U.S. patent application number 11/877751 was filed with the patent office on 2008-02-28 for molding of polypropylene with enhanced reheat characteristics.
This patent application is currently assigned to INVISTA NORTH AMERICA S.AR.L.. Invention is credited to J. Paul Davis, David A. Harrison, Stephen D. Jenkins, Michael A. Neal.
Application Number | 20080050544 11/877751 |
Document ID | / |
Family ID | 32961916 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080050544 |
Kind Code |
A1 |
Neal; Michael A. ; et
al. |
February 28, 2008 |
MOLDING OF POLYPROPYLENE WITH ENHANCED REHEAT CHARACTERISTICS
Abstract
Bottles, containers and other articles are formed from
polypropylene compositions that include a reheating agent, such as
antimony, carbon black, graphite, titanium, copper, manganese,
iron, tungsten, graphite, infra-red absorbing dyes or other
infra-red absorbing material. The reheating time for the
polypropylene composition is shortened for injection stretch blow
molding or thermoforming, and the polypropylene granule composition
with reheating agent has an L* value of at least 80% of the L*
value for a polypropylene granule control without added reheating
agents as measured by the Gardner color test. The reheating agent
may be incorporated into the polypropylene composition by in situ
chemical reduction of a metal compound, such as antimony
triglycolate, with a reducing agent, such as hypophosphorous acid.
In addition, the polypropylene composition with reheating agent may
be derived from a polypropylene masterbatch with high
concentrations of reheating agent.
Inventors: |
Neal; Michael A.; (Martan,
GB) ; Harrison; David A.; (Redcar, GB) ;
Jenkins; Stephen D.; (Stokesley, GB) ; Davis; J.
Paul; (Billingham, GB) |
Correspondence
Address: |
INVISTA NORTH AMERICA S.A.R.L.
THREE LITTLE FALLS CENTRE/1052
2801 CENTERVILLE ROAD
WILMINGTON
DE
19808
US
|
Assignee: |
INVISTA NORTH AMERICA
S.AR.L.
Wilmington
DE
|
Family ID: |
32961916 |
Appl. No.: |
11/877751 |
Filed: |
October 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10387600 |
Mar 13, 2003 |
7303795 |
|
|
11877751 |
Oct 24, 2007 |
|
|
|
Current U.S.
Class: |
428/34.7 ;
264/322 |
Current CPC
Class: |
B29B 2911/14326
20130101; B29B 2911/14026 20130101; B29K 2023/12 20130101; B29C
49/12 20130101; B29B 2911/14133 20130101; B29B 11/08 20130101; B29K
2105/258 20130101; B29B 2911/1404 20130101; B29B 2911/14106
20130101; B29C 49/00 20130101; B29B 2911/1444 20130101; B29B
2911/1402 20130101; B29C 49/4205 20130101; B29L 2031/7158 20130101;
Y10T 428/1321 20150115; B29C 49/0005 20130101; B29B 11/14 20130101;
B29K 2623/12 20130101; B29C 48/12 20190201; B29C 49/06 20130101;
B29B 2911/14033 20130101; Y10T 428/1352 20150115; B29C 48/91
20190201; C08K 3/08 20130101; B29C 2035/0822 20130101; C08K 3/08
20130101; C08L 23/12 20130101 |
Class at
Publication: |
428/034.7 ;
264/322 |
International
Class: |
B29D 22/00 20060101
B29D022/00 |
Claims
1. A method for injection stretch molding a polypropylene bottle,
comprising: (a) forming a preform from a polypropylene composition
containing a reheating agent, wherein the reheating agent comprises
one or more metal particles, and wherein said metal particles are
selected from the group consisting of one or more of antimony,
titanium, copper, manganese, iron and tungsten; (b) reheating the
preform to a desired temperature, wherein the time for the preform
to reach the desired temperature is less than the time for
reheating to the desired temperature a control preform of
equivalent dimensions that is formed from the polypropylene
composition without the reheating agent; and (c) injection stretch
blow molding the reheated preform to form the bottle; wherein the
polypropylene composition containing a reheating agent when it is
in a granule form prior to forming the preform has an L* value as
measured by the Gardner color test of at least about 80% of an L*
value of the polypropylene composition in granule form in the
absence of the reheating agent.
2. (canceled)
3. A method for injection stretch molding a polypropylene bottle,
comprising: (a) forming a preform from a polypropylene composition
containing a reheating agent, wherein the reheating agent comprises
carbon black, graphite or an infra-red dye in the form of particles
incorporated into the polypropylene composition in an amount in the
range of 2 ppm to 1000 ppm; (b) reheating the preform to a desired
temperature, wherein the time for the preform to reach the desired
temperature is less than the time for reheating to the desired
temperature a control preform of equivalent dimensions that is
formed from the polypropylene composition without the reheating
agent; and (c) injection stretch blow molding the reheated preform
to form the bottle; wherein the polypropylene composition
containing a reheating agent when it is in a granule form prior to
forming the preform has an L* value as measured by the Gardner
color test of at least about 80% of an L* value of the
polypropylene composition in granule form in the absence of the
reheating agent.
4. The method of claim 1, wherein the reheating agent is
incorporated into the polypropylene composition in the form of
particles having sizes in the range of 10 nm to 100 microns and in
an amount in the range of 2 ppm to 1000 ppm.
5. The method of claim 1 or 3, wherein the reheating agent is
incorporated into the polypropylene composition in the form of
particles having sizes in the range of 10 nm to 10 microns and in
an amount in the range of 2 ppm to 50 ppm.
6. The method of claim 1, wherein the reheating agent is generated
within the polypropylene composition by in situ chemical reduction
of a metal compound with a reducing agent.
7. The method of claim 6, wherein the metal compound contains one
or more of antimony, titanium, copper, manganese, iron and
tungsten, and the reducing agent is selected from the group
consisting of one or more of organic phosphorous acids, inorganic
phosphorous acids, tannic, gallic, and pyrogallic acids, hydrazine,
sulphites, tin II salts and nickel hydroxide.
8. The method of claim 6, wherein the metal compound is antimony
triglycolate and the reducing agent is hypophosphorous acid.
9. The method of claim 1, wherein the reheating agent is
incorporated into the polypropylene composition in the form of
particles having sizes in the range of 10 nm to 100 microns and in
an amount in the range of 50 ppm to 25,000 ppm to form a
polypropylene masterbatch.
10. A polypropylene bottle made according to the method of claim 1
or 3.
11.-33. (canceled)
34. The method of claim 3, wherein the reheating agent is
incorporated into the polypropylene composition in the form of
particles having sizes in the range of 10 nm to 100 microns.
35. The method of claim 3, wherein the reheating agent is
incorporated into the polypropylene composition in an amount in the
range of from 2 ppm to 350 ppm.
36. The method of claim 3, wherein the reheating agent is
incorporated into the polypropylene composition in an amount in the
range of from 2 ppm to 50 ppm.
37. The method of claim 6, wherein the metal compound is antimony
trioxide.
38. The method of claim 6, wherein the metal compound is antimony
trioxide and the reducing agent is hypophosphorous acid.
39. A method for injection stretch molding a polypropylene bottle,
comprising: (d) forming a preform from a polypropylene composition
containing a reheating agent selected from metal particles that
intrinsically absorb radiation in the wavelength region of 500 nm
to 2000 nm; (e) reheating the preform to a desired temperature,
wherein the time for the preform to reach the desired temperature
is less than the time for reheating to the desired temperature a
control preform of equivalent dimensions that is formed from the
polypropylene composition without the reheating agent; and (f)
injection stretch blow molding the reheated preform to form the
bottle; wherein the polypropylene composition containing a
reheating agent when it is in a granule form prior to forming the
preform has an L* value as measured by the Gardner color test of at
least about 80% of an L* value of the polypropylene composition in
granule form in the absence of the reheating agent.
40. The method of claim 39, wherein the reheating agent is
incorporated into the polypropylene composition in the form of
particles having sizes in the range of 10 nm to 100 microns and in
an amount in the range of 2 ppm to 1000 ppm.
41. The method of claim 39, wherein the reheating agent is
incorporated into the polypropylene composition in the form of
particles having sizes in the range of 10 nm to 10 microns and in
an amount in the range of 2 ppm to 50 ppm.
42. The method of claim 39, wherein the reheating agent is
generated within the polypropylene composition by in situ chemical
reduction of a metal compound with a reducing agent.
43. The method of claim 39, wherein the reheating agent is
incorporated into the polypropylene composition in the form of
particles having sizes in the range of 10 nm to 100 microns and in
an amount in the range of 50 ppm to 25,000 ppm to form a
polypropylene masterbatch.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the manufacture of bottles,
containers and other articles from polypropylene polymer
compositions, in particular by injection stretch blow molding and
thermoforming techniques.
BACKGROUND OF THE INVENTION
[0002] Polyester compositions, such as polyethylene terephthalate
or copolymers thereof (hereinafter collectively referred to as
"PET"), are well known packaging materials. For example, in U.S.
Pat. No. 4,340,721, a PET composition is used to manufacture
beverage bottles and other containers (hereinafter referred to as
"bottles") by various molding methods.
[0003] In current practice PET bottles of the size and shape for
most beverage applications are usually made by an injection stretch
blow molding technique. Injection stretch blow molding has two main
steps. First, the PET, in the form of granules, is melted in an
injection molding machine and the melt injected into a cooled mold
to form a precursor to the final bottle known as a "preform".
Commonly, the preform has a threaded neck with a shortened bottle
body shape length about 8 to 20 cm and a material thickness between
3 mm and 6 mm. Second, the preform is transferred to a stretch blow
molding machine where its external surfaces are reheated by
infra-red (IR) lamps. Once the preform has reached a desired
temperature, it is stretched and blown to form the final
bottle.
[0004] The time it takes to reheat the preform is the rate-limiting
factor for the overall process. The preform starts at ambient
temperature and has to be heated to above the glass transition
temperature of the polyester (generally to about 110.degree. C.) so
that the preform becomes sufficiently flexible to permit the
stretch-blow step to work. In general, polyester polymers have a
poor ability to absorb IR radiation. Hence, as well as extending
the overall production time, the preform reheating step also
requires a significant amount of energy. To address this problem,
certain prior patents have taught that adding black materials
and/or metal particles to PET compositions can reduce the time and
energy required for reheating. Hence, prior patents teach adding
carbon black (U.S. Pat. No. 4,476,272), iron oxide (U.S. Pat. No.
4,250,078), and antimony and other metal particles (U.S. Pat. Nos.
5,419,936 and 5,529,744) to reduce PET preform reheating time.
Antimony metal particles were indicated as preferred because such
particles preferentially absorb radiation at or near the infra-red
wavelengths emitted by the IR lamps in most stretch blow mold
machines, e.g., 500 nm to 2000 nm. Furthermore, as described in
U.S. Pat. Nos. 5,419,936 and 5,529,744, antimony compounds are
usually present in the polyester composition itself (as the
catalyst for melt polymerization) and can be converted to antimony
metal particles, with the desired IR absorption characteristics, by
the addition of a reducing agent in the melt polymerization stage
of manufacture.
[0005] Although PET has found widespread application for beverage
bottles, the cost of raw materials for making PET is much higher
than for some non-PET polymers. Therefore, the industry continually
seeks to switch from PET to lower cost alternatives. Whilst seeking
these alternatives, container manufacturers do not wish to invest
substantial resources in new capital equipment to process a new
polymer material, but would prefer to adapt their existing PET
injection blow molding equipment for use with the new material.
[0006] One possible alternative to PET for use in injection stretch
blow molding of beverage bottles is polypropylene. U.S. Pat. No.
6,258,313 teaches that injection stretch blow molding of a
polypropylene preform is possible if the preform is heated
simultaneously both from the outside and inside. Nevertheless, it
has heretofore been more difficult to produce satisfactory beverage
bottles from polypropylene by this method. First, polypropylene has
a lower density and specific heat than PET and hence exhibits a
significantly narrower processing window. Second, polypropylene
suffers from the same limitations as PET in terms of its poor
ability to absorb IR radiation. Furthermore, polypropylene
generally has greater opacity than PET, which detracts from its
aesthetic appearance. The industry thus continues to seek ways to
improve the IR absorption properties of polypropylene such that it
can be used to make beverage bottles on the same injection stretch
blow molding equipment as PET and/or used to make other
thermoformed articles.
SUMMARY OF THE INVENTION
[0007] In a first aspect, the invention is a method for injection
stretch blow molding a polypropylene bottle from a preform that
comprises a polypropylene composition containing a reheating agent.
The reheating agent may be one or more metal particles of antimony,
titanium, copper, manganese, iron and tungsten, where antimony is
most preferred. The reheating agent also may be particles of carbon
black, graphite, infra-red absorbing dyes or other infra-red
absorbing material.
[0008] The preform is reheated, usually by heating with one or more
heating lamps, to a desired reheat temperature. The time for
reheating the preform is shorter than the time for reheating a
control preform of equivalent dimensions formed from the
polypropylene composition without a reheating agent. The polymer
granules used to make the preform have an L* value of at least
about 80% of an L* value of the polymer granules used to make the
control preform. The L* values are measured by the Gardner color
test. For example, where the control polypropylene composition
granules have an L* value of about 75, the granules used to
manufacture the preform according to the invention have an L* value
of about 60 or above. The closer the L* value is to the L* value of
the control, the more the final bottle will resemble the
color/aesthetics of a bottle made from the control
polypropylene.
[0009] Preferably, the reheating agent is incorporated into the
polypropylene in the form of particles having particle sizes in the
range of about 10 nanometers (nm) to about 100 micrometers, and
more preferably in the range of 10 nm to 10 microns. Preferably,
the reheating agent particles are incorporated into the
polypropylene in an amount in the range of about 2 ppm to 1000 ppm,
more preferably from 2 ppm to 350 ppm, most preferably from 2 ppm
to 50 ppm. The reheating agent particles also may be incorporated
into the polypropylene composition in the form of particles having
sizes in the range of 10 nm to 100 microns and in an amount in the
range of 50 ppm to 25,000 ppm to form a polypropylene masterbatch.
The masterbatch then may be blended with other polypropylene
compositions (possibly free of reheating agents or containing
different reheating agents or different proportions of the same
reheating agents) to form a polypropylene composition with desired
proportion(s) of reheating agent(s).
[0010] In addition, the reheating agent may be generated within the
polypropylene composition by in situ chemical reduction of a metal
compound with a reducing agent.
[0011] Thus, the metal compound can contain one or more of
antimony, titanium, copper, manganese, iron and tungsten, and the
reducing agent can be one or more organic phosphorous acids or
inorganic phosphorous acids, or tannic, gallic, and pyrogallic
acids, or hydrazine, or sulphites, or tin II salts, nickel
hydroxide or any organic or inorganic compound with an
electrochemical potential sufficient to reduce the metal compounds
to the metallic state. Preferably, the metal compound is antimony
triglycolate and the reducing agent is hypophosphorous acid.
[0012] The preforms, polypropylene bottles and other polypropylene
articles made from the polypropylene compositions with reheating
agents are also claimed. Examples of other polypropylene articles
include three-dimensional articles, such as cups or serving trays
or food containers, and two-dimensional articles, such as sheets.
Depending upon the desired aesthetics of the final articles, the L*
values for the polypropylene granules with reheating agents used to
form these other polypropylene articles may be outside the
preferred range for L* for compositions used to form bottle
preforms that are injection stretch blow molded into bottles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will be described in the following
detailed description with reference to the following drawings:
[0014] FIGS. 1A to 1D are schematic diagrams of the typical steps
in an injection stretch blow molding method for bottle making;
[0015] FIG. 2 is a schematic diagram showing an apparatus for
heating a polymer plaque with a single IR lamp, which apparatus may
be used to determine the through heating time of the polymer;
[0016] FIG. 3 is a graph of plaque temperature data over reheating
time for plaque surface reheat experiments conducted with plaques
formed with different polypropylene compositions;
[0017] FIG. 4 is a graph of data showing the variation in the time
required to through heat a polypropylene plaque to a target
temperature (i.e., 80.degree. C.) in relation to the amount of
reheat agent in the polypropylene composition forming the plaque;
and
[0018] FIG. 5 is a graph of data comparing reheat time (seconds to
80.degree. C.) versus the amount of reheat agent added to the
polypropylene compositions forming the plaques; and
[0019] FIG. 6 is a graph of data comparing L* (for degree of color)
versus the amount of reheating agent added to the polypropylene
compositions forming the plaques.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The present invention is directed to polypropylene
compositions that are useful in the production of stretch blow
molded containers, particularly bottles, with good color quality
and transparency. Such compositions may also be used to make other
polypropylene containers and polypropylene articles with other
two-step techniques, such as thermoforming. The polypropylene
compositions contain as reheating agents certain metal particles
that intrinsically absorb radiation in the wavelength region of 500
nm to 2000 nm, which are the typical wavelengths of the radiation
from infra-red lamps used in IR heating in PET injection stretch
blow molding. The metal particles are present in sufficient amount
to reduce the reheating time that would otherwise be required to
reheat a preform of a polypropylene composition to the desired
temperature during injection stretch blow molding or thermoforming.
Such polypropylene compositions with reheating agents still have
acceptable color and clarity for the desired end use
applications.
[0021] Referring first to FIGS. 1A to 1D, a known injection stretch
blow molding method involves certain steps. First, an injection
molded preform 10 as shown in FIG. 1A has a threaded neck portion
12 and a bottle body portion 14. The preform 10 is injection molded
from either a polypropylene composition containing reheat agents or
from a reheat agent concentrate masterbatch of granules that are
mixed with polymer granules without reheat agents. Most commonly,
each polypropylene granule is from 2.5 to 4.0 mm long and 2.0 to
3.0 mm in diameter. The polypropylene composition or mixture of
polypropylene granules is heated to melt the composition/granules
to form a flowable polymer melt that is introduced by injection
into the mold. The injection mold has a cavity and a mating ram to
form the preform into the desired contoured shape. The preform 10
is removed from the mold, cooled and stored until it is ready to be
formed into a bottle.
[0022] As shown in FIG. 1B, the preform 10 is then installed over a
fixture 18 and held within a reheating or preheating cavity 20.
Heating lamp 22, which may be one or a series of lamps, emits
infra-red radiation that heats the outer surface of the preform 10
as the preform 10 is rotated on the fixture 18. The reheating can
be conducted from the outside of the preform as shown in FIG. 1B,
from the inside of the preform, or from both the outside and the
inside of the preform, although heating just from the outside is
the most common technique when forming PET bottles.
[0023] When the preform 10 reaches a desired temperature, the
reheated preform 10 is then ready for stretch blow molding.
Referring next to FIGS. 1C and 1D, the fixture 18 with the reheated
preform 10 is held within a mold cavity 30 having the contours to
mold the polymer material into a bottle. A gas, such as air or
nitrogen, is injected into the internal volume of the preform 10
through a nozzle in the fixture 18 as a push rod 32 urges the
polymer material to expand outwardly to conform to the internal
contours of the mold. Once the injection stretch blow molding has
been completed, the finished bottle (not shown) is removed from the
mold. In one aspect, the present invention concerns injection
stretch blow molding of polypropylene compositions using the
equipment now commonly used by industry for injection stretch blow
molding of PET.
[0024] Reheating agents added to the polypropylene composition to
reduce reheating time according to the invention include antimony
(Sb), manganese (Mn), iron (Fe), carbon black, graphite, infra-red
dyes, titanium (Ti), tungsten (W), and copper (Cu). Antimony and
carbon black are preferred reheating agents, and antimony is
particularly preferred. The reheating agents preferably are added
to the polypropylene composition in amounts from about 2 ppm to
about 1000 ppm, more preferably about 2 ppm to 350 ppm, and most
preferably from about 2 ppm to 50 ppm, and with particle sizes in
the range of about 10 nm to about 100 microns, most preferably in
the range 10 nm to 10 microns.
[0025] The reheating agents may be incorporated into the
polypropylene compositions in a number of ways. As one alternative,
the reheating agents may be directly mixed with the polypropylene
granules prior to introducing the mixture to an injection mold to
form the preform. As another more preferred alternative, the reheat
agents can be directly mixed with the polypropylene granules and
passed through a twin screw compounding extruder or similar piece
of equipment to form a well dispersed and distributed polypropylene
compound before being introduced to an injection moulding machine.
As an alternate more preferred alternative, the reheating agents
can be generated within the polypropylene composition by in situ
chemical reduction of a metal compound with a reducing agent. As a
fourth and even more preferred alternative, the reheating agents
can be incorporated into the polypropylene composition by one of
the alternatives above, but in high concentrations to form
masterbatch granules. Then, such masterbatch granules may be
blended with polypropylene granules having a different
concentration of reheating agent or no reheating agent or a
concentration of a different reheating agent to form a desired
polypropylene composition containing one or more reheating agents
in desired concentrations. For example, the polypropylene
masterbatch may incorporate reheating agent(s) in the form of
particles having sizes in the range of 10 nm to 100 microns,
preferably less than 10 microns, and in an amount in the range of
50 ppm to 25,000 ppm, preferably less than 1250 ppm.
[0026] The degree of reheating agent distribution and dispersion in
the polypropylene composition affects the reheating efficacy. That
is to say, the more evenly distributed and more widely dispersed
the reheating agents in the polymer, the better the reheating
efficacy. Similarly, better distribution and dispersion of
reheating agents in the polymer improves the aesthetics of the
polymer.
[0027] In one of the more preferred embodiments, the reheating
agent is formed by an in situ chemical reduction of a metal
compound with a reducing agent. The metal compound preferably
contains one or more of antimony, titanium, copper, manganese, iron
and tungsten, and the reducing agent preferably is selected from
the group consisting of one or more of organic phosphorous acids,
inorganic phosphorous acids, tannic, gallic, and pyrogallic acids,
hydrazine, sulphites, tin II salts and nickel hydroxide, or any
organic or inorganic compound with an electrochemical potential
sufficient to reduce the metal compounds to the metallic state.
[0028] Antimony as reheating agent preferably is formed by an in
situ chemical reduction of an antimony compound with a reducing
agent, such as hypophosphorous acid or other organic phosphorous
acid or inorganic phosphorous acid. Preferred antimony compounds
include antimony triglycolate (ATG), antimony triacetate (ATA) or
antimony trioxide (ATO). The hypophosphorous acid reduces antimony
compounds to antimony, which is dispersed in the polypropylene
composition. The antimony particles appear to be more uniformly
dispersed when introduced into the polypropylene composition in
this manner. In particular, we discovered that the antimony
particles deposited by the reaction of ATA, ATO or ATG with
hypophosphorous acid and/or phosphorous acid have a particularly
favorable particle size and are particularly well dispersed in the
polypropylene.
[0029] The present invention provides a method of making
polypropylene containers, such as bottles, and other polypropylene
articles that have aesthetic characteristics close to polypropylene
compositions without reheating agents. At the same time, the method
also reduces the energy requirements for reheating compared to
polypropylene compositions without reheating agents. One immediate
advantage is cost savings though reduced cycle time or energy
savings. Yet another advantage of the present invention is that
polypropylene can be used at a higher temperature than PET in
subsequent processing, such as pasteurization or cleaning. In
addition, polypropylene is recyclable to the same extent as
PET.
[0030] The following examples further illustrate the present
invention. All parts and percentages are expressed by weight unless
otherwise specified.
EXAMPLES
[0031] Two methods for measuring the reheat temperature were used
to assess reheating times for polypropylene compositions containing
different reheating agents. First, injection molded plaques were
formed from the polypropylene compositions and through heat times
for such plaques were measured according to the procedure described
below. Second, plaques were molded from the polypropylene
compositions and surface reheat times for such plaques were
measured according to the procedure described below.
Preparing the Polypropylene Masterbatch Compositions
[0032] Polypropylene polymer granules with a size of about 2.5 to
4.0 mm in length and 2.0 to 3.0 mm in diameter were mixed with
reheating agents according to the following steps. First, about 5-7
kg polypropylene polymer was mixed with liquid paraffin (about 20
ml) in a plastic bag. The polymer in the bag was tumbled to coat
the polymer granules with a thin film of oil. Next, the reheating
agents were added to the bag and the admixture was tumbled again.
Then, the coated polypropylene polymer granules were compounded
using an APV MP2030 twin screw extruder, followed by a Boston
Mathews single screw extruder fitted with a 4-section cavity
transfer mixer. The resultant compound was then injection molded to
form plaques for further testing.
Procedure for Measuring Plaque Through Heating Temperature
[0033] Polypropylene plaque through heating temperature
measurements were made as follows:
[0034] A polypropylene plaque of one hundred millimeters (100 mm)
in diameter and four millimeters (4 mm) in cross-sectional
thickness was used to evaluate the reheating time for various
polypropylene compositions. Each polypropylene plaque of a polymer
composition containing a reheating agent and each plaque of the
corresponding control composition were made by a standard injection
molding method using NB90 Negri Bossi 90te injection molding
equipment available from Negri Bossi of Milan Italy. All of the
sample and control plaques were made to exactly the same
dimension--100 mm in diameter and 4 mm in cross-sectional
thickness. The plaques were clean and free of surface contaminants,
and had flat upper and lower surfaces.
[0035] As illustrated schematically in FIG. 2, a single IR
radiation lamp 22a, which is a 300 watt bulb made by Phillips, was
positioned to heat one side of the plaque 26. A series of flat
thermocouples were positioned on the opposite side of the plaque 26
to measure the radiated and conducted temperature. The temperature
measuring device was a TC-08 8 channel thermocouple data logger
from Pico Technology Limited of The Mill House, Cambridge Street,
St. Neots, PE19 1QB, and the temperature measuring software was a
Pico Technology Limited proprietary program supplied with the TC-08
unit. The plaque was 165 mm below the bottom of the infra-red lamp.
This test method reflects the amount of heat transferred through
the plaque from the heated side. The temperature was recorded as
the mean of five measurements on five different plaques from each
test sample and from a standard control plaque. We believe data
from this plaque through-heat method represents more realistically
the heat transfer and distribution in an article, such as a
preform, which is processed by a typical injection stretch blow
molding method, or for an article which is processed by a reheating
method followed by physical forming, such as thermoforming.
[0036] The measuring apparatus was calibrated by using control
plaques with a defined composition. These control plaques were
tested repeatedly and showed consistent reheat measurements. Then,
the reheating times for plaques that were tested for comparison
were expressed in reference to the control. Two measurements were
used: (1) time (seconds) to heat the plaque to 80.degree. C.; and
(2) temperature of the plaque after 300 seconds heating time. We
have found that for proper comparison the plaques used in this
method should have the same starting ambient temperature. Newly
molded plaques should be cooled down to room temperature for a
sufficient amount of time before testing. In our tests, freshly
molded plaques were allowed to cool down at room temperature for at
least 30 minutes before the reheating test was conducted.
[0037] Referring to FIGS. 4, 5 and 6, the reheating profiles for
plaques formed from a polypropylene control and from polypropylene
compositions containing different amounts of antimony or carbon
black were evaluated.
[0038] For the reheating test in FIG. 4, the compositions tested
were: Sb1: 25 ppm antimony formed by reducing reaction of equal
parts by weight of antimony triglycolate and hypophosphorous acid;
Sb2: 25 ppm antimony metal (milled) of particle size range 600 nm-2
microns; CB1: 25 ppm of 40 nm carbon black; and CB2: 25 ppm of
larger particle size 6-30 microns carbon black. The reheating
agents were all used in the same amount, 25 ppm, based on the
weight of the polypropylene. As shown in FIG. 4, the polypropylene
plaques that incorporated reheating agents all reheated more
rapidly than the control polypropylene without reheating agents.
All reached a desired 80.degree. C. reheating temperature within
300 to 360 seconds, whereas the control took more than 480 seconds
to reach this reheating temperature, which represents a 30% to 35%
or better reduction in the reheating time.
[0039] FIGS. 5 and 6 compare the reheat time to 80.degree. C. for
the control and polypropylene containing antimony or carbon black
in varying amounts. In FIGS. 5 and 6, the reheating agents were:
Sb1: 10 ppm as Sb formed using equal parts by weight antimony
triglycolate and hypophosphorous acid; Sb2: 25 ppm antimony metal
(milled); CB1: 40 nm carbon black; and CB2: larger particle size
600 nm-2 microns carbon black. While both antimony and carbon black
can effectively reduce the reheating time (FIG. 5), the carbon
blacks at low levels can result in a significantly darker
coloration (L* significantly below 60 where the control L* was 75)
(FIG. 6), which can aesthetically detract from its use as a
reheating agent for polypropylene compositions. The combination of
antimony triglycolate and hypophosphorous acid resulting in an
antimony content in the polypropylene of from 2 to 350 ppm, most
preferably from 10 to 30 ppm, was particularly effective.
[0040] Introducing reheating agents in polypropylene compositions
can result in undesired coloration of the final container, article
or bottle product. The extent of coloration induced by reheating
agents varies depending on the type and the amount of agents used.
For a given reheating agent, the less amount of the agent is used,
the less coloration will be in the final product. If the amount of
the reheating agent used is low enough to minimize the unwanted
coloration to an accepted level, that amount may not be sufficient
to reduce reheating time. The challenge, therefore, is to find a
reheating agent that can effectively reduce the reheating time and
still produce a final container, article or bottle with minimum
coloration.
[0041] We used a color measurement (L*) from the Gardner
calorimeter to evaluate coloration of polypropylene compositions
caused by different reheating agents. The color measurement (L*)
reflects the absorption and scattering of light by the testing
material. The Gardner BYK Color-View spectrophotometer Model No.
9000 is available from BYK Gardner, Inc., Columbia, Md. USA. L*
values for polypropylene plaques made from polypropylene
compositions containing different reheating agents in different
amounts were measured.
[0042] The L* measurements shown in FIG. 6 illustrate the
relationship between the coloration of polypropylene plaques and
the amount of reheating agents in the polypropylene compositions
from which the plaques were made. The control plaque was
polypropylene without adding reheating agents. The control plaque
had an L* value of about 75. The lesser coloration a polypropylene
composition has, the closer its L* value is to that of the control.
As shown in FIG. 6, the polypropylene composition with 10 ppm
antimony (composition Sb1) had the aesthetic characteristics that
are the closest to those of the polypropylene without any reheating
agents (control). In these examples, the samples having L* values
of about 60 and above as compared to L* of about 75 for the
polypropylene control had color aesthetics that were at least 80%
of the L* value of the control.
[0043] Table 1 below summarizes the energy savings due to the
reduction of reheating time and the relative color aesthetics of
these certain tested polypropylene compositions. TABLE-US-00001
TABLE 1 Energy Savings and Aesthetics of Reheating Agents in
Blowing Trials. Blowing Trial 1 Reheating Energy Aesthetics (L*)
Agent Level (ppm) Saving (%) (Granules) Control 0 0 75.71 Sb1 10 10
68.31 CB1 10 20 51.58 Sb1: antimony (as described above); CB1: 40
nm carbon black (as described above). Blowing Trial 2 Reheating
Cycle time Aesthetics (L*) Agent Level (ppm) Saving (%) (Granules)
Control 0 0 73.94 Sb1 10 24 65.26 Sb2 10 24 63.79 CB1 5 24 59.96
CB1 10 31 47.74 Sb1: antimony (as described above); Sb2; antimony
(as described above) CB1: 40 nm carbon black (as described
above).
Blowing Trial Details
[0044] The preforms for the blowing trial were made on a laboratory
scale combined injection moulding and blowing machine. The preforms
were injection moulded with typical polypropylene processing
conditions--the melt temperature was 220.degree. C., the mould
temperature was 15.degree. C., and the cycle time was 27 seconds.
We then used a separate laboratory blowing machine which had been
designed specifically for polypropylene. This blowing machine had
two heating ovens, each having 10,000 watts heating capacity and
each fitted with forced air ventilation. Several spinning preform
holders were used to index the preforms through two ovens separated
by an air gap. Each preform was indexed through the first oven in
about 60 to 80 seconds. Then, the preform was indexed through an
air space to allow the heated preform to equilibrate for about 60
to 80 seconds. Next, the preform was indexed through a second oven
for about 60 to 80 seconds, and then, after a further 10-second
period indexing in air, it was delivered to the blowing
station.
[0045] For the energy saving experiment, the machine indexing speed
was set at a constant 750 bottles per hour output, and the oven
settings were adjusted (reduced) for each sample to provide an
optimum injection moulded bottle. Energy savings were then
calculated based on the lesser amount of heating energy required to
reheat the bottles formed from a polypropylene composition that
contained reheating agents versus the amount of heating energy
required to reheat the control bottle. In Table 1, energy savings
are expressed as a percentage.
[0046] For the cycle time saving experiment, both ovens were set to
a constant 8900 watts output (for a combined 17,800 watts output).
The cycle time was then increased until the preforms were heated
sufficiently to allow the optimum blowing of the bottle. The
increased cycle time of each sample was calculated against the
control cycle time and expressed as a percentage.
[0047] The results in Table 1 indicate that the use of 10 ppm Sb
produced from antimony triglycolate with hypophosphorous acid
reduced the preform reheating energy and cycle time to the same
level as 5 ppm carbon black, but the color and visual aesthetics of
the polypropylene granule containing antimony was much better than
the granules that contained carbon black. Thus, the resulting
bottles formed from the polypropylene composition with antimony had
better color and visual aesthetics than did the bottles formed from
the polypropylene composition containing 5 ppm or 10 ppm carbon
black.
[0048] The preforms with reheating agents as compared to the
control preforms produced energy savings in the range of about 10%
to 30%, preferably 15 % to 20%, and cycle time savings in the range
of about 25% to 35% (see Table 1). Thus, the polypropylene
compositions with reheating agents shorten reheating time and still
produce bottles with acceptable color and visual aesthetics.
[0049] We further explored the reheating and aesthetic
characteristics of different types of antimony reagents. More
specifically, we tested antimony triglycolate, antimony trioxide
and antimony triacetate at different concentrations. We
additionally explored the reheating and aesthetic characteristics
of other reheating agents. We also tested different methods for
mixing the reheating agents with the polypropylene, namely, by
direct application to the polypropylene granules, and by mixing
polypropylene granules with masterbatch granules containing high
concentrations of reheating agents. For reducing agents, different
phosphorous acids with different dosages were also tested. See
Tables 2 and 3 below for a summary of these results.
[0050] We found that adding antimony as a reheating agent was
preferred to carbon black in view of the aesthetics. We further
found that adding antimony compounds in combination with phosphoric
acid, preferably hypophosphoric acid, more thoroughly disperses the
metal particles in the polypropylene composition. Lastly, the
antimony triglycolate, antimony trioxide or antimony triacetate
with hypophosphoric acid combinations that resulted in from 2 ppm
to 350 ppm antimony metal particles in the polypropylene
composition achieved the best results for reheat performance and
color aesthetics.
Procedure for Measuring Plaque Surface Reheat Temperature
[0051] Plaques injection molded from polypropylene compositions as
specified in Tables 1, 2 and 3 were rotated while heated by
radiation emitted by an IR heating lamp (a 175 Watt lamp model
IR-175C-PAR from Phillips at 2400.degree.K) (See, e.g., FIG. 2A).
An infra-red pyrometer (model number Cyclops 300AF from Minolta
Land) (not shown in FIG. 2) was positioned on the opposite side of
the plaque with respect to the IR lamp. The surface temperature of
the plaque was monitored and recorded during reheating.
[0052] The plaques tested contained various reheating agents, such
as antimony (Sb), manganese (Mn), iron (Fe), titanium (Ti),
tungsten (W), copper (Cu), graphite, infra-red dye and carbon
black, in various amounts. The results are reported in Tables 2 and
3 below. For the compositions set forth in Tables 2 and 3, the
controls were plaques made from polypropylene without reheating
additives. All of the reheating agents tested improved the plaque
surface reheating time as compared with the control polypropylene.
However, certain of the reheating agents when incorporated into
polypropylene granules (and plaques) had L* values much lower than
the target L* (80% of the control), and thus may not be as suitable
for use in injection stretch blow molding of bottles. These
compositions still may have utility when making other polypropylene
articles with thermoforming techniques.
[0053] Data for surface reheating times for certain of the
polypropylene compositions that included reheating agent, compared
to the control C1, is shown graphically in FIG. 3. TABLE-US-00002
TABLE 2 Comparison of L* and Reheating Characteristics Through-
Through- Sample Control Plaque heat heat in 300 secs No. Target
Formulation Polymer Granule L* L* to 80.degree. C. (sec) (.degree.
C.) C1 Eltex PPC KV 276 73.99 75.17 500 69.2 Control A C2 Eltex PPC
KV 276 70.25 75.11 458 69.2 Control A C3 Eltex PPC KV 276 71.24
75.71 419 70.4 Control A C4 Borealis PP RE420M0 70.96 78.84 466
67.3 Control B C5 Borealis PP RE420M0 68.73 79.4 401 72.1 Control B
1 5 ppm Cu A 66.11 75.28 439 67 2 50 ppm Cu A 53.90 61.18 386 72 3
5 ppm coarse carbon A 56.73 75.85 366 74.3 black 4 10 ppm coarse
carbon A 48.5 72.64 334 76.7 black 5 20 ppm coarse carbon A 37.83
37.30 331 76.7 black 6 10 ppm Elftex 254 CB B 46.85 53.73 325 77.2
7 2 ppm 20 nm fine CB N B 61.51 73.11 443 69.1 8 5 ppm 20 nm fine
CB N B 53.96 61.32 442 69.2 9 10 ppm fine carbon B 45.82 53.93 336
76.4 black 10 25 ppm fine carbon B 39.10 31.95 336 76.7 black 11 50
ppm fine carbon B 26.32 15.53 292 80.4 black 12 Infra-red dye-10
ppm B 63.54 75.07 407 71.6 Avecia pro-jet 830 NP 13 10 ppm Fe A
64.80 72.88 412 71 14 100 ppm 100 nm Fe N A 47.48 49.49 341 75.4 15
200 ppm M Fe N A 70.21 78.94 498 66.9 16 10 ppm Fe(III)oxide B
58.36 71.54 413 71.6 17 10 ppm graphite EP B 64.15 72.16 389 72.9
1020 18 10 ppm 1-2micron B 63.89 72.94 366 73.8 graphite 19 200 ppm
M Mn N A 62.44 71.00 417 70.6 20 2.5 ppm Sb via A 67.22 76.15 436
70 ATG/H.sub.3PO.sub.2 21 5 ppm Sb via ATG/ A 59.84 67.64 418 70.4
H.sub.3PO.sub.2+ 10 ppm Ti 22 5 ppm fine Sb B 68.00 75.65 405 71.6
23 10 ppm Sb via ATG/ A 59.91 69.20 388 72.7 H.sub.3PO.sub.2 24 10
ppm fine Sb B 63.37 72.32 380 73.6 25 20 ppm Sb via ATG/ B 57.74
69.44 349 75 H.sub.3PO.sub.2 26 30 ppm Sb via ATG/ B 54.27 65.01
337 76.2 H.sub.3PO.sub.4 27 50 ppm Sb via ATG/ A 64.48 71.17 327
77.3 H.sub.3PO.sub.3 N 28 50 ppm Sb via A 73.62 78.27 457 68.8
ATG/TNPP low N 29 50 ppm Sb via A 70.19 77.89 457 68.8
ATG/TNPP/H.sub.3PO.sub.2 30 50 ppm fine Sb B 46.58 51.69 315 78.8
31 100 pm Sb/P A 58.39 68.8 390 72.2 32 50 ppm Sb via ATA/ A 56.30
65.67 394 72.2 H.sub.3PO.sub.2 N 33 50 ppm Sb via H.sub.3PO.sub.3 N
A 58.86 69.92 415 70.6 34 5 ppm coarse Sb A 66.39 75.85 391 72.7 35
10 ppm coarse Sb A 64.3 72.64 365 74.4 36 25 ppm coarse Sb A 57.31
64.25 329 77.2 37 100 ppm coarse Sb A 42.19 39.68 287 81.8 38 200
ppm M Sb N A 40.43 39.29 301 79.6 39 10 ppm Sb via Sb.sub.20.sub.3/
B 66.3 76.81 417 71 H.sub.3PO.sub.2 40 200 ppm Ti N A 29.35 20.87
352 74.5 41 100 ppm 100 nm W N A 58.98 68.73 415 70.8 M/b:
masterbatch. N: nucleated. M: milled. ATG: antimony triglycolate.
ATA: antimony triacetate. TNPP: trisnonylphenyl phosphite.
H.sub.3PO.sub.3 = phosphorous acid, H.sub.2PO.sub.3 =
Hypophosphorous acid
[0054] TABLE-US-00003 TABLE 3 Comparison of L* and Reheating
Characteristics for Masterbatch Compositions Through- M/b M/b let
Final Through- heat in Sample M/b Target Control granule down
granule heat to 300 secs No. Formulation Polymer L* ratio L*
80.degree. C. (sec) (.degree. C.) 42 250 ppm fine 20 nm B 17.57
12.5:1 47.74 -- -- CB 43 250 ppm copper (I) B 61.21 -- 61.21 412
71.1 oxide 44 250 ppm copper (II) B 60.32 -- 60.32 427 70.6 oxide
45 125 ppm Avecia B 39.7 12.5:1 63.54 -- -- projet 803NP (dye) 46
1000 ppm Fe A 23.09 -- 23.09 301 79.8 47 250 ppm Fe(II) B 62.67 --
62.67 398 71.9 oxalate + H.sub.3PO.sub.2 48 250 ppm Fe(III) B 66.5
-- 66.5 415 70.5 oxalate + H.sub.3PO.sub.2 49 250 ppm Fe(II + III)
B 52.15 -- 52.15 327 77.7 oxide 50 250 ppm Aldrich 1-2 B 30.87
25.0:1 63.89 -- -- micron graphite 51 1000 ppm M Mn A 47.47 --
47.47 -- -- 52 250 ppm ATG + H.sub.3PO.sub.2 B 28.83 25.0:1 63.37
-- -- 53 250 ppm Aldrich B 65.92 -- 65.92 374 73.5 fine
Sb.sub.2O.sub.3 54 250 ppm Aldrich B 37.25 25.0:1 66.3 -- -- fine
Sb.sub.2O.sub.3 + H.sub.3PO.sub.2 55 1000 ppm Sb/P A 32.97 -- 32.97
421 70.4 56 266 ppm milled Sb B 34.19 25.0:1 63.79 -- -- 57 1000
ppm 100 nm A 24.06 -- 24.06 329 773 Ti 58 1000 ppm 100 nm W A 31.45
-- 31.45 -- --
[0055] Polypropylene compositions with reheating agents according
to the invention preferably result in at least a 10% reduction in
reheating time, more preferably at least a 25% reduction in
reheating time, and most preferably at least a 35% reduction in
reheating time, as compared to the reheating time for the control
composition. Thus, from Tables 2 and 3, the polypropylene
compositions with reheating agents that had reheat times to
80.degree. C. of 375 seconds and under, and particularly 300
seconds and under were most advantageous.
[0056] The invention has been illustrated by detailed description
and examples of the preferred embodiment. Various changes in form
and detail will be within the skill of persons skilled in the art.
Therefore, the invention must be measured by the claims and not by
the description of the examples or the preferred embodiments.
* * * * *