U.S. patent application number 10/978286 was filed with the patent office on 2005-06-09 for flame retardant composites.
This patent application is currently assigned to SAINT-GOBAIN CERAMICS & PLASTICS, INC.. Invention is credited to Bauer, Ralph, Yener, Doruk.
Application Number | 20050124745 10/978286 |
Document ID | / |
Family ID | 35954041 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050124745 |
Kind Code |
A1 |
Bauer, Ralph ; et
al. |
June 9, 2005 |
Flame retardant composites
Abstract
A flame retardant polymer composite is disclosed. The composite
includes a polymer base material and a flame retardant filler
provided in the polymer base material, the flame retardant filler
containing seeded boehmite particulate material having an aspect
ratio of not less than 3:1
Inventors: |
Bauer, Ralph; (Niagara
Falls, CA) ; Yener, Doruk; (Shrewsbury, MA) |
Correspondence
Address: |
TOLER & LARSON & ABEL L.L.P.
5000 PLAZA ON THE LAKE STE 265
AUSTIN
TX
78746
US
|
Assignee: |
SAINT-GOBAIN CERAMICS &
PLASTICS, INC.
|
Family ID: |
35954041 |
Appl. No.: |
10/978286 |
Filed: |
October 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10978286 |
Oct 29, 2004 |
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10414590 |
Apr 16, 2003 |
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10978286 |
Oct 29, 2004 |
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10823400 |
Apr 13, 2004 |
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60374014 |
Apr 19, 2002 |
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Current U.S.
Class: |
524/437 ;
524/404; 524/405 |
Current CPC
Class: |
C01P 2004/62 20130101;
C08K 3/22 20130101; C08K 7/08 20130101; C01P 2004/10 20130101; C01P
2004/20 20130101; C01P 2004/45 20130101; C01F 7/448 20130101; C08K
7/08 20130101; C08L 101/00 20130101; C08K 2201/016 20130101; C08L
101/00 20130101; C09K 21/02 20130101; C01P 2006/12 20130101; C08K
3/22 20130101; C01F 7/02 20130101 |
Class at
Publication: |
524/437 ;
524/405; 524/404 |
International
Class: |
C08K 003/10; C08K
003/38 |
Claims
1. A flame retardant polymer composite, comprising: a polymer base
material; and a flame retardant filler provided in the polymer base
material, the flame retardant filler comprising seeded boehmite
particulate material having an aspect ratio of not less than
3:1.
2. The composite of claim 1, wherein the composite has a flame
retardancy of V-0 or V-1 according to UL94
3. The composite of claim 2, wherein the composite has a flame
retardancy of V-0.
4. The composite of claim 2, wherein the composite has said flame
retardancy in cured form.
5. The composite of claim 4, wherein the composite is a polymer
component.
6. The composite of claim 4, wherein the composite is in the form
of a surface coating solution, the composite having said flame
retardancy in coated form.
7. The composite of claim 1, wherein the polymer base material has
a flame retardancy of V-2 or higher, the filler functioning to
improve the flame retardancy to composite to V-1 or V-0 according
to UL 94.
8. The composite of claim 1, wherein the polymer base material is
selected from the group consisting of polyolefins, polyesters,
fluoropolymers, polyamides, polyimides, polycarbonates, polymers
containing styrene, epoxy resins, polyurethane, polyphenyl,
silicone, and combinations thereof.
9. The composite of claim 8, wherein the polymer base material is a
non-chlorinated polymer and is a non-fluorinated polymer, and is
selected from the group consisting of polyolefins, polyesters,
polyamides, polyimides, polycarbonates, polymers containing
styrene, epoxy resins, polyurethane, polyphenyl, and combinations
thereof.
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. The composite of claim 1, wherein the composite comprises about
0.5 to 50.0 wt % flame retardant filler.
16. The composite of claim 15, wherein the composite comprises
about 2.0 to 30.0 wt % flame retardant filler.
17. The composite of claim 16, wherein the composite comprises
about 2.0 to 15.0 wt % flame retardant filler.
18. The composite of claim 1, wherein the seeded boehmite
particulate material has an aspect ratio of not less than 4:1.
19. The composite of claim 1, wherein the seeded boehmite
particulate material has an aspect ratio of not less than 6:1.
20. (canceled)
21. The composite of claim 1, wherein the seeded boehmite
particulate material predominantly comprises platelet-shaped
particles, having a secondary aspect ratio of not less than
3:1.
22. (canceled)
23. (canceled)
24. The composite of claim 1, wherein the seeded boehmite
particulate material predominantly comprises needle-shaped
particles.
25. The composite of claim 24, wherein the needle-shaped particles
have a secondary aspect ratio of not greater than 3:1.
26. (canceled)
27. The composite of claim 1, wherein the average particle size of
the seeded boehmite particulate material is not greater than 1000
nm.
28. The composite of claim 27, wherein the average particle size is
between about 100 and 1000 nm.
29. (canceled)
30. (canceled)
31. The composite of claim 28, wherein the average particle size is
not greater than 500 nm.
32. The composite of claim 31, wherein the average particle size is
not greater than 400 nm.
33. (canceled)
34. The composite of claim 1, wherein the boehmite particulate
material has a specific surface area of not less than about 10
m.sup.2/g.
35. The composite of claim 34, wherein the specific surface area is
not less than about 50 m.sup.2/g.
36. (canceled)
37. (canceled)
38. A method of forming a flame retardant polymer composite,
comprising: providing a polymer base material; and combining a
flame retardant filler with the polymer base material to form the
flame retardant polymer composite, the flame retardant filler
comprising seeded boehmite particulate material having an aspect
ratio of not less than 3:1.
39. The method of claim 38, further including shape forming
following combining, the flame retardant composite being a polymer
component.
40. The method of claim 38, wherein the flame retardant composite
is a surface coating solution.
41. The method of claim 38, wherein the composite has a flame
retardancy of V-0 or V-1 according to UL94.
42. The method of claim 41, wherein the composite has a flame
retardancy of V-0.
43. The method of claim 38, wherein the polymer base material has a
flame retardancy of V-2 or higher, the filler functioning to
improve the flame retardancy to composite to V-1 or V-0 according
to UL 94.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is (i) a continuation-in-part application
of U.S. patent application Ser. No. 10/414,590, filed Apr. 16,
2003, which in turn is a non-provisional application of U.S.
Provisional Application 60/374,014 filed Apr. 19, 2002, and (ii) a
continuation-in-part application of U.S. patent application Ser.
No. 10/823,400, filed Apr. 13, 2004, and (iii) a
continuation-in-part of U.S. patent application Ser. No.
10/845,764, filed May 14, 2004. Priority to the foregoing
applications is hereby claimed, and the subject matter thereof
hereby incorporated by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention is generally directed to flame
retardant composites, and more particularly to flame retardant
composites that include a polymer base material and a flame
retardant filler to improve flame retardancy.
[0004] 2. Description of the Related Art
[0005] With rapid improvement in technology over the past decades,
increasing demand has been created for high performance materials,
including ceramics, metals and polymers for a myriad of
applications. For example, in the context of microelectronic
devices, market pressures dictate smaller, faster and more
sophisticated end products, which occupy less volume and operate at
higher current densities. These higher current densities further
increase heat generation and, often, operating temperatures. In
this context, it has become increasingly important for safety
concerns to implement microelectronic packaging materials that
provide exemplary flame resistance. Use of flame resistant
packaging materials is but one example among many in which product
designers have specified use of flame resistant materials. For
example, flame resistant thermoplastic polymers are in demand as
construction materials.
[0006] In addition, governmental regulatory bodies have also sought
flame resistant materials in certain applications to meet
ever-increasing safety concerns. Accordingly, the industry has
continued to demand improved composite materials, for example,
improved polymer-based materials that have desirable flame
retardant characteristics.
SUMMARY
[0007] According to an aspect of the present invention, a flame
retardant polymer composite is provided. The composite includes a
polymer base material and a flame retardant filler provided in the
polymer base material, the flame retardant filler containing seeded
boehmite particulate material having an aspect ratio of not less
than 2:1, typically not less than 3:1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention may be better understood, and its
numerous objects, features, and advantages made apparent to those
skilled in the art by referencing the accompanying drawings.
[0009] FIG. 1 illustrates a process flow for forming a polymer
composite according to an embodiment of the present invention.
[0010] FIG. 2 illustrates a thermogravimetric analysis (TGA) of
seeded boehmite vs. conventional ATH.
[0011] The use of the same reference symbols in different drawings
indicates similar or identical items.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0012] According to one aspect of the present invention, a flame
retardant polymer composite is provided, which includes a polymer
base material and a flame retardant filler. Notably the flame
retardant filler includes a seeded boehmite particulate material
having an aspect ratio of not less than about 3:1. Typically, the
polymer based material is a material that has commercial
significance and demand in industry, but oftentimes does not
exhibit native flame retardant properties. Quantitatively, flame
retardancy may be measured according to underwriter laboratories
test UL 94, the so called vertical burn test. The UL 94 test is
carried out by ASTM D635 standards, and materials are given a V
rating based upon several observed characteristics including flame
time, glow time, extent of burning, as well as the ability of the
sample to ignite cotton. Typically, the polymer based materials of
interest and in need of flame retardant characteristics have a UL
94 rating of V-2 or above, indicating volatility under certain
conditions. Additional features of the polymer base material
according to embodiments of the present invention are discussed
below. First, we turn to the flame retardant filler, particularly,
the seeded boehmite particulate material according to embodiments
of the present invention that contributes to significant
improvement in flame retardancy.
[0013] According to a particular feature, the seeded boehmite
particulate material is utilized rather than boehmite derived from
non-seeded processing pathways, including non-seeded hydrothermal
treatment and precipitation pathways. As discussed in more detail
below, embodiments of the present invention have demonstrated
exemplary flame retardancy, even without relying on additional
flame retardant components to improve performance.
[0014] Seeded boehmite particulate material is generally formed by
a process that includes providing a boehmite precursor and boehmite
seeds in a suspension, and heat treating (such as by hydrothermal
treatment) the suspension (alternatively sol or slurry) to convert
the boehmite precursor into boehmite particulate material formed of
particles or crystallites. According to a particular aspect, the
boehmite particulate material has a relatively elongated
morphology, described generally herein in terms of aspect ratio,
described below.
[0015] The term "boehmite" is generally used herein to denote
alumina hydrates including mineral boehmite, typically being
Al.sub.2O.sub.3.H.sub.2O and having a water content on the order of
15%, as well as psuedoboehmite, having a water content higher than
15%, such as 20-38% by weight. It is noted that boehmite (including
psuedoboehmite) has a particular and identifiable crystal
structure, and accordingly unique X-ray diffraction pattern, and as
such, is distinguished from other aluminous materials including
other hydrated aluminas such as ATH (aluminum trihydroxide) a
common precursor material used herein for the fabrication of
boehmite particulate materials.
[0016] The aspect ratio, defined as the ratio of the longest
dimension to the next longest dimension perpendicular to the
longest dimension, is generally not less than 2:1, and preferably
not less than 3:1, 4:1, or 6:1. Indeed, certain embodiments have
relatively elongated particles, such as not less than 9:1, 10:1,
and in some cases, not less than 14:1. With particular reference to
needle-shaped particles, the particles may be further characterized
with reference to a secondary aspect ratio defined as the ratio of
the second longest dimension to the third longest dimension. The
secondary aspect ratio is generally not greater than 3:1, typically
not greater than 2:1, or even 1.5:1, and oftentimes about 1:1. The
secondary aspect ratio generally describes the cross-sectional
geometry of the particles in a plane perpendicular to the longest
dimension.
[0017] Platey or platelet-shaped particles generally have an
elongated structure having the aspect ratios described above in
connection with the needle-shaped particles. However,
platelet-shaped particles generally have opposite major surfaces,
the opposite major surfaces being generally planar and generally
parallel to each other. In addition, the platelet-shaped particles
may be characterized as having a secondary aspect ratio greater
than that of needle-shaped particles, generally not less than about
3:1, such as not less than about 6:1, or even not less than 10:1.
Typically, the shortest dimension or edge dimension, perpendicular
to the opposite major surfaces or faces, is generally less than 50
nanometers.
[0018] Morphology of the seeded boehmite particulate material may
be further defined in terms of particle size, more particularly,
average particle size. Here, the seeded boehmite particulate
material, that is, boehmite formed through a seeding process
(described in more detail below) has a relatively fine particle or
crystallite size. Generally, the average particle size is not
greater than about 1000 nanometers, and fall within a range of
about 100 to 1000 nanometers. Other embodiments have even finer
average particle sizes, such as not greater than about 800
nanometers, 600 nanometers, 500 nanometers, 400 nanometers, and
even particles having an average particle size smaller than 300
nanometers, representing a fine particulate material. In certain
embodiments, the average particle size was less than 200
nanometers, such as within a range of about 100 nanometers to about
150 nanometers.
[0019] As used herein, the "average particle size" is used to
denote the average longest or length dimension of the particles.
Due to the elongated morphology of the particles, conventional
characterization technology is generally inadequate to measure
average particle size, since characterization technology is
generally based upon an assumption that the particles are spherical
or near-spherical. Accordingly, average particle size was
determined by taking multiple representative samples and physically
measuring the particle sizes found in representative samples. Such
samples may be taken by various characterization techniques, such
as by scanning electron microscopy (SEM).
[0020] The present seeded boehmite particulate material has been
found to have a fine average particle size, while oftentimes
competing non-seeded based technologies are generally incapable of
providing such fine average particle sizes in the context of
anisotropic particles. In this regard, it is noted that oftentimes
in the literature, reported particle sizes are not set forth in the
context of averages as in the present specification, but rather, in
the context of nominal range of particle sizes derived from
physical inspection of samples of the particulate material.
Accordingly, the average particle size will lie within the reported
range in the prior art, generally at about the arithmetic midpoint
of the reported range, for the expected Gaussian particle size
distribution. Stated alternatively, while non-seeded based
technologies may report fine particle size, such fine sizing
generally denotes the lower limit of an observed particle size
distribution and not average particle size.
[0021] Likewise, in a similar manner, the above-reported aspect
ratios generally correspond to the average aspect ratio taken from
representative sampling, rather than upper or lower limits
associated with the aspect ratios of the particulate material.
Oftentimes in the literature, reported particle aspect ratios are
not set forth in the context of averages as in the present
specification, but rather, in the context of nominal range of
aspect ratios derived from physical inspection of samples of the
particulate material. Accordingly, the average aspect ratio will
lie within the reported range in the prior art, generally at about
the arithmetic midpoint of the reported range, for the expected
Gaussian particle morphology distribution. Stated alternatively,
while non-seeded based technologies may report aspect ratio, such
data generally denotes the lower limit of an observed aspect ratio
distribution and not average aspect ratio.
[0022] In addition to aspect ratio and average particle size of the
particulate material, morphology of the particulate material may be
further characterized in terms of specific surface area. Here, the
commonly available BET technique was utilized to measure specific
surface area of the particulate material. According to embodiments
herein, the boehmite particulate material has a relatively high
specific surface area, generally not less than about 10 m.sup.2/g,
such as not less than about 50 m.sup.2/g, 70 m.sup.2/g, or not less
than about 90 m.sup.2/g. Since specific surface area is a function
of particle morphology as well as particle size, generally the
specific surface area of embodiments was less than about 400
m.sup.2/g, such as less than about 350 or 300 m.sup.2/g.
[0023] Turning to the details of the processes by which the
boehmite particulate material may be manufactured, generally
ellipsoid, needle, or platelet-shaped boehmite particles are formed
from a boehmite precursor, typically an aluminous material
including bauxitic minerals, by hydrothermal treatment as generally
described in the commonly owned patent described above, U.S. Pat.
No. 4,797,139. More specifically, the boehmite particulate material
may be formed by combining the boehmite precursor and boehmite
seeds in suspension, exposing the suspension (alternatively sol or
slurry) to heat treatment to cause conversion of the raw material
into boehmite particulate material, further influenced by the
boehmite seeds provided in suspension. Heating is generally carried
out in an autogenous environment, that is, in an autoclave, such
that an elevated pressure is generated during processing. The pH of
the suspension is generally selected from a value of less than 7 or
greater than 8, and the boehmite seed material has a particle size
finer than about 0.5 microns. Generally, the seed particles are
present in an amount greater than about 1% by weight of the
boehmite precursor (calculated as Al.sub.2O.sub.3), and heating is
carried out at a temperature greater than about 120.degree. C.,
such as greater than about 125.degree. C., or even greater than
about 130.degree. C., and at a pressure greater than about 85 psi,
such as greater than about 90 psi, 100 psi, or even greater than
about 110 psi.
[0024] The particulate material may be fabricated with extended
hydrothermal conditions combined with relatively low seeding levels
and acidic pH, resulting in preferential growth of boehmite along
one axis or two axes. Longer hydrothermal treatment may be used to
produce even longer and higher aspect ratio of the boehmite
particles and/or larger particles in general.
[0025] Following heat treatment, such as by hydrothermal treatment,
and boehmite conversion, the liquid content is generally removed,
such as through an ultrafiltration process or by heat treatment to
evaporate the remaining liquid. Thereafter, the resulting mass is
generally crushed, such to 100 mesh. It is noted that the
particulate size described herein generally describes the single
crystallites formed through processing, rather than the aggregates
which may remain in certain embodiments (e.g., for those products
that call for and aggregated material).
[0026] According to data gathered by the present inventors, several
variables may be modified during the processing of the boehmite raw
material, to effect the desired morphology. These variables notably
include the weight ratio, that is, the ratio of boehmite precursor
to boehmite seed, the particular type or species of acid or base
used during processing (as well as the relative pH level), and the
temperature (which is directly proportional to pressure in an
autogenous hydrothermal environment) of the system.
[0027] In particular, when the weight ratio is modified while
holding the other variables constant, the shape and size of the
particles forming the boehmite particulate material are modified.
For example, when processing is carried at 180.degree. C. for two
hours in a 2 weight % nitric acid solution, a 90:10 ATH:boehmite
seed ratio forms needle-shaped particles (ATH being a species of
boehmite precursor). In contrast, when the ATH:boehmite seed ratio
is reduced to a value of 80:20, the particles become more
elliptically shaped. Still further, when the ratio is further
reduced to 60:40, the particles become near-spherical. Accordingly,
most typically the ratio of boehmite precursor to boehmite seeds is
not less than about 60:40, such as not less than about 70:30 or
80:20. However, to ensure adequate seeding levels to promote the
fine particulate morphology that is desired, the weight ratio of
boehmite precursor to boehmite seeds is generally not greater than
about 99:1, or 98:2. Based on the foregoing, an increase in weight
ratio generally increases aspect ratio, while a decrease in weight
ratio generally decreased aspect ratio.
[0028] Further, when the type of acid or base is modified, holding
the other variables constant, the shape (e.g., aspect ratio) and
size of the particles are affected. For example, when processing is
carried out at 100.degree. C. for two hours with an ATH:boehmite
seed ratio of 90:10 in a 2 weight % nitric acid solution, the
synthesized particles are generally needle-shaped, in contrast,
when the acid is substituted with HCl at a content of 1 weight % or
less, the synthesized particles are generally near spherical. When
2 weight % or higher of HCl is utilized, the synthesized particles
become generally needle-shaped. At 1 weight % formic acid, the
synthesized particles are platelet-shaped. Further, with use of a
basic solution, such as 1 weight % KOH, the synthesized particles
are platelet-shaped. If a mixture of acids and bases is utilized,
such as 1 weight % KOH and 0.7 weight % nitric acid, the morphology
of the synthesized particles is platelet-shaped.
[0029] Suitable acids and bases include mineral acids such as
nitric acid, organic acids such as formic acid, halogen acids such
as hydrochloric acid, and acidic salts such as aluminum nitrate and
magnesium sulfate. Effective bases include, for example, amines
including ammonia, alkali hydroxides such as potassium hydroxide,
alkaline hydroxides such as calcium hydroxide, and basic salts.
[0030] Still further, when temperature is modified while holding
other variables constant, typically changes are manifested in
particle size. For example, when processing is carried out at an
ATH:boehmite seed ratio of 90:10 in a 2 weight % nitric acid
solution at 150.degree. C. for two hours, the crystalline size from
XRD (x-ray diffraction characterization) was found to be 115
Angstroms. However, at 160.degree. C. the average particle size was
found to be 143 Angstroms. Accordingly, as temperature is
increased, particle size is also increased, representing a directly
proportional relationship between particle size and
temperature.
[0031] The following examples focus on seeded boehmite
synthesis.
Example 1
Plate-Shaped Particle Synthesis
[0032] An autoclave was charged with 7.42 lb. of Hydral 710
aluminum trihydroxide purchased from Alcoa; 0.82 lb of boehmite
obtained from SASOL under the name--Catapal B pseudoboehmite; 66.5
lb of deionized water; 0.037 lb potassium hydroxide; and 0.18 lb of
22 wt % nitric acid. The boehmite was pre-dispersed in 5 lb of the
water and 0.18 lb of the acid before adding to the aluminum
trihydroxide and the remaining water and potassium hydroxide.
[0033] The autoclave was heated to 185.degree. C. over a 45 minute
period and maintained at that temperature for 2 hours with stirring
at 530 rpm. An autogenously generated pressure of about 163 psi was
reached and maintained. Thereafter the boehmite dispersion was
removed from the autoclave. After autoclave the pH of the sol was
about 10. The liquid content was removed at a temperature of
65.degree. C. The resultant mass was crushed to less than 100 mesh.
The SSA of the resultant powder was about 62 m.sup.2/g. Average
particle size (length) was within a range of about 150 to 200 nm
according to SEM image analysis.
Example 2
Needle-Shaped Particle Synthesis
[0034] An autoclave was charged with 250 g of Hydral 710 aluminum
trihydroxide purchased from Alcoa; 25 g of boehmite obtained from
SASOL under the name--Catapal B pseudoboehmite; 1000 g of deionized
water; and 34.7 g of 18% nitric acid. The boehmite was
pre-dispersed in 100 g of the water and 6.9 g of the acid before
adding to the aluminum trihydroxide and the remaining water and
acid.
[0035] The autoclave was heated to 180.degree. C. over a 45 minute
period and maintained at that temperature for 2 hours with stirring
at 530 rpm. An autogenously generated pressure of about 150 psi was
reached and maintained. Thereafter the boehmite dispersion was
removed from the autoclave. After autoclave the pH of the sol was
about 3. The liquid content was removed at a temperature of
95.degree. C. The resultant mass was crushed to less than 100 mesh.
The SSA of the resultant powder was about 120 m.sup.2/g. Average
particle size (length) was within a range of about 150 to 200 nm
according to SEM image analysis.
Example 3
Ellipsoid Shaped Particle Synthesis
[0036] An autoclave was charged with 220 g of Hydral 710 aluminum
trihydroxide purchased from Alcoa; 55 g of boehmite obtained from
SASOL under the name--Catapal B pseudoboehmite; 1000 g of deionized
water; and 21.4 g of 18% nitric acid. The boehmite was
pre-dispersed in 100 g of the water and 15.3 g of the acid before
adding to the aluminum trihydroxide and the remaining water and
acid.
[0037] The autoclave was heated to 172.degree. C. over a 45 minute
period and maintained at that temperature for 3 hours with stirring
at 530 rpm. An autogenously generated pressure of about 120 psi was
reached and maintained. Thereafter the boehmite dispersion was
removed from the autoclave. After autoclave the pH of the sol was
about 4. The liquid content was removed at a temperature of
95.degree. C. The resultant mass was crushed to less than 100 mesh.
The SSA of the resultant powder was about 135 m.sup.2/g. Average
particle size (length) was within a range of about 150 to 200 nm
according to SEM image analysis.
Example 4
Near Spherical Particle Synthesis
[0038] An autoclave was charged with 165 g of Hydral 710 aluminum
trihydroxide purchased from Alcoa; 110 g of boehmite obtained from
SASOL under the name--Catapal B pseudoboehmite; 1000 g of deionized
water; and 35.2 g of 18% nitric acid. The boehmite was
pre-dispersed in 100 g of the water and 30.6 g of the acid before
adding to the aluminum trihydroxide and the remaining water and
acid.
[0039] The autoclave was heated to 160.degree. C. over a 45 minute
period and maintained at that temperature for 2.5 hours with
stirring at 530 rpm. An autogenously generated pressure of about
100 psi was reached and maintained. Thereafter the boehmite
dispersion was removed from the autoclave. After autoclave the pH
of the sol was about 3.5. The liquid content was removed at a
temperature of 95.degree. C. The resultant mass was crushed to less
than 100 mesh. The SSA of the resultant powder was about 196
m.sup.2/g.
[0040] Turning to the polymer base material of the composite, the
material may be formed of polymers including elastomeric materials,
such as polyolefins, polyesters, fluoropolymers, polyamides,
polyimides, polycarbonates, polymers containing styrene, epoxy
resins, polyurethane, polyphenyl, silicone, or combinations
thereof. In one exemplary embodiment, the polymer composite is
formed of silicone, silicone elastomer, and silicone gels.
Silicone, silicone elastomer, and silicone gels may be formed using
various organosiloxane monomers having functional groups such as
alkyl groups, phenyl groups, vinyl groups, glycidoxy groups, and
methacryloxy groups and catalyzed using platinum-based or peroxide
catalyst. Exemplary silicones may include
vinylpolydimethylsiloxane, polyethyltriepoxysilane, dimethyl
hydrogen siloxane, or combinations thereof. Further examples
include aliphatic, aromatic, ester, ether, and epoxy substituted
siloxanes. In one particular embodiment, the polymer composite
comprises vinylpolydimethylsiloxane. In another particular
embodiment, the polymer composite comprises dimethyl hydrogen
siloxane. Silicone gels are of particular interest for tackiness
and may be formed with addition of a diluent.
[0041] Aspects of the present invention are particularly useful for
polymer base materials that do not have a native, robust flame
retardancy, such as those polymers that have a flame retardancy of
V-2 or greater. For example, Nylon 6, noted below, has been
characterized as having a native flame retardancy of V-2.
Accordingly, as a subset of polymers that benefit from flame
retardancy additives according to aspects of the present invention
include: non-chlorinated polymers, non-fluorinated polymers, and
may be selected from the group consisting of polyolefins,
polyesters, polyamides, polyimides, polycarbonates, polymers
containing styrene, epoxy resins, polyurethane, polyphenyl, and
combinations thereof.
[0042] The polymer composite may comprise at least about 0.5 to
about 50 wt % boehmite particulate material, such as about 2 to
about 30 wt %. According to one feature, exemplary flame retardancy
may be achieved even a low loadings, such as within a range of
about 2 to 15 wt % of the total composite.
[0043] Oftentimes the composite material is in the form of a
component (cured form), and may find practical use as a polymer
structural component such as a construction material. Typically,
the polymer base material is combined with the boehmite filler
material to form the composite, such as by mixing the components
and, in the case of structural components, followed shape forming.
Shape forming would not be required in the case of coating
compositions.
[0044] Turning to FIG. 1, a process for forming a polymer component
in which a polymer base component is combined with boehmite. In the
particular process flow, a molded polymer component is formed by
injection molding. FIG. 1 details the process flow for nylon
6-based polymer component that may take on various contours and
geometric configurations for the particular end use. As described,
nylon-6 raw material is first dried, followed by premixing with
boehmite under various loading levels. The premixed nylon-boehmite
is then extruded to form pelletized extrudates, which are then
cooled and dried. The final article is then formed by injection
molding, the pelletized extrudates providing the feedstock material
for the molding process. The particular geometric configuration may
vary widely depending upon the end use, but here, flat bars were
extruded that were then used as test samples for flame
retardancy.
[0045] Following the foregoing process flow, two different filler
loading levels were selected for flame retardancy testing, 3 wt. %
and 5 wt. % of needle shaped (alternatively referred to as whisker
or rod-shaped) fine boehmite. The samples were tested according to
UL 94V, utilizing the classifying criteria below in Table 1.
1 TABLE 1 Criteria Conditions 94 V-0 94 V-1 94 V-2 Flame time, T1
or T2 .ltoreq.10 s .ltoreq.30 s .ltoreq.30 s Flame Time, T1 + T2
.ltoreq.50 s .ltoreq.250 s .ltoreq.250 s Glow Time, T3 .ltoreq.30 s
.ltoreq.60 s .ltoreq.60 s Did sample burn to No No No holding
clamp? yes/no Did sample ignite No No Yes cotton? Yes/no
[0046] As a result of testing, both the 3 wt. % and 5 wt. % loading
levels provided the highly desirable V-0 rating. Such exemplary
flame retardancy is notable, for various reasons. For example, the
V-0 rating was achieved at very moderate loading levels, and
without inclusion of additional flame retardant fillers. It should
be noted, however, that additional fillers may be incorporated in
certain embodiments to achieve additional flame retardancy,
although the particular seeded boehmite material described above
provides a marked improvement in flame retardancy without relying
upon additional fillers.
[0047] The above-reported flame retardancy takes on even additional
significance when compared to the state of the art. For example,
other reports have been provided in which fine boehmite material
has only been able to provide limited flame retardancy, and not V-0
as reported herein. However, the boehmite additives utilized in
these other reports is generally not a seeded boehmite, and is
formed through a non-seeded process, including non-seeded
hydrothermal processing pathways, or by precipitation. While not
wishing to be bound by any particular theory, it is believed that
the seeded processing pathway contributes to the exemplary flame
retardancy reported herein. One possible explanation for this is
that the seeded boehmite material has unique morphological
features, perhaps even beyond the morphologies described above in
connection with primary and secondary aspect ratios forming
elongated platelet and needle-shaped particulates. However, it is
additionally believed that the high aspect ratio morphologies
enabled by seeded processing pathway may also further contribute to
the exemplary flame retardancy. The high aspect ratio particles may
provide a serpentine or tortuous pathway for oxygen migration,
thereby inhibiting flame propagation due to reduced oxygen
migration to the flame front or area.
[0048] Turning to FIG. 2, the results of thermogravimetric analysis
(TGA) are reported for whisker (needle) shaped boehmite, as
compared to conventional ATH. As shown, the needle-shaped boehmite
particulate material loses crystalline (as opposed to adsorbed or
absorbed) water at lower temperatures and continues losing water at
temperatures above ATH, extending into the 500.degree. C. range.
The dynamics associated with water loss associated with the seeded
boehmite particulate material may also partially explain the flame
retardancy characteristics reported herein.
[0049] While the foregoing has focused on polymer composite
components, such as structural components, it is also noted that
the polymer composite may also be in the form of a surface coating
solution, such as a polymer-containing paint formulation. Of
course, like the polymer component described above, the flame
retardancy characteristics are generally associated with the cured
material. Accordingly, in the case of surface coating solutions,
flame retardancy is associated with the cured, dried coating. For
additional details of surface coating solutions, the reader is
directed to co-pending U.S. patent application Ser. No. 10/823,400,
filed Apr. 13, 2004, Attorney Docket Number 1055-A4363,
incorporated herein by reference.
[0050] According to a further aspect of the invention, the flame
retardant filler may also be in the form of a blend of flame
retardant components, including iron oxide, and a vitrifying
component, such as metal borates, preferably zinc borate, along
with the seeded boehmite particulate material described in detail
above. Conventional ATH may also be incorporated. Other filler may
include materials such as glass fibers, nano-clays, alumina (e.g.,
submicron alpha alumina), and carbon.
[0051] The polymer composite may further include thermally
conductive fillers, such as alumina and boron nitride. As a result,
the composite may have a thermal conductivity not less than about
0.5 W/m-K, such as not less than 1.0 W/m-K or not less than 2.0
W/m-K, particularly suitable for applications requiring a thermal
transfer performance, such as a thermal interface material used in
microelectronic applications.
[0052] While the invention has been illustrated and described in
the context of specific embodiments, it is not intended to be
limited to the details shown, since various modifications and
substitutions can be made without departing in any way from the
scope of the present invention. For example, additional or
equivalent substitues can be provided and additional or equivalent
production steps can be employed. As such, further modifications
and equivalents of the invention herein disclosed may occur to
persons skilled in the art using no more than routine
experimentation, and all such modifications and equivalents are
believed to be within the scope of the invention as defined by the
following claims.
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