Note: Descriptions are shown in the official language in which they were submitted.
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PLASTIC SHIPPING AND STORAGE CONTAINERS
AND COMPOSITION AND METHOD THEREFORE
Field of the Invention
This invention relates to plastic shipping and storage containers and to
polymeric compositions and methods useful for producing them.
Background Art
l0 Plastic shipping and storage containers are widely used in national and
international commerce. Containers protect and support their contents during
storage
and shipment and there is an increasing demand that containers be effective in
helping
to maintain the quality of their contents.
A particularly useful shipping and storage container is the pallet (a
structural
15 platform made of metal, wood, or plastic materials). Wooden pallets have
been in use
for a number of years but they tend to be heavy, bulky, and expensive to make
and
maintain. Additionally, they are subject to deterioration due to adverse
weather and
can fail due to rotting when wet. Additionally, wooden pallets are fastened
together by
means such as glue, nails, staples, etc. Inclement weather also accelerates
deterioration
20 of these fastening means.
The potential for infestations by insects has created increasing demand for
treatment of wooden pallets prior to export. Since October 1, 2001, for
example, the
European Union requires heat or chemical treatment for all coniferous non-
manufactured wood packaging. Shipments that do not comply may be refused at
the
25 border; more likely, non-compliant packaging will be destroyed at the
shipper's
expense.
Metallic pallets also present problems. Typically, they are expensive, heavy
and subject to corrosion.
Plastic pallets overcome many of the problems of wooden and metallic pallets,
30 but they present problems of their own. During fires they are subject to
flowing, which
results in molten plastic spreading heat and fire. The National Fire
Protection
Association has passed stringent regulations that have diminished the utility
of plastic
pallets.
References disclosing plastic pallets are known. WO 00/20495 discloses high
35 performance plastic pallets having a composition comprising a thermosetting
resin,
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which can be an epoxy resin, as well as a plurality of thermoplastic resins.
The
composition can include, for example, flame retardants. No polyolefin is
disclosed.
U.S. Patent No. 5,879,495 relates to constructions of polyvinyl chloride
pallets. WO
00/05143 discloses plastic pallets having a polyolefin top deck and a
polycarbonate or
polyphenilin derivative bottom deck. JP 11278485 relates to
polyolefin/halogenated
epoxy compositions useful to make a pallet. The halogenated epoxy acts as a
flame
retardant, optionally in combination with a second flame retardant.
U.S. Pat. No. 4,428,306 discloses a thermoformed pallet constructed of a
thermoplastic resin material. A film to create a laminated non-skid surface is
provided.
to U.S. Patent No. 4,051,787 discloses a plastic pallet having a deckboard
provided with a rubber anti-slip member or coating. U.S. Patent No. 6,006,677
provides a synthetic resin pallet with a slip-resistant scuffed texture
surface, created by
brushing the surface with a cup-shaped wire brush.
Plastic pallets having a foamed structure have been disclosed. U.S. 3,581,681
relates to structural foamed pallets comprising a variety of components
including
polyolefin and epoxy. No additives are included in their compositions. U.S.
Patent No.
4,375,265 discloses a one piece molded pallet container comprising a foam
composition comprising a variety of thermoplastic resins, for example,
polyethylene,
polyphenylene oxide, polyamide, and others. No epoxy resins axe disclosed, nor
are
2o any additives. Thermoplastic thermoset hybrid foams have been disclosed in
WO
01/23462 having use as flexographic mounting tapes. No molded articles are
disclosed.
U.S. Patent No. 5,709,948 discloses semi-interpenetrating polymer networks
(semi-IPNs) of epoxy and polyolefin resins useful, for example, as tape
backings,
fibers, coatings, foamed constructions, and molded foamed parts.
Summary of the Invention
Briefly, the present invention provides a plastic shipping and storage
container
comprising a composition of matter including
(a) one or more of polyolefin resins and blends thereof, and
(b) one or more of thermosetting resins;
the plastic shipping and storage container further comprising an effective
amount of
friction material on at least one surface thereof.
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The friction material useful in the present invention provides the protected
surface of the container with a static coefficient of friction of dry or wet
surfaces in the
range of 0.60 to 1.20, preferably in the range of 0.75 to 1.00, and more
preferably in the
range of 0.80 to 1.00. For oily surfaces, a desirable container coefficient of
friction is in
the range of 0.30 to 1.00, preferably in the range of 0.40 to 1.00, and more
preferably in
the range 0.50 to 0.95. In some embodiments of the invention it may be
desirable to
provide the container with different coefficients of friction in different
locations on the
container. For example, it may be desirable to have the locations in contact
with fork
truck tines at lower levels of friction to avoid damage to the fork truck
tines due to
to abrasion.
Optionally, the plastic container composition comprises one or more of radio
frequency identification (RFm) tags, and property enhancement additives, such
as
flame retardants, antimicrobial agents, foaming agents, UV stabilizers,
antioxidants,
and fillers. The plastic shipping container preferably meets the requirements
of
Underwriters Laboratory (UL) 2335 protocol for pallets.
Preferably, the resins are free of halogen in the interest of environmental
safety.
Preferably, the composition of matter comprises:
a) 1 to 49 parts by weight of a curable thermosetting resin, the parts being
based on the total composition;
2o b) 51 to 99 parts by weight of at least one of a fully prepolymerized
uncrosslinked hydrocarbon polyolefin resin and a fully prepolymerized
uncrosslinked
functionalized polyolefin resin, the weight percent being based on the total
composition,
wherein the hydrocarbon polyolefin is present in the range of 25 to 99 parts
by weight
of the total composition and the functionalized polyolefin is present in the
range of 0 to
50 parts by weight of the total composition, and
c) performance enhancement additives in the range of 0 to 70 parts by
weight, preferably more than 0 to 70 parts by weight, of the total
composition.
In a preferred embodiment, the present invention provides a plastic shipping
or
storage container comprising a composition including a semi-interpenetrating
polymer
network comprising a thermally cured epoxy resin, a fully pre-polymerized
hydrocarbon polyolefin homopolymer or copolymer, and optionally, a fully pre-
polymerized functionalized polyolefin resin. More preferably, the plastic
container
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comprises an effective amount of at least one of a surface friction material
and a flame
retardant.
The present invention provides a method for producing a plastic container
comprising the steps:
a) admixing a composition comprising
(1) one or more thermosetting resins and curing agent therefor,
(2) a fully pre-polymerized uncrosslinked hydrocarbon polyolefin resin,
and optionally a fully pre-polymerized uncrosslinked functionalized
polyolefin, and
b) exposing said composition to curing conditions after forming the
composition into a useful article.
In another aspect, the present invention comprises a curable polymeric
composition comprising
a) a polyolefin resin or blends thereof,
b) a thermosetting resin, and
c) an effective amount of a flame retardant.
Curing can be accomplished by exposure to curing conditions such as by
exposure to heat or irradiation by light until the composition is formed in
place,
molded, coated, or otherwise prepaxed in a useful format.
In another aspect, the present invention describes a method of preparing a
shaped article or sheet article comprising a semi-interpenetrating polymer
network
comprising the steps of (a) intimately mixing a composition comprising a fully
pre-
polymerized hydrocarbon thermoplastic polyolefin resin or copolymer thereof;
optionally, a fully pre-polymerized polyolefin resin comprising polar
functionality; a
curable thermosetting resin, and at least one curing agent for the
thermosetting resins;
(b) forming the composition into a shaped article or a sheet article; (c)
laminating or
bonding friction material onto or within a surface of the shaped article or
sheet article;
and (d) at the appropriate time, activating the curing agent by supplying
sufficient
energy to the composition . Lamination is preferably free of added adhesive.
The
thermosetting resin and the curing agent can be added together or in separate
steps. The
lamination can take place in process, preferably in in-mold lamination, or it
can take
place after shaping the article or sheet.
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The thermosetting resin curing agent can be thermally curable or photocurable.
A high temperature stable thermal curing agent or a photocatalyst can be added
to the
curable admixture. Activation of the curing agent can be immediate or delayed.
In a preferred embodiment, the shipping container is a plastic pallet that has
an
open deck design, and on at least one surface thereof it comprises a friction
or anti-slip
material that has been in-mold laminated. In another preferred embodiment, the
container composition comprises at least two resins and optionally includes
one or
more of (a) a flame retardant, (b) an antimicrobial additive, an antimicrobial
coating,
and/or antimicrobial granules, and (c) other performance enhancing additives.
In a
to more preferred embodiment, the. cured composition can be microcellular
foamed. What
has not been described in the art is how these have been synergistically
combined.
It is advantageous in the art for plastic shipping containers and their
precursor
compositions to have one or more of the following characteristics: increased
fire
resistance (including such as meeting the Underwriters Laboratories (UL) 2335
protocol for pallets), increased coefficient of friction to reduce slippage
and damage,
increased surface energy for improved bonding, improved control of thermal
expansion
and thermal deflection, improved pathogenic performance, improved chemical
resistance for industrial applications, improved resistance to UV and
oxidative
degradation, and improved processing ease due to reduced viscosity, pressure,
2o temperatures, and equipment size. The present inventive plastic containers
can exhibit
these desirable characteristics.
In this application:
"hydrocarbon polyolefin" means a fully pre-polymerized uncrosslinked
polymeric hydrocarbon bearing essentially no organic functional groups,
prepared from
homopolymerization and/or copolymerization of an olefinic monomer(s);
"friction surface" means a surface, in whole or in part, which comprises a
friction material laminated or bonded therein or thereon;
"friction" and "anti-slip" have the same meaning;
"functionalized polyolefin" means a fully pre-polymerized uncrosslinked
polymeric hydrocarbon bearing polar organic functional groups;
"filler" means a dispersed particle, fiber, flake, or the like;
"in-mold lamination" means placed in a mold and becomes laminated to
subsequently added resin without added adhesive;
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"mildewcide" means an antifungal agent;
"plastic" means a material comprised substantially of an organic polymer; and
"semi-interpenetrating polymer networks (semi-IPNs)" means polymer
networks of two or more polymers wherein at least one polymer is crosslinked
and at
least one polymer is uncrosslinked.
Contamination of foodstuffs by bacteria, viruses and parasites has recently
become of growing concern, because the resulting infections living beings
often are
refractory to drug treatment. However, a need exists for an antimicrobial
composition
that will simultaneously inhibit the growth of fungi, viruses, actinomycetes
and
to parasites, as well as bacteria.
The present invention provides for the reduction of microbial contamination of
plastic shipping containers, including but not limited to containers useful
for the
processing and storage of foodstuffs. In general terms, the present invention
relates to
the incorporation of antimicrobial agents into polymeric materials, such that
the activity
15 of the agents will reduce the microbial contamination of the plastic
container. In a
preferred embodiment, antimicrobial agents are mixed with polymer compositions
during formation of the plastic molded containers and thereafter serves to
reduce or
destroy the bacteria on that portion of the foodstuffs with which it comes
into contact.
Another embodiment of the invention provides antimicrobial protection that
allows for
20 controlled migration of an anti-microbial agent throughout a polymer. The
invention
can also provide a container having an antimicrobial agent that is
substantially
insoluble in water, thereby preventing any significant leaching of the agent
during use
of the container.
It is believed not known in the art to use antimicrobial materials in
conventional
25 plastic shipping containers. Furthermore, the prior art is generally
deficient in affording
a composition that will not only control bacterial growth, but will also
simultaneously
control the growth of fungi, viruses, and parasites.
Plastic pallets in general are capital and labor intensive to manufacture. The
temperatures, viscosities, and pressures involved in their manufacture are
generally
3o very high and require significant capital outlay. In the present invention,
the addition
of the uncured thermosetting resin advantageously reduces viscosity and hence
creates
the ability to reduce processing temperatures such that flame retardant,
antimicrobial,
and blowing agent additives can be added without loss of additive
effectiveness. Not
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only is the ability to add these important properties enhanced but the ability
to improve
productivity and reduce equipment size is also achieved.
Chemical and physical foaming of thermoplastic materials has been practiced
for a number of years. Physical methods that use carbon dioxide as a foaming
agent
comprise one of the new and most promising trends for the continuous
manufacture of
foamed goods. In this invention use of carbon dioxide is preferred as a
blowing agent
to aid in the simultaneous incorporation and foaming of an uncured
thermosetting resin
into a thermoplastic resin. This invention also teaches the use of chemical
means to
foam some thermoplastic resins that contain a thermosetting monomer. Polymeric
foams include a plurality of voids, also called cells, in a polymer matrix. By
replacing
solid plastic with voids, polymeric foams use less raw material than solid
plastics for a
given volume.
Improvements in properties are realized through cure of the thermoset. This
can
be done during or after the foam has been formed. Reinforcing properties such
as
flexural modulus, impact strength, tensile strength, and compressive strength
are
obtained by means of the foam, as are increased monomer miscibility in the
matrix, cell
formation and enhanced surface compatibility. For example, improvement in
compressive strength of the cured material over that of a control or its
plasticized
uncured version has been obtained as described in WO 0123462.
2o The present invention, by providing compositions of increased surface
energy,
overcomes the problem of tracking plastic pallets on an individual basis. The
low
surface energy of many polymeric materials requires specials adhesives for
labels and
tags that still can be too easily removed during use and cleaning. Methods to
conveniently insert tags and protect tags are not adequately described in the
art.
The present invention discloses a plastic shipping container comprising a
curable composition including a curable thermosetting resin, i.e., preferably
an epoxy
resin, an unmodified fully pre-polymerized hydrocarbon polyolefin resin, and
optionally a fully pre-polymerized functionalized polyolefin, wherein the
curable epoxy
resin preferably is not exposed to curing conditions (i.e., temperatures
greater than
3o about 200 degree C or irradiation by light) until the composition is formed
in place,
molded, coated, or otherwise prepared in a useful format.
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Brief Description of the Drawing
Fig. 1 shows a pallet of the invention having an open deck design and friction
material on its upper surface.
Detailed Description of Preferred Embodiments
The present invention provides a curable composition comprising:
a) 1 to 49 part by weight, preferably 1 to 30, most preferably 5 to 15 parts
by weight, of a curable thermosetting resin, the parts by weight being based
on the total
composition;
b) an effective amount of a curative for the curable thermosetting resin; and
c) 51 to 99 parts by weight of at least one of a fully prepolymerized
uncrosslinked hydrocarbon polyolefin resin and a fully prepolymerized
uncrosslinked
functionalized polyolefin resin, the weight percent being based on the total
composition,
wherein said hydrocarbon potyolefin is present in the range of 25 to 99 parts
by weight
of the total composition and said functionalized polyolefin is present in the
range of 0
to 50 parts by weight of the total composition.
Preferably, blending of the components takes place at a temperature that is
below the thermal activation temperature of the catalyst. Preferably, the
functionalized
polar group comprises at least one O, N, S, or P atom.
As noted above, the inclusion of thermosetting resins in a fully pre-
polymerized
hydrocarbon polyolefin continuous phase provides the polyolefin with a number
of
advantageous properties. Thermosetting resins include epoxy, curable
potyolefins
including ethylene propylene dime monomer (EPI~M), ethylene propylene rubber
(EPR), ethylene butylene rubber (EBR), phenotics, polyurethanes, unsaturated
polyesters, furan, allyls, vinyls, silicones, alkyds, and nitrite rubber
including carboxyl
terminated butadiene nitrite rubber (CTBN) , amine terminated butadiene
nitrite rubber
(ATBN), hydroxyl terminated butadiene nitrite rubber (HTBN), and epoxy
terminated
butadiene nitrite rubber (ETBN).
Epoxy resins are characterized by the presence of a three membered ring known
as the epoxy, epoxide, oxirane or ethoxyline group. Commercial epoxy resins
contain
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aliphatic, cycloaliphatic, or aromatic backbones. The most widely used ones
are
epichlorohydrin and bisphenol-A derived resins. The outstanding performance
characteristics of these resins are conveyed by the bisphenol-A (toughness,
rigidity, and
elevated temperature performance), the ether linkages (chemical resistance),
and the
hydroxyl and epoxy groups (adhesive properties and formulation latitude, or
reactivity
with a wide variety of chemical curing agents).
Curable monomeric epoxy resins serve to decrease the melt viscosity of the
polyolefins, imparting improved handling and processing. Lowered processing
temperatures also allows the inclusion of heat-sensitive performance enhancing
to additives, such as certain flame-retardants and anti-microbial agents, not
otherwise
usable in high-melting polyolefins. Low-molecular weight epoxy resins improve
adhesion of the semi-IPNs to various substrates, in part because such low-
molecular
weight species can quickly migrate to the resin-substrate interface for
improved
bonding, perhaps through improved wetting or reaction of the epoxy
functionality with
functional groups on the substrate surface. These semi-IPN's have been
disclosed in
U.S. Patent No. 5,709,948.
The thermosettable epoxy resins of the invention preferably comprise
compounds which contain one or more 1,2-, 1,3- and 1,4-cyclic ethers, which
also may
be known as 1,2-, 1,3- and 1,4-epoxides. The 1,2-cyclic ethers are preferred.
Such
2o compounds can be saturated or unsaturated, aliphatic, alicyclic, aromatic
or
heterocyclic, or can comprise combinations thereof. Compounds that contain
more than
one epoxy group (i.e., polyepoxides) are preferred.
A wide variety of commercial epoxy resins are available and are listed or
described in, e.g., the Handbook of Epoxy Resins, by Lee and Neville, McGraw-
Hill
Book Co., New York (1967), Epoxy Resins, Chemistry and Technology, Second
Edition, C. May, ed., Marcell Decker, Inc., New York (1988), and Epoxy Resin
Technology, P. F. Bruins, ed., Interscience Publishers, New York, (1968). Any
of the
epoxy resins described therein may be useful in preparation of the semi-IPNs
of the
invention.
3o It is within the scope of the present invention to include, as a bireactive
comonomer, compounds having both epoxy functionality and at least one other
chemical functionality, such as, e.g., hydroxyl, acrylate, ethylenic
unsaturation,
carboxylic acid, carboxylic acid ester, and the like. An example of such a
monomer is
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EbecrylTM 3605, commercially available from UCB Radcure, Inc., Atlanta, Ga., a
bisphenol-A-type monomer having both epoxy and acrylate functionality.
Curatives of the present invention can be thermal curing agents or
photocatalysts.
Certain thermally-activated curing agents for epoxy resins (e.g., compounds
that
effect curing and crosslinking of the epoxide by entering into a chemical
reaction
therewith) are useful in the present invention. Preferably, such curing agents
are
thermally stable at temperatures at which mixing of the components takes
place.
Suitable thermal curing agents include aliphatic and aromatic primary and
l0 secondary amines, e.g., di(4-aminophenyl)sulfone, di(4-aminophenyl)ether,
and 2,2-
bis-(4-aminophenyl)propane; aliphatic and aromatic tertiary amines, e.g.,
dimethylamino-propylamine and pyridine; fluorene diamines, such as those
described
in U.S. Pat. No. 4,684,678; boron trifluoride complexes such as BF3Et20 and
BF3HZNCZH40H: imidazoles, such as methylimidazole; hydrazines, such as
adipohydrazine; and guanidines, such as tetramethylguanidine and dicyandiamide
(cyanoguanidine, also commonly known as DiCyTM Air Products, Allentown, PA).
It is
to be understood that a careful choice among these curing agents must be made,
since
many of them would be unsuitable for use when high-melting polyolefin
components
are present, but they can be useful in preparing semi-IPNs of the invention
that
2o comprise low-melting polyolefins and epoxy resins.
Thermal curatives can be present in an amount such that the ratio of epoxy
equivalents to thermal curative equivalents is in the range of 0.9:1 to 2:1.
Catalysts of the present invention (also known as "initiators," the terms
being
used interchangeably in the present invention) can also be activated by
photochemical
means. Known photocatalysts are of two general types: free radical and
cationicPhotoinitiators useful in the invention can be present in an amount in
the range
of 0.01 to 10 parts by weight, preferably 0.01 to 5, most preferably 0.1 to 2
parts by
weight based on total resin composition.
The uncrosslinked prepolymerized polyolefin resin can be homopolymers,
copolymers, blends with other polyolefins, blends with high impact polymers
such as
polyphenylene oxide, polyphenylene ether, polycarbonate, high impact
polystyrene
polyethersulfone, polyetherimides or blends with rubbers/elastomers such as
ethylene
r
propylene dime monomer, ethylene propylene rubber, ethylene butylene rubber,
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polybutadiene, acrylonitrile butadiene styrene, styrene butadiene styrene,
styrene
ethylene butylene styrene, polyisoprene, polybutylacrylate, polyurethane.
More particularly, homopolymeric polyolefins useful in the invention include
polyethylene, polypropylene, poly-1-butene, poly-1-pentene, poly-1-hexene,
poly-1
octene and related polyolefins. Preferred homopolymeric polyolefins include
polyethylene (e.g., Dow HDPETM , available from Dow Chemical Co., Midland,
Mich.)
and polypropylene (e.g., Shell DS5D45TM, available from Shell Chemicals,
Houston,
Tex., or ExxonMobil EscoreneTM 3445 and 35056, available from Exxon Chemicals,
Houston, Tex.). Also useful are copolymers of these alpha-olefins, including
l0 polyethylene-co-propylene) (e.g., SRD7TM-462, SRD7-463 and DS7C50TM, each
of
which is available from Shell Chemicals), polypropylene-co-1-butene) (e.g.,
SRD6TM_
328, also available from Shell Chemicals), and related copolymers. Preferred
copolymers are polyethylene-co-propylene). Also useful is the VestoplastTM
series of
polyolefins, available from Huls America Inc., Piscataway, N.J.
The semi-IPNs of the invention also comprise functionalized polyolefins, i.e.,
polyolefins that have additional chemical functionality, obtained through
either
copolymerization of an olefin monomer with a functional monomer or graft
copolymerization subsequent to olefin polymerization. Typically, such
functionalized
groups include O, N, S, or P. Such reactive functionalized groups include
carboxylic
acid, hydroxyl, amide, nitrile, or carboxylic acid anhydride. Many
functionalized
polyolefins are available commercially. For example, copolymerized materials
include
ethylene-vinyl acetate copolymers, such as the ElvaxTM series, commercially
available
from DuPont Chemicals, Wilmington, Del., the ElvamideTM series of ethylene-
polyamide copolymers, also available from DuPont, and AbciteTM 1060WH, a
polyethylene-based copolymer comprising approximately 10% by weight of
carboxylic
acid functional groups, commercially available from Union Carbide Corp.,
Danbury,
Conn. Examples of graft-copolymerized functionalized polyolefins include
malefic
anhydride-grafted polypropylene, such as the EpoleneTM series of waxes
commercially
available from Eastman Chemical Co., Kingsport, Tenn. and QuestronTM,
commercially
available from Himont U.S.A., Inc., Wilmington, Del.
The present invention provides a process for producing a foam, including a
microcellular foam, that includes a midlevel amount of a blowing agent. The
microcellular foams can be produced in typical polymer processing techniques
such as
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extrusion, injection molding and blow molding. The foams exhibit excellent
mechanical properties and can be formed over a broad range of densities into a
number
of different foam plastic shipping containers. This process is described in
PCT Patent
document No. WO 0123462.
Structural foam as a plastic product has an integral skin and cellular core.
The
combination of the skin, which is normally solid, that is, without voids or
cells, and
cellular core, produces a relatively high strength to weight ratio. When
structural foam
is in the form of a pallet, it typically has rigidity for holding and
transporting a load.
U.S. Pat No. 3,268,636 and WO 0123462 discloses the basic process for making
structural foam articles by melting thermoplastic resin and forcing it into a
mold in the
presence of blowing agent to mold the article. Upon entry of the molten resin
into the
mold, the blowing agent foams the resin to create the cellular core of the
molded
article. The mold is kept at a temperature below the softening or melting
temperature
of the resins so that the resultant rapid solidification of the resin coming
in contact with
the surface of the mold surface remains sufficiently fluid in the mold to
permit its
foaming by the blowing agent. Thermoplastic/thermoset hybrid foams are
described in
patent document WO 0123462. Foams were prepared using a blowing agent that was
used as a swelling agent and plasticizer for a thermoplastic polymer matrix
and as a
solvent that allows thermosettable material to be introduced into the
thermoplastic
matrix.
Any of a wide variety of physical and chemical blowing agents known to those
of ordinary skill in the art such as hydrocarbons, chlorofluorocarbons,
nitrogen, carbon
dioxide, and the like can be used in connection with this embodiment of the
invention.
Blowing agents that are in the supercritical fluid state in an extruder are
especially
preferred, in particular supercritical carbon dioxide and supercritical
nitrogen. These
are disclosed in PCT Patent Doc. WO 0123462.
Microcellular foams have smaller cell sizes and higher cell densities than
conventional polymeric foams. Typically, microcellular foams are defined as
having
average cell sizes of less than 100 micrometers and a cell density of greater
than 106
cells/cm3 of solid plastic. In a typical continuous process for forming
microcellular
foam (e.g. extrusion), the pressure on a single-phase solution of blowing
agent and
polymer is rapidly dropped to nucleate the cells.
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It should be understood that the above described formulation and process is
not
limiting. Modifications, well-known in the art, can be made to the formulation
and
process in various embodiments of the invention.
Various adjuvants can also be added to the compositions of the invention to
alter the physical characteristics of the cured semi-IPN. Included among
useful
adjuvants are thixotropic agents such as fumed silica; colorants and pigments
to
enhance color tones such as ferric oxide, carbon black and titanium dioxide;
fillers such
as mica, silica, acicular wollastonite, calcium carbonate, magnesium sulfate
and
calcium sulfate; clays such as bentonite; glass beads and bubbles, reinforcing
materials
such as unidirectional woven and nonwoven webs of organic and inorganic fibers
such
as polyester, polyimide, glass fibers, polyamides such as polyp-phenylene
terephthalamide), carbon fibers, and ceramic fibers, LTV stabilizers,
antioxidants, and
mildewcides. Amounts up to about 200 parts of adjuvant per 100 parts of
polyolefin-
epoxy composition can be used.
More particularly, we have found it desirable to use certain ammonium
polyphosphates as a flame retardant agent for semi-IPN resins of the
compositions of
the present invention. Also suitable as flame-retardant additives for this
invention are
compounds containing phosphorus -nitrogen bonds, such as phosphonitrilic
chloride,
phosphorus ester amides, phosphoric acid amides, tris(aziridinyl) phosphine
oxide,
cyclic phosphates, or tetrakis(hydroxymethyl) phosphonium chloride. These
flame-
retardant additives are commercially available and in the preferred embodiment
are
non-halogenated.
The semi-IPNs of the present invention synergistically provide the ability to
add
flame retardants since many flame retardants cannot exceed 204°C
without activation.
Process temperatures in the art may be as high 260°C or more. The
reduction in
viscosity allows for reduced processing temperatures which in turns allows
flame
retardant additives to be incorporated. Semi-IPN formulations improve the fire
resistance such that less flame retardant additives are required. This
prevents the loss in
properties and the added costs of expensive raw materials.
The flame retardant can be present in at least the minimum amount necessary to
impart a degree of flame retardancy to the composition to comply with the
requirements of the UL 2335 protocol for pallets. The particular amount will
vary,
depending on the molecular weight of the organic phosphate, the amount of the
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flammable resin present and possibly other normally flammable ingredients,
which may
also be included in the composition.
Preferably performance enhancement additives can be included in an amount of
0 to 70 parts by weight of the total composition. Most preferably, flame
retardants can
be added in an amount of 0-25 parts by weight, fillers (particulate and
fibrous) 0-20
parts by weight, foaming or blowing agents (chemical and physical) 0-5 parts
by
weight, and others (colorants, UV stabilizers, etc.) 0-5 parts by weight, all
based on
100 parts by weight of total composition. Fillers~in polymeric foams are
typically
added in amounts of at least 20 parts by weight polymeric material, and in
many cases
to greater than 30 parts by weight, based on the total composition, to
reinforce the
polymeric foam.
Thermal and photochemical curing of the epoxy component can occur before
and/or after fabrication of the container. Prior to fabrication of the
container, curing can
take place in the extruder during compounding of epoxy with polyolefin and
additives
or during the injection molding process to make the container. Photochemical
curing
requires pre-irradiation of the mixture with radiation such as UV or visible
light.
Compounding and molding conditions should be chosen such that significant
curing
does not take place prior to fabrication of the container as this will pose
processing and
equipment cleaning problems. Curing of epoxy after fabrication of the
container can
2o take place at a constant temperature in an oven or autoclave. The post-
fabrication cure
temperature should be chosen such that a high degree of cure is obtained while
maintaining the shape of the container. Also, a sufficient cure time should be
provided.
For thick containers, thermal curing is preferred to photocuring during the
post-
fabrication curing stage.
Plastic shipping containers, including pallets, of the present invention can
be of
a variety of shapes and constructions, as is known in the art. Any of the
constructions
and conventional plastic shaping processes known in the art (for example, U.S.
Pat.
Nos. 4,597,338, 6,006,677, 3,938,448, 4,316,419, 4,879,956, 4,843,976,
4,550,830,
4,427,476, and 4,428,306) can be used with the formulations, materials, and
innovations of this invention. The containers of the present invention can be
produced
by a variety of melt processing techniques such as injection molding,
thermoforming,
extrusion, co-extrusion, and the like. They can be produced in a single piece
or in a
plurality of pieces that can be snapped, fused, or otherwise secured together.
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A typical design for a plastic shipping container of the present invention is
shown in FIG. 1 wherein plastic pallet 10 has an open deck design in
accordance with a
preferred embodiment and comprises two separately molded horizontal members
including upper deck 4 and lower deck 2. Preferably, the container comprises a
semi-
s IPN formulation and meets the requirements of UL 2335. Also, included in the
invention are pallets having closed deck designs.
Upper and lower decks (4 and 2) have solid surfaces that are interrupted by a
series of holes 6 of any suitable size or dimension, and that reduce the
weight of the
decks and allow for drainage in the event the pallet becomes wet.
l0 Four corner supports 8 project upwardly from lower deck 2 at the corners
thereof. Four medial supports 12 project upwardly from lower deck 2. A central
support (not shown) projects upwardly from the center of lower deck 2. Each
support
preferably is hollow.
Synthetic resins used to form the pallet can have a rather slippery finish
when
15 the pallet is new. This is undesirable in certain areas, viz., the top of
the upper deck 4,
the underside of the lower deck 2, and the underside of the upper deck 4 in
the regions
between the supports, which can rest on the forks of a forklift.
In accordance with the invention, any of the surfaces of the pallet can be
provided with friction material, which comprises, for example, insert-molding
strips of
20 surface friction materials 14, preferably a thermoplastic polymer (although
a
thermosetting polymer may also be used) such as an ionically crosslinked
ethylene/methacrylic acid copolymer (e.g., SurlynTM, available from DuPont,
Wilmington, DE) having quartz, ceramic, or other mineral particles partially
embedded
or exposed in or on the polymer surface. The friction material can comprise an
25 inorganic or organic anti-slip agent that provides the protected surface of
the container
with a static coefficient of friction in the range of 0.60 to 1.20, e.g.,
inorganic materials
including inorganic oxides such as silica or alumina, ceramic, or other
mineral
particles, as well as organic materials such as abrasive polymeric beads, all
of which
can be in-mold laminated, or which can be applied or adhered uniformly, or in
a
3o patterned or random fashion. Preferably, anti-slip agent particles are
rubber-free,
because the coefficient of friction of rubber tends to drop in the presence of
oils and
moisture, and as the rubber hardens (from aging and low temperatures). The
polymer
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of the friction material preferably has a composition different from that of
the pallet or
container.
Friction inserts can be, for example, friction particles or fibers
incorporated in
or on a polymeric surfaces, microreplicated or embossed polymeric surfaces,
particles
or fibers impregnated in a web, and the like. Friction inserts overcome
slippage
problems by controlling the surface coefficient of friction of plastic
shipping
containers. One of the major roadblocks to use of plastic pallets and other
shipping
containers is their low coefficient of friction. It is known that loads can
fall off pallets,
pallets can fall off fork trucks, and stacks of pallets can topple over.
Temperature,
to moisture, durability requirements, and the need for recyclability have
hindered efforts
to completely resolve these issues. This invention provides the ability to
include
designed frictional surfaces for the containers involved, in the locations of
concern on
the containers; it provides the ability to recycle the containers, and it
provides the
ability to incorporate the friction material into the manufacture of the
plastic container
itself. Additives to the friction insert can include granules that contain
antimicrobial
properties.
Compatibility of materials and process as well as recyclability in
constructions
is required. The friction surface desirably resists melting and losing its
coefficient of
friction during processing. Melting can be sufficient to promote bonding yet
not
2o envelop exposed textured surfaces of friction material. The semi-IPN
container
formulations synergistically provide reduced pressures and temperatures to
minimize
the loss of friction. The friction surface desirably is compatible with the
plastic
container so that it can be bonded to or preferably in-mold laminated to the
container
and recycled with the container. The semi-IPN formulations synergistically
provide
better bondability through increased surface energy. The semi-IPN formulations
synergistically bond the recyclable friction materials into the containers
resin composite
matrix without added adhesive. The friction surface desirably does not damage
tooling.
In a preferred embodiment, the particles can be rounded granules that are less
abrasive
(such as washed sand). The friction particles or granules preferably have a
shape and
hardness that minimizes damage to tooling and they can be readily removed by
filtration during recycling. In another preferred embodiment, the friction
surface can be
covered prior to insert molding to protect tooling. The cover methods include
but are
not limited to masking tape, aluminum foil tapes, foam tapes, and water
soluble
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coatings. Useful friction particles have an average size of about 5 to 6550
micrometers
or more (corresponding to American National Standards Institute (ANSI) Grade
mesh
of about 900 to 3), preferably 50 to 5000 micrometers, more preferably 100 to
500
micrometers. Examples of useful friction particles include fused aluminum
oxide
(including fused alumina-zirconia), ceramic aluminum oxide, aluminum oxide,
silicon
carbide (including green silicon carbide), silicon oxide, garnet, diamond,
cubic boron
nitride, boron carbide, chromia, ceria, coal slag, quartz, ceramic spheres,
and
combinations thereof. Examples of particles that not only provide friction but
also
provide reflectivity are glass and ceramic particles such as beads and
bubbles. Particles
of this type having a diameter of about 30 to 850 micrometer are particularly
useful.
To produce a conductive material, metal, carbon black, graphite particles, or
the like
can be incorporated and used for antistatic or static dissipative properties.
Thermoplastic and thermoset particles, for example polyester and nylon, and
melamine formaldehyde and phenol formaldehyde, may also be used as the
friction
particles, but care should be taken to avoid processing conditions such as
high
temperatures that would melt or degrade these particles. These polymeric
particles can
include fillers such as graphite or carbon black or any other fillers.
The friction particles used in the present invention can be irregular or
precisely
shaped. Irregularly shaped particles are made, for example, by crushing the
precursor
2o material. Examples of shaped particles include rods (having any suitable
cross-
sectional area), pyramids, and thin faced particles having polygonal faces.
Shaped
particles and methods of making them are described, for example, in U.S. Pat.
Nos.
5,090,968 and 5,201,916. Spherical glass or polymeric beads can be useful
friction
particles and have been used for pavement marking applications. Polymeric
particles
can be any shape either irregular or shaped (for example, cubes, spheres,
discs, etc.).
The friction particles used in the present invention may be in the form of an
agglomerate, i.e., multiple particles bonded together to form an agglomerate.
Useful
abrasive agglomerates are further described in U.S. Pat. Nos. 4,311,489,
4,652,275,
4,799,939, 5,039,311, and 5,500,273.
3o It is also contemplated to have a surface coating on the friction
particles.
Surface coatings may be used to increase the adhesion of the polymer of the
friction
material to the particle, alter the friction characteristics of the particles,
or for other
purposes. Examples of useful surface coatings on abrasive particles are
taught, for
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example, in U.S. Pat Nos. 4,997,461, 5,011,508, 5,131,926, 5,213,591, and
5,474,583.
Coupling agents such as silanes, titanates, and zirconates are common coatings
used on
particles to increase their adhesion to organic materials and are useful in
the present
invention. A particularly useful coupling agent is 3-
aminopropyltrimethoxysilane
(Union Carbide Corp., Danbury, CT, under the trade designation "A-1100" brand
silane).
This invention provides a cost effective method for imbedding friction
surfaces
into plastic containers in order to provide a designed frictional and/or
protective
surface. In a preferred embodiment the friction material can comprise a film
or
to substrate that includes friction particles impregnated in a polymer similar
to that of the
plastic container such that the friction material can be subsequently
thermally bonded to
the plastic container. The particles protrude from the surface so as to
provide the
desired friction properties thereto. The particle impregnated substrate can be
formed or
produced by numerous methods including those described in U.S. Patent Nos.
6,024,824 and 5,152,917.
Other suitable friction materials include particle impregnated webs disclosed
in
U.S. Pat. Nos. 6,024,824 and 6,258,201, microreplicated webs disclosed in U.S.
Pat.
Nos. 5,897,930 and 5,152,917 and PCT publication WO 0064296.
Alternatively, the friction surface can consist of cured microreplicated
surfaces
2o as outlined in WO 0064296. However, the friction material preferably is
different in
composition from the plastic container. The plastic container with the
friction material
embedded or attached to desired surfaces can be formed or produced by numerous
methods including in-mold laminate injection molding, compression molding,
blow
molding, heat staking, and thermal forming.
In a preferred embodiment of the invention an anti-slip film or tape can be
laminated to a plastic pallet. The pallet preferably is made of polyolefin
because it is
inexpensive. Polyolefins, however, are normally difficult to attach things to
because of
their low surface energy. The present invention polyolefin-containing polymer
blends
provide improved adhesion (because of increased surface energy), improved
processability through lower viscosity than the base polyolefin alone, and
inherent
flame retardance. Preferably the polymer of the friction material is chosen
such that is
has a composition that is amenable to sticking well to the polymer of the
pallet (for
example, the film can be made of SURLYNTM), therefore not requiring the
addition of
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an adhesive on its back side to achieve lamination. Such adhesive-free
lamination is
also called "in-mold" lamination. The film composition is also chosen so that
it
effectively retains anti-slip particles without allowing them to become either
detached
or buried when the film is made, during in-mold lamination, or during pallet
use.
Polymers useful in the friction material include, but are not limited to
either a
thermoplastic, thermoplastic elastomer, thermosetting material, or
combinations of
those. If combined, it is preferred that the mixture be homogenous. However,
in some
instances it may be preferred that the polymeric sheet comprising the friction
material
have areas of different material, depending on the desired properties.
Preferably, the
to polymeric sheet is either a thermoplastic or thermoplastic elastomer.
Suitable
thermoplastic materials include polyethylene, polyesters, polystyrenes,
polycarbonates,
polypropylene, polyamides, polyurethanes, polyvinyl chloride, nylons, poly
alpha
olefins, functionalized olefins, and combinations thereof. Particularly useful
thermoplastic polymeric materials include SURLYNTM, an ionically crosslinked
ethylene/methacrylic acid copolymer, NUCRELTM, an ethylene acid copolymer
(both
available from DuPont, Wilmington, DE), and polypropylene (available for
example as
3365TM from Fina Inc., Dallas, TX). Examples of suitable thermoset materials
include
phenolic resins, rubbers, acrylates, vinyl esters, unsaturated polyesters, and
epoxies.
The friction surfaces preferably are not treated with an antimicrobial agent
prior
to molding the pallet. Alternatively the friction surface can be laminated to
an
antimicrobial film or an antimicrobial agent can be incorportated throughout
the pallet
body. The antimicrobial additive chosen preferably is essentially insoluble in
water to
prevent any leaching of the compound during use. In use, the antimicrobial
agent
migrates through the polymer material to the exposed surface thereof from the
amorphous zones of the polymer until equilibrium of the internal vapor
pressure is
reached. If the antimicrobial substance on the surface of the pallet or the
friction
surface is removed by friction, or other means, antimicrobial agent moves to
the surface
until the agent's internal vapor pressure is once again at equilibrium.
Antimicrobials such as mildewcides, antiseptics, disinfectants, sanitizers,
germicides, algaecides, slimicides, antifouling agent, or preservatives are
typically
employed to remove microbes from an area and prevent their recurrence. The use
of
antimicrobials in the control or prevention of microbial growth requires
effective
contact between the antimicrobial agent and the microbe. One problem in
achieving
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effective and long lasting control of microbial growth has been the ease by
which
commercially available antimicrobial compositions can be washed from most
substrates
by the application of moderate volumes of water. In moist environments such as
a food
preparation, for example, the pallets often experience daily exposure to
significant
volumes of water. This daily exposure to water washes conventional
antimicrobials
from the surfaces to which they are applied, requiring frequent reapplication
to retain a
desired level of antimicrobial action. For the present invention, the addition
of epoxy
improves the surface chemistry of low surface energy surfaces such as
polyolefins and
enable antimicrobials to remain on a substrate for an extended period of time
to make
frequent reapplication unnecessary.
An antimicrobial additive can be incorporated in resin concentrate form into
the
amorphous zones of the molecular structure of the polymer from which
containers are
injection molded, thereby incorporating the antimicrobial agent into the
container. The
preferred method of associating the antimicrobial agent with a pallet is to
incorporate
the antimicrobial agent into a synthetic, polymeric master batch prior to
forming the
pallet body.
In the most basic form of the present invention, the pallet can include a
broad
spectrum antimicrobial agent associated therewith to inhibit bacterial,
fungal, viral and
other pathogen growth. The pallet can have a topdeck with an open deck design,
a
2o plurality or polymeric friction surfaces attached to the pallet, and an
antimicrobial agent
integrally associated with the pallet. Preferably, an antimicrobial agent is
associated or
incorporated into the polymeric material from which the pallet is made. Thus,
an
effective amount of an antimicrobial substance (e.g., 5-chloro-2-(2,4-
dichlorophenoxy)phenol) is incorporated therein. Levels of active ingredients
or
antimicrobial substance range preferably from 1000 to 5000 parts per million
(ppm) by
weight. These levels can be substantially higher than would otherwise be
required for
antimicrobial efficacy in order to enhance migration from the pallet body into
friction
surfaces.
The pallet having the antimicrobial agent therein has enhanced resistance to
growth of fungus, yeast, virus, and gram positive and gram negative bacteria
including
S. aureus, E. coli, K. pneumoniae, and Salmonella. The antimicrobial
substance, which
is non-toxic and free of heavy metal, may be a chlorinated phenol (e.g., 5-
chloro-2-
(2,4- dichlorophenoxy)phenol). An alternative antimicrobial agent is
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polyhexamethylene biguanide hydrochloride (PHMB). Other chemical compounds
having known antimicrobial characteristics may also be used in the present
invention.
In a preferred embodiment, 5-chloro-2-(2,4-dichlorophenoxy)phenol can be
incorporated in resin-concentrated form into the amorphous zones of the
polymers from
which pallets can be injection-molded. Polymeric materials used for the
friction
material are preferably an ionomer, such as SurlynTM. More preferably, the
friction
material is Surlyn 1705. Surlyn used to form the friction is a difficult
material to
incorporate antimicrobial agents therein because of the high temperatures
associated
with producing and forming Surlyn and abrasive granules. In a preferred
embodiment
to of the present invention, antimicrobial agents can be incorporated into the
pallet body
and migrate into the friction material. The antimicrobial agent incorporated
into the
pallet body is characterized in that the agent moves from areas of high
concentrations
of agent to low concentrations of agent. The antimicrobial additive chosen can
be
essentially insoluble in water which can prevent any leaching of the compound
during
use.
By controlling the amount of antimicrobial agent incorporated into the pallet
body, migration of antimicrobial agent from the pallet body into the friction
material is
accomplished while maintaining the structural integrity of the pallet body.
Surprisingly,
even when different polymeric materials are used for the friction surfaces and
pallet
2o body, the selected antimicrobial agent migrates across the interface
between the pallet
body and the friction surface into the friction surface when incorporated
using the
method described herein. Incorporating an appropriate amount of antimicrobial
agent
into the pallet body is important. High concentrations of antimicrobial agent
incorporated into the pallet can result in degradation of the physical
properties of the
polymer composing the pallet body. Low concentrations of antimicrobial agent
incorporated into the pallet body minimize the migration of antimicrobial
agent into the
friction material. The appropriate concentration range of antimicrobial agent
in the
pallet body is carefully chosen to effectively provide nontoxic, antimicrobial
protection
to the pallet without sacrificing desirable physical properties of the polymer
used to
3o form the pallet body.
Incorporating antimicrobial agent into the polymer during manufacture of the
pallet requires care because of the high temperatures and varying physical
parameters
involved. Organic antimicrobial agents typically have a vaporization point
less than the
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temperatures involved during manufacture of the polymer. For example, 5-chloro-
2-
(2,4- dichlorophenoxy)phenol has a range of liquid phase from about
57°C to about
74°C and a vaporization point of about 204°C, whereas the
temperatures associated
with forming plastic are typically above 204°C. If antimicrobial agent
was introduced
into the polymer during manufacture, the agent typically vaporized and did not
become
incorporated into the polymer. Alternatively, the antimicrobial agent could
crosslink
with the polymer. Crosslinking of the antimicrobial agent with the polymer is
undesirable because the physical properties of the polymer can be degraded.
Furthermore, crosslinking prevents the migration of antimicrobial agent
through the
polymer of the pallet body and eventually into the friction surfaces through
the
interface of the pallet body. The antimicrobial agent in concentrate pellet
form can be
added as a component to the mixture comprising the synthetic polymeric
material in a
ratio which results in a final concentration of active ingredient of from
about 0.005
parts to about 2.0 parts by weight. The active antimicrobial biocidal or
biostatic agent
preferably comprises from about 0.15 parts to about 0.25 parts by weight of
the
synthetic polymer into which the agent is incorporated. The semi-IPN
formulation
synergistically provides the ability to reduce temperatures during manufacture
or
production such that biocides can be incorporated into the plastic shipping
container.
By combining antimicrobial agent pellets from a master batch production with
other polymer pellets, the resulting polymer in the pallet body that is formed
has a
known concentration of antimicrobial agent. A range of from about 0.1 parts to
about
0.5 parts by weight of antimicrobial agent in the resulting polymer is
preferred. The
preferable range of antimicrobial agent incorporated into the polymer is from
about
0.15 parts to 0.25 parts by weight, based on the weight of the total
composition.
Because of the encapsulation of the antimicrobial agent in pellet form, the
antimicrobial
agent can survive the heating process and can be incorporated into the
amorphous
zones of the polymer. The characteristics of the antimicrobial agent allow the
agent to
migrate through the polymer to the surface of the pallet body from the
amorphous
zones until equilibrium of the agent's internal vapor pressure is reached. As
the
antimicrobial agent on the surface of the pallet is removed by friction or
other means,
more antimicrobial agent will move to the surface until the agent's internal
vapor
pressure is once again at equilibrium. Normally the antimicrobial agent melts
at
approximately 66°C, and loses its biocidal properties at high
temperatures.
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The present invention provides water-based coatable antimicrobial
compositions that can be applied to a suitable plastic container to provide
long lasting
protection from the growth of any of a variety of microbes such as mold,
mildew, algae,
fungi, and the like. The antimicrobial compositions of the invention may be
applied as a
liquid over a plastic container and, upon drying, will form protective and
adherent
polymeric coatings which slowly release biocide to the surrounding substrate
for
extended periods of time. The polymeric coatings of the invention may be
easily
removed from the substrate (e.g., by alkaline washing) but are capable of
remaining on
the substrate even after exposure to significant and even continuous warm
water rinsing
l0 for prolonged periods of time. The semi-IPN formulation synergistically
provides the
ability to increase surface energy such that biocides can be effectively
coated onto
plastic shipping containers.
Mildewcides are known in the art and are disclosed in U.S. Patent No.
5,585,407.
It should be understood that the above described compositions and processes
are
not limiting. Modifications can be made to the formulation and process in
various
embodiments of the invention. While the present invention article can be
described as
a pallet, the present invention is not intended to be limited to pallets and
may be applied
to containers having diverse designs.
2o It should be understood that any of the above described embodiments may be
suitably combined with one another. The present invention discloses the
simultaneous
incorporation, using inert gases, of thermosetting monomers into
thermoplastics and
their foaming. These monomers can be crosslinked at any point during
processing or
subsequently, to improve the properties of the foamed structure, with the
thermoplastic
acting as the continuous phase or matrix. We have found the use of thermally
decomposable and organic physical blowing agents in some
thermoplastic/thermoset
systems to be advantageous. Other desirable effects or properties found are
the
reinforcement of the foam with crosslinked monomers, the increased miscibility
of the
monomer in the matrix, the microencapsulation effect observed and the increase
surface
compatibility with other foams, skin layers, adhesives, liners or substrates.
These
thermoplastic/thermoset foams can be advantageous in the cured and uncured
state.
Objects and advantages of this invention are further illustrated by the
following
examples, but the particular materials and amounts thereof recited in these
examples, as
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well as other conditions and details, should not be construed to unduly limit
this
invention.
Effect of Epoxy Component on Shear Viscosity - Shear Rate Behavior
Rheological data shown below in Table 1 were acquired using an Instron
capillary rheometer (Instron Corp., Canton, MA) to demonstrate the influence
of
uncured epoxy on the viscosity. The capillary had a length of 2.032
centimeters and a
diameter of 0.055 centimeter with a die aspect ratio L/D of 37. The experiment
was
conducted at 195° C at speeds ranging from 0.127 centimeter per minute
to 20.32
to centimeters per minute. The data were corrected using Rabinowitsch
correction factor
to account for the velocity gradient at the die wall for non-Newtonian fluids.
A die
entrance effect (Bagley correction) was not done. This effect was negligible
due to the
long die aspect ratio.
Table 1. Shear Rate - Shear Viscosity Data
Sample Shear Rate Shear Viscosity (Kg
(s 1) m 1 s 1))
PPl (100%) 63.775 1278.2
159.44 517.24
318.87 308.9
637.75 191.24
1594.4 103.46
3188.7 63.136
6377.5 37.4482
12755 22.599
25510 13.93
PP1 (90%)/Epoxy 54.595 946.64
(10%)
136.49 343.5
272.97 210.7
545.95 152.95
1364.9 92.463
2729.7 64.677
5459.5 41.083
10919 24.924
21838 14.777
Table 1 shows that in the 100-1000 s 1 shear rate region, which is normally
encountered
during extrusion compounding of thermoplastics, addition of epoxy reduced the
shear
viscosity of the polyolefin (PPl). Thus one of the processing advantages of
the present
pallet formulations was the decrease in viscosity during compounding in
standard
2o mixing equipment such as screw extruders. The viscosity reduction enabled
additives
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such as flame-retardants, fillers, blowing agents, etc to be added at reduced
temperatures, which can reduce both material processing and energy costs.
Process for In'Lection Moldin~of Curable Polymeric Compositions
An injection molding machine (Engel, Guelph, Ontario, Canada) was utilized to
make plate, bar, and disk specimens for mechanical property measurements. The
injection molding machine included a 136 metric tons press (molding machine)
with a
30-mm injection unit along with Sterlco (Sterling, Inc., Milwaukee, WI) mold
temperature controllers and a multi-cavity mold. The mold had a cold runner
melt
delivery system. Standard processing conditions were used for all samples.
Average
melt temperature was set at 199° C, while barrel temperature set-points
were 199° C,
199° C, 199° C, and 177° C at the rear zone. Shot size
was set at 57.9 mms. Injection
velocity was set at 100 millimeters per second with switch over to hold by
position at 8
millimeters. The resultant fill pressure was recorded at 3.31 x 106 kilogram
per meter
per second, hydraulic pressure. Hold pressure (hydraulic) was set at 1.38 x
106
kilogram per meter per second. Bold time was set for 3.0 seconds with a 30-
second
mold cooling time. Elapsed fill time was recorded at 0.61 seconds.
Backpressure was
set at 3.45 x 105 kilogram per meter per second with screw speed set at 40
percent of
system speed. Screw recovery time average was 15.6 seconds. Total cycle time
was
2o recorded at 41.5 seconds.
Examples
Example 1-7 and Comparative Examples C1 and C2
Formulation of Curable Polymeric Compositions
Curable polymeric compositions for pallets and containers were compounded in
a 33-mm co-rotating twin-screw extruder (Sterling Extruder Corporation,
Plainfield,
New Jersey) using the components and amounts (in parts by weight) shown in
Table 2.
The extruder had a length to diameter (L/D) ratio of 24:1, multiple feeding
ports, and
was capable of compounding plastics/additives in the form of pellets and
powders and
output either as film strands or pellets in a single pass. Two volumetric
feeders
(Accurate Dry Materials Feeders, Whitewater, Wisconsin) were used to feed the
additives into the extruder. Liquids such as uncured epoxy liquid were fed
separately
via a variable speed pump (Zenith Pumps, Sanford, North Carolina). The
compounding
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temperature range from hopper to die was 50° C to 200° C. Screw
speed was 250
revolutions per minute. Die output rate was 5897 grams per hour. The extrudate
coming out from the die was pelletized and dried for several days at room
temperature.
Table 2. Polymeric Compositions
Example* PP1 PP2 Epoxy FR FillerMPP BA
1 73.1 0 12.9 14 0 0 0
2 0 73.1 12.9 14 0 0 0
3 62.9 0 11.1 14 10 2 0
4 0 62.9 11.1 14 10 2 0
5 (Low) 71.4 0 12.6 14 0 0 2
6 (High) 71.4 0 12.6 14 0 0 2
7 73.1 0 12.9 14 0 0 0
C1 100 0 0 0 0 0 0
CZ 0 100 0 0 0 0 0
Table 2 above shows typical plastic container compositions in parts by weight.
Detail
material information is given below:
to PPl (in pellet form): propylene-ethylene random copolymer having low
ethylene
content '
(available as ESCORENETM PP7033N from ExxonMobil
Chemical, Houston, TX)
PP2 (in pellet form): propylene-ethylene random copolymer having high ethylene
content
(available as ESCORENETM PP7032N from ExxonMobil
Chemical, Houston, TX)
Epoxy (in liquid form): Uncured diglycidyl ether of bisphenol-A (available as
EPONTM
828 from Shell Chemicals, Houston, TX)
FR (in powder form): nitrogen/phosphorus-based flame retardant (available as
EXOLITTM AP750 from Clariant, Charlotte, NC)
MPP (in pellet form): malleated polypropylene (available as EPOLENETM 63003
from
Eastman Chemicals, Kingsport, TN)
Filler (in powder form): mica (aluminosilicate) having an average particle
size of 5
micrometers (available from Micro-Lite, Inc., Chanute,
Kansas)
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BA (in pellet form): azo dicarbonamide blowing agent in polyethylene base (30
wt %
percent), available from Ampacet, Cincinnati, OH.
Low: Activation of blowing agent (BA) at low temperature (200° C)
High: Activation of BA at high temperature (220° C)
* Curing agent for the epoxy was radiation-activated triarylsulfonium
hexafluoro-
antimonate salt (available as SarCatTM SR1010 from Sartomer Company, Exton,
PA),
except for Example 7 where the curing agent was heat-activated dicyandiamide
(DiCyTM, available from Air Products and Chemicals, Allentown, PA)
to Examples 8-14 and Comparative Examples C3 and C4
Thermal Expansion and Contraction Evaluations:
Molded specimens were made according to the injection molding process above
using the compositions in Table 2 and evaluated for thermal expansion and
contraction
according to ASTM Standard Test Method E831-93 for linear thermal expansion
and
15 contraction using a thermo mechanical analyzer (Perkin Elmer Corporation,
Norwalk,
Connecticut). For the expansion evaluations, specimens were heated at
10° C per
minute from -50° C to 100° C. For the contraction evaluations
the samples were cooled
at 10° C per minute from 100° C to -50° C. The applied
force was 50 x 10-3 kilogram
per meter per second while Helium gas was used as the purge gas. For each
2o formulation, five samples were evaluated to obtain average expansion
coefficient/total
expansion and average contraction coefficient/total contraction data. The
results are
shown in Table 3.
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CA 02464047 2004-04-19
WO 03/045801 PCT/US02/35499
M
d-N O M N M
U U O in cV N
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M .~ N .~: M M
U U ~n ~n N N
M N
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CA 02464047 2004-04-19
WO 03/045801 PCT/US02/35499
As the data of Table 3 show, the compositions of Examples 8-14 (the
compositions of Examples 1-6) had lower values for both expansion and
contractions
relative to Comparative Examples C3 and C4 (Comparative Examples C1 and C2
(polyolefins alone)). In some compositions such as Examples 3 and 4, the
difference
between expansion and contraction values was almost zero. The benefit of the
reduced
thermal expansion/contraction was that stability in automated injection
molding
equipment was ensured. Also, dimensional integrity of any container or pallet
made
from these compositions can be maintained.
Flexural Moduli Evaluations:
to Injection-molded bars (12.7 centimeters long by 1.27 centimeters wide by
0.635
centimeter thick) made as described above were evaluated for flexural moduli
using
ASTM D 790-89 Test Method I (three-point loading system utilizing center
loading on
a simply supported beam). For the evaluation, a Sintec 20 Computerized Testing
Machine (MTS Corporation, Eden Prairie, Minnesota) was used. The load cell
used
15 was 45.26 kilograms, while the crosshead speed was 0.279 centimeters per
minute.
The resulting flexural modulus data is shown in Table 4.
Table 4. Flexural Modulus of Molded Compositions
Exam le 8 9 10 11 14 C3 C4
Composition Example 1 2 3 4 7 C 1 C2
Flexural Modulus (MPa)1.66 1.62 2.09 2.10 1.73 1.42 1.06
The data of Table 4 show the average flexural moduli obtained. The results
show that
2o the presence of cured epoxy, flame retardant, and filler, enhanced the
flexural strength
of the molded specimens of Examples 8-14 (made from compositions of Examples 1-
7)
relative to Comparative Examples C3 and C4 (made from compositions of
Comparative Examples Cl and C2 with polyolefins only). Samples of Examples 12
and 13 (made from composition Examples 5 (Low) and 6 (High)) were not
evaluated
25 for flexural modulus.
Izod and Falling Dart Impact Strength Evaluations:
Injection molded bars made as described above were evaluated for Izod and
falling dart impact strength. The Izod impact test was performed by Aspen
Research
3o Corporation, White Bear Lake, Minnesota. Samples were notched according to
ASTM
D256 by Aspen Research Corporation. Prior to evaluation, notched samples were
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WO 03/045801 PCT/US02/35499
conditioned for 40 hours at 23° C and 59% relative humidity according
to the test
method. Samples were ran on the lowest pendulum scale, which was equal to
0.2883
meters kilogram full scale. For the falling dart impact evaluation, the
reference test
methods were ASTM D5628-96 and D3763-99. The test was done using Dynatup
Impact Testing Systems (Dynatup General Research Corporation, Santa Barbara,
California). The load used was 27.7 kilograms, while the Tup diameter was
0.127
centimeters. The samples were in the form injection-molded plates of dimension
10.16
centimeters long by 10.16 centimeters wide by 0.64 centimeter thick. The
resulting
impact strength data is shown in Table 5.
l0 Table 5. Notched Izod Impact Strength and Falling Dart Impact Strength of
Molded
Compositions
Example 8 9 10 11 14 C3 C4
Composition
1 2 3 4 7 C 1 C2
Example
Notched Izod 35.8 46.8 52.3 71.8 36 87 145
Impact 6 0 7
Strength (J/m) . . .
Falling Dart 48.2 47.6 44.2 56 47 87 88
Impact 2 4 8 4
Strength (J) . . . .
The average impact strengths shown in Table 5 confirmed that the impact
strengths of
Examples 8-14 (made from compositions of Examples 1-7) were below those of
Comparative Examples C3 and C4 (made from composition Comparative Examples C 1
and C2 with polyolefins only), which was in agreement with the flexural
modulus
results on Table 4. Typically, when flexural modulus is higher, it is expected
that
impact strength is lower. The impact strengths of Examples 8-14 were
acceptable, and
modification in the blend ratios was expected to increase impact strengths.
Samples of
2o Examples 12 and 13 (made from composition Examples 5 (Low) and 6 (High))
were
not evaluated for impact strength.
Fire Resistance Evaluations:
For the evaluation, ASTM Standard Test Method E1354-97 was followed for
heat and visible smoke release for materials and products using an oxygen
consumption
calorimeter known commonly as cone calorimeter. The heat and visible smoke
release
were useful parameters for the assessment of fire hazards. The procedures
followed
were as described in the test method. For each molded composition prepared as
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WO 03/045801 PCT/US02/35499
described above, five different samples, each of dimension 10.16 centimeters
long by
10.16 centimeters wide by 0.64 centimeter thick, were evaluated. The specimen
orientation was horizontal with spark igniter using 35 x 103 Watt per square
meter
exposure. The resulting fire resistance evaluation data is shown in Table 6.
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CA 02464047 2004-04-19
WO 03/045801 PCT/US02/35499
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CA 02464047 2004-04-19
WO 03/045801 PCT/US02/35499
The data of Table 6 show that Examples 8, 9, 10, 11, and 14 (made from
compositions of Examples 1, 2, 3, 4, and 7 performed best in reducing the
hazard in a fire situation when compared to Comparative Examples C3 and C4
(made from compositions of Comparative Examples C1 and C2 with
polyolefins only) because the heat release rate was a direct measure of the
intensity of the fire. These results indicated that a container made with
these
compositions would pass the UL 2335 protocol. Samples of Examples 12 and
13 (made from compositions of Examples 5 (Low) and 6 (High)) were not
available for fire resistance testing.
Tensile Property Evaluations:
Molded compositions prepared as described above were made into a standard
dumbbell shape with the dimensions of 3.81 centimeter long by 1.59 centimeters
wide
at end by 0.48 centimeter wide at center by 0.32 centimeter thick. The tensile
moduli
were determined following ASTM Test Method D 638-99. For the evaluations, an
Instron Corporation (Canton, Massachusetts) Series X Automated Testing System
was
used with a crosshead speed of 5.08 centimeter per minute at 23° C and
41 % relative
humidity. For each molded composition, five samples were evaluated to obtain
an
average modulus. The results are shown in Table 7.
Table 7. Tensile Moduli of Molded Compositions
Example 8 9 10 11 12 13 14 C3 C4
CEmamii~ 1 2 3 4 5 (Low)6 7 C1 C2
n
Hi
h)
Tensile
Modulus 1156.91273.71506.41372.51080.2987.4 1184.61136.7931.9
(MPa)
The data show that higher modulus was obtained for Examples 8-14 (made from
compositions of Examples 1-7) relative to Comparative Examples C3 and C4 (made
from compositions of Comparative Examples C 1 and C2 with polyolefin only).
Overlap Shear Strength Evaluations:
The surface properties of the molded container compositions with respect to
heat and adhesives bonding was evaluated by determining overlap shear
strengths. For
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both bonding tests, molded bars 12.7 centimeters long by 1.27 centimeters wide
by 0.32
centimeter thick, prepared as described above were used. Prior to bonding, the
surfaces
of the bars were cleaned by rubbing with a piece of dry cloth. Pairs of
samples were
heat-bonded at 200° C using a hot plate, or they were adhesive-bonded
using CA-4
Cyanoacrylate Adhesive (available from 3M, St. Paul, MN). A bond area 2.54 cm
long
and 1.27 cm wide was made for each sample. Holding the bonded samples under
pressure for at least a day prior to overlap shear measurement ensured uniform
and firm
bonds. Samples were evaluated with Instron Corporation (Canton, Massachusetts)
Series X Automated Testing System. A total of five samples were evaluated to
obtain
an aver age value of overlap shear strength for each composition. The results
are shown
in Table 8.
Table 8. Overlap Shear Strengths (Adhesive and Heat Bonding) of Molded
Compositions
Exam le 8 9 10 11 12 13 14 C3 C4
Composition 1 2 3 4 5 6 7 C C2
1
Example (Low) (High)
Heat Bonding1.92 1.87 1.99 2.31 1.74 1.77 2.06 2.61 2.4
(MPa)
Adhesive
Bonding 1.25 1.36 0.47 0.47 0.4 0.33 1.33 0.17 0.42
(MPa)
The data of Table 8 show that adhesive bond strengths comparable to heat bond
strengths were obtained for Examples 8, 9, and 14. This suggested that
standard
adhesives can be used to adhere identification and tracking labels to
containers as well
as for bonding container components together when using the molded composition
of
the present invention.
Examplesl5-19 and Comparative Examples C5 and C6
Coefficient of Static Friction Determination:
Friction surfaces were desired on pallets because loads can fall off pallets,
stacks of pallets can tip over, and pallets can fall off fork trucks without
sufficient
friction on their surfaces. The coefficient of static friction values of
several friction
materials useful in the present invention were determined as well as those of
comparative polypropylene in film form and a pine wood pallet. The film was
prepared
by extruding Comparative Example C1 composition into a 0.36 mm thick film
form.
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The wood pallet was a commonly available pallet. The friction material (anti-
slip film)
was inserted into the mold and then the curable polymeric composition
containing
epoxy of Example 1 was injected into the mold as described above. This process
of
sequentially adding the friction material during the injection molding process
was an
in-mold lamination process. The reduced viscosity provided by the epoxy-
containing
composition aided in the process of laminating the friction material by a)
minimizing
the chance that the friction material would shift during the injection molding
process,
and b) by minimizing the tendency of the friction particles to become imbedded
into the
substrate, which would reduce the effectiveness of the friction material. The
friction
to material evaluated for Example 15 was prepared in the same manner as
Example 2 in
U.S. Pat. No. 6,258,201. Aluminum oxide particles with an average particle
size of 400
micrometers (ANSI Grade 46) were passed through a thermal sprayer and embedded
into a 0.356 mm thick Surlyn extruded film. The friction material evaluated
for
Example 16 was prepared in the same manner as Example 2 in U.S. Pat. No.
6,258,201
except that 400 micrometer particle size quartz particles (50 mesh obtained
from US
Silica Company, Berkely Springs, WV) were embedded in the Surlyn film. The
friction
material for Example 17 was also prepared in the same manner as Example 2 in
U.S.
Pat. No. 6,258,201 except that 1000 micrometer particle size ceramic spheres
(Carbo
PropTM 20140, obtained from Carbo Ceramics, Irving, TX) were embedded into the
2o Surlyn film.
The friction material evaluated for Example 18 was prepared by
microreplicating a thermoplastic rubber sheet with cylindrical stems that had
a stem
density of 50 stems per square centimeter, a substrate thickness of 0.127 mm,
a stem
height of approximately 0.94 mm, a stem diameter of 0.44 mm, and a stem
spacing of
l.4mm. The friction material consisted of the resulting stem layer material
(described in
WO 9732805, but with none of the mechanical fastener layers were formed). The
stem
layer material was formed from impact copolymer resin available from Shell
Polypropylene Company, Houston, Texas under the designation SRD7-560.
The friction material evaluated for Example 19 was prepared by miroreplicating
a 0.356 mm thick Surlyn sheet with a pyramidal shape (made according to U.S.
Pat.
No. 5,897,930 and U.S. Pat. No. 5,152,917). In particular, Surlyn was extruded
onto an
array outlined in FIG. 18 of U.S. Pat. No. 5,152,917.
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Coefficient of static friction values were determined under wet, dry, and oily
conditions. The oil used was vegetable oil.
The following friction materials were evaluated: in Example 15, 0.356 mm thick
Surlyn
film coated with 400 micrometer average diameter aluminum oxide particles
(made
according to U.S. Pat. No. 6,258,201); in Example 16, 0.356 mm thick Suryln
film
coated with 400 micrometer average diameter quartz particles (made according
to U.S.
Pat. No. 6,258,201); in Example 17, 0.356 mm thick Surlyn film coated with
1000
micrometer average diameter ceramic spheres (made according to U.S. Pat. No.
6,258,201); in Example 18, 1.02 mm thermoplastic rubber sheet with
microreplicated
l0 surface of cylindrical shape (made according to WO 9732805); and in Example
19,
0.356 mm thick Surlyn microreplicated surface of pyramidal shape (made
according to
U.S. Pat. No. 5,897,930 and U.S. Pat. No. 5,152,917). Coefficient of static
friction
values were determined under wet, dry, and oily conditions. The test method
used was
ASTM C1028-89. The equipment used was ASM 725 American Slip Meter (available
from American Slip Meter, Inc., Englewoods, Florida) with NEOLTTETM (synthetic
rubber soling available as CROWN NEOLITE from Goodyear Tire & Rubber Co.)
pads. This was a horizontal drag meter type, which measured the horizontal
force when
the unit was moved across the surface of the sample. The results are shown in
Table 9.
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Table 9. Coefficients of Static Friction of Surfaces for Shipping and Storage
Containers
Example Material ASM 725
American
Slip
Meter
-
Neolite
Pads
Dry Wet Oil
C5 Polypropylene* 0.56 0.57 0.22
C6 Wood (rough 0.91 0.82 0.78
pine)
15 Aluminum Oxide 0.90 0.94 0.95
16 Quartz 0.90 0.91 0.63
17 Ceramic spheres0.84 0.81 0.51
18 Microreplicated0.90 0.75 0.18
thermoplastic
rubber with
cylindrical
shape
19 Microreplicated0.80 0.71 0.61
Surlyn with
pyramidal shape
* polypropylene was representative of commodity plastic surfaces including
polyolefins
The data in Table 9 show that the coefficient of friction was tailorable such
that a
shipping container having these surfaces was not so abrasive that it abraded
or damaged
the contents on or in the shipping container. For example, aluminum oxide was
more
abrasive than quartz, which was more abrasive than ceramic spheres. Blends of
particle
size, shape, durability, and abrasiveness were useful. It should be noted that
it was
preferred to have the friction material compatible with recycling, including
materials
compatibility and equipment capability (i.e. does not damage the equipment via
abrasive action). It is a preferred embodiment that the particles are of such
size
(typically greater than 100 micrometers and up to 5000 micrometers or even
larger) that
they can be readily captured upstream (for example, by filtration during
recycling) in
the process sequence to prevent damage to barrels, screws, dies, and or
tooling, and
prevent contamination of the recycled composition, which could cause a loss in
strength or durability.
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These materials and methods can be used by those skilled in the art to make
containers and pallets using conventional plastic shaping procedures such as
injection
molding, extrusion, thermoforming, blow molding, rotational molding, and the
like.
Various modifications and alterations of this invention will become apparent
to
those skilled in the art without departing from the scope and intent of this
invention,
and it should be understood that this invention is not to be unduly limited to
the
illustrative embodiments set forth herein.
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