Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DEGRADABLE COMPOSITE POLYMER AND
METHOD OF MAHING SUCH COMPOSITE POLYMER
Statement Regarding Federall~r-Sponsored Research or Development
Not applicable.
Cross Reference To Related Ap~Iications_
This application claims priority from U.S. Provisional Application No.
60/040,779, filed March 14, 1997.
Background of the Invention
The present invention relates to composite polymers and methods for
making such composite polymers. More specifically, the composite polymers of
the
present invention are degradable. Still further, the present invention
includes applications
for using composite polymers as printable plastic material or as plastic media
blast
material.
Plastic materials are any synthetic materials comprised of polymers which
1 S can be shaped or molded. Printable plastic materials are plastic materials
which are able
to receive and retain ink. There are a number of disadvantages with currently
available
printable plastic materials. Many plastic materials used by the printing
industry have a
plasticizer incorporated into their formula which creates a residue on the
surface of the
finished plastic products. This residue prevents ink from sticking to the
surface during
printing, and surface treatment prior to printing often does not remove all of
the
plasticizer residue. Furthermore, many plastic materials currently used by the
printing
industry are not degradable.
Polylactic acid resin, a degradable material, offers a quality printing
surface since the biopolymer-based plasticizers used in the manufacture of
this resin tend
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to stay within the material. However, polylactic acid resin does not
thermoform well.
Still further, because polylactic acid is extremely hard, it is very abrasive
on cutting tools.
Furthermore, when polylactic acid is extruded into sheets, it tends to curl
and become
quite brittle. For instance, if a polylactic acid resin is rolled, it tends to
stay rolled
S forever. Also, because polylactic acid is a brittle material, it fractures,
especially at
corners, when cut, and when it is extruded into thicker sheets, it fractures
even more.
Other degradable plastics, such as the multipolymer resins sold by
Novamont S.p.A., via G. Fauser, 8-28100 Novara, Italy, under the trademark
Mater BiTM,
have a great deal of flexibility, but are too ineffective to use in many sheet
extrusion
applications. These resins, which are comprised of a thermoplastic polymer,
destructured
starch, and a plasticizer, are very soft and rubbery, and ink cannot be
printed on such
resins. It is thus desirable to find a sheet extruded material with high
elasticity and an
exceptional ability to retain ink during printing.
There are a number of disadvantages with current methods for removing
coatings from various substrate materials. Commonly used methods for removing
powder coatings include dipping the substrate material to be stripped into a
pot of molten
salt so as to turn the powder coating to ash and vapor. Another method
involves putting
the substrate material in a high temperature oven, approximately 600-
900° F, to turn the
coating to ash. The problem with these methods is that many substrates that
are coated
with powdered paint cannot survive the coating removal process, or if they do,
their
structural properties are significantly damaged due to the extreme heat used
to remove
the coating. Still another method involves using small glass beads in an
abrasive process
to remove the coatings. However, when used on relatively soft substrates, the
impacting
beads provide an unsatisfactory result by causing surface stress and possibly
also
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changing the texture of the substrate. Thus, many coated materials must be
scrapped
since they cannot withstand the conditions of these conventional removal
processes.
Another conventional method for removing coatings involves using plastic
media blast material. Plastic media blast is an effective way to surface clean
various
materials without damaging the surface of the material being blasted.
Currently, certain
petroleum-based plastics which are not too hard or too coarse are used as
plastic media
blast material. However, degradable plastics have been found to be too brittle
or too
weak to perform adequately as plastic media blast.
In order to overcome the deficiencies found with conventional degradable
polymers, a degradable composite polymer and a method for making such a
composite
polymer are needed for a variety of applications including those in which
enhanced
strength and flexibility are needed. Still further, such a degradable
composite polymer
should have improved printability characteristics for use as a printable
plastic material
and should be able to be produced in a variety of hardnesses for use as
plastic media blast
material.
Summary of the Inventi n
It is an object of the present invention to provide a degradable composite
polymer and a method for producing the same wherein the composite polymer can
be
used as a plastic.
A further object of this invention is to provide degradable composite
polymers and methods of producing the same wherein the composite polymer can
be
produced in various textures and ranges of flexibilities.
It is a further object of the present invention to provide a degradable
composite polymer and a method for producing the same wherein the composite
polymer
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is produced in a range of hardnesses so that it can be used as a plastic media
blast
material for a variety of surfaces.
Still another object of this invention is to provide a degradable composite
polymer and a method for producing the same wherein the composite polymer has
the
ability to retain ink during printing so that it can be used as a printable
plastic material.
It is a further object of this invention to provide a degradable composite
polymer and a method for producing the same wherein the composite polymer is
able to
be cut easily without fracturing so that it may be cut into small plastic
sheets.
Another object of this invention is to provide a degradable composite
polymer and a method of producing the same wherein the composite polymer has a
high
elasticity so that it is able to be extruded into sheets without curling or
becoming brittle
and is able to be injection or compression molded.
Still another object of this invention is to provide a method for
manufacturing a degradable composite polymer without the use of any corrosive
or
caustic chemicals in order to eliminate the hazards associated with using and
disposing
of such chemicals.
Still another object of this invention is to provide a process for producing
a degradable composite polymer which creates little waste.
According to the present invention, the foregoing and other obj ects are
achieved by a degradable composite polymer comprised of a polymer comprised of
lactic
acid monomers and a resin comprised of a thermoplastic polymer, destructured
starch and
a plasticizer. This composite polymer is first created by combining the
polymer and the
resin, and subsequently, extruding them through a heated extruder. This
degradable
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composite polymer may be used, among other things, as plastic media blast
material or
as a printable plastic material.
Additional objects, advantages and novel features of the invention will be
set forth in part in the description which follows, and in part will become
apparent to
S those skilled in the art upon examination of the following, or may be
learned from
practice of the invention. The objects and advantages of the invention may be
realized
and attained by means of the instrumentalities and combinations particularly
pointed out
in the appended claims.
Detailed Description of the Preferred Embodiment
The novel degradable composite polymers of the present invention are
comprised of a polymer and a resin. The polymer is comprised of lactic acid
monomers,
and the resin is comprised of a thermoplastic polymer, destructured starch,
and a
plasticizer. If the polymer comprised of lactic acid monomers is a copolymer,
in addition
to the lactic acid monomers, the other monomers in this polymer should be
degradable
monomers. Preferably, the polymer is polylactic acid (PLA).
One method of producing PLA includes catalyzing crude lactic acid,
which may contain impurities such as carbohydrates, proteins, amino acids,
salts, metal
ions and other organic acids, with 0.05-0.15 weight percent tin oxide (Sn0).
Other
methods for making PLA also are conventionally available.
Preferably, the polymer comprised of lactic acid monomers has a
molecular weight of between 5,000 and 200,000, depending on the physical
properties
of the composite polymer which are desired in a specific application. For
example,
polymers having molecular weights at the higher end of this range produce
composite
polymers which are relatively stronger and harder. The lactic acid monomers in
the
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polymer may be comprised of between about 0 and 90% n-lactide by weight.
Preferably,
between approximately 0 and 25% by weight of the lactic acid in the polymer is
n-lactide.
Most preferably, the lactic acid in the polymer is comprised of about I % or
less n-lactide
by weight.
The starch component of the resin may be any starch of natural or plant
origin which is composed essentially of amylose and/or amylopectin. It can be
extracted
from various plants, such as potatoes, rice, tapioca, maize, as well as
cereals, such as rye,
oats, wheat and the like. Maize starch is preferred. Preferably, the starch
component has
an amylopectin content of more than 70% by weight. Chemically-modified
starches and
IO starches of different genotypes can also be used. Still further, ethoxy
derivatives of
starch, starch acetates, cationic starches, oxidized starches, cross-linked
starches and the
like may be used.
Starch is provided without processing, such as drying, and without the
addition of any water (the intrinsic bound water content of the commercial
products is
approximately 10-I3% by weight). The starch is then destructured at
temperatures above
90°C and preferably above 120°C. The term "destructured starch"
means a starch which
has been heat-treated above the glass transition temperatures and melting
points of its
components, so that the components are subjected to endothermic transitions to
thereby
produce a consequent disorder in the molecular structure of the starch
granules. In other
words, the crystallinity of the starch is destroyed.
The plasticizer used in the resin is preferably a polyol, polyol derivative,
polyol reaction product, polyol oxidation product or a mixture thereof.
Preferably, the
plasticizer has a boiling point of at least 150°C. Examples of
plasticizers that can be used
include, but are not limited to, glycerine, polyglycerol, glycerol,
polyethylene glycol,
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ethylene glycol, propylene glycol, sorbitol, mannitol, and their acetate,
ethoxylate, or
propoxylate derivatives, and mixtures thereof. Specific plasticizers that can
be used
include, but are not limited to, ethylene or propylene diglycol, ethylene or
propylene
triglycol, polyethylene or polypropylene glycol, 1,2-propandiol, 1,3-
propandiol, 1,2, 1,3,
1,4-butandiol, 1,5-pentandiol, 1,6-, 1,5-hexandiol, 1,2,6-, 1,3,5-hexantriol,
neopentylglycol, trimethylolpropane, pentaerythritol, sorbitol acetate,
sorbitol diacetate,
sorbitol monoethoxylate, sorbitol dipropoxylate, sorbitol diethoxylate,
sorbitol
hexaethoxylate, aminosorbitol, trihydroxymethylaminomethane, glucose/PEG, the
product of reaction of ethylene oxide with glucose, trimethylolpropane,
monoethoxylate,
mannitol monoacetate, mannitol monoethoxylate, butyl glucoside, glucose
monoethoxylate, alpha-methyl glucoside, the sodium salt of
carboxymethylsorbitol,
polyglycerol monoethoxylate and mixtures thereof. The amount of plasticizer in
the resin
is approximately 0.05-100% of the weight of the starch, and preferably about
20-100%
of the weight of the starch.
The thermoplastic polymer in the resin is a synthetic polymeric component
which includes a polymer or copolymer of at least one ethyienically
unsaturated
monomer, the polymer or copolymer having repeating units provided with at
least a polar
group such as hydroxy, alkoxy, carboxy, carboxyalkyl, alkyl carboxy or acetal
group.
Preferred polymeric components included in the resin are polyethylene,
polyvinyl
alcohol, polyacrylonitrile, ethylene-vinyl alcohol copolymer, ethylene-acrylic
acid
copolymer and other copolymers of an olefin selected from ethylene, propylene,
isobutene and styrene with acrylic acid, vinyl alcohol, and/or vinyl acetate
and mixtures
thereof. Most preferably, one of the polymers in the resin is an ethylene-
acrylic acid
copolymer with ethlylene contents of from about 10 to 44% by weight. The resin
also
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_g_
may contain relatively low amounts, approximately 5% or less by weight of the
overall
composition, of hydrophobic polymers, such as polyethylene, polypropylene and
polystyrene. Still further, other polymers such as polyamide, polyacrylic,
polyester, and
polyether may be in the resin. The polymer and starch may be combined in a
1:19 to 19:1
ratio by weight. Preferably, the polymer component of the resin has a higher
molecular
weight than the polymer comprised of lactic acid monomers, the other component
used
in forming the composite polymer of the present invention.
Other components such as destructuring agents, cross-linking agents and
neutralizing agents may, optionally, be added to the resin but are not
essential
components. Preferably, a destructuring agent is added while making the resin.
The
destructuring agent may be urea, alkaline and alkaline-earth hydroxides, and
mixture
thereof. Examples of alkaline and alkaline-earth hydroxides include but are
not limited
to sodium, potassium and calcium hydroxides. Most preferably, urea is added as
the
destructuring agent. Urea improves the gelling of the starch with small
amounts of water,
and hence enables the production of a uniform film. Preferably, the amount by
weight
of destructuring agent added to the resin is 2-20% of the weight of the
starch. However,
if a destructuring agent is not added, it is still possible to destructure the
starch through
heat or pressure.
The resin also may contain cross-linking agents such as aldehydes like
formaldehyde, paraformaldehyde, and paraldehyde; keytones and glyoxals;
epoxides like
epichlorohydrin; process coadjuvants and release agents; and lubricants which
are
normally incorporated in compositions for molding or extrusion such as fatty
acids, esters
of fatty acids, higher alcohols, polythene waxes, and low density polyethylene
(LDPE).
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The resin further may contain a neutralizing agent, such as ammonia or
any amine, sufficient to neutralize some or all of the acid groups of the
polymer if an
acidic polymer such as ethylene-acrylic acid copolymer is used. Ammonia may be
added
to the resin in quantities up to about 7% of the weight of the dry starch.
However, most
of the ammonia should be removed before or during extrusion. Preferably, about
0.5%
or less by weight of the ammonia remains in the final resin formulation. Urea,
in addition
to functioning as a destructuring agent, also may function as a neutralizing
agent.
Although optional, the use of boron containing compounds results in
substantially better interpenetration between the hydrophilic starchy phase
and the
hydrophobic polymeric phase, with a resultant substantial improvement in
mechanical
properties, particularly tear strength and transparency of sheets and films
obtained from
various formulations of the resin. Boron, boric acid, borax, metaboric acid,
or other
boron derivatives may be used in the resin. Preferably, the boron containing
compound,
expressed as the boron content, is between about 0.002 and 0.4% and preferably
between
about 0.01 and 0.3% of the total weight of the resin.
Other additives also may be mixed into the resin. For example, polyvinyl
alcohol may be added to change the behavior of molded articles with water; UV
stabilizers, such as, carbon black, may be added to improve the resistance of
the articles
to sunlight; and flame-proofing agents may be added if desired. The addition
of
inorganic salts of alkali or alkaline-earth metals, particularly lithium
chloride and sodium
chloride at concentrations between about 0.1 and 5% by weight of the resin,
preferably
between about 0.5 and 3% by weight, also was found advantageous. Other
additives
which may be in the resin include the conventional additives generally
incorporated in
starch-based molding compositions, such as fungicides, herbicides,
antioxidants,
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fertilizers, opacifiers, stabilizers and plasticizers. All these additives may
be used in
conventional quantities as known to experts in the field or as easily
determined by routine
tests, and these additives may constitute up to about 20% by weight of the
final
composition.
The resin is made by mixing the essential components, namely, the starch,
plasticizes and thermoplastic polymer, and any other optionally included
components, in
a conventional device, such as a heated extruder, which ensures conditions of
temperature
and shearing stress suitable to render the starch and the polymer compatible
from a
Theological point of view. The starch's structure is interpenetrated or at
least partially
interpenetrated by the thermoplastic polymer so as to obtain a thermoplastic
melt. The
starch may be destructured before it is combined with the polymer, or as it is
combined.
A destructuring agent may be mixed with the starch and the plasticizes in a
heated
extruder to destructure it. Preferably, the mixture is extruded to form the
resin at a
temperature between about 100 ° C and 220 °C.
Preferably, according to one formulation of the present invention, the resin
is a film-grade material comprised of about 10-90% by weight polymer or
copolymer,
about 10-90% by weight destructured starch, about 2-40% by weight plasticizes,
about
0-20% by weight destructuring agent, and about 0-6% by weight water. More
preferably,
the resin is comprised of about 20-70% by weight destructured starch, about 10-
50% by
weight polymer or copolymer, about 2-40% by weight plasticizes, about 0-10% by
weight
destructuring agent, about 1-5% by weight water, and about 0.002-0.4% by
weight boron
compounds. One of the most preferred formulations of the resin is 41 % by
weight
ethylene-acrylic acid copolymer with 20% by weight acrylic acid, 12% by weight
urea,
41 % by weight destructured starch, 20% by weight plasticizes, and 6% by
weight water.
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Most preferably, the resin which is used in making the degradable
composite polymers of this invention is resin sold by Novamont, S.p.A., via G.
Fauser,
8-28100 Novara, Italy, under the trademark Mater BiTM
The lactic acid polymer, which is preferably PLA, and the resin, which is
preferably Mater BiTM, may be combined to form the degradable composite
polymers of
the present invention in a range of proportions depending upon the resultant
hardness,
flexibility, and texture which is desired. The addition of the resin to the
lactic acid
polymer reduces its brittleness and improves its flow and process ability.
Composite
polymers of this invention which contain more resin are softer and more
flexible.
Anywhere between about I O and 90% by weight of the degradable composite
polymer
may be a lactic acid polymer and the remaining 10-90% by weight of the
composite
polymer is the resin.
This degradable composite polymer is made by first combining the
polymer and the resin, and by subsequently extruding the combination through a
heated
extruder. The polymer and the resin may be combined in a container and then
fed into
the extruder, or the polymer and the resin may be combined in the extruder.
Any
conventional extruder capable of melting the mixture may be used. The extruder
may
have any of a variety of screw configurations, including single, twin, or
mixing screws.
A colorant also may optionally be added to the mixture. Preferably, the
particles of resin
and polymer added to the extruder are relatively close in size.
The extruder should be sufficiently heated so that the composite polymer
may form at any temperature between about 140 and 230°C. Preferably, it
forms at a
temperature of about 160-190°C if used as a printable plastic material,
and at a
temperature of about 140-230°C if used as plastic media blast material.
If the mixture
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is heated above 230°C, volatile compounds in the resin begin to
evaporate. The
temperature at which the composite polymer forms affects its resultant
hardness.
Therefore, the extruder should be at higher temperatures to form harder
composite
polymers. Furthermore, the temperature chosen for the process should be
influenced by
the melting point of the polymer used. For instance, if a lactic acid polymer
having a
relatively higher melting point is used, the composite polymer should be
formed at a
higher temperature within the acceptable temperature range. Also, if the
lactic acid
polymer has a relatively higher molecular weight, then, preferably, the
composite
polymer is formed at higher temperatures within the disclosed temperature
range.
The degradable composite polymer forms in the heated extruder after the
polymer and the resin are extruded for about 30-240 seconds. Preferably, the
composite
polymer forms after the polymer and the resin are extruded for about 50-90
seconds.
When the mixture comes out of the extruder, it is a very soft, molten
material. Because
the crystallinity of the mixture is changed when it is extruded, the product
cannot be
reprocessed without re-annealing the mixture.
Preferably, the resulting degradable composite polymer is cut with a
specially hardened die so as not to dull the die. This is especially
preferable for those
formulations containing high percentages of a lactic acid polymer. Preferably,
for cutting
purposes, the polymer and the resin are combined in approximately a 1:1 ratio
by weight
so as to cause the least amount of die abrasion.
The degradable composite polymer of the present invention has enhanced
elongation viscosity, improved strength and flexibility, and improved
printability
characteristics when compared to other degradable plastics. It also is
resistant to tearing
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and perforation, and it is a good oxygen and carbon dioxide barrier. Still
further, it has
a high melting point and the ability to thermoform.
The degradable composite polymer of the present invention is an
environmentally-friendly product because it is made from renewable resources
and
degrades in two years or less when composted. Degrades, in this context, means
it is
chemically decomposed. Certain formulations of the present invention that
contain high
percentages of the resin are even biodegradable, which means they are capable
of being
decomposed by naturally biological processes.
The novel degradable composite polymer of the present invention is useful
for a variety of applications. It may be used as a plastic substitute for a
wide range of
applications such as those currently reserved for petroleum-based plastics.
Articles may
be formed with this composite polymer by injection molding, thermoforming or
blowing.
Two specific applications particularly suited for this novel degradable
composite polymer
include use as a printable plastic material or as a plastic media blast
material.
If used as a printable plastic material, the composition should be
comprised of approximately 10-90% by weight of a polymer comprised of lactic
acid
monomers, and approximately 10-90% by weight of a resin comprised of a
thermoplastic
polymer, destructured starch, and a plasticizer. Preferably, for cutting
purposes, it is
comprised of approximately 30-70% by weight of the polymer, and approximately
30-
70% by weight of the resin. Most preferably, for cutting purposes, it is
comprised of
approximately 50% by weight of the polymer, and approximately 50% by weight of
the
resin.
This printable plastic material is made by first combining a polymer and
a resin and then extruding this mixture as discussed above . The extruded
mixture can
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be formed into sheets by any method known to those skilled in the art. One
method
involves feeding the extruded mixture, which is a soft, hot, molten resin into
a sheet die
and forming the composite polymer into a continuous sheet. The composite
polymer is
fed through a series of cylindrical rollers, for example, three vertically-
arranged rollers,
which are evenly spaced apart so as to shape the composite polymer into a
sheet having
a uniform thickness. The spacing of the rollers determines the thickness of
the sheets
formed. Conventionally, steam is pumped into the rollers when forming sheets,
but with
the present invention, the rollers should be cooler than the temperature of
the mixture
leaving the extruder. Preferably, water having a temperature of about 10-
SO°C is pumped
through the rollers. As the continuous sheet leaves the last roller, it is
tensioned to keep
it flat until it cools and hardens enough to be moved. Once the sheets are
formed, they
may be cut into large sheets or rolled for storage. It is preferable to store
those composite
polymer formulations containing relatively large percentages of lactic acid
polymer in
sheets rather than in rolls because if rolled they tend to remain curled.
The stored plastic sheets are subsequently processed. They may be cut
into smaller sheets so as to be used as plastic cards, such as phone cards or
credit cards.
If used as credit cards or phone cards, consumers prefer the feel of a
material that is 10%
by weight resin and 90% by weight polymer comprised of lactic acid monomers.
This
preference must be weighed against the desirability of a 50/50 mixture for
cutting
purposes.
Ink is then printed onto the sheets, and this novel degradable composite
polymer is able to act as a substrate and retain the ink. The degradable
composite
polymer of the present invention may be printed with conventional or
ultraviolet (UV)
inks. Preferably, for printing purposes, the polymer and resin are in about a
50/50
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combination by weight so that the printing dies are not worn. If printed with
conventional inks, the ink sets up at ambient temperature when exposed to
light. If the
material is printed with UV ink, then UV light must be used to cure or dry the
ink.
Preferably, if UV light is used, the UV light is flashed in intervals which
last for a
fraction of a second so as to reduce heat build-up on the composite polymer.
Still further,
preferably, one does not print on the same print line of both sides of the
composite
polymer substrate at the same time because this brings too much heat to the
material.
Instead of being extruded into sheets, the degradable composite polymer
of the present invention may be injection or compression molded into shapes
and forms
while retaining its ability to be printed upon. This degradable composite
polymer can be
molded into stiff and thin wall articles. Preferably, the composite polymer,
which is later
molded, is formed at a temperature of about 160-190°C, if used as a
printable plastic
material.
Conventional injection molding equipment, such as that used in the
1 S plastics industry, may be used. However, processing conditions should be
adjusted to
allow for the fact that the degradable composite polymer of the present
invention has a
slower cooling time than typical plastics. Subject to the size and complexity
of the
mold's shape, the mold release time, as compared to typical plastics, can be
increased
negligibly up to approximately 200%. The usual time increase appears to be
about 30%.
However, use of an air cooled or liquid cooled mold will allow cycle times
which are
comparable to those of conventional plastics.
If the degradable composite polymer is injection molded, the injection
temperature, preferably, is about 180 to 200°C. The injection speed can
be varied
depending upon the size and shape of the mold and the number of cavities in
the mold.
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Preferably, the nozzle pressure is about 1300 to 1400 bar. Preferably, the
mold
temperature is between approximately 10 and 65°C. Either cold or hot
runners may be
used in the injection system, and the minimum gate size is about I mm full
round.
Preferably, the mold is made of an acid-resistant material such as an acid-
resistant metal.
The flowability of this degradable composite polymer into the mold
cavities is enhanced when the molds are specially designed for a degradable
material.
One preferable design incorporates the use of rounded corners inside the mold,
as
opposed to 90 degree corners, because the degradable composite polymer does
not like
to flow into "sharp dead-ends." Most preferably, the mold design should take
into
account the following parameters or properties: 1 ) The rheological and other
physical
properties of the resin; 2) if cold runners systems are used, the sprue length
should be as
short as possible to avoid the composite polymer breaking inside the mold; 3)
flow
channels should have reduced cross-sectional area, free of stagnation points;
and 4) gates
should be fully rounded.
Molded articles can be colored in numerous ways. The coloring of the
degradable composite polymer can either be accomplished by compounding the PLA
with the desired colorant or by substitution waxes as the matrix for the
colorant.
Still further, the materials used in making the degradable composite
polymers of the present invention should be dried before being processed.
Also, during
the start-up and shutdown of the extrusion process, to reduce the material
costs, the start-
up can he performed using low density polyethylene (LDPE). Once the operating
temperatures have been achieved, the components comprising the degradable
composite
polymer of the present invention can be substituted for the LDPE. At the end
of the run,
LDPE can be used to cleanse the equipment of the degradable composite polymer.
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A plastic media blast process is a process for the rapid, economic, and safe
removal of coating from almost any product. It resembles sandblasting but does
not use
a hard abrasive, such as silica sand. A plastic media blast process is a dry
stripping
method by which small angular plastic particles are propelled against a
covered surface
lifting the covering off and leaving a clean, unmarred substrate. The process
employs
specially designed equipment which propels and recovers the sharp-edged non-
toxic
plastic granules. It is especially useful on surfaces which cannot tolerate
damaging
mechanical sanding or wet chemical stripping. The degradable composite polymer
of the
present invention is particularly useful as plastic media blast material. The
plastic
particles are pneumatically applied at pressures of about 10-40 psi.
Plastic media blast material is made by first combining a polymer and a
resin and subsequently extruding this mixture as discussed above. The extruded
mixture
can be formed into particles by any method known to those skilled in the art.
One
method involves feeding the extruded mixture, which is a soft, hot, molten
resin, into a
1 S rod die and forming the composite polymer into a continuous rod.
Preferably, the rod is
cooled as it exits the rod die. This may be accomplished with a water bath, a
fan or
moving the rod through static air. Once the rod has cooled and hardened, it
may be cut
into pellets. The pellets are then further reduced in size by grinding so as
to form
composite polymer particles of a prescribed fineness. A hammer mill or any
type of
conventional grinder may be used to form the particulates. The hardness of the
resulting
composite polymer should affect the particular choice of grinders. For
degradable
composite polymers of this invention containing a large percentage of lactic
acid
polymer, an especially durable grinder must be used. Conventional steel blades
may be
destroyed through the grinding of the invented substance.
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Still further, the plastic media blast material of the present invention may
consist entirely of a polymer comprised of lactic acid monomers. Polymers or
copolymers made from lactic acid monomers make an effective plastic media
blast which
is relatively very hard. This is a novel use for such polymers or copolymers.
However,
plastic media blast material made entirely from lactic acid polymers cannot be
made in
a full range of hardnesses. Thus, in order to make softer plastic media blast
material, the
lactic acid polymer must be combined with a resin comprised of a thermoplastic
polymer,
destructured starch and a plasticizes.
The grit size of the plastic media blast particles can be varied. However,
particles which are too large or too hard can damage the surface of a
substrate.
Preferably, the degradable composite polymer of the present invention is
ground to a very
fine powder so that it will not plug up the nozzles of the device which sprays
the plastic
media blast material. Preferably, the plastic media blast particles have
equivalent
diameters between about 0.2 and 2.5 mm. Most preferably, the plastic media
blast
particles have equivalent diameters of between about 0.4 and 1.2 mm. The
plastic media
blast material may be created in a variety of hardnesses to remove different
substances
from different surfaces. Specifically, it may be created so as to have a
hardness between
about 10 and 70 on the Rockwell scale.
The plastic media blast material of the present invention can be used in
a variety of processes including coating removal, substrate abrasion,
industrial cleaning,
particle removal, surface finishing, and deflashing molded items. Types of
coatings that
can be removed include paint, powder, primers, top coats, residues,
contaminants, burrs,
polymer coatings, and epoxy coatings. It may be used on any surface including
flexible
surfaces and sensitive substrates such as plastic, honeycomb-shaped
structures, fiberglass,
~ _ . _....____,~__.T
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polymers, composite materials, metals, and woods, without harming these
substrates.
Applications where plastic media blast material can be used include, but are
not limited
to, the dry stripping or cleaning of an endless range of consumer household
products,
industrial machinery and equipment, vehicles, aerospace components, weapons
systems
S and marine vessel hulls.
The plastic media blast process is environmentally sound and is an
effective replacement for wet chemical strippers, such as methylene chloride
based
chemical strippers which cause adverse environmental impacts. Using the
degradable
composite polymer of the present invention as a plastic media blast material
avoids the
use of methylene chloride, phenol, corrosives and caustics, methanol, toluene
and
acetone.
Using proper techniques, the combination of low operating pressures, soft
plastic particles and high flow rate permits rapid removal without warping
panels or
damaging surfaces. Furthermore, clad, anodized, galvanized and phosphate
coatings may
be left in tact. And, in many cases, paint can be removed layer by layer down
to the base
substrate or to the primer coating.
The following are examples of various degradable composite polymers
which are within the scope of this invention. These examples are not meant in
any way
to limit the scope of this invention.
Exa~rtRe 1
A composition containing the following components was prepared:
47.5% by weight of semicrystalline polylactic acid (PLA) containing a trace
amount of
D-lactide with a molecular weight of 150,000, 47.5% by weight of ZF03U/A class
Mater
Bi'~M, and 5% by weight of titanium oxide as white colorant.
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All the components were pre-dried at 40°C for 23 hours and premixed.
The premixed components were then fed into an extruder attached with a
flexible lip
sheet die having an opening width of 724 mm (28.5 in). The screw diameter was
63.5
mm (2.5 in.), with a screw length/diameter ratio of 24:1. The extruder barrel
was divided
into 4 zones. The temperatures employed were 180, 180, 190 and 190°C,
respectively,
for the first, second, third and fourth zones.
The operating conditions were as follows: The rotating speed of the screw
was 75 rev/min. The feed flow rate was 85.4 kg/hr (188 lb/hr). The sheeting
rolls
consisted of three vertically arranged cylindrical rolls measuring 305 x 1016
mm. The
temperatures for the three rolls were 48, 60, and 43 °C, respectively
for the top, middle
and bottom rolls.
The extruded sheets were cooled and cut into 610 mm by 610 mm (24 in
by 24 in) squares and packed.
Example 2
A composition containing the following components was prepared:
90% by weight of amorphous polylactic acid (PLA) containing 18% n-lactide by
weight
with a molecular weight of 80,000, and 10% by weight of ZF03U/A class Mater
BiTM
All the components were pre-dried at 40°C for 24 hours and premixed.
The premixed components were then fed into a twin screw extruder. The screw
diameter
was 20 mm, and the screw length/diameter ratio was 40. The diameter of the
nozzle
opening was 3 mm. The extruder barrel was divided into 5 zones. The
temperatures
employed were 90, 150, 150, 145, and 145 °C, respectively for the
first, second, third,
fourth and fifth zones.
_T~ .~. ........_. T
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The operating conditions were as follows: The rotating speed of the screw
as 100 rev/min.
The extrudates were air cooled and then granulated using a C. W.
Brabender laboratory pelletizer. The obtained resins were then ground to
particle sizes
S having equivalent diameters of about 1.5 mm using a C. W. Brabender Granu-
grinder
rotating at 3500 rev/min.
A composition containing the following components was prepared:
70% by weight of semicrystalline polylactic acid (PLA) containing a trace
amount of D-
lactide with a molecular weight of 150,000, and 30% by weight of ZF03U/A class
Mater
BiTM. All the components were then fed into a twin screw extruder. The screw
diameter
was 20 mm, and screw length/diameter ratio was 40. The diameter of the nozzle
opening
was 3 mm. The extruder barrel was divided into 5 zones. The temperatures
employed
were 140, 190, 190, 185, and 185 °C, respectively for the first,
second, third, fourth and
fifth zones.
The operating conditions were as follows: The rotating speed of the screw
as 100 rev/min.
The extrudates were air cooled and then granulated using a C.W.
Brabender laboratory pelletizer. The obtained resins were then ground to
particle sizes
having equivalent diameters of about 1.0 mm using a C. W. Brabender Granu-
grinder
rotating at 3500 rev/min.
A composition containing the following components was prepared:
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47.5% by weight of amorphous polylactic acid (PLA) containing 18% n-lactide by
weight with a molecular weight of 80,000, 47.5% by weight of ZF03U/A class
Mater
BiTM, and 5% by weight of titanium oxide as a white colorant.
All the components were pre-dried at 40°C for 24 hours and
premixed.
The premixed components were then fed into an extruder attached with a
flexible lip
sheet die having an opening width of 724 mm (28.5 in). The screw diameter was
63.5
mm (2.5 in.), and screw length/diameter ratio was 24:1. The extruder barrel
was divided
into 4 zones. The temperatures employed were 152, 149, 160 and 160°C,
respectively
for the first, second, third and fourth zones.
The operating conditions were as follows: The rotating speed of the screw
was 75 rev/min. The feed flow rate was 85.4 kg/hr (188 lb/hr). The sheeting
rolls
consisted of three cylindrical rolls arranged vertically. The temperatures for
the three
rolls were 48, 60, and 43°C, respectively for the top, middle and
bottom rolls.
The extruded sheets were cooled and cut into 610 mm by 610 mm (24 in
by 24 in) squares and packed.
A composition containing the following components was prepared:
67.5% by weight of semicrystalline polylactic acid (PLA) containing Iess than
3% D-
lactide by weight with a molecular weight of 80,000, 27.5% by weight of
ZF03U/A class
Mater BiTM, and 5% by weight of titanium oxide as white colorant.
All the components were pre-dried at 40°C for 24 hours and
premixed.
The premixed components were then fed into an extruder attached with a
flexible lip
sheet die having an opening width of 724 mm (28.5 in). The screw diameter was
63.5
mm (2.5 in.), and screw length/diameter ratio was 24:1. The extruder barrel
was divided
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into 4 zones. The temperatures employed were 152, 149, 160 and 160°C,
respectively
for the first, second, third and fourth zones.
The operating conditions were as follows; The rotating speed of the screw
was 75 rev/min. The feed flow rate was 85.4 kg/hr (188 Ib/hr). The sheeting
rolls
consisted of three cylindrical rolls arranged vertically. The temperatures for
the three
rolls were 48, 60 and 43°C, respectively for the top, middle and bottom
rolls.
The extruded sheets were cooled and cut into 610 mm by 610 mm (24 in
by 24 in) squares and packed.
The degradable composite polymers of the present invention can be used
as a plastic. It can be produced in various textures and ranges of
flexibilities. It also can
be produced in a range of hardnesses so that it can be used as a plastic media
blast
material for a variety of surfaces. The composite polymer also has the ability
to retain
ink during printing so that it can be used as a printable plastic material.
The composite
polymer is able to be cut easily without fracturing so that it may be cut into
small plastic
sheets. It also has a high elasticity so that it is able to be extruded into
sheets without
curling and becoming brittle. Still further, it degrades by composting in two
years or less
and is made from renewable resources, thus making it an environmentally-
friendly
product.
From the foregoing, it will be seen that this invention is one well adapted
to attain all the ends and objects hereinabove set forth together with other
advantages
which are obvious and inherent to the structure. It will be understood that
certain features
and subcombinations are of utility and may be employed without reference to
other
features and subcombinations. This is contemplated by and is within the scope
of the
claims. Since many possible embodiments may be made of the invention without
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departing from the scope thereof, it is to be understood that all matter
herein set forth or
shown in the accompanying drawings is to be interpreted as illustrative and
not in a
limiting sense.
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