugging the same with PET particles. In accordance
with still another embodiment, the relatively simpler BEPEX .sup.R
design omits the catalyst bed, so consequently, the guard bed can
be placed immediately after the solid state fluidized bed or in the
bag house filter assembly. In accordance with techniques employed
in connection with placing the guard bed within the bag house
filter assembly, the bag house filter can be coated with a basic
solid, such as, for example, calcium oxide, lime, caustic soda, or
bicarbonate, so as to neutralize the acid. In this case, the
conventional filter bags would be replaced by those of the present
invention. Still yet alternatively, the guard bed may also take the
form of a spray chamber which sprays water or bicarbonate.
[0040] With reference continuing to be made to FIG. 2, suitable
monitors may also be incorporated within the processing line or
system for detecting the levels of HCl present within the system or
the various processing components thereof. The levels of HCl could
occasionally rise due to the presence of PVC material within the
solid state fluidized bed. A simple HCl monitor can comprise a
small fluid stream of known flow rate into a scrubber-bubbler
attached to an automated titration unit, and the consumption of
bases or basic materials so as to maintain constant pH values would
constitute a simple yet direct way to measure HCl levels.
[0041] Due to the fact that steel or even stainless steel is likely
to corrode at excessive rates when liquid water is in the presence
of HCl or Cl.sub.2, the apparatus of the present invention may be
constructed from alternatively viable construction materials, such
as, for example, CPPC, PP, or a steel having a corrosion-resistant
coating. The 13.times. molecular sieves used in the BEPEX .sup.R
desiccant process are also known to degrade in the presence of
acids. Accordingly, a larger bed may have to be used so as to
compensate for the lost drying capacity. The deterioration of the
sieves may also produce powdered sieves. If this happens, the
powder could be carried into the PET production materials and/or
accumulate within the lower end of the desiccant vessel and thereby
impede gas flow. In order to prevent this from occurring, a section
of the production facility or plant could be provided with suitable
filters so as to filter out the generated powder materials and
thereby prevent PET contamination with the same, and easily
accessible access ports could be provided within the bottom regions
of the apparatus whereby cleaning of the facility is readily
facilitated. In accordance with still another embodiment, the
nitrogen may be drenched, as the same passes through the fluidized
bed, with by-pass desiccant fumes. In any case, once the nitrogen
has been purified of its contaminants by any one of the foregoing
processes, the purified nitrogen can be conducted back into the
bottom of the bin so as to undergo another nitrogen cycle. The
process can be conducted either as a batch process or as a
continuous process. One of the important factors in connection with
the process of the present invention is that the nitrogen gas
removes volatile polymerization reaction products, including
ethylene glycol and other impurities, which can cause undesirable
secondary reactions. If, for example, more than twenty parts per
million of PVC is still contained within the flakes after the
preheater stage, the flakes will produce HCl and degrade the
desiccant which is used to purify the nitrogen used in the second
stage of the solid state polymerization (SSP) process. As such, the
desiccant would have to be replaced more than once per year due to
the reactions between the HCl and the desiccant.
[0042] As briefly noted hereinabove, after the flakes have passed
through the hopper and bin structures of the first and second
stages, respectively, of the solid state polymerization process,
the flake products are removed from the bin of the second stage of
the solid stage polymerization process and directly fed in a hot
state to the feed hopper of the extruder from which the
high-performance strapping is to be produced. The feeding of the
hot flake products or materials directly from the solid state
polymerization second stage bin to the strap-producing extruder is
economically advantageous in that such processing conserves
significant heat within the polymer materials and accordingly
reduces the power requirements per pound of polymer to be
extruded.
[0043] The degree of uniformity of the product resulting from the
process of the present invention is surprising in view of the
variety and relatively wide range of the intrinsic viscosity (IV)
values of the initial materials. In addition, in view of the
incorporation of the destoner or similar apparatus into the process
of the present invention, heating and solid state polymerization of
the PET flakes proceeds readily, rapidly, and without any
substantial problems, such as, for example, agglomeration of the
polymers, sticking of the polymers to the processing equipment, or
degradation of the polymers, as is often the case with pellets. An
unexpected result achieved by means of the process of the present
invention is the production of a product which has a relatively
high average IV value and which was obtained using materials having
a wide range of relatively low initial IV values. Stated
alternatively, an initially narrow range of IV values is not in
fact required in either the initial materials which will undergo
the solid state polymerization process and which will be used to
manufacture strapping, or in the final strapping itself so as to
obtain high quality, high-performance plastic strapping.
[0044] Thus, it may be seen that the solid state polymerization
process of the present invention advantageously leads to the
production of high-performance strapping in an economically
desirable manner from both material flow-through and production
downtime points of view, although obviously, many modifications and
variations of the present invention are possible in light of the
above teachings. For example, the precise operating or procedural
parameters of the process of the present invention may be altered
somewhat in order to achieve desired intrinsic viscosity (IV)
values. Intrinsic viscosity increases with increased amounts of
nitrogen gas, with increased temperature levels within the solid
state polymerization stages, as well as with increased residence
times within the solid state polymerization stages. It has also
been determined that preheating the flakes to reaction temperature
levels reduces the size of the bin necessary to effect solid state
polymerization. In addition, it has been further determined that
relatively thin flakes exhibit increased IV values much faster than
pellets or relatively thick chunks, and they obtain high IV values,
and most significantly or importantly, flakes, unlike pellets or
chunks, are most desirable in view of the fact that the flakes do
not become sticky or cause agglomeration either in the first or
second stage of the solid state polymerization. Nevertheless, it is
to be appreciated that the neck portions of, for example, the
bottles or beverage containers from which the material chunks are
derived are valuable or important components in that subsequent to
the solid state polymerization processing of the PET flake
components, the neck material chunk portions, along with recycled
pellets that are not solid state polymerized, or low intrinsic
value (IV) flakes may, as an alternative or option, be added to the
solid state polymerized flakes as the latter are being fed into the
extruder, as shown in FIG. 1B, in order to adjust the resulting
intrinsic value (IV) of the mixture being fed into the extruder
whereby the resulting strapping will have predetermined or
particularly desired characteristics or parameters.
[0045] It is also noted that oxygen is not added during either the
preheat or solid state polymerization stages because the presence
of oxygen will degrade and color the polymers, nitrogen therefore
being the preferred gas to be used in the solid state
polymerization process because it does not lead to the adverse
effects that would be caused by oxygen. In addition, nitrogen is
also economical and readily available. It is therefore to be
understood that within the scope of the appended claims, the
present invention may be practiced otherwise than as specifically
described herein.
* * * * *