Note: Descriptions are shown in the official language in which they were submitted.
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THERMOPLASTIC COMPOSITIONS, METHODS, APPARATUS, AND USES
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims benefit to U.S. Patent Application No.
16/904,819
filed June 18, 2020, which is a continuation-in-part of U.S. Patent
Application No.
15/965,363, filed on April 27, 2018, which claims the benefit of U.S.
Provisional Patent
Applications No. 62/492,054, filed April 28, 2017, and U.S. Provisional Patent
Application
No. 62/500,262, filed May 2, 2017, the entire contents of each of which are
hereby
incorporated by reference and the priority of which are hereby claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The accompanying drawings are part of this disclosure and are
incorporated into
the specification. The drawings illustrate example embodiments of the
disclosure and, in
conjunction with the description and claims, serve to explain various
principles, features, or
aspects of the disclosure. Certain embodiments of the disclosure are described
more fully
below with reference to the accompanying drawings. However, various aspects of
the
disclosure may be implemented in many different forms and should not be
construed as being
limited to the implementations set forth herein. Like numbers refer to like,
but not
necessarily the same or identical, elements throughout.
[0003] FIG. 1 is an isometric top view of a screen element, according to an
embodiment.
[0004] FIG. 1A is a top view of the screen element shown in FIG. 1,
according to an
embodiment.
[0005] FIG. 1B is a bottom isometric view of the screen element shown in
FIG. 1,
according to an embodiment.
[0006] FIG. 1C is a bottom view of the screen element shown in FIG. 1,
according to an
embodiment.
[0007] FIG. 2 is an enlarged top view of a break out portion of the screen
element shown
in FIG. 1, according to an embodiment.
[0008] FIG. 3 is an isometric view of an end subgrid showing screen
elements prior to
attachment to the end subgrid, according to an embodiment.
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[0009] FIG. 3A is an exploded isometric view of the end subgrid shown in
FIG. 3 having
the screen elements attached thereto, according to an embodiment.
[0010] FIG. 4 illustrates an example screening assembly that was generated
from
screening members and subgrid structures as described below with reference to
FIGS. 1 to
3A, according to an embodiment.
[0011] FIG. 5 illustrates results of actual field testing of screening
assemblies, according
to an embodiment.
[0012] FIG. 6A illustrates a top view of a screen element that includes
screening
openings having rounded corners, according to an embodiment.
[0013] FIG. 6B illustrates a side view of the screen element of FIG. 6A,
according to an
embodiment.
[0014] FIG. 6C illustrates a top exploded view of a surface region of the
screen element
of FIG. 6A showing screening openings having rounded corners, according to an
embodiment.
[0015] FIG. 7A illustrates a top view of a screen element that includes
transversely
aligned screening openings, according to an embodiment.
[0016] FIG. 7B illustrates an exploded top view of a portion of the screen
element of
FIG. 7A showing details of transversely aligned screening openings, according
to an
embodiment.
[0017] FIG. 7C illustrates a top view of a screen element that includes
longitudinally
aligned screening openings, according to an embodiment.
[0018] FIG. 7D illustrates an exploded top view of a portion of the screen
element of
FIG. 7C showing details of longitudinally aligned screening openings,
according to an
embodiment.
[0019] FIG. 8A illustrates cross sectional view of a surface element having
a thickness of
approximately 0.007 inch, according to an embodiment.
[0020] FIG. 8B illustrates cross sectional view of a first surface element
having a
thickness of approximately 0.005 inch, according to an embodiment.
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[0021] FIG. 8C illustrates cross sectional view of a second surface element
having a
thickness of approximately 0.005 inch, according to an embodiment.
[0022] FIG. 9 illustrates a top view of a screen element and frame assembly
with various
regions that may be laser welded to an underlying subgrid, according to an
embodiment.
[0023] FIG. 10 illustrates a vibrational amplitude profile of a screen
element that is
partially bonded to a subgrid, according to an embodiment.
DESCRIPTION OF EMBODIMENTS
[0024] This disclosure generally relates to compositions, apparatus,
methods, and uses of
thermoplastic polyurethanes (TPU). Disclosed embodiment TPU compositions may
be used
in injection molding processes to generate screening members for use in
vibratory screening
machines. Vibratory screening machines provide a capability to excite an
installed screen
such that materials placed upon the screen may be separated to a desired
level. Oversized
materials are separated from undersized materials. The disclosed compositions
and screening
members may be used in technology areas related to the oil industry, gas/oil
separation,
mining, water purification, and other related industrial applications.
[0025] Disclosed embodiments provide screening members that satisfy
demanding
requirements, such as: fine openings of approximately 43 p.m to approximately
100 p.m that
effectively screen similar-sized particles; large area screens on the order of
several square
feet having large open screening area on the order of 30% to 35%; screens that
are thermally
and mechanically stable that can withstand severe conditions during operation,
such as
compression loading (e.g. forces from 1,500 lbs. to 3,000 lbs. applied to
edges of screening
members and vibrational accelerations of up to 10 G) and loading of high
temperature
materials (e.g. between 37 C and 94 C), with significant weight loads and
severe chemical
and abrasive conditions of the materials being screened.
[0026] Disclosed embodiment materials and methods provide a hybrid approach
in which
small screen elements are micro-molded using disclosed TPU materials to
reliably generate
fine features on the order of 43 p.m to approximately 100 p.m to yield screen
elements having
large open screening area. The disclosed TPU materials, as discussed in more
detail below,
include embodiments that feature optimized amounts of filler, heat stabilizer,
and flow agent
as additives to the appropriate thermoplastic polyurethane. These additives in
turn allow for
the small screen elements to be attached securely, such as via laser welding,
to the subgrid
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structures to provide mechanical stability that may withstand the large
mechanical loading
and accelerations mentioned above. For example, glass fibers may be used as
filler material,
which allow for strengthening of the TPU material and in turn allow the screen
elements to be
securely attached to the subgrid structures with increased structural
stability. However,
addition of large amounts of glass fibers may lead to increased difficulty in
laser welding,
given that the refractive properties of the glass provide obstacles to the
laser systems. Any
amount of additive will also necessarily require dilution of the thermoplastic
urethane.
Similarly, a minimal but effective amount of heat stabilizer should be added,
wherein the
additive should be of sufficient amount to allow the end structure to
withstand the addition of
high-temperature materials as described above.
[0027] As discussed in more detail below, the amount of additives in the
disclosed TPU
compositions may also be varied based on the desired thickness T of the screen
element
surface elements, as discussed in detail in U.S. Patent Application Nos.
15/965,195 and
62/648,771, which are hereby incorporated by reference herein. For example, as
discussed in
U.S. Patent Application No. 15/965,195 in Paragraphs [00366] to [00373] and
corresponding
Tables 1 to 4, the thickness T of the screen element surface elements may be
varied in an
effort to maximize the percentage of open area on the overall screen assembly,
which allows
for increased effectiveness of the screening assembly when in use.
[0028] A plurality of these optimized subgrid structures may then be
assembled into
screening structures having large surface areas, on the order of several
square feet. The
screen assemblies based on the disclosed TPU compositions may be utilized, for
example, in
the manner described in U.S. Patent Application Nos. 15/965,195 and
62/648,771. For
example, as outlined in U.S. Patent Application No. 15/965,195 in Paragraphs
[0017] to
[0021] of the Specification, the grid framework based upon the disclosed TPU
compositions
may provide the required durability against damage or deformation under the
substantial
vibratory load burdens it is subjected to when secured to a vibratory
screening machine. The
subgrids, when assembled to form the complete screen assembly, are strong
enough not only
to withstand the forces required to secure the screen assembly to the
vibratory screening
machine, but also to withstand the extreme conditions that may be present in
the vibratory
loading. As discussed in detail in Paragraphs [00280] to [00282] of the
Specification of U.S.
Patent Application No. 15/965,195, a method of securing the screen elements to
the subgrid
may include laser welding of the fusion bars arranged on the subgrids. The
disclosed TPU
compositions may therefore be utilized to create the referenced vibratory
screening apparatus,
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capable of withstanding the extreme conditions discussed herein and in U.S.
Patent
Application No. 15/965,195.
[0029] Screen assemblies based on disclosed TPU compositions may also be
configured
to be mounted on vibratory screening machines described in U.S. Patent Nos.
7,578,394;
5,332,101; 6,669,027; 6,431,366; and 6,820,748. Such screen assemblies may
include: side
portions or binder bars including U-shaped members configured to receive over
mount type
tensioning members, as described in U.S. Patent No. 5,332,101; side portions
or binder bars
including finger receiving apertures configured to receive under mount type
tensioning, as
described in U.S. Patent No. 6,669,027; side members or binder bars for
compression
loading, as described in U.S. Patent No. 7,578,394; or may be configured for
attachment and
loading on multi-tiered machines, such as the machines described in U.S.
Patent No.
6,431,366.
[0030] Screen assemblies and/or screen elements based on disclosed TPU
compositions
may also be configured to include features described in U.S. Patent 8,443,984,
including the
guide assembly technologies described therein and preformed panel technologies
described
therein. Still further, screen assemblies and screen elements based on
disclosed TPU
compositions may be configured to be incorporated into pre-screening
technologies,
compatible with mounting structures and screen configurations, described in
U.S. Patent Nos.
7,578,394; 5,332,101; 4,882,054; 4,857,176; 6,669,027; 7,228,971; 6,431,366;
6,820,748;
8,443,984; and 8,439,203. The disclosure of each of these patent documents,
along with their
related patent families and applications, and the patents and patent
applications referenced in
these documents, are expressly incorporated herein by reference in their
entireties.
Example Screen Embodiments
[0031] Screening members fabricated from thermosetting and thermoplastic
polymers are
described in the above referenced patent documents (i.e., U.S. Provisional
Patent Application
Serial Nos. 61/652,039 and 61/714,882; U.S. Patent Application No. 13/800,826;
U.S. Patent
No. 9,409,209; U.S. Patent No. 9,884,344; and U.S. Patent Application No.
15/851,099), the
disclosures of which are incorporated herein by reference in their entireties.
[0032] FIGS. 1 to 3A illustrate example embodiment screening members
generated by
injection molding processes using disclosed TPU compositions. FIGS. 1 to 1C
show an
embodiment screen element 416 having substantially parallel screen element end
portions 20,
and substantially parallel screen element side portions 22, that are
substantially perpendicular
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to the screen element end portions 20. Screen element 416 may include a
plurality of tapered
counter bores 470, which may facilitate extraction of screen element 416 from
a mold, as
described in greater detail in the above-referenced patent documents. Screen
element 416
may further include location apertures 424, which may be located at a center
of screen
element 416 and at each of the four corners of screen element 416. Location
apertures 424
are useful for attaching screen element 416 to subgrid structures, as
described in greater detail
below with reference to FIGS. 3 and 3A.
[0033] As shown in FIGS. 1 and 1A, screen element 416 has a screening
surface 13 that
includes solid surface elements 84 running parallel to the screen element end
portions 20 and
forming screening openings 86, as also shown in the close-up view of FIG. 2,
as described in
greater detail below.
[0034] FIGS. 1B and 1C show a bottom view of screen element 416 having a
first screen
element support member 28 extending between the end portions 20 and being
substantially
perpendicular to the end portions 20. FIG. 1B also shows a second screen
element support
member 30 perpendicular to the first screen element support member 28
extending between
the side edge portions 22, being approximately parallel to the end portions 20
and being
substantially perpendicular to the side portions 22. The screen element may
further include a
first series of reinforcement members 32 substantially parallel to the side
edge portions 22,
and a second series of reinforcement members 34 substantially parallel to the
end portions 20.
The end portions 20, the side edge portions 22, the first screen element
support member 28,
the second screen element support member 30, the first series reinforcement
members 32, and
the second series of reinforcement members 34, structurally stabilize the
screen surface
elements 84 and screening openings 86 during various loadings, including
distribution of a
compression force and/or vibratory loading conditions.
[0035] As shown in FIGS. 1B andl C, screen element 416 may include one or
more
adhesion arrangements 472, which may include a plurality of extensions,
cavities, or a
combination of extensions and cavities. In this example, adhesion arrangement
472 is a
plurality of cavity pockets. Adhesion arrangement 472 is configured to mate
with
complementary adhesion arrangements of a subgrid structure. For example,
subgrid structure
414 (shown in FIGS. 3 and 3A) has a plurality of fusion bars, 476 and 478,
that mate with
cavity pockets 472 of screen element 416, as described in greater detail below
with reference
to FIGS. 3 and 3A.
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[0036] As illustrated in FIG. 2, the screening openings 86 may be elongated
slots having
a length L along a first direction, and width W along a second direction,
separated by surface
elements 84 have a thickness T along the second direction. Thickness T may be
varied
depending on the screening application and configuration of the screening
openings 86.
Thickness T may be chosen to be approximately 0.003 inch to about 0.020 inch
(i.e., about 76
p.m to about 508 m), depending on the open screening area desired, and the
width W of
screening openings 86. In an exemplary embodiment, the thickness T of the
surface elements
may be 0.015 inch (i.e., 381 p.m). However, properties of disclosed TPU
compositions allow
formation of thinner surface elements, such as surface elements having a
thickness T of 0.007
inch (i.e., 177.8 p.m). The smaller the thickness, T, of the surface elements,
the larger the
screening area of the screen element. For example, a thickness T of 0.014 inch
will provide a
screen element that is about 10-15% open, while a thickness T of 0.003 inch
will provide a
screen element that is about 30-35% open, thus increasing open screening area.
[0037] As mentioned above, screening openings 86 have a width W. In
exemplary
embodiments, the width W may be approximately 38 p.m to approximately 150 p.m
(i.e.,
about 0.0015 to about 0.0059 inch) between inner surfaces of each screen
surface element 84.
The length-to-width ratios of the openings may be from 1:1 (i.e. corresponding
to round
pores) to 120:1 (i.e., long narrow slots). In exemplary embodiments, openings
may preferably
be rectangular and may have a length-to-width ratio of between about 20:1
(e.g. length 860
p.m; width 43 p.m) to about 30:1 (i.e., length about 1290 m, and width about
43 p.m). The
screening openings are not required to be rectangular but may be thermoplastic
injection
molded to include any shape suitable to a particular screening application,
including
approximately square, circular, and/or oval.
[0038] As described in greater detail below, for increased stability, the
screen surface
elements 84 may include integral fiber materials (e.g., glass fibers) which
may run
substantially parallel to end portions 20. Screen element 416 may be a single
thermoplastic
injection molded piece. Screen element 416 may also include multiple
thermoplastic injection
molded pieces, each configured to span one or more grid openings. Utilizing
small
thermoplastic injection molded screen elements 416, which are attached to a
grid framework
as described below, provides substantial advantages over prior screen
assemblies, as
described in greater detail in the above-referenced patent documents.
[0039] FIGS. 3 and 3A illustrate a process for attaching screen elements
416 to an end
subgrid unit 414, according to an embodiment. Screen elements 416 may be
aligned with end
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subgrid unit 414 via elongated attachment members 444 (of subgrid 414) that
engage with
location apertures 424 on an underside of the screen element 416 (e.g., see
Figures 1 to 1C).
In this regard, elongated attachment members 444 of subgrid 414 pass into
screen element
location apertures 424 of screen element 416. Elongated attachment members 444
of end
subgrid 414 may then be melted to fill tapered bores of screen element
attachment apertures
424, to thereby secure screen element 416 to the subgrid unit 414. Attachment
via elongated
attachment members 444 and screen element location apertures 424 is only one
method for
attaching screen member 416 to subgrid 414.
[0040] Alternatively, screen element 416 may be secured to end subgrid unit
414 using
adhesives, fasteners and fastener apertures, laser welding, etc. As described
above, fusion
bars 476 and 478, of subgrid 414 (e.g., see FIGS. 3 and 3A), may be configured
to fit into
cavity pockets 472 of screen element 416 (e.g., see FIGS. 1 to 3C). Upon
application of heat
(e.g., via laser welding, etc.), fusion bars, 476 and 478, may be melted to
form a bond
between screen element 416 and subgrid 414 upon cooling.
[0041] Arranging the screen elements 416 on subgrids (e.g., subgrid 414),
which may
also be thermoplastic injection molded, allows for easy construction of
complete screen
assemblies with very fine screening openings. Arranging screen elements 416 on
subgrids
also allows for substantial variations in overall size and/or configuration of
the screen
assembly 10, which may be varied by including greater or fewer subgrids or
subgrids having
different shapes, etc. Moreover, a screen assembly may be constructed having a
variety of
screening opening sizes or a gradient of screening opening sizes simply by
incorporating
screen elements 416 with the different size screening openings onto subgrids
and joining the
subgrids to form a desired configuration.
[0042] The screens described above with reference to Figures 1 to 3, and
disclosed in the
above-reference patent documents, have small screening openings suitable for
use as
screening members. The disclosed TPU compositions additionally allow these
screens to
perform effectively in each of the following key areas: structural stability
and durability;
ability to withstand compression type loading; ability to withstand high
temperatures;
extended commercial life despite potential abrasion, cuts, or tearing; and
fabrication methods
that are not overly complicated, time consuming, or error-prone.
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[0043] There is thus a need for improved TPU compositions having improved
chemical
properties that may be formed by injection molding into screening members and
screening
assemblies having improved physical properties.
[0044] Disclosed compositions generally include a TPU material, a heat
stabilizer
selected to optimize heat resistance of the composition, a flow agent selected
to optimize use
of the composition in injection molding, and a filler material selected to
optimize rigidity of
the resulting composite material. The filler may be included in an amount of
less than about
10% by weight of the TPU. In one embodiment, the filler is provided in an
amount of about
7% by weight of the TPU. In other exemplary embodiments, the filler is
provided in amounts
of less than about 7%, less than about 5%, or less than about 3%, of the
weight of the TPU.
[0045] One example of a filler material includes glass fibers. Glass fibers
may be
introduced in an amount that allows use of the composition in injection
molding, improves
rigidity of the composition upon hardening, increases temperature resistance
of the final
product, and yet does not preclude laser welding of the composition to other
materials.
[0046] An initial length of glass fibers may be between about 1.0 mm to
about 4.0 mm. In
an embodiment, glass fibers may have an initial length of about 3.175 mm
(i.e., 1/8 inch).
Glass fibers may also have a diameter of less than about 20 p.m, such as
between about 2 p.m
and about 20 m. In one exemplary embodiment, the glass fibers have a diameter
of between
about 9 p.m to about 13 p.m. In further embodiments, the glass fibers have a
diameter of
between about 10 p.m to about 14 p.m. In further embodiments, glass fibers may
have an
initial length of 1/8 inch or less. For example, glass fibers may have an
initial length of 1/8
inch, 1/16 inch, 1/32 inch, 1/64 inch, etc. In other embodiments, glass fibers
may have an
initial length that is in a range from approximate 200 p.m to approximately
800 p.m. After
processing, glass fibers may have a length that is considerably smaller than
the starting
length. For example, glass fibers may have a final length of less than 1 p.m.
In further
embodiments, glass fibers may have an initial length of approximately 4 mm and
may have a
final length after processing of approximately 0.5 mm.
[0047] The TPU material may be made from a low free isocyanate monomer
prepolymer.
In an example embodiment, the low free isocyanate monomer prepolymer may be
chosen to
be p-phenylene di-isocyanate. In further embodiments, other prepolymers may be
chosen.
The TPU may first be generated by reacting a urethane prepolymer with a curing
agent. The
urethane prepolymer may be chosen to have a free polyisocyanate monomer
content of less
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than 1% by weight. In further embodiments, the TPU material may be a methylene
diphenyl
di-isocyanate (MDI) or a toluene di-isocyanate (TDI) modified polyester
polyurethane. In
various embodiments, a modified polyester is a material in which side chains
have been
modified to increase hydrolysis resistance.
[0048] The resulting material may then be thermally processed by extrusion
at
temperatures of 150 C, or higher, to form the TPU polymer. The urethane
prepolymer may
be prepared from a polyisocyanate monomer and a polyol including an alkane
diol, polyether
polyol, polyester polyol, polycaprolactone polyol, and/or polycarbonate
polyol. In an
example embodiment, the curing agent may include a diol, a triol, a tetrol, an
alkylene polyol,
a polyether polyol, a polyester polyol, a polycaprolactone polyol, a
polycarbonate polyol, a
diamine, or a diamine derivative.
[0049] According to an embodiment, the heat stabilizer, mentioned above,
may be
included in an amount of about 0.1% to about 5% by weight of the TPU. The heat
stabilizer
may be a sterically hindered phenolic antioxidant. The sterically hindered
phenolic
antioxidant may be pentaerythritol tetrakis (3-(3,5-di-tert-buty1-4-
hydroxyphenyl)propionate)
(CAS Registry No. 6683-19-8). Optionally, an ultraviolet (UV) light stabilizer
may be
included. In some embodiments, the heat stabilizer will also serve as a UV
light stabilizer.
[0050] According to an embodiment, the flow agent, mentioned above, may be
included
in an amount of about 0.1% to about 5% by weight of the TPU. The flow agent
may be
chosen to be an ethylene steramide wax. The ethylene steramide wax may include
octadecanamide, N,N'-1,2-ethanediylbis (CAS Registry No. 110-30-5) and stearic
acid (CAS
Registry No. 57-11-4). In other embodiments, other flow agents may be chosen.
[0051] According to an embodiment, glass fibers, mentioned above, may have
a diameter
or width between about 2 to about 20 p.m, between about 9 to about 13 p.m, or
may have a
diameter or width about 11 p.m. The glass fibers may have an initial length of
between about
3.1 mm to about 3.2 mm. A final average length of the glass fibers, in a
hardened state after
injection molding, may be less than about 1.5 mm due to breakage of fibers
during
processing. In a final hardened state after injection molding, the fibers may
be characterized
by a distribution of lengths ranging from about 1.0 mm to about 3.2 mm, with
some fibers
remaining unbroken. In other embodiments, glass fibers may have initial and
final lengths
that are smaller. For example, glass fibers after processing may have an
initial length that is
1/8 inch, 1/16 inch, 1/32 inch, 1/64 inch, etc. In other embodiments, glass
fibers may have an
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initial length that is in a range from approximate 200 um to approximately 800
um. After
processing, glass fibers may have a length that is considerably smaller than
the initial length.
For example, glass fibers may have a final length of less than lmm, less than
1 um, etc.
[0052] Disclosed embodiments include methods of making and using TPU
compositions
suitable for use in injection molding of articles of manufacture having fine
pores.
Embodiment methods include reacting a TPU, a heat stabilizer, a flow agent,
and a filler
material, at a temperature greater than about 150 C, to generate a TPU
composition. In other
embodiments, a material may be generated by incorporating fewer components.
For
example, a composition may be generated that omits that heat stabilizer, omits
the flow agent,
omits the filler material, or that omits two or more of these components. The
filler may
include a glass fiber having a diameter of between about 2 um to about 20 m,
in an amount
selected to optimize rigidity of articles of manufacture molded from the TPU
composition.
The TPU may be polycarbonate TPU or may be a polyester or modified polyester
TPU. The
TPU may be a pre-polymer prior to the reacting step. The glass fiber may be
present in an
amount between about 1% to about 10% by weight of the TPU. In one embodiment,
the glass
fiber may be present in an amount of about 7% by weight of the TPU.
[0053] Articles of manufacture molded from compositions disclosed herein
are suitable to
be joined by various methods including laser welding. In this regard, the
resulting articles
may be laser welded to other articles, such as support structures.
[0054] Example articles of manufacture include screening members for
vibratory shaker
screens, as described above. Disclosed TPU material, described above, may then
be used in
an injection molding process to generate a screening member. In this regard,
the TPU
material may be introduced/injected into a suitably designed mold at an
elevated temperature.
The temperature may be chosen to be a temperature at which the TPU material
has a
sufficiently reduced viscosity to allow the material to flow into the mold.
Upon cooling, the
resulting solidified screening member may be removed from the mold.
[0055] The resulting screening member may be designed to have a plurality
of openings
having opening widths ranging from about 38 um to about 150 m. Screens with
such
openings may be used for removing particles from various industrial fluids to
thereby
filter/clean the fluids. Particles that are larger than widths of screening
openings may be
effectively removed. The desirable thermal properties of the TPU material
allows screening
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members made from the TPU material to effectively screen particles at elevated
temperatures
(e.g., service temperatures of up to about 82 to 94 C).
[0056] Characteristics of disclosed TPU compositions, and products
generated therefrom,
include temperature and flow characteristics that facilitate production of
very fine, high-
resolution structures using techniques such as injection molding. Resulting
end products also
have excellent thermal stability at elevated operating temperatures (e.g. up
to about 94 C).
Resulting structures also exhibit sufficient structural rigidity to withstand
compression
loading while maintaining small openings that allow for screening of micron-
scale particulate
matter. Structures generated from disclosed TPU materials also exhibit cut,
tear, and abrasion
resistance, as well as chemical resistance in hydrocarbon-rich environments
(e.g.
environments including hydrocarbons such as diesel fuel).
Thermoplastic Polyurethanes
[0057] Disclosed embodiments provide thermoplastic compositions including
polyurethanes, which are a class of macromolecular plastics known as polymers.
Generally,
polymers, such as polyurethanes, include smaller, repeating units known as
monomers.
Monomers may be chemically linked end-to-end to form a primary long-chain
backbone
molecule with or without attached side groups. In an example embodiment,
polyurethane
polymers may be characterized by a molecular backbone including carbonate
groups (-
NHCO2), for example.
[0058] While generally categorized as plastics, thermoplastic compositions
include
polymer chains that are not covalently bonded, or crossed linked, to one
another. This lack of
polymer chain crosslinking allows thermoplastic polymers to be melted when
subjected to
elevated temperatures. Moreover, thermoplastics are reversibly thermoformable,
meaning
that they may be melted, formed into a desired structure, and re-melted in
whole or in part at
a later time. The ability to re-melt thermoplastics allows optional downstream
processing
(e.g., recycling) of articles generated from thermoplastics. Such TPU based
articles may also
be melted at discrete locations by applying a heat source to a specific
location on an article.
In this regard, articles generated from disclosed TPU composition are amenable
to joining
using welding (e.g., laser welding) to effectively secure TPU-based screening
members to
suitable screening frames.
[0059] Disclosed TPU materials exhibit desirable properties under extreme
conditions of
temperature and harsh chemical environments. In exemplary embodiments, such
TPU materials
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may be made from a prepolymer. An example prepolymer may include a p-phenylene
di-
isocyanate (PPDI) with low free isocyanate content. In other embodiments,
different suitable
prepolymers may be used.
[0060] Disclosed herein are thermoplastic polyurethanes suitable for use in
fabricating
the disclosed screen elements. The disclosed polyurethanes comprise hard and
soft segments
which can be artfully manipulated by the fabricator to produce final
polyurethanes having the
desired properties, for example, abrasion control, flowable during injection
molding, anti-
fracture properties and the like. In one aspect the disclosed polyurethanes,
as described
herein, have from a 85 Shore A to 59 Shore D.
[0061] The disclosed thermoplastic polyurethanes can be fabricated from a
prepolymer and a
curing agent. The prepolymer, as well as, the curing agent can be purchased
from chemical
suppliers or the prepolymer and curing agent can be synthesized by the
fabricator.
Prepolymers
[0062] The disclosed prepolymer can comprise any urethane forming unit. The
urethane
forming units comprise two types: aryl diisocyanates and aliphatic
diisocyanates. In general
the urethane forming unit is reacted with a polyol that serves to connect two
diisocyanate
moieties. For example, the prepolymer can be formed by the following reaction:
H H
2 ONC_R¨NCO + HO¨RI-OH OCN R N c 0 R1_0_c_N_R_NCO
wherein R is a carbon skeleton of 2 to 15 carbon atoms, and/or a bivalent
aromatic radical of
6 to 18 carbon atoms.
[0063] In one embodiment R is an alkylene unit having 2 to 15 carbon atoms,
i.e., from 2
to 15 methylene units, ¨(CH2)2¨ to ¨(CH2)15¨. As such, R can comprise from 2
to 15
methylene units, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or
15 methylene units.
Non-limiting examples of ONC¨R¨NCO include 1,6-hexamethylene diisocyanate, 1-
isocyanato-3-isocyanatomethy1-3,5,5-trimethyl-cyclohexane (isophorone
diisocyanate, IPDI)
and 4,4'-diisocyanato dicyclohexylmethane.
[0064] In another embodiment R is a bivalent aromatic radical of 6 to 18
carbon atoms.
In one iteration, R is formed from a methylene diphenyl diisocyanate (MDI)
wherein R has
the formula:
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= CH2 441
= CH2 = CH =2
r=rf
, or
[0065] In a further embodiment, R can be a 1,2-phenylene. 1,3-phenylene, of
a 1,4-
phenylene unit having the formula:
=
,or
[0066] Utilization of these R units results in polyphenylene diisocyanate
prepolymer units.
Linking le Units
[0067] The disclosed le units can be alkylene unit having 2 to 10 carbon
atoms, i.e., from
2 to 10 methylene units, ¨(CH2)2¨ to ¨(CH2)to¨. As such, le can comprise from
2 to 10
methylene units, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10 methylene units.
Non-limiting
examples of HO¨R¨OH include 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol,
1,5-
pemtanediol, 1,6-hexanediol, 1,7-heptanediol, 1-8-octanediol, 1,9-nonanediol,
and 1,10-
decanediol.
Polycaprolactone Diol-Based Polyester Prepolymers
[0068] The disclosed le units can be derived from a caprolactone diol unit
having the
formula:
0
HOO ________________________________________ (CH2)x-0H
- n
[0069] A non-limiting example of a polycaprolactone diol prepolymer has the
formula:
0 0 0 0
H
OCN-R-N-C-0 ou-
(CH2)x0(CH2)x 0J-(CH2)5
wherein the index x is from 2 to about 6, the index n is from 2 to about 8.
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[0070] A further non-limiting example of a prepolymer derived from a
polycaprolactone
diol unit has the formula:
ii I ii I ii
OCN¨R¨N1¨ trI_T2) \
k, x5- (CH2)x- t-11-\11¨R ¨NCO
L in
wherein the index x is from 2 to about 6, the index n is from 2 to about 8.
Polyglycidyl Diol Prepolymers
[0071] The disclosed units can be derived from a polyglycidyl diol
having the
formula:
0
H.0 JL
0 ¨( cH2)x-0H
n
[0072] _
[0073] A non-limiting example of a polyglycidyl diol prepolymer has the
formula:
H
wherein the index x is from 2 to about 6, the index n is from 2 to about 8.
[0074] A further non-limiting example of a prepolymer derived from a
polyglycidyl diol
unit has the formula:
H
OCN¨R ¨N¨C ¨0 (CH2)¨ (CH2),,_ 0_ R NCO
wherein the index x is from 2 to about 6, the index n is from 2 to about 8.
Polylactide Diol Prepolymers
[0075] The disclosed le units can be derived from a polylactide diol having
the formula:
Ht 'CH2)x_0H
H3
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[0076] A non-limiting example of a polylactide diol prepolymer has the
formula:
0 t cH3 0 0 cH3 lc, 0 H
H a
OCN¨R¨N¨C-0 (6¨t-0 (CH2)x0(CH2)õ 0¨t¨(6_ ¨t¨N¨R¨NCO
n n
wherein the index x is from 2 to about 6, the index n is from 2 to about 8.
[0077] A further non-limiting example of a prepolymer derived from a
polylactide diol
unit has the formula:
0 _[ cH3 0 0
H u
OCN¨R¨N¨C-0 (L4) ¨ ¨0 (CH2)0¨t-11-\11¨R¨NCO
n
wherein the index x is from 2 to about 6, the index n is from 2 to about 8.
Polycarbonate Prepolymers
[0078] The disclosed It' units can be derived from diols having the
formula:
0
H (CH2), ¨t¨ (CH2)x¨ 1-1 1
n
[0079] A non-limiting example of a polycarbonate diol prepolymer has the
formula:
0 0 1 0
OCNRLIt0 __________________ (CH2),0¨t-0 (CH2)x-0-8_1V¨R¨NCO
n
wherein the index x is from 2 to about 6, the index n is from 2 to about 8.
Polyalkylene Diol Prepolymers
[0080] The disclosed It' units can be derived from polyalkylene diols
having the formula:
1-1 ¨(CH2)7-0H
wherein the index z is from about 4 to about 25.
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[0081] One embodiment of the disclosed polyalkylene diol prepolymers has
the formula:
0 0
Hi ii H
[0082] A non-limiting example of a polyalkylene diol prepolymer has the
formula:
OCN = CH2 = (CH
2)2. )21 Mk CH2 Mk NCO
Polyether Diol Prepolymers
[0083] 1. Polyethylene glycol prepolymers
[0084] The disclosed le units can be derived from a polyether diol. In one
embodiment,
the le comprises a polyethylene glycol having the formula:
Ho_[(042a120)yicH2042-0H
wherein the index y is from about 4 to about 25. The following is a non-
limiting embodiment
of the disclosed PEG prepolymers:
0 0
UH
OCN-R_IN-t-O¨RCH2CH20)3,1CH2CH2-0-8_N-R-NCO
2. Polypropylene glycol prepolymers
[0085] In anoather embodiment of the disclosed polyether diol prepolymers,
the disclosed
R' units can be derived from a polyethylene glycol having the formula:
cH3 cH3
HO¨Rt FicH2O1ykCH2-01
wherein the index y is from about 4 to about 25. The following is a non-
limiting embodiment
of the disclosed PPG prepolymers:
o cH3 cH3 0
OCN-R-INIJ-0¨[(tHCH20iy4ICH2-0J-INI-R-NCO
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Curing Agents
[0086] The disclosed prepolymers are further reacted with one or more
curing agents to
form the disclosed thermoplastic polyurethanes having the formula:
- o o o o o o o o
0 8 LI R NI 0 R1_0 8 LI R NI 0 R2 0 8 LI R NI 0
R1_0_8_LR_NH_LO_R2
_ m
=
wherein the index m is from 3 to 20. The curing agents are chosen from
polycaprolactone
diols, polyglycidyl diols, polylactide diols, polycarabonate diols,
polyethylene glycols,
polypropylene glycols, or polyalkylene diols.
[0087] The disclosed R2 units are chosen from:
[0088] i) Polyester polyurethane forming unit:
- -
0
____________________________________________________ (CH2)xi-
- n .
,
[0089] ii) Polyester polyurethane forming unit:
0_
_,40,A
0_(cH2)x_,_
_ n .
,
[0090] iii) Polyester polyurethane forming unit:
0-
0 rot, ,
n ¨,......x.2)x¨_
__[o .
,
[0091] iv) Polycarbonate polyurethane forming unit:
0
(C112)X--
[
n .
,
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[0092] v) Polyalkylene polyurethane forming unit:
4-(cH2A-.
[0093] vi) Polyether polyurethane forming unit:
--[(CH2cH20),,icH2C111-
; or
[0094] vii)Polyether polyurethane forming unit:
cH3 cH3
+[(LCH2013,LICH21-
[0095] In some embodiments the curing agent can be a repeating or non-
repeating polyol.
For example, a branched polyol having the formula:
OH
Ho/\/\/oH
can react with three prepolymer units thereby providing a means for
crosslinking the
polyurethane chains. In one iteration a non-stoichiometric amount of a first
curing agent can
be combined with a polyol in an amount that provides the necessary hydroxyl
units to
consume the available isocyanate groups.
[0096] As stated herein above, in one aspect the disclosed polyurethanes,
as described
herein, have from a 85 Shore A to 59 Shore D durometer value. The desired
hardness of the
resulting thermoplastic polyurethanes can be achieved either by the artful
selection of the
disclosed R, R' and R2 units together with the proper selection of the indices
x, y, m and n.
Another disclosed method is to select two polymers having different Shore D
durometer
values and to admix the two polymers to obtain an intermediary Shore D
durometer hardness
value between the values of the two polymers. In addition, a 95 Shore A could
convert to a
45 Shore D which can be combined with a 56 Shore D to form a polymer having an
intermediate hardness.
[0097] Disclosed herein is a screen element, comprising:
[0098] i) a first thermoplastic polyurethane having a first hardness; and
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[0099] ii) a second thermoplastic polyurethane having a second hardness;
wherein the first and second polyurethanes are combined to form a final
thermoplastic
polyurethane having a hardness of from approximately 85 Shore A to 59 Shore D;
wherein the screen element is a single injection molded piece having a
plurality of openings
from 43 i_tm to 1001_1111; and
wherein the amount of openings is from 10% to 35% of the screen element.
[00100] The first polyurethane and the second polyurethane are formed by
reacting a
prepolymer having the formula chosen from:
i)
oF ol 0
H ii I ii I
OCN¨R¨N¨C-0 (CI_T \ )x-0- LIILR_NCO
ks...,.2)5-¨C) (CH2
L in
ii)
0 0 0
H
ocN¨R¨N¨c¨o (0-12)--0 (cH2)x¨oJ-11-\11¨R¨NCO
=
ill)
0 0 0
H
ocN¨R¨N¨c¨o (0-12)--0 (cH2)x-0J-111¨R¨NCO
iv)
H u
OCN¨R¨N¨C-0 (&) ¨t¨ (CH2)7-0¨t_INI_R_NCO
v)
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0 0 1 0
H ii
OCNRNCO (CH2) J¨ (CH2)x-0-8 1
_11¨R¨NCO
II
vi)
0 0
H ii iiH
0CN¨R¨N¨C-0 M.,,xxtrI_I
2)z-O-C-N-R-NCO or
vii)
o 043 CH3 0
Ho
iiH
OCN¨R¨N¨C-0¨RtHCH2013,41CH2-0¨C¨N_R¨NCO
wherein the index x is from 2 to about 6, the index y is from about 4 to about
25, index z is
from about 4 to about 25, and the index n is from 2 to about 8;
and wherein further the prepolymer contains less than 0.1% by weight of excess
isocyanate
moieties;
with a curing agent, wherein the curing agent is chosen from polycaprolactone
diols,
polyglycidyl diol s, polylactide diol s, polycarabonate diol s, polyethylene
glycols,
polypropylene glycols, or polyalkylene diol s.
[00101] Example TPU materials may be generated as follows. A TPU polymer may
be
produced by reacting a urethane prepolymer, having a free polyisocyanate
monomer content
of less than 1% by weight, with a curing agent. The resulting material may
then be thermally
processed by extrusion at temperatures of 150 C (or higher) to form the TPU
material. The
urethane prepolymer may be prepared from a polyisocyanate monomer and a polyol
including an alkane diol, a polyether polyol, a polyester polyol, a
polycaprolactone polyol,
and/or a polycarbonate polyol. The curing agent may include a diol, a triol, a
tetrol, an
alkylene polyol, a polyether polyol, a polyester polyol, a polycaprolactone
polyol, a
polycarbonate polyol, a diamine, or a diamine derivative.
[00102] Disclosed TPU materials may then be combined with a heat stabilizer, a
flow
agent, and a filler material, according to various embodiments. In further
embodiments, other
additives may be included as needed.
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[00103] Generally, disclosed embodiments provide TPU compositions that may be
formed
by reacting a polyol with a polyisocyanate and polymer chain-extender. Example
embodiments include synthetic production methods and processes for making TPU
compositions. Disclosed methods may include reacting monomers, curing agents,
and chain
extenders in a reaction vessel to form pre-polymers. Disclosed methods may
further include
forming pre-polymers by reacting a di-isocyanate (OCN-R-NCO) with a diol (HO-R-
OH).
Formation of a pre-polymer includes chemically linking two reactant molecules
to produce a
chemical product having an alcohol (OH) at one position and an isocyanate
(NCO) at another
position of the product molecule. In an embodiment, a disclosed pre-polymer
includes both a
reactive alcohol (OH) and a reactive isocyanate (NCO). Articles generated
using the TPU
compositions disclosed herein may be fully cured polymer resins that may be
stored as a solid
plastic.
[00104] Disclosed embodiments provide pre-polymers that may be prepared from a
polyisocyanate monomer and a curing agent. Non-limiting examples of curing
agents may
include ethane diol, propane diol, butane diol, cyclohexane dimethanol,
hydroquinone-bis-
hydroxyalkyl (e.g., hydroquinone-bis-hydroxyethyl ether), diethylene glycol,
dipropylene
glycol, dibutylene glycol, triethylene glycol, etc., dimethylthio-2,4-
toluenediamine, di-p-
aminobenzoate, phenyldiethanol amine mixture, methylene dianiline sodium
chloride
complex, etc.
[00105] In example embodiments, a polyol may include an alkane diol, polyether
polyol,
polyester polyol, polycaprolactone polyol, and/or polycarbonate polyol. In
certain
embodiments, the polyol may include a polycarbonate polyol either, alone or in
combination
with other polyols.
Heat stabilizers
[00106] Disclosed heat/thermal stabilizers may include additives such as
organosulfur
compounds, which are efficient hydroperoxide decomposers that thermally
stabilize
polymers. Non-limiting example heat stabilizers include: organophosphites such
as triphenyl
phosphite, tris-(2,6-dimethylphenyl) phosphite, tris-(mixed mono-and di-
nonylphenyl)
phosphite etc.; phosphonates such as dimethylbenzene phosphonate, etc.;
phosphates such as
trimethyl phosphate, etc.; dihexylthiodiformate dicyclohexy1-10,10'-
thiodidecylate
dicerotylthiodiformate diceroty1-10,10'-thiodidecylate diocty1-4,4-
thiodibutyrate diphenyl-
2,2'-thiodiacetate (thiodiglycolate) dilaury1-3,3'-thiodipropionate disteary1-
3,3'-
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thiodipropionate di(p-toly1)-4,4'-thiodibutyrate lauryl myristy1-3,3'-
thiodipropionate palmityl
steary1-2,2'-thiodiacetate dilaury1-2-methyl-2,2'-thiodiacetatedodecyl 3-
(dodecyloxycarbonylmethylthio) propionate stearyl 4-
(myristyloxycarbonylmethylthio)
butyrate dihepty1-4,4-thiodibenzoate dicyclohexy1-4,4'-thiodicyclohexanoate
dilaury1-5,5'-
thio-4-methylbenzoate; and mixtures thereof etc. When present, thermal
stabilizers may be
included in amounts of about 0.0001% to about 5% by weight, based on the
weight of the
base-polymer component used in the TPU composition. Inclusion of organosulfur
compounds
may also improve thermal stability of TPU compositions as well as articles
produced
therefrom.
[00107] In an exemplary embodiment, a heat stabilizer may be a sterically
hindered
phenolic antioxidant, such as Pentaerythritol Tetrakis (3-(3,5-di-tert-buty1-4-
hydroxyphenyl)propionate) (CAS Registry No. 6683-19-8). In example
embodiments, the
heat stabilizer may be included in amounts ranging from about 0.1% to about 5%
by weight
of the TPU.
Flow agents
[00108] Flow agents are used to enhance flow characteristics of TPU materials
so that
such TPU materials may be easily injected into a mold. Injection times for
disclosed TPU
materials are preferably between about 1 to about 2 seconds. In an embodiment,
flow times
averaging about 1.6 seconds have been achieved. Flow agents are used to
achieve such
injection times.
[00109] Disclosed TPU compositions may include flow agents that improve
lubrication to
increase the flow of melted polymer compositions relative to an external
surface (i.e., to
increase external flow). Flow agents may also increase the flow of individual
polymer chains
within a thermoplastic melt (i.e., to increase internal flow).
[00110] Disclosed embodiments provide TPU compositions that may include an
internal
flow agent that may be readily compatible with the polymer matrix. For
example, the internal
flow agent may have a similar polarity that improves the ease of flow of the
melt by
preventing internal friction between the individual particles of the polymer.
In certain
embodiments, TPU compositions including internal flow agents may improve
molding
characteristics. For example, in a specific embodiment, TPU compositions may
be used to
produce articles having small or very small openings. In another embodiment,
TPU
compositions may be used to produce articles having very fine openings by
injection
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molding. In further embodiments, the improved flow of the TPU compositions
allows
production of high-resolution articles having small or very small openings.
[00111] Disclosed embodiments provide TPU compositions that may include an
external
flow agent that may be more or less compatible with the polymer matrix of a
TPU
composition. For example, an external flow agent may have a different polarity
relative to the
TPU composition polymer. Since external flow agents may not be compatible with
the TPU
polymer matrix of the composition, external flow agents may act as an external
lubricating
film between the polymer and hot metallic surfaces of processing machines.
Thus, external
lubricants may prevent a polymer melt from adhering to machine parts (e.g.,
such as an
extruder), and may also reduce the force required to remove a cured polymer
from a mold
(i.e., may improve demolding) in the case of injection molding.
[00112] Non-limiting, examples of flow agents that may be included in TPU
compositions
include amines (e.g., ethylene bisstearamide), waxes, lubricants, talc, and
dispersants.
Disclosed embodiments provide TPU compositions that may also include one or
more
inorganic flow agents such as hydrated silicas, amorphous alumina, glassy
silicas, glassy
phosphates, glassy borates, glassy oxides, titania, talc, mica, fumed silicas,
kaolin, attapulgite,
calcium silicates, alumina, and magnesium silicates. The amount of flow agent
may vary with
the nature and particle size of the particular flow agent selected.
[00113] In exemplary embodiments, the flow agent may be a wax, such as an
ethylene
steramide wax. An ethylene steramide wax may include octadecanamide, N,N'-1,2-
ethanediylbis (C38H76N202; CAS Registry No. 100-30-5) and stearic acid
[CH3(CH2)16COOH; CAS Registry No. 57-11-4]. In exemplary embodiments, the flow
agent
may be present in amounts from about 0.1% to about 5% by weight of the TPU.
[00114] Improved flow characteristics of TPU compositions may be achieved by
reducing
or eliminating the presence of certain compounds, such as calcium stearate,
for example.
Fillers
[00115] As described above, disclosed embodiments provide TPU compositions
that may
also include fillers that may include inorganic materials. Fillers strengthen
and stiffen the
TPU based material, enhancing properties of objects injection molded from the
TPU material.
For example, fillers help to maintain shapes of small openings, holes, or
pores, formed in
objects injection molded from the TPU composition. In some embodiments, for
example, the
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fibers allow transmission of light for use in laser welding of molded TPU
components to
support structures.
[00116] In exemplary embodiments, glass fibers may be used as filler material,
as
described above. Glass fibers may take the form of solid or hollow glass
tubes. In exemplary
embodiments, glass tubes may have a diameter (or width, if not round) of
between about 2
p.m to about 20 p.m. In an exemplary embodiment, glass fibers may have a
diameter (or
width, if not round) of between about 9 p.m to about 13 p.m. In an embodiment,
glass fibers
may have a 11 p.m diameter or width. Glass fibers may have an initial length
of between
about 3.0 mm to about 3.4 mm. In an exemplary embodiment, glass fibers may
have an initial
length of 1/8 inch (i.e., 3.175 mm). In further embodiments, glass fibers may
have an initial
length that is 1/16 inch, 1/32 inch, 1/64 inch, etc. During processing of the
TPU material,
however, glass fibers may break and thereby become shorter. In a hardened
state after
injection molding, glass fibers may have an average length of less than about
1.5 mm, with a
range of most fibers being between about 1.0 mm to about 3.2 mm. After
processing, glass
fibers may have a length that is considerably smaller than the starting
length. For example,
glass fibers may have a final length of less than 1 p.m. Some of the fibers
retain their original
length, but most are broken into smaller pieces.
[00117] To allow laser welding of the TPU composition, it is desirable to
use as little glass
fiber as possible. Too much glass fiber leads to an unacceptably high amount
of
reflection/refraction of laser light. Additionally, desired properties of the
TPU composition
may degrade with increasing glass fiber content. Glass fibers having a
sufficiently large
diameter may work better for laser weldable compositions. Such large diameter
fibers may
also provide desirable strengthening and stiffening properties. The diameter
of glass fibers
should not be too large, however, as desirable flow properties may degrade
with increasing
diameter of glass fibers, reducing the suitability of the resulting
composition for injection
molding.
[00118] Glass fiber filler materials should not contain fibers having a
diameter of greater
than 50 p.m, and should preferably have a diameter of less than 20 p.m, in
compositions
developed for injection molding of structures having features on a sub-
millimeter scale.
Carbon fibers should be avoided in that they may not work for laser welding
because they are
not translucent. TPU based objects that are designed to be joinable via laser
welding may
have optical properties that allow laser light to pass through the TPU
material. As such, laser
light may pass through the TPU object and may hit an adjacent structure such
as to a nylon
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subgrid. The nylon material of the subgrid is a thermoplastic having a dark
color that absorbs
laser light and may thereby be heated by the laser. Upon absorption of laser
light, the TPU
and the adjacent nylon may be heated to a temperature above their respective
melting
temperatures. In this way, both materials may be melted, and upon cooling, a
mechanical
bond may be formed at an interface between the TPU and the nylon, thereby
welding the
components together.
[00119] Disclosed embodiments provide TPU compositions that may also include
particulate fillers, which may be of any configuration including, for example,
spheres, plates,
fibers, acicular (i.e., needle like) structures, flakes, whiskers, or
irregular shapes. Suitable
fillers may have an average longest dimension in a range from about 1 nm to
about 500 p.m.
Some embodiments may include filler materials with average longest dimension
in a range
from about 10 nm to about 100 p.m. Some fibrous, acicular, or whisker-shaped
filler materials
(e.g., glass or wollastonite) may have an average aspect ratio (i.e.,
length/diameter) in a range
from about 1.5 to about 1000. Longer fibers may also be used in further
embodiments.
[00120] Plate-like filler materials (e.g., mica, talc, or kaolin) may have
a mean aspect ratio
(i.e., mean diameter of a circle of the same area/mean thickness) that is
greater than about 5.
In an embodiment, plate-like filter materials may have an aspect ratio in a
range from about
to about 1000. In a further embodiment, such plate-like materials may have an
aspect
ratio in a range from about 10 to about 200. Bimodal, trimodal, or higher
mixtures of aspect
ratios may also be used. Combinations of fillers may also be used in certain
embodiments.
[00121] According to an embodiment, a TPU composition may include natural,
synthetic,
mineral, or non-mineral filler materials. Suitable filler materials may be
chosen to have
sufficient thermal resistance so that a solid physical structure of the filler
material may be
maintained, at least at the processing temperature of the TPU composition with
which it is
combined. In certain embodiments, suitable fillers may include clays,
nanoclays, carbon
black, wood flour (with or without oil), and various forms of silica. Silica
materials may be
precipitated or hydrated, fumed or pyrogenic, vitreous, fused or colloidal.
Such silica
materials may include common sand, glass, metals, and inorganic oxides.
Inorganic oxides
may include oxides of metals in periods 2, 3, 4, 5 and 6 of groups TB, IIB,
IIIA, IIIB, IVA,
IVB (except carbon), VA, VIA, VITA, and VIII, of the periodic table.
[00122] Filler materials may also include oxides of metals, such as aluminum
oxide,
titanium oxide, zirconium oxide, titanium dioxide, nanoscale titanium oxide,
aluminum
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trihydrate, vanadium oxide, magnesium oxide, antimony trioxide, hydroxides of
aluminum,
ammonium, or magnesium. Filler materials may further include carbonates of
alkali and
alkaline earth metals, such as calcium carbonate, barium carbonate, and
magnesium
carbonate. Mineral based materials may include calcium silicate, diatomaceous
earth, fuller
earth, kieselguhr, mica, talc, slate flour, volcanic ash, cotton flock,
asbestos, and kaolin.
[00123] Filler materials may further include alkali and alkaline earth metal
sulfates, for
example, sulfates of barium and calcium sulfate, titanium, zeolites,
wollastonite, titanium
boride, zinc borate, tungsten carbide, ferrites, molybdenum disulfide,
cristobalite,
aluminosilicates including vermiculite, bentonite, montmorillonite, Na-
montmorillonite, Ca-
montmorillonite, hydrated sodium calcium aluminum magnesium silicate
hydroxide,
pyrophyllite, magnesium aluminum silicates, lithium aluminum silicates,
zirconium silicates,
and combinations of the above-described filler materials.
[00124] Disclosed embodiments provide TPU compositions that may include
fibrous
fillers such as glass fibers (as described above), basalt fibers, aramid
fibers, carbon fibers,
carbon nanofibers, carbon nanotubes, carbon buckyballs, ultra-high molecular
weight
polyethylene fibers, melamine fibers, polyamide fibers, cellulose fiber, metal
fibers,
potassium titanate whiskers, and aluminum borate whiskers.
[00125] In certain embodiments, TPU compositions may include glass fiber
fillers, as
described above. Glass fiber fillers may be of E-glass, S-glass, AR-glass, T-
glass, D-glass
and R-glass. In certain embodiments, the glass fiber diameter may be within a
range from
about 5 [im to about 35 [im. In other embodiments, the diameter of the glass
fibers may be in
a range from about 9 to about 20 [im. In further embodiments, glass fibers may
have a length
of about 3.2 mm or less. As described above, TPU compositions including glass
fillers may
confer improved thermal stability to the TPU compositions and articles
produced them.
[00126] Disclosed embodiments may include compositions containing a glass
filler with
concentrations in a range from about 0.1% to about 7% by weight. Embodiments
may also
include glass filler at concentrations ranging from about 1% to about 2%;
about 2% to about
3%; 3% to about 4%; about 4% to about 5%; about 5% to about 6%; about 6% to
about 7%;
about 7% to about 8%; about 8% to about 9%; about 9% to about 10%; about 10%
to about
11%; about 11% to about 12%; about 12% to about 13%; about 13% to about 14%;
about
14% to about 15%; about 15% to about 16%; about 16% to about 17%; about 17% to
about
18%; about 18% to about 19%; and about 19% to about 20%. In certain
embodiments a glass
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filler concentration may be about 1%. In certain embodiments a glass filler
concentration may
be about 3%. In certain embodiments a glass filler concentration may be about
5%. In certain
embodiments a glass filler concentration may be about 7%. In certain
embodiments a glass
filler concentration may be about 10%.
[00127] As described above, embodiments may include glass filler material
wherein
individual glass fibers may have a diameter or width in a range from about 1
um to about 50
um. In certain embodiments, the glass filler may be characterized by a narrow
distribution of
fiber diameters such that at least 90% of the glass fibers have a specific
diameter or width.
Other embodiments may include a glass filler having a broader distribution of
diameters or
widths spanning a range from about 1 um to about 20 um. Further embodiments
may include
glass filler having a glass fiber diameter or width distribution spanning a
range: from about 1
um to about 2 um; from about 2 um to about 3 um; from about 3 um to about 4
um; from
about 4 um to about 5 um; from about 5 um to about 6 m; from about 6 um to
about 7 um;
from about 7 um to about 8 um; from about 8 um to about 9 um; from about 9 um
to about
m; from about 10 um to about 11 um; from about 11 um to about 12 m; from
about 12
um to about 13 um; from about 13 um to about 14 um; from about 14 um to about
15 um;
from about 15 um to about 16 um; from about 16 um to about 17 m; from about
17 um to
about 18 um; from about 18 um to about 19 m; and from about 19 um to about 20
um. In
certain embodiments the glass filler may have a diameter or width distribution
centered about
a specific value. For example, the specific diameter or width value may be 10
um 2 um,
according to an embodiment.
[00128] TPU compositions may include glass fiber fillers that include a
surface treatment
agent and optionally a coupling agent, according to an embodiment. Many
suitable materials
may be used as a coupling agent. Examples include silane-based coupling
agents, titanate-
based coupling agents, or a mixture thereof. Applicable silane-based coupling
agents, for
example, may include aminosilane, epoxysilane, amidesilane, azidesilane, and
acrylsilane.
[00129] Disclosed embodiments provide TPU compositions that may also include
other
suitable inorganic fibers such as: carbon fibers, carbon/glass hybrid fibers,
boron fibers,
graphite fibers, etc. Various ceramic fibers can also be utilized such as
alumina-silica fibers,
alumina fibers, silicon carbide fibers, etc. Metallic fibers, such as aluminum
fibers, nickel
fibers, steel, stainless steel fibers, etc., may also be used.
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[00130] Disclosed TPU compositions may be generated by a process in which TPU
reactants may be combined with filler materials (e.g., fiber fillers) and
other optional
additives. The combination of materials may then be physically mixed in a
mixing or
blending apparatus.
[00131] An example mixing or blending apparatus may include: a Banbury, a twin-
screw
extruder, a Buss Kneader, etc. In certain embodiments, filler and base TPU
composition
materials may be mixed or blended to generate a TPU composition blend having
fibers
incorporated therein. The resulting TPU composition having fillers (e.g.,
glass fibers), and
optionally other additional additives, may be cooled to generate a solid mass.
The resulting
solid mass may then be pelletized or otherwise divided into suitable size
particles (e.g.,
granulated) for use in an injection molding process. The injection molding
process may be
used to generate an article of manufacture such as a screen or screen element.
[00132] Optional additives to TPU compositions, mentioned above, may include
dispersants. In certain embodiments, dispersants may help to generate a
uniform dispersion of
base TPU composition and additional components such as fillers. In certain
embodiments, a
dispersant may also improve mechanical and optical properties of a resulting
TPU
composition that includes fillers.
[00133] In certain embodiments, waxes may be used as dispersants. Non-limiting
examples of wax dispersants, suitable for use in disclosed TPU compositions,
include:
polyethylene waxes, amide waxes, and montan waxes. TPU compositions disclosed
herein
may include an amide wax dispersant, such as N,N-bis-stearyl ethylenediamine.
The use of
such a wax dispersant may increase thermal stability of the TPU composition
yet may have
little impact on polymer transparency. As such, inclusion of dispersants in
disclosed TPU
compositions may have at least to desirable effects: (1) improved thermal
stability of
compositions and articles produced therefrom, and (2) desirable optical
properties that are
suitable for downstream processing including laser welding.
[00134] Disclosed TPU compositions may further include antioxidants, according
to an
embodiment. Antioxidants may be used to terminate oxidation reactions, that
may occur due
to various weathering conditions, and/or may be used to reduce degradation of
a TPU
composition. For example, articles formed of synthetic polymers may react with
atmospheric
oxygen when placed into service. In addition, articles formed of synthetic
polymers may
undergo auto-oxidization due to free-radical chain reactions. Oxygen sources
(e.g.,
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atmospheric oxygen, alone or in combination with a free radical initiator) may
react with
substrates included in disclosed TPU compositions. Such reactions may
compromise integrity
of the TPU composition and articles produced therefrom. Inclusion of
antioxidants, therefore,
may improve chemical stability of TPU compositions as well as improving
chemical stability
of articles generated therefrom.
[00135] Polymers may undergo weathering in response to absorption of UV light
that
causes radical initiated auto-oxidation. Such auto-oxidation may lead to
cleavage of
hydroperoxides and carbonyl compounds. Embodiment TPU compositions may include
Hydrogen-donating antioxidants (AH), such as hindered phenols and secondary
aromatic
amines. Such AH additives may inhibit oxidation of TPU compositions by
competing with
organic substrates for peroxy radicals. Such competition for peroxy radicals
may terminate
chain reactions and thereby stabilize or prevent further oxidation reactions.
Inclusion of
antioxidants in disclosed TPU compositions may inhibit formation of free
radicals. In
addition to AH being a light stabilizer, AH may also provide thermal stability
when included
in disclosed TPU compositions. Accordingly, certain embodiments may include
additives
(e.g., AH) that enhance stability of polymers exposed to UV light and heat.
Articles generated
from disclosed TPU compositions having antioxidants may, therefore, be
resistant to
weathering and have improved function and/or lifespan, when deployed under
high-
temperature conditions, relative to articles generated from TPU compositions
lacking
antioxidants.
[00136] Disclosed TPU compositions may further include UV absorbers, according
to an
embodiment. UV absorbers convert absorbed UV radiation to heat by reversible
intramolecular proton transfer reactions. In some embodiments, UV absorbers
may absorb
UV radiation that would otherwise be absorbed by the TPU composition. The
resulting
reduced absorption of UV rays by the TPU composition may help to reduce UV
radiation
induced weathering of the TPU composition. Non-limiting example UV-absorbers
may
include oxanilides for polyamides, benzophenones for polyvinyl chloride (PVC),
and
benzotriazoles and hydroxyphenyltriazines for polycarbonate materials. In an
embodiment, 2-
(2'-Hydroxy-3'-sec-buty1-5'-tert-butylphenyl)benzotriazole may provide UV
light
stabilization for polycarbonate, polyester, polyacetal, polyamides, TPU
materials, styrene-
based homopolymers, and copolymers. These and other UV absorbers may improve
the
stability of disclosed TPU compositions and articles produced therefrom,
according to
various embodiments.
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[00137] TPU compositions may further include anti-ozonants which may prevent
or slow
degradation of TPU materials caused by ozone gas in the air (i.e., may reduce
ozone
cracking). Non-limiting exemplary embodiments of antiozonates may include: p-
Phenylenediamines, such as 6PPP (N-(1,3-dimethylbuty1)-N'-phenyl-p-
phenylenediamine) or
IPPD (N-isopropyl-N'-phenyl-p-phenylenediamine); 6-ethoxy-2,2,4-trimethy1-1,2-
dihydroquinoline, (ETMQ) ethylene diurea (EDU), and paraffin waxes that may
form a
surface barrier. These and other antiozonants may improve the stability of
disclosed TPU
compositions as well as articles produced therefrom, according to various
embodiments.
[00138] According to an embodiment, an example mixture may be prepared as
follows.
The starting material may be chosen to be a polycarbonate-based thermoplastic
polyurethane.
A filler material may be chosen to be small diameter (as described above)
glass fibers
included in an amount from between about 3% and about 10% by weight. A flow
agent may
then be chosen to be included in an amount of between about 0.1% to about 5%
by weight.
In this example, the flow agent may be taken to be a mixture of
octadecanamide, N,N'-1,2-
ethanediylbis and stearic acid. A thermal-stabilizing agent may be chosen to
be
pentaerythritol tetrakis(3-(3,5-di-tert-buty1-4-hydroxyphenyl)propionate)
included in an
amount of between about 0.1% to about 5% by weight. The above-described
thermoplastic
mixture may then be injected into bulk thermoplastic rods then pelletized for
downstream
injection molding.
Methods
[00139] Disclosed embodiments provide methods and processes for generating TPU
compositions. Disclosed methods may include reacting (i.e., linking) pre-
polymer units
including an alcohol (OH) and an isocyanate (NCO) to effectively "grow" and/or
extend a
polymer chain or backbone. For example, in an embodiment, a TPU composition
may be
prepared by reacting a polyurethane pre-polymer and a curing agent, typically
at temperatures
from about 50 C to about 150 C, for example, or from about 50 C to about
100 C.
Temperatures outside these ranges may also be employed in certain embodiments.
[00140] Disclosed TPU compositions may be melted and formed into a desired
shape, for
example, by injection molding. Disclosed methods may further include a post
curing step
including heating the TPU material at temperatures from about 50 C to about
200 C, or
from about 100 C to about 150 C, for a predetermined period of time. For
example, TPU
materials may be heated for about 1 hour to about 24 hours. Alternatively,
various methods
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may include an extrusion step wherein a post-cured TPU composition may be
extruded at
temperatures from about 150 C to about 270 C, or from about 190 C or
higher, to render
the TPU composition in an intermediate form. The intermediate form may be
suitable for
downstream processing to generate a final form, such as a TPU based screen
element.
[00141] Disclosed methods may include a variety of additional processing
operations. For
example, a disclosed method or process may include: reacting a polyurethane
pre-polymer
and a curing agent (i.e., polymerization); post curing the polyurethane;
optionally grinding
the material to generate a post cured polyurethane polymer in granulated form;
extruding the
post cured and/or optionally granulated polyurethane polymer; and optionally
pelletizing the
extruded TPU.
[00142] In an embodiment, the TPU composition may be generated by a process in
which
a pre-polymer is mixed with a curing agent at temperatures of from about 50 C
to about 150
C to form a polymer. The method may then include heating the polymer at
temperatures from
about 50 C to about 200 C for about 1 to about 24 hours to obtain a post-
cured polymer.
The post-cured polymer may then optionally be ground to generate a granulated
polymer.
Optionally, the method may further include processing either the post-cured
polymer or the
granulated polymer in an extruder at temperatures from about 150 C, or
higher, to yield a
TPU composition. Further operations may optionally include pelletizing the TPU
composition, re-melting the pelletized TPU composition, and extruding the
melted TPU
composition.
[00143] Disclosed methods may further include generating TPU compositions
containing
optional additives. In an embodiment, optional additives may include
antioxidants (including
phenolics, phosphites, thioesters, and/or amines), antiozonants, thermal
stabilizers, inert
fillers, lubricants, inhibitors, hydrolysis stabilizers, light stabilizers,
hindered amine light
stabilizers, UV absorbers (e.g., benzotriazoles), heat stabilizers,
stabilizers to prevent
discoloration, dyes, pigments, inorganic and organic fillers, organosulfur
compounds, thermal
stabilizers, reinforcing agents, and combinations thereof
[00144] Disclosed methods include generating TPU compositions containing
optional
additives in effective amounts customary for each respective additive. In
various
embodiments, such optional additional additives may be incorporated into the
components of,
or into the reaction mixture for, the preparation of the TPU composition. In
other
embodiments, a base TPU composition lacking optional additives may be
generated and
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optionally processed. Optional processing operations may include grinding TPU
materials to
generate a granulated material, or to form a powdered base TPU composition
material to
which optional additives may then be mixed prior to further processing.
[00145] In other embodiments, powdered mixtures including a base TPU
composition and
optional additives may be mixed, melted, and extruded to form a composition.
In other
embodiments, the TPU composition may be prepared through a reactive extrusion
process
wherein pre-polymer, curing agent, and any optional additives are fed directly
into an
extruder, and then are mixed, reacted, and extruded at an elevated
temperature. Various
alternative combinations of these formulation operations may also be employed
in various
embodiments.
[00146] Further embodiments may include many different types of polymer
additives.
Such additives may include an acid scavenger, an antiblock, an anti-fogging
agent, an
antioxidant/heat stabilizer, a blowing agent, a compatibilizer/adhesion
promotor, a
conductivity enhancer, a flame retardant, a fragrance, an impact modifier, a
light diffuser, a
nucleating/clarifying agent, an optical brightener, a pigment, a slip
agent/lubricant/mold
release/processing aid, a UV protector/light stabilizer, a filler,
reinforcements/coupling
agents, etc.
[00147] An antioxidant/heat stabilizer, as described above, helps to prevent
degradation
via oxidation, especially at elevated temps. An antistatic agent helps
dissipate static
electricity. Such additives may be advantageous for use in oilfield
applications. A blowing
agent creates a cellular (foamed) structure within the polymer which tends to
reduce density,
increases thermal and acoustic insulation, and increases stiffness. A
compatibilizer/adhesion
promotor helps to create more stable phase morphologies between blended
polymers. Such a
compatibilizer/adhesion promotor may be useful for embodiments in which a TPU
is blended
with another type of plastic. A slip agent/lubricant/mold release/processing
aid, as described
above helps the polymer flow into and release from the mold during processing.
Such
materials may include fluoropolymers which may be used for casting urethanes.
A UV
protector/light stabilizer, as described above, helps prevent photodegradation
from interaction
of UV light with TPU materials. Fillers reinforcements/coupling agents, as
described above,
are used for strengthening, stiffening, and increased processability of the
TPU material.
Fillers may include glass fibers, aramid fibers, carbon fibers, etc. Use of
aramid and carbon
fibers may affect the optical properties of the material and, as such, may
influence to degree
to which a particular material may be used for laser welding.
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Articles of Manufacture
[00148] Disclosed embodiments include apparatus, articles of manufacture, and
products
generated using TPU compositions. Non-limiting example embodiments may include
coatings or adhesives, and/or articles having a predetermined three-
dimensional structure
upon curing after being cast or extruded into a mold. Disclosed embodiments
provide TPU
compositions that may exhibit significantly higher load bearing properties
than other
materials based on natural and synthetic rubber, for example.
[00149] In various embodiments, articles generated from disclosed TPU
compositions may
be thermostable. In this regard, although thermoplastics may generally be re-
melted and
reformed, articles produced from disclosed TPU compositions may exhibit
resistance to
effects resulting from thermal strain at temperatures sufficiently lower than
a melting
temperature. For example, articles generated from disclosed TPU compositions
may retain
their shape (i.e., they may exhibit modulus retention) at elevated
temperatures corresponding
to service conditions, including temperatures in a range from about 170 C to
about 200 C.
Disclosed TPU compositions may be used to form articles that may retain their
structure,
mechanical strength, and overall performance at elevated temperatures.
[00150] Disclosed TPU compositions may exhibit thermal stability in a
temperature range
from about 160 F to about 210 F. Embodiment TPU compositions may also
exhibit thermal
stability for temperatures in a range from about 170 F to about 200 F, while
further
embodiments may exhibit thermal stability for temperatures in a range from
about 175 F to
about 195 F. Disclosed embodiments may also provide a TPU composition that
may exhibit
thermal stability for temperatures near 180 F. In one embodiment, the polymer
compositions
have a Vicat softening measured by ISO 306 or ASTM D1525 is above 220 F
[00151] Disclosed embodiments include TPU compositions having favorable
mechanical
properties, as characterized by cut/tear/abrasion resistance data, relative to
known
thermoplastic compositions. In certain embodiments, improved properties may
include:
greater tear strength, better modulus retention at high temperature, low
compression set,
improved retention of physical properties over time and upon exposure to
harmful
environments. Certain embodiments provide TPU compositions that may have a
combination
of improved characteristics such as superior thermal stability, abrasion
resistance, and
chemical resistance (e.g., to oils and grease). In certain embodiments,
articles generated from
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disclosed TPU compositions may have characteristics that are highly desirable
for oil, gas,
chemical, mining, automotive, and other industries.
[00152] In an exemplary embodiment, an example TPU composition, provided in
pellet
form, may be loaded into a cylinder of an injection press. Once loaded into
the cylinder, the
pellet may be heated for a period of time to thereby melt the TPU composition
material. The
injection press may then extrude the melted exemplary TPU composition material
into a mold
cavity according to a predetermined injection rate. The injection press may be
adapted to
include specialized tips and/or nozzles configured to achieve a desired
injection output.
[00153] Various parameters may be controlled or adjusted to achieve desired
results. Such
parameters may include, but are not limited to, barrel temperature, nozzle
temperature, mold
temperature, injection pressure, injection speed, injection time, cooling
temperature, and
cooling time.
[00154] In an embodiment method, barrel temperatures of an injection molding
apparatus
may be chosen to range from about 148 C to about 260 C, from about 176 C to
about 233
C, from about 204 C to about 233 C, from about 210 C to about 227 C, and
from about
215 C to about 235 C. Nozzle temperatures of an injection molding apparatus
may be
chosen to range from about 204 C to about 260 C, from about 218 C to about
246 C, from
about 234 C to about 238 C, and from about 229 C to about 235 C.
[00155] In an embodiment method, injection pressure of an injection molding
apparatus
may be chosen to range from about 10,000 psi to about 15,000 psi. In further
embodiments,
injection pressures may be considerably higher. In still further embodiments
the injection
pressure is about 30,000 psi. Injection speed of an injection molding
apparatus may be
chosen to range from about 1.0 cubic inch/second to about 3.0 cubic
inch/second, from about
1.5 cubic inch/second to about 2.5 cubic inch/second, from about 1.75 cubic
inch/second to
about 2.5 cubic inch/second, and from about 2.1 cubic inch/second to about 2.4
cubic
inch/second. For fine mesh injection the speed is about 5.0 cubic inch/second
to about 7.0
inch/second, from about 5.5 cubic inch/second to about 6.5 cubic inch/second,
from about 5.0
cubic inch/second to about 6.0 cubic inch/second.
[00156] In an embodiment method, injection time may be chosen to range from
about 0.25
seconds to about 3.00 seconds, from about 0.50 second to about 2.50 seconds,
from about
0.75 seconds to about 2.00 seconds, and from about 1.00 second to about 1.80
seconds.
Moreover, the injection time may be modified to include a "hold" for a certain
period of time
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in which injection is paused. Hold periods may be any particular time. In an
exemplary
embodiment, the hold time may range from 0.10 seconds to 10.0 minutes. Other
hold times
may be use in other embodiments.
[00157] In an embodiment method, mold temperatures may be chosen to range from
about
37 C to about 94 C, from about 43 C to about 66 C, and from about 49 C to
about 60 C.
Cooling temperatures may be gradually reduced to control curing of a disclosed
TPU
composition. The temperature may be gradually reduced from that of the mold
temperature to
ambient temperature over a period of time. The time period for cooling may be
chosen to be
virtually any time period ranging from second to hours. In an embodiment, the
cooling time
period may range from about 0.1 to about 10 minutes.
[00158] The following method describes an injection molding process that
generates
screening members based on disclosed TPU compositions. As described above, TPU
compositions may be formed as TPU pellets. The TPU composition material may
first be
injected into a mold that is designed to generate a screening member. The TPU
composition
may then be heated to a temperature suitable for injection molding to thereby
melt the TPU
material. The melted TPU material may then be loaded into an injection molding
machine. In
an embodiment, the mold may be a two-cavity screening member mold. The mold
containing
the injected melted TPU material may then be allowed to cool. Upon cooling,
the TPU
material solidifies into a screening member shape defined by the mold. The
resulting
screening members may then be removed from the mold for further processing.
[00159] Embodiments of the present disclosure provide injection molded screen
elements
that are of a practical size and configuration for manufacture of vibratory
screen assemblies
and for use in vibratory screening applications. Several important
considerations have been
taken into account in the configuration of individual screen elements. Screen
elements are
provided that: are of an optimal size (large enough for efficient assembly of
a complete
screen assembly structure yet small enough to injection mold (micro-mold in
certain
embodiments) extremely small structures forming screening openings while
avoiding
freezing (i.e., material hardening in a mold before completely filling the
mold)); have optimal
open screening area (the structures forming the openings and supporting the
openings are of a
minimal size to increase the overall open area used for screening while
maintaining, in
certain embodiments, very small screening openings necessary to properly
separate materials
to a specified standard); have durability and strength, can operate in a
variety of temperature
ranges; are chemically resistant; are structural stable; are highly versatile
in screen assembly
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manufacturing processes; and are configurable in customizable configurations
for specific
applications.
[00160] Embodiments of the present disclosure provide screen elements that are
fabricated
using extremely precise injection molding. The larger the screen element the
easier it is to
assemble a complete vibratory screen assembly. Simply put, the fewer pieces
there are to put
together, the easier the system will be to put together. However, the larger
the screen element,
the more difficult it is to injection mold extremely small structures, i.e.
the structures forming
the screening openings. It is important to minimize the size of the structures
forming the
screening openings so as to maximize the number of screening openings on an
individual
screen element and thereby optimize the open screening area for the screening
element and
thus the overall screen assembly. In certain embodiments, screen elements are
provided that
are large enough (e.g., one inch by one inch, one inch by two inches, two
inches by three
inches, one inch by six inches etc.) to make it practical to assemble a
complete screen
assembly screening surface (e.g., two feet by three feet, three feet by four
feet, etc.). The
relatively "small size" (e.g., one inch by one inch, one inch by two inches,
two inches by
three inches, etc.) is fairly large when micro-molding extremely small
structural members
(e.g., opening sizes and structural members as small as 43 microns). The
larger the size of the
overall screen element and the smaller the size of the individual structural
members forming
the screening openings, the more prone the injection molding process is to
errors such as
freezing. Thus, the size of the screen elements must be practical for screen
assembly
manufacture while at the same time small enough to eliminate problems such as
freezing
when micro-molding extremely small structures. Sizes of screening elements may
vary based
on the material being injection molded, the size of the screening openings
required and the
overall open screening area desired.
[00161] In embodiments of the present invention a thermoplastic is used to
injection mold
screen elements. As opposed to thermoset type polymers, which frequently
include liquid
materials that chemically react and cure under temperature, use of
thermoplastics is often
simpler and may be provided, e.g., by melting a homogeneous material (often in
the form of
solid pellets) and then injection molding the melted material. Not only are
the physical
properties of thermoplastics optimal for vibratory screening applications but
the use of
thermoplastic liquids provides for easier manufacturing processes, especially
when micro-
molding parts as described herein. The use of thermoplastic materials in the
present invention
provides for excellent flexure and bending fatigue strength and is ideal for
parts subjected to
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intermittent heavy loading or constant heavy loading as is encountered with
vibratory screens
used on vibratory screening machines. Because vibratory screening machines are
subject to
motion, the low coefficient of friction of the thermoplastic injection molded
materials
provides for optimal wear characteristics. Indeed, the wear resistance of
certain
thermoplastics is superior to many metals. Further, use of thermoplastics as
described herein
provides an optimal material when making "snap-fits" due to its toughness and
elongation
characteristics. The use of thermoplastics in embodiments of the present
invention also
provides for resistance to stress cracking, aging and extreme weathering. The
heat deflection
temperature of thermoplastics is in the range of 200 F. With the addition of
glass fibers, this
will increase from approximately 250 F to approximately 300 F or greater and
increase
rigidity, as measured by Flexural Modulus, from approximately 400,000 PSI to
over
approximately 1,000,000 PSI. All of these properties are ideal for the
environment
encountered when using vibratory screens on vibratory screening machines under
the
demanding conditions encounter in the field.
[00162] In this way, screen elements are provided that: are of an optimal size
(large
enough for efficient assembly of a complete screen assembly structure yet
small enough to
injection mold (micro-mold in certain embodiments) extremely small structures
forming
screening openings while avoiding freezing (i.e., material hardening in a mold
before
completely filling the mold)); have optimal open screening area (the
structures forming the
openings and supporting the openings are of a minimal size to increase the
overall open
area used for screening while maintaining, in certain embodiments, very small
screening
openings necessary to properly separate materials to a specified standard);
have durability
and strength, can operate in a variety of temperature ranges; are chemically
resistant; are
structurally stable; are highly versatile in screen assembly manufacturing
processes; and
are configurable in customizable configurations for specific applications.
[00163] Further, screening elements, subgrids, and screen assemblies may have
different
shapes and sizes as long as structural support members of subgrids are
provided to support
corresponding reinforcement members of screening elements. Screens, subgrids,
and
screen assemblies are designed to withstand high vibratory forces (e.g.,
accelerations in a
range of 3 ¨ 9G), abrasive materials (e.g., fluids having several percent to
up to 65 percent
abrasive solids) and high load demands (e.g., fluids having specific gravity
up to 3 pounds
per gallon). Screen assemblies are also designed to withstand up to 2000 ¨
3000 lb
compressive loading of screen assembly edges as described, for example, in
U.S. Patent
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Nos. 7,578,394 and 9,027,760, the entire disclosure of each of which is hereby
incorporated by references. Further, the disclose screening assemblies are
designed so that
a size of screening openings is maintained under service conditions including
the above-
mentioned compressive loading, high vibratory forces, and in the presence of
heavy fluids
Development of Suitable Compositions
[00164] The above-described embodiments provide TPU compositions expressed in
ranges
of the various components. Improved materials were obtained by varying the
composition of
TPU materials and percentages of fillers, flow agents, and other additives.
Screening
members were generated using injection molding processes based on the various
compositions. The screening members were attached to subgrid structures and
assembled
into large-area screening assemblies that were used in field testing
applications.
[00165] FIG. 4 illustrates an example screening assembly that was generated
from
screening members and subgrid structures as described above with reference to
FIGS. 1 to
3A, according to disclosed embodiments.
[00166] FIG.
5 illustrates results of actual field testing of screening assemblies, accord
to
an embodiment. The data presented in FIG. 5 represents results of testing
embodiment
screening assemblies for screening materials produced during oil and gas
exploration at
depths extending to at least about 100,000 feet 5,000 feet. The best
performing
composition BB had a glass fiber (10 p.m diameter) content of about 7%, while
the next-best
performing composition BA had a glass fiber (10 p.m diameter) content of about
5%. Each
composition also had flow agent content of about 0.5%, and a heat stabilizer
content of about
1.5%. The screen element surface elements 84 (e.g., see FIG. 2) had thickness
T about 0.014
inch in all of the tests for which results are presented in FIG. 5.
[00167] In additional embodiments, screening members having surface elements
84 having
smaller thicknesses including T = 0.007 inch, 0.005 inch, and 0.03 inch, where
generated.
For large bar thickness, for example, 0.014 inch, a larger amount of glass
filler can be added
whereas for intermediate thicknesses, i.e., 0.005 inch and 0.007 inch a lesser
amount of filler
is necessary to sufficiently stiffen the structure while still allowing for
facile injection
molding. For elements having a small bar thickness, for example, 0.003 inch, a
small amount
of filler is necessary. For these embodiments, it was advantageous to use
lower
concentrations of filler, flow agent, and thermal stabilizers as shown in
Table 1 below.
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TABLE 1
T = 0.014 inch T = 0.007 inch T = 0.005 inch T = 0.003
inch
filler 7% 5% 3% 2%
heat 1.5% 1.5% 1.13% 0.85%
stabilizer
flow agent 0.5% 0.5% 0.38% 0.28%
[00168] As features sizes are reduced, it may be advantageous to include
higher filler
percentages to allow the material to better fill all spaces in the mold.
Tables 2, 3, 4, and 5,
show filler percentages that were found to be advantageous for various screen
opening widths
W, for each of the four values of T shown above in Table 1.
[00169] Table 2 shows filler percentages as a function of screen opening width
W for
screen opening thickness T = 0.014 inch.
TABLE 2
W> 0.0046 in 0.0046 in > W> 0.0033 in W < 0.0033 in
filler 0.0% 0.0% 0.0%
[00170] Thus, for T = 0.0014 in, all values of W in the above recited ranges
may be
manufactured with virgin material (i.e., no filler).
[00171] Table 3 shows filler percentages as a function of screen opening width
W for
screen opening thickness T = 0.007 inch.
TABLE 3
W> 0.0046 in 0.0046 in > W> 0.0033 W < 0.0033 in
in
filler 0.0% 2.5% or greater 5.0% or greater
[00172] Table 4 shows filler percentages as a function of screen opening width
W for
screen opening thickness T = 0.005 inch.
TABLE 4
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W> 0.0046 in 0.0046 in > W> 0.0033 W < 0.0033 in
in
filler 0.0% 2.5% or greater 5.0% or
greater
[00173] Table 5 shows filler percentages as a function of screen opening width
W for
screen opening thickness T = 0.003 inch.
TABLE 5
W> 0.0046 in 0.0046 in > W> 0.0033 W < 0.0033 in
in
filler 5.0% or greater 5.0% or greater 5.0% or
greater
[00174] A variety of screen elements having a range of sizes for length L,
width W, and
thickness T, were generated using the above-described compositions, as shown
below in
Tables 6 to 9 below.
[00175] Table 6 illustrates the percent open area of example embodiments of
screen
elements with fixed thickness T = 0.014 in, fixed length L = 0.076 in, and
variable width W.
TABLE 6
mesh W (in) T (in) L (in) % open area
80 0.0071 0.014 0.076 23.3
100 0.0059 0.014 0.076 20.3
120 0.0049 0.014 0.076 17.6
140 0.0041 0.014 0.076 13.4
170 0.0035 0.014 0.076 12.2
200 0.0029 0.014 0.076 10.3
230 0.0025 0.014 0.076 9.1
270 0.0021 0.014 0.076 7.9
325 0.0017 0.014 0.076 6.2
[00176] Table 7 illustrates the percent open area of example embodiments of
screen
elements with fixed thickness T = 0.007 in, fixed length L = 0.046 in, and
variable width W.
TABLE 7
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mesh W (in) T (in) L (in) % open area
80 0.0071 0.007 0.046 27.3
100 0.0059 0.007 0.046 25.2
120 0.0049 0.007 0.046 23.1
140 0.0041 0.007 0.046 20.5
170 0.0035 0.007 0.046 18.5
200 0.0029 0.007 0.046 16.5
230 0.0025 0.007 0.046 14.9
270 0.0021 0.007 0.046 12.8
325 0.0017 0.007 0.046 10.1
[00177] Table 8 illustrates the percent open area of example embodiments of
screen
elements with fixed thickness T = 0.005 in, fixed length L = 0.032 in, and
variable width W.
TABLE 8
mesh W (in) T (in) L (in) % open area
80 0.0071 0.005 0.032 31.4
100 0.0059 0.005 0.032 29.3
120 0.0049 0.005 0.032 27.0
140 0.0041 0.005 0.032 24.1
170 0.0035 0.005 0.032 22.0
200 0.0029 0.005 0.032 19.7
230 0.0025 0.005 0.032 16.4
270 0.0021 0.005 0.032 14.7
325 0.0017 0.005 0.032 12.1
[00178] Table 9 illustrates the percent open area of example embodiments of
screen
elements with fixed thickness T = 0.003 in, fixed length L = 0.028 in, and
variable width W.
TABLE 9
mesh W (in) T (in) L (in) % open area
80 0.0071 0.003 0.028 32.2
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100 0.0059 0.003 0.028 30.1
120 0.0049 0.003 0.028 27.8
140 0.0041 0.003 0.028 25.2
170 0.0035 0.003 0.028 23.1
200 0.0029 0.003 0.028 20.1
230 0.0025 0.003 0.028 17.2
270 0.0021 0.003 0.028 15.3
325 0.0017 0.003 0.028 13.2
[00179] The above-described embodiments relate to varying a filler percentage
based on
screening opening dimensions T, L, and W. In further embodiments, fiber length
and
diameter may be varied to determine optimal values of length and diameter as a
function of
T, L, and W.
[00180] In some embodiments, a presence of filler material may affect a
materials'
durability over time. In certain embodiments, a larger percentage of filler
may lead to a
shorter lifetime of the material. In this way, for a given application, there
may be tradeoff in
material properties vs. concentration of filler material. For example,
increasing a percentage
of filler material may strengthen the material, may help to avoid material
shrinkage, and may
make the material less prone to sticking to the mold. However, the improvement
of
mechanical properties must be weighed against the potential for the material
to have a
reduced lifetime due to the larger percentage of filler.
[00181] Further, increasing a percentage of filler material may change the
materials'
optical properties, which may affect the materials' suitability for use with
laser welding. In
addition to the percentage of filler material, the choice of filler material
may also affect the
materials' optical properties. For example, use of carbon fibers may lead to
greater optical
absorption relative to a material in which glass fibers are used. Further,
optical absorption is
generally frequency/wavelength dependent. In this regard, darker materials
(e.g., materials
with carbon fibers) may require the use of longer wavelength laser radiation
for laser welding
in comparison to lighter materials (e.g., materials with glass fibers).
[00182] Further compositions may be provided that do not include fillers,
additional heat
stabilizers, and/or flow agents. Further, hardness and other properties of the
resulting
composition may be controlled by appropriate mixing of various materials
having different
hardness values and other properties. For example, a composition may be
provided that
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includes a mixture of a first thermoplastic polyurethane having a first
hardness, and a second
thermoplastic polyurethane having a second hardness. In an example embodiment,
the first
and second thermoplastic polyurethanes may each include a modified ester and
the first and
second thermoplastic polyurethanes may be chosen to have different hardness
values. For
example, the first thermoplastic polyurethane may have a hardness of
approximately 59
Shore D durometer, and the second thermoplastic polyurethane may have a
hardness of
approximately 95 Shore A durometer. In this way, a composition having a
mixture of the
first and second thermoplastic polyurethanes may be generated that has a has a
hardness in a
range from approximately 95 Shore A durometer to 59 Shore D durometer.
[00183] Further compositions, for example, may have a hardness in a range from
approximately 48 to 53 Shore D durometer or may have a hardness in a range
from
approximately 54 to 58 Shore D durometer. Further embodiments may have a
variety of
hardness values depending on the hardness values of the materials in the
mixture and the
relative proportions of such materials. For example, a composition may be
provided having a
50/50 mixture of the first and second polyurethanes or may have any suitable
ratio of first and
second polyurethanes depending on the desired properties of the resulting
material.
[00184] Each of the first and second thermoplastic polyurethanes may be
obtained by a
process in which a urethane prepolymer, having a free polyisocyanate monomer
content of
less than 1% by weight, is reacted with a curing agent, and then the resulting
material is
processed by extrusion at temperatures of 150 C or higher. The resulting
composition may
be suitable for use in injection molding of articles that have pore sizes in a
range from
approximately 35 microns to approximately 150 microns. Such articles may
include screen
elements having an open screening area in a range from approximately 10% to
approximately
35%.
[00185] The urethane prepolymer, mentioned above, may be prepared from a
polyisocyanate monomer and a polyol comprising an alkane diol, polyether
polyol, polyester
polyol, polycaprolactone polyol and/or polycarbonate polyol, and the curing
agent includes a
diol, triol, tetrol, alkylene polyol, polyether polyol, polyester polyol,
polycaprolactone polyol,
polycarbonate polyol, diamine or diamine derivative.
[00186] A disclosed method of manufacturing a screen element may include
generating a
composition having a thermoplastic polyurethane and injection molding the
screen element
using the generated composition. The screen element may be injection molded to
have
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openings having a size in a range from approximately 35 microns to
approximately 150
microns and to have an open screening area of the screen element in a range
from
approximately 10% to approximately 35%.
[00187] In this method, the composition may be generated by reacting a first
thermoplastic
polyurethane having a first hardness with a second thermoplastic polyurethane
having a
second hardness at a temperature greater than about 150 C. The first and
second
polyurethanes may be chosen to each include a modified ester and to have a
specific hardness
value. For example, the first thermoplastic polyurethane may have a hardness
of
approximately 59 Shore D durometer, and the second thermoplastic polyurethane
may have a
hardness of approximately 95 Shore A durometer. In this way, a composition
having a
mixture of the first and second thermoplastic polyurethanes may be generated
that has a has a
hardness in a range from approximately 95 Shore A durometer to 59 Shore D
durometer.
[00188] In various embodiments, the resulting screen element may have openings
having a
shape that is approximately rectangular, square, circular, or oval shaped. In
other
embodiments, the screen element may have openings that are elongated slots
having a length
L, and width W, separated by surface elements having a thickness T, as
described above with
reference to FIG. 2, and with reference to Tables 6 to 9. The thickness T of
the surface
elements, for example, may be in a range from approximately 0.003 inch to
0.020 inch, or the
thickness T may be approximately 0.014 inch, 0.007 inch, 0.005, inch, 0.003
inch, etc. The
width W of the surface elements, for example, may be in a range from
approximately 0.0015
inch to approximately 0.0059 inch in some embodiments, and in further
embodiments, a
length-to-width ratio L/W of the elongated slots may have a value in a range
from
approximately 1:1 to approximately 30:1. Further geometric parameters of
screen elements
may be varied, as described below with reference to FIGS. 6A to 8C and Table
10, and
corresponding suitable compositions may be developed having properties that
are tailored to
specific geometries of articles to be injection molded.
[00189] FIGS. 6A to 6C illustrate various views of a screen element 600 that
includes
screening openings having rounded corners, according to an embodiment. FIG. 6A
illustrates
a top view of screen element 600 and FIG. 6B illustrates a side view 604 of
screen element
600 of FIG. 6A, according to an embodiment. A small portion 602 of screen
element 600 of
FIG. 6A is shown in an exploded view 606 in FIG. 6C, according to an
embodiment. As
shown in FIG. 6C, each of the screening openings 608 includes rounded corners.
The
rounded corners of screening openings 608 act to reduce local stress
concentrations that
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typically form near sharp corners, such as corners of screening openings in
other
embodiments.
[00190] For example, in certain other embodiments, sharp corners may create an
increased
stress concentration factor near intersection points of the screen surface
elements and walls of
the screen element. These stress concentration factors may cause premature
panel failure. A
common point of failure may occur when a surface element breaks away from a
wall of the
screen element. To extend screen life, a fillet has been added to each of the
sharp edges in
the embodiments of FIGS. 6A to 6C to yield rounded corners, as shown. The
presence of this
added fillet reduces geometric discontinuities and leads to a decrease in the
intensity of the
local stress field where the bars connect to the walls. Additional advantages
include improved
ease of injection molding by allowing a wider path through which material may
travel during
filling. The reduction in sharp corners also promises to reduce material shear
during injection
molding, which may otherwise be a cause of premature material degradation. The
advantages of embodiments having rounded corners may possibly be offset by
disadvantages
including slightly reduced open area caused by the fillets. There may also be
a potential for
increased blinding due to the decreased slot width due to the presence of the
fillets.
[00191] FIGS. 7A to 7D illustrate embodiments in which screening apertures may
have
different orientations, according to an embodiment. FIG. 7A illustrates a top
view of a screen
element 700 that includes transversely aligned screening openings, according
to an
embodiment. FIG. 7B illustrates an exploded top view of a portion of the
screen element 700
of FIG. 7A showing details of transversely aligned screening openings,
according to an
embodiment. FIG. 7C illustrates a top view of a screen element 702 that
includes
longitudinally aligned screening openings, and FIG. 7D illustrates an exploded
top view of a
portion of the screen element 702 of FIG. 7C showing details of longitudinally
aligned
screening openings, according to an embodiment.
[00192] FIGS. 8A to 8C illustrate cross-sectional views of several embodiment
surface
elements 84 (e.g., see FIG. 2). Each surface element 84 has a top flat surface
802 having a
thickness T. While FIG. 2 presents a top view of a screen element having
surface elements
84, each of FIGS. 8A to 8C presents an edge cross-section view of a single
surface element
84 viewed from a direction looking right-to-left in the plane of FIG. 2. Thus,
a bottom-to-up
direction in each of FIGS. 8A to 8C corresponds to a direction perpendicular
to the screen
element surface of FIG. 2. The surface elements in FIGS. 8A to 8C respectively
have
thicknesses T of 0.007 inch, 0.005 inch, and 0.005 inch. Surface elements 84
may have
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various geometries extending into the surface (i.e., downwardly in FIGS 8A to
8C). Surface
elements 84 in each of FIGS. 8A to 8A have a tapered shape, although surface
elements 84
may have many other shapes in other embodiments.
[00193] Surface elements 84 in FIGS. 8A and 8B each have a tapered shape
having flat
side surfaces 804 that are inclined at an angle relative to a vertical
direction (i.e., an up-down
direction in FIGS. 8A, 8B, and 8C). In this regard, the surfaces 804 in FIG.
8A subtend an
angle 806 of approximately 15 degrees, while surfaces 804 in FIG. 8B subtend
an angle 806
of approximately 12 degrees. In the geometry of FIGS. 8A and 8B, the surface
thickness T
and angle 806 of the surface element 84 side edges 804 determines a depth 808
of the surface
elements 84 into the surface. In this example, surface element 84 of FIG. 8A
extends to a
depth 808 of approximately 0.015 inch, while surface element 84 of FIG. 8B
extends to a
depth 808 of approximately 0.009 inch. Bottom edges 810 of surface elements 84
in FIGS.
8A and 8B may have various geometries. In this example, surface elements 84 of
FIGS. 8A
and 8B each have a rounded shape characterized by a radius of curvature. The
radius of
curvature of surface elements 84 in FIGS. 8A and 8B is approximately 0.0018
inch.
[00194] FIG. 8C illustrates a surface element having a different geometry from
that of
FIGS. 8A and 8B. In this regard, side edges of surface element 84 in FIG. 8C
may have a
dual-taper design. A first portion 812 of side edges of surface element 84 in
FIG. 8C may
subtend a first angle 814, while a second portion 816 of side edges of surface
element 84 in
FIG. 8C may subtend a second angle 818. For example, first portion 812 may
subtend an
angle 814 of approximately 15 degrees and extend to a depth 820 of
approximately 0.004
inch. Similarly, second portion 816 may subtend an angle of approximately 4
degrees and
extend to a depth 822 of approximately 0.008 inch. In this example, first 812
and second 816
portions together extend to a depth 824 of approximately 0.012 inch. As with
surface
elements 84 of FIGS. 8A and 8B, surface element 84 of FIG. 8C may have a
rounded bottom
edge 810 characterized by a radius of curvature. In this example, bottom edge
810 of surface
element 84 of FIG. 8C has a radius of curvature of approximately 0.0018 inch.
[00195] A comparison of FIGS. 8B and 8C shows that surface element 84 of FIG.
8C
extends to a greater depth (i.e., approximately 0.012 inch) than surface
element 84 of FIG. 8B
(i.e., extending to approximately 0.008 inch). The greater depth of surface
element 84 of
FIG. 8C may allow surface element 84 of FIG. 8C to have greater strength than
surface
element 84 of FIG. 8B. Second portion 816 has a smaller width than the width
of first
portion 812. As such, adjacent surface elements 84 having the dual-taper shape
of FIG. 8C
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allow greater space between adjacent surface elements 84 relative to surface
elements 84 of
FIG. 8B. As such, a screen element having surface elements 84 having a
configuration as
shown in FIG. 8C may be stronger and may be less prone to blinding (i.e.,
blocking of screen
openings 86 of FIG. 2) relative to a screen element having surface elements 84
of FIG. 8B,
due to the additional space between adjacent surface elements 84 of FIG. 8C.
[00196] In certain screening applications, it may be advantageous to adapt or
alter an
amount of, and location of, attachment of screen elements to subgrids. As
described above
with reference to FIGS. 3 and 3A, a screen element 416 may be attached to a
subgrid 414.
For example, screen element 416 may be attached to subgrid 414 via laser
welding. In this
regard, fusion bars 476 and 478 may engage with corresponding cavity pockets
472 (e.g., see
FIGS. 1B and 1C) of screen element 416. Application of laser radiation may
then be used to
melt fusion bars 476 to thereby form a bond between screen element 416 and
subgrid 414. In
some embodiments, it may be advantageous to melt all of the fusion bars 476 to
thereby form
a tight connection between screen element 416 and subgrid 414. In other
embodiments, it
may be advantageous to laser weld only a sub-set of fusion bars 476 to thereby
form a less-
tight connection between screen element 416 and subgrid 414. Points at which
fusion bars
476 are not laser welded to subgrid 414 allow motion of screen element 416
relative to
subgrid 414, as described in greater detail below.
[00197] FIG. 9 illustrates a top view of a screen element and frame assembly
900 with
various regions 901 to 920 that may be laser welded to an underlying subgrid,
according to an
embodiment. As described above, laser welding all of regions 901 to 920 leads
to a strong
binding between screen element 900 and subgrid. Such a fully-welded
configuration allows
little relative motion between screen element 900 and the underlying subgrid.
In further
configurations, some of the potential laser weld locations (i.e., some of
regions 901 to 920)
may be left un-welded to allow relative motion between screen element 900 and
the
underlying subgrid.
[00198] In a first example application, a screen element fully bonded to a
subgrid would
be desirable for a situation in which a screening operation is needed to be
performed for
dewatering of a high-solids slurry. In such an application, it would be
desirable to assure that
the screen is completely and securely attached to the support subgrid. In this
regard, screen
element 900 may be laser welded to the underlying subgrid around a perimeter
and across the
middle of the screen element including laser welding all regions 901 to 920.
Such a
configuration would allow the assembly (screen and subgrid) to move as a rigid
unit in
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unison with vibrating motion of the vibrating screening machine. This is
especially useful
when dewatering heavy solids at high flow rates and at high accelerations
(i.e., high G
forces). Such solids must be moved quickly along a screening surface. This
sometimes
occurs at high G forces or large amplitudes of motion at the screen surface.
In such a
situation, any relative movement of the subgrid and screen surface that is not
in sync with the
vibrating screening machine may cause a reduction in conveyance of solids and,
in turn, a
reduction in a flow of material through the screen.
[00199] In other situations, it may be desirable to have a screen element that
is not fully
laser-welded to the underlying subgrid. As such, during operation, relative
motion (i.e., 2'
order movement) between the screen element and the subgrid may be beneficial.
For
example, in a dry screening or sifting application (i.e., attrition screening)
a 2nd order
movement or vibration of the screen element or surface relative to the subgrid
may aid in de-
blinding of the screen (i.e., removing particles that may in certain
situations become stuck in
screen openings). A slight vertical impact or force could be applied in order
to dislodge
particles that are transitionally retained in the tapered screen openings.
Such a situation may
occur, for example, in square or slotted screen openings.
[00200] For this type of application, it may be beneficial to generate a
partially bonded
screen element in screen element and frame assembly 900 (e.g., see FIG. 9) by
bonding (e.g.,
via laser welding) regions 905, 906, 907, 901, 909, 910, 912, 913, 915, 916,
917, and 920,
while leaving regions 902, 903, 904, 908, 911, 914, 918, and 919 un-bonded.
Such a
configuration would allow vertical movement of the screen element surface and
would aid in
dislodging transitionally retained particles form screen element openings due
to impacts
between screen element 900 and a surface of the subgrid.
[00201] FIG.
10 illustrates a vibrational amplitude profile of a screen element 900 that is
partially bonded to a subgrid 1000, according to an embodiment. In this
example, screen
element 900 is bonded to subgrid 1000 to allow movement in only one direction
perpendicular to a surface of subgrid 1000. In this configuration, vibrational
motion of
screen element 900 relative to subgrid 1000 occurs in a direction
perpendicular to the surface
of subgrid 1000 such that the amplitude has maxima at first 1002a and second
locations
1002b, as shown in FIG. 10. Further, screen element 900 is bonded to have zero
amplitude of
relative motion at first 1004a, second 1004b, and third 1004c locations such
that screen
element 900 moves rigidly with subgrid 1000 at these locations. In this
example, vertical
motion causes screen element 900 to pull away from subgrid 1000 on an up stoke
and to
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impact subgrid 1000 on a down stroke. As described above, such motion may be
useful in
dry screening application to aid in de-blinding.
[00202] In addition to a bonding configuration of screen element 900 to
subgrid 1000 (e.g.,
see FIGS. 9 and 10), material properties of subgrid 1000 may influence
relative motion of
screen 900 and subgrid. For example, subgrids 1000 may be configured to be
more or less
rigid based on thickness and the types of materials used to construct subgrid
1000. As such,
it may be desirable to have a subgrid 1000 that is more rigid for applications
in which screen
element 900 is tightly bonded to subgrid 1000. Alternatively, in other
applications, it may be
advantageous to have subgrids 1000 that are less rigid to allow more relative
motion between
subgrid 1000 and partially bonded screen element 900. Further, toughness of
subgrid
materials may influence relative motion of screen element 900 and subgrid 1000
due to the
relative tendency of subgrid materials to absorb more/less vibrational energy
for materials
having greater/lesser toughness.
[00203] In addition to the mechanical properties of the subgrid, the
mechanical properties
of screen elements may be varied as needed for a given embodiment. For
example, as
described above, the hardness of the material used to generate screen elements
may be chosen
based on the composition. A harder material may be desirable for applications
requiring the
screen element to be tightly secured to the subgrid to prevent relative motion
of the screen
element. In contrast, a softer material may be more suitable for applications
in which the
screen element is partially secured to the subgrid, thereby allowing relative
motion between
the screen element and the subgrid (e.g., see FIG. 10). A such, a softer
material may allow
increased relative vibrational motion between the screen element and the
subgrid relative to a
harder material.
[00204] As described above, hardness and other properties of the resulting
composition
may be controlled by appropriate mixing of various materials having different
hardness
values and other properties. For example, a composition may be provided that
includes a
mixture of a first thermoplastic polyurethane having a first hardness, and a
second
thermoplastic polyurethane having a second hardness. For example, the first
thermoplastic
polyurethane may have a hardness of approximately 59 Shore D durometer, and
the second
thermoplastic polyurethane may have a hardness of approximately 95 Shore A
durometer. In
this way, a composition having a mixture of the first and second thermoplastic
polyurethanes
may be generated that has a has a hardness in a range from approximately 95
Shore A
durometer to 59 Shore D durometer. Further embodiments may have a variety of
hardness
CA 03182802 2022-11-08
WO 2021/257662 PCT/US2021/037568
values depending on the hardness values of the materials in the mixture and
the relative
proportions of such materials. For example, other compositions may have
hardness in a
range from approximately 48 to 53 Shore D durometer or may have a hardness in
a range
from approximately 54 to 58 Shore D durometer, as described above.
[00205] Example embodiments are described in the foregoing. Such example
embodiments, however, should not be interpreted as limiting. In this regard,
various
modifications and changes may be made thereunto without departing from the
broader spirit
and scope hereof. The specification and drawings are accordingly to be
regarded in an
illustrative rather than in a restrictive sense. The breadth and scope of
embodiments of the
disclosure should not be limited by any of the above-described example
embodiments, but
should be defined only in accordance with the following claims and their
equivalents.
[00206] Conditional language, such as, "can," "could," "might," or "may,"
unless
specifically stated otherwise, or otherwise understood within the context as
used, is generally
intended to convey that certain implementations could include, while other
implementations
do not include, certain features, elements, and/or operations. Thus, such
conditional language
generally is not intended to imply that features, elements, and/or operations
are in any way
required for one or more implementations or that one or more implementations
necessarily
include logic for deciding, with or without user input or prompting, whether
these features,
elements, and/or operations are included or are to be performed in any
particular
implementation.
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