U.S. patent application number 13/743909 was filed with the patent office on 2013-05-23 for surface-treated metal oxide particles.
This patent application is currently assigned to CABOT CORPORATION. The applicant listed for this patent is CABOT CORPORATION. Invention is credited to Joachim K. Floess, Dmitry Fomitchev, William R. Williams.
Application Number | 20130129597 13/743909 |
Document ID | / |
Family ID | 39792775 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130129597 |
Kind Code |
A1 |
Fomitchev; Dmitry ; et
al. |
May 23, 2013 |
SURFACE-TREATED METAL OXIDE PARTICLES
Abstract
The invention provides metal oxide particles surface-treated
with at least one alkoxysilane compound, methods of making such,
and toners comprising same.
Inventors: |
Fomitchev; Dmitry;
(Lexington, MA) ; Floess; Joachim K.; (Urbana,
IL) ; Williams; William R.; (Reading, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CABOT CORPORATION; |
Boston |
MA |
US |
|
|
Assignee: |
CABOT CORPORATION
Boston
MA
|
Family ID: |
39792775 |
Appl. No.: |
13/743909 |
Filed: |
January 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11774478 |
Jul 6, 2007 |
|
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13743909 |
|
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|
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60844828 |
Sep 15, 2006 |
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Current U.S.
Class: |
423/335 |
Current CPC
Class: |
C09C 3/12 20130101; C09C
3/041 20130101; Y10T 428/2995 20150115; C01P 2006/10 20130101; C09C
1/3081 20130101; C09C 1/3018 20130101; C01P 2006/11 20130101; G03G
9/09725 20130101; C01P 2004/62 20130101; C01P 2002/86 20130101;
C07F 7/1804 20130101; C01P 2006/12 20130101; G03G 9/09716 20130101;
C09C 3/006 20130101; C09C 1/309 20130101 |
Class at
Publication: |
423/335 |
International
Class: |
G03G 9/097 20060101
G03G009/097 |
Claims
1.-23. (canceled)
24. A method of preparing hydrophobic metal oxide particles
comprising (a) providing an aqueous dispersion of hydrophilic metal
oxide particles, (b) combining the dispersion with at least one
alkoxysilane treating agent to provide a reaction mixture, wherein
the reaction mixture is basic, and (c) drying the reaction mixture
to provide hydrophobic metal oxide particles having a tap density
of about 110 g/l to about 420 g/l or less and a BET surface area of
about 200 m.sup.2/g or less.
25. The method of claim 24, wherein the at least one alkoxysilane
compound is octyltriethoxysilane.
26. The method of claim 24, wherein the metal oxide particles are
treated with two alkoxysilane compounds.
27. The method of claim 26, wherein the two alkoxysilane compounds
are octyltriethoxysilane and 3-aminopropyltriethoxysilane.
28. The method of claim 24, wherein the particle size of the
hydrophobic metal oxide particles is reduced after the reaction
mixture is dried.
29. The method of claim 24, wherein the dispersion is prepared by
mixing a metal oxide dispersion with water and then with a
water-soluble organic solvent.
30. The method of claim 29, wherein the water-soluble organic
solvent to water volume ratio is about 0.2 to about 2.
31. The method of claim 24, wherein the reaction mixture is
maintained at a temperature of about 45.degree. C. to about
75.degree. C. for about 1 hour or longer.
32. The method of claim 24, wherein the dispersion comprises about
10 wt. % to about 25 wt. % metal oxide particles.
33. The method of claim 24, wherein the metal oxide particles are
non-aggregated metal oxide particles.
34. The method of claim 24, wherein the metal oxide particles are
colloidal silica particles.
35. A method of preparing hydrophobic metal oxide particles
comprising (a) providing an aqueous dispersion of non-aggregated
hydrophilic metal oxide particles, (b) combining the dispersion
with at least one alkoxysilane treating agent to provide a reaction
mixture, wherein the reaction mixture is basic, (c) drying the
reaction mixture to provide hydrophobic metal oxide particles, and
(d) reducing the agglomerate size of the hydrophobic metal oxide
particles by jet milling or hammer milling.
36. The method of claim 35, wherein the metal oxide particles have
a tap density of about 110 g/l to about 420 g/l.
37. The method of claim 35, wherein the metal oxide particles are
colloidal silica particles.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims the benefit of U.S.
Provisional Patent Application No. 60/844,828, filed Sep. 15, 2006,
which is incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] Hydrophobic metal oxide particles possess physical
properties that are useful in a number of applications requiring a
high degree of dispersibility. Some hydrophobic metal oxide
particles have physical properties that are desirable for use in
toner compositions.
[0003] Untreated metal oxide particles are hydrophilic due to the
presence of polar groups, such as hydroxyl groups (--OH), on the
surface of the untreated silica particles. By treating hydrophilic
metal oxide particles, the hydrophilic nature of the particles can
be reduced, thereby imparting varying degrees of hydrophobicity to
the particles. Many different methods are known for treating the
surface of metal oxide particles. However, the direct treatment of
an aqueous dispersion of metal oxide particles is often inefficient
or difficult to achieve.
[0004] Thus, there remains a desire for additional treated metal
oxide particles, especially those that are useful for modifying the
charge of toner particles, and for additional methods of preparing
such hydrophobic metal oxide particles, especially methods that can
be used to prepare hydrophobic metal oxide particles directly from
an aqueous dispersion. However, not all such particles afford the
charge-controlling characteristics that are required for some
applications.
BRIEF SUMMARY OF THE INVENTION
[0005] The invention provides a particle composition comprising
metal oxide particles surface-treated with at least one
alkoxysilane compound, which metal oxide particles are hydrophobic,
non-aggregated, and have a tap density of about 110 g/l to about
420 g/l, and a BET surface area of less than about 200
m.sup.2/g.
[0006] The invention also provides a toner composition comprising
toner particles and metal oxide particles surface-treated with at
least one alkoxysilane compound, which metal oxide particles are
hydrophobic, non-aggregated, and have a tap density of about 110
g/l to about 420 g/l and a BET surface area of less than about 200
m.sup.2/g.
[0007] The invention further provides a method of preparing
hydrophobic metal oxide particles comprising (a) providing an
aqueous dispersion of hydrophilic metal oxide particles, (b)
combining the dispersion with at least one alkoxysilane treating
agent to provide a reaction mixture, wherein the reaction mixture
is basic, and (c) drying the reaction mixture to provide
hydrophobic metal oxide particles having a tap density of about 110
g/l to about 420 g/l and a BET surface area of less than about 200
m.sup.2/g.
[0008] The invention additionally provides a method of preparing
hydrophobic metal oxide particles comprising (a) providing an
aqueous dispersion of non-aggregated hydrophilic metal oxide
particles, (b) combining the dispersion with at least one
alkoxysilane treating agent to provide a reaction mixture, wherein
the reaction mixture is basic, (c) drying the reaction mixture to
provide hydrophobic metal oxide particles, and (d) reducing the
agglomerate size of the hydrophobic metal oxide particles by jet
milling or hammer milling.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0009] FIG. 1 depicts the NMR spectra of untreated silica particles
and silica particles treated with OTES (octyltriethoxysilane).
[0010] FIG. 2 is a graph of particle size distribution by volume of
volume % particles versus diameter of particles (.mu.m) for silica
particles treated with OTES (octyltriethoxysilane) that have been
jet milled and silica particles treated with OTES that have not
been jet milled.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The invention provides a particle composition comprising
metal oxide particles surface-treated with at least one
alkoxysilane compound, which metal oxide particles are hydrophobic,
non-aggregated, and have a tap density of about 110 g/l to about
420 g/l, and a BET surface area of less than about 200 m.sup.2/g.
The inventive particles can be utilized in compositions containing
toner particles. The method of preparing the inventive metal oxide
particles comprises (a) providing an aqueous dispersion of
hydrophilic metal oxide particles, (b) combining the dispersion
with at least one alkoxysilane treating agent to provide a reaction
mixture, wherein the reaction mixture is basic, and (c) drying the
reaction mixture to provide hydrophobic metal oxide particles. The
resulting hydrophobic metal oxide particles can have a tap density
of about 110 g/l to about 420 g/l and a BET surface area of less
than about 200 m.sup.2/g and/or the method can further comprise an
additional step wherein the average particle size of the
hydrophobic metal oxide particles is reduced.
[0012] "Hydrophobic" metal oxide particles, as the term is used
herein, encompasses varying levels or degrees of hydrophobicity.
The degree of hydrophobicity imparted to the metal oxide particles
will vary depending upon the type and amount of treating agent
used. Hydrophobic metal oxide particles according to the invention
preferably, but not necessarily, have about 25% or more (e.g.,
about 35% or more, about 45% or more, or about 50% or more) of the
available metal oxide surface hydroxyl groups reacted. Generally,
the hydrophobic metal oxide particles according to the invention
have about 85% or less (e.g., about 75% or less, or about 65% or
less) of the available metal oxide surface hydroxyl groups
reacted.
[0013] The metal oxide particle can comprise any suitable type of
metal oxide particle, such as silica, alumina, ceria, or titania.
Preferably, the metal oxide particle is a colloidal metal oxide
particle, such as a colloidal silica particle. Colloidal metal
oxide particles are non-aggregated, individually discrete
particles, which typically are spherical or nearly spherical in
shape, but can have other shapes (e.g., shapes with generally
elliptical, square, or rectangular cross-sections). Such particles
are structurally different from fumed or pyrogenically prepared
particles, which are chain-like structures of aggregated primary
particles.
[0014] Non-aggregated metal oxides (e.g., colloidal metal oxides),
which can be treated to provide a surface treated metal oxide in
accordance with the invention, are commercially available, or can
be prepared by known methods from various starting materials (e.g.,
wet-process type metal oxides). Silica particles can be prepared,
for example, from silicic acid derived from an alkali silicate
solution having a pH of about 9 to about 11, wherein the silicate
anions undergo polymerization to produce discrete silica particles
having the desired average particle size in the form of an aqueous
dispersion. Typically, the colloidal metal oxide starting material
will be available as a sol, which is a dispersion of colloidal
metal oxide in a suitable solvent, most often water alone or with a
co-solvent and/or stabilizing agent. See, e.g., Akitoshi Yoshida,
Silica Nucleation, Polymerization, and Growth Preparation of
Monodispersed Sols, in Colloidal Silica Fundamentals and
Applications 47-56 (H. E. Bergna & W. O. Roberts, eds., 2006).
Non-limiting examples of commercially available colloidal silica
suitable for use in the invention include SNOWTEX.RTM. products
from Nissan Chemical, NexSil.TM. and NexSil A.TM. series products
available from Nyacol Nanotechnologies, Inc., and Levasil.RTM.
products available from H.C.Starck.
[0015] The colloidal silica from which the treated metal oxide
particle can be prepared often contains alkali metal cations as a
result of the method by which such colloidal silica was
manufactured or stabilized in dispersion. The alkali metal cations
may be present both in the interior portions of the particles, as
well as on the surface of the particles. "Free alkali metal cation"
refers to an alkali metal cation that is solubilized in the aqueous
phase of a dispersion of colloidal silica, or that is present at
the surface of the metal oxide particle, and does not refer to
alkali metal cation that may be bound or trapped within the
interior of the metal oxide particles and thus inaccessible to the
aqueous phase. The alkali metal cation can be sodium, potassium, or
any other Group I metal cation.
[0016] The free alkali metal cation content of the metal oxide
dispersion of silica can be reduced, for example, by treatment of
the aqueous colloidal dispersion with an acidic ion exchange resin.
Alternatively, or in addition, the free alkali metal cation content
of the base-stabilized dispersion of silica can be reduced by using
ultrafiltration, e.g., difiltration. Reduction of the free alkali
metal cation content also may reduce the pH of the dispersion. If
desired, the pH can be adjusted without increasing the alkali metal
content by addition of an amine or ammonium hydroxide (NH.sub.4OH).
In this respect, it is also possible to avoid the need to reduce
the alkali metal cation content of the dispersion, in accordance
with this preferred aspect of the invention, by using an
ammonium-stabilized aqueous dispersion of metal oxide as a starting
material.
[0017] Reduction of the free alkali metal cation content of the
aqueous dispersion of metal oxide, to the extent it is required,
can be performed at any time before or after the at least one
alkoxysilane is added to the aqueous dispersion of metal oxide. For
example, the free alkali metal cation reducing treatment (e.g, ion
exchange, ultrafiltration, or the like) can be performed as part of
the production process of the metal oxide dispersion, or can be
performed on a commercially available aqueous dispersion of metal
oxide before use in the invention (e.g., about 1 hour or less
before use, or about 1 day or less before use, or about 1 week or
less before use). Alternatively, such treatment can be employed
after the at least one alkoxysilane is combined with the dispersion
of metal oxide particles. Instead, or in addition, free alkali
metal cation reducing treatment also can be used to reduce the
alkali metal content of the treated metal oxide particles at a
later time, for example, by dispersing dried, treated metal oxide
particles in water or an acceptable solvent and reducing the alkali
metal content of the dispersion, after which the treated metal
oxide particles can be isolated and/or dried by any suitable
method.
[0018] An ion-exchanged aqueous dispersion is typically
characterized by having a pH of about 1 to about 7 and having a
content of free alkali metal cation of about 0.05 wt. % or less.
The basic aqueous dispersion is typically characterized by having a
pH of about 7 to about 12. Such a dispersion can be used to prepare
the inventive particles, provided that the pH of the reaction
mixture is adjusted to a pH of about 7 or more.
[0019] The hydrophilic metal oxide particle is treated with at
least one alkoxysilane compound. The at least one alkoxysilane
compound has the general formula: R.sup.1.sub.xSi(OR.sup.2).sub.4-x
wherein R.sup.1 is selected from the group consisting of
C.sub.1-C.sub.30 branched and straight chain alkyl, aminoalkyl,
alkenyl, and aminoalkenyl, C.sub.3-C.sub.10 cycloalkyl, and
C.sub.6-C.sub.10 aryl, R.sup.2 is a C.sub.1-C.sub.10 branched or
straight chain alkyl, and x is an integer of 1-3. Examples of
suitable alkoxylsilane compounds include but are not limited to
trimethylmethoxysilane, dimethyldimethoxysilane,
methyltrimethoxysilane, and the like.
[0020] Preferably, the alkoxysilane compound is a trialkoxysilane
compound. The trialkoxysilane compound can be any suitable
trialkoxysilane. For example, the trialkoxysilane compound can have
the formula: R.sup.1Si(OR.sup.2).sub.3 wherein R.sup.1 is selected
from the group consisting of C.sub.1-C.sub.30 branched and straight
chain alkyl, aminoalkyl, alkenyl, and aminoalkenyl, and
C.sub.3-C.sub.10 cycloalkyl, and R.sup.2 is a C.sub.1-C.sub.10
branched or straight chain alkyl. Preferably, the trialkoxysilane
compound is selected from the group consisting of
methyltrimethoxysilane, ethyltrimethoxysilane,
propyltrimethoxysilane, butyltrimethoxysilane,
pentyltrimethoxysilane, hexyltrimethoxysilane,
heptyltrimethoxysilane, octyltrimethoxysilane,
nonyltrimethoxysilane, decyltrimethoxysilane,
undecyltrimethoxysilane, dodecyltrimethoxysilane,
tetradecyltrimethoxysilane, stearyltrimethoxysilane,
methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane,
butyltriethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane,
heptyltriethoxysilane, octyltriethoxysilane, nonyltriethoxysilane,
decyltriethoxysilane, undecyltriethoxysilane,
dodecyltriethoxysilane, tetradecyltriethoxysilane,
stearyltriethoxysilane, and combinations thereof. More preferably,
the trialkoxysilane compound is selected from the group consisting
of hexyltrimethoxysilane, heptyltrimethoxysilane,
octyltrimethoxysilane, nonyltrimethoxysilane,
decyltrimethoxysilane, undecyltrimethoxysilane,
dodecyltrimethoxysilane, tetradecyltrimethoxysilane,
stearyltrimethoxysilane, methyltriethoxysilane,
ethyltriethoxysilane, propyltriethoxysilane, butyltriethoxysilane,
pentyltriethoxysilane, hexyltriethoxysilane, heptyltriethoxysilane,
octyltriethoxysilane, nonyltriethoxysilane, decyltriethoxysilane,
undecyltriethoxysilane, dodecyltriethoxysilane,
tetradecyltriethoxysilane, stearyltriethoxysilane,
3-aminopropyltriethoxysilane, 3-aminobutyltriethoxysilane,
3-aminobutyltriethoxysilane, and combinations thereof.
[0021] The metal oxide particle can be treated with more than one
alkoxysilane compound (e.g., at least two alkoxysilane compounds,
or at least three alkoxysilane compounds). For example, the metal
oxide particles can be treated with octyltriethoxysilane and
3-aminopropyltriethoxysilane.
[0022] The hydrophobic metal oxide particle has a pour density of
less than about 300 g/l. Typically, the metal oxide particle has a
pour density of about 50 g/l or more (e.g., about 60 g/l or more,
about 70 g/l or more, about 80 g/l or more, about 90 g/l or more,
or about 100 g/l or more). The pour density of the metal oxide
particle typically will be about 280 g/l or less, more typically
will be about 270 g/l or less (e.g., about 250 g/l or less, about
240 g/l or less, about 230 g/l or less, about 220 g/l or less, or
about 210 g/l or less). Preferably, the pour density of the metal
oxide particle is about 20 g/l to about 300 g/l, and more
preferably about 30 g/l to about 300 g/l (e.g., about 50 g/l to
about 300 g/l, about 75 g/l to about 300 g/l, about 80 g/l to about
280 g/l, about 100 g/l to about 300 g/l, or about 100 g/l to about
280 g/l).
[0023] Typically, the metal oxide particle has a tap density of
about 75 g/l or more, or about 100 g/l or more. The tap density of
the metal oxide particle typically will be about 450 g/l or less,
more typically will be about 420 g/l or less (e.g., about 400 g/l
or less, about 380 g/l or less, about 350 g/l or less, about 320
g/l or less, about 300 g/l or less, about 280 g/l or less, about
250 g/l or less, about 230 g/l or less, about 210 g/l or less, or
about 180 g/l or less). Preferably, the tap density of the metal
oxide particle is about 50 g/l to about 420 g/l, about 75 g/l to
about 400 g/l, about 80 g/l to about 380 g/l, about 110 g/l to
about 420 g/l, or about 150 g/l to about 400 g/l. The tap density
of the metal oxide particle can be determined using a tap volumeter
and the following equation: tap density (g/1)=(weight of the
treated metal oxide particles in grams).times.(1000/(volume of the
treated metal oxide particles in ml)). The ratio of pour to tap
density is approximately 0.7. Any suitable number of taps can be
taken by the tap volumeter. Preferably, the tap volumeter takes
about 300 taps or more (e.g., about 600 taps or more, about 1250
taps or more, or 3000 taps or more) of the sample of treated metal
oxide particles. All tap densities described herein, unless
otherwise indicated, were measured after 3000 taps were taken.
[0024] The hydrophobic metal oxide particle has a BET surface area
of less than about 200 m.sup.2/g (determined by the method of S.
Brunauer, P. H. Emmet, and I. Teller, J. Am. Chemical Society, 60,
309 (1938), which is commonly referred to as the BET method).
Typically, the metal oxide particle has a BET surface area of about
10 m.sup.2/g or more (e.g., about 20 m.sup.2/g or more, about 30
m.sup.2/g or more, about 40 m.sup.2/g or more, about 50 m.sup.2/g
or more, or about 60 m.sup.2/g or more). The BET surface area of
the metal oxide particle typically will be about 180 m.sup.2/g or
less, more typically will be about 160 m.sup.2/g or less (e.g.,
about 140 m.sup.2/g or less, about 120 m.sup.2/g or less, about 100
m.sup.2/g or less, about 80 m.sup.2/g or less, about 70 m.sup.2/g
or less, or about 50 m.sup.2/g or less). Preferably, the BET
surface area of the metal oxide particles is about 10 m.sup.2/g to
about 200 m.sup.2/g, and more preferably about 20 m.sup.2/g to
about 180 m.sup.2/g (e.g., about 20 m.sup.2/g to about 160
m.sup.2/g, about 20 m.sup.2/g to about 140 m.sup.2/g, about 20
m.sup.2/g to about 130 m.sup.2/g, about 20 m.sup.2/g to about 120
m.sup.2/g, or about 20 m.sup.2/g to about 100 m.sup.2/g).
[0025] The treated metal oxide particles can have any suitable
average non-agglomerated particle size. The particle size refers to
the diameter of the smallest sphere that encloses the
non-agglomerated particle. Agglomerated particles (agglomerates)
are composed of several primary particles loosely attached to each
other, usually by van der Waals forces. This is in contrast to
aggregated particles (aggregates), in which the bonds between
primary particles are stronger, as is the case when the particles
sinter. As a result, de-agglomeration can be easily achieved for
agglomerates. For example, dispersion of treated metal oxide
particles with toner particles (dry dispersion) or in a suitable
liquid (e.g., tetrahydrofuran (THF)) using high speed agitation or
sonication can be used to reverse agglomeration. However, it is
considerably more difficult or even impossible to reverse
aggregation to any significant extent. The average particle size of
the non-agglomerated hydrophobic metal oxide particles can be, for
example, less than about 1 micron (e.g., about 0.8 microns or less,
about 0.7 microns or less, about 0.5 microns or less, or about 0.3
microns or less). The average particle size of the non-agglomerated
hydrophobic metal oxide particles can be about 0.01 microns or more
(e.g., about 0.05 microns or more, about 0.1 microns or more, about
0.2 microns or more, or about 0.3 microns or more). Thus, the
average particle size of the non-agglomerated hydrophobic metal
oxide particles can be, for example, from about 0.01 microns to
about 5 microns (e.g., from about 0.05 microns to about 3 microns,
from about 0.1 microns to about 1 micron, from about 0.2 microns to
about 0.8 microns, or from about 0.3 microns to about 0.6
microns).
[0026] The hydrophilic metal oxide particle can have any suitable
true density. Typically, the metal oxide particle has a true
density of about 1.5 g/cm.sup.3 or more (e.g., about 1.6 g/cm.sup.3
or more, about 1.7 g/cm.sup.3 or more, about 1.8 g/cm.sup.3 or
more, about 1.9 g/cm.sup.3 or more, or about 2 g/cm.sup.3 or more).
The true density of the metal oxide particle typically will be
about 5 g/cm.sup.3 or less, more typically will be about 4
g/cm.sup.3 or less (e.g., about 3.5 g/cm.sup.3 or less, about 3
g/cm.sup.3 or less, about 2.8 g/cm.sup.3 or less, or about 2.5
g/cm.sup.3 or less). Preferably, the true density of the metal
oxide particle is about 0.1 g/cm.sup.3 to about 5 g/cm.sup.3, and
more preferably about 0.5 g/cm.sup.3 to about 4 g/cm.sup.3 (e.g.,
about 1 g/cm.sup.3 to about 3.5 g/cm.sup.3, about 1.5 g/cm.sup.3 to
about 3 g/cm.sup.3, about 1.8 g/cm.sup.3 to about 2.8 g/cm.sup.3,
about 2 g/cm.sup.3 to about 2.5 g/cm.sup.3, or about 2.2 g/cm.sup.3
to about 2.4 g/cm.sup.3).
[0027] The surface treatment of a hydrophilic metal oxide particle
with an alkoxysilane generates various patterns of substituted
silicon atoms attached to the surface of the metal oxide particle
or attached indirectly to the surface of the metal oxide particle.
These substitution patterns have been referred to in the literature
as M sites, D sites, and T sites. See, for example, Sindorf, Dean
William, "Silicon-29 and Carbon-13 CP/MAS NMR Studies of Silica Gel
and Bonded Silane Phases," Department of Chemistry, Colorado State
University, Fort Collins, Colo., 1982. The correlation of the M
sites, D sites, and T sites to the resonance signals in the
CP/MAS.sup.29Si NMR spectrum also is discussed in Maciel, G.,
Sindorf, D. W., J. Am. Chem. Soc., 102: 7607-7608 (1980), Sindorf,
D. W., Maciel, G., J. Phys. Chem., 86: 5208-5219 (1982), and
Sindorf, D. W., Maciel, G., J. Am. Chem. Soc., 105: 3767-3776
(1983).
[0028] In particular, the surface treatment of a hydrophilic metal
oxide particle with at least one trialkoxysilane compound in
accordance with one embodiment of the invention provides metal
oxide particles having predominantly substitution patterns referred
to as T2 and T3 sites. As used herein, T2 sites correspond to a
silicon atom originating from the alkoxysilane compound having two
bonds to oxygen atoms further bonded to silicon atoms, at least one
of which is on the metal oxide particle surface, one bond to an
oxygen atom comprising a silanol (Si--OH) group, and one bond to a
carbon atom. T2 sites are represented by formula (I):
R--Si(OH)--(OSi--P.sup.1)(OSiP.sup.2) wherein the group R is as
defined herein for the alkoxysilane compound, and P.sup.1 and
P.sup.2 independently represent a bond to a silicon atom on a
particle surface and/or a silicon atom of another silane-containing
molecule. Si atoms corresponding to T2 sites have been correlated
with the resonance signals with chemical shifts in the range from
-56 ppm to -59 ppm in the CP/MAS.sup.29Si NMR spectrum, wherein the
chemical shift in ppm is measured relative to the standard
tetramethylsilane.
[0029] As used herein, T3 sites correspond to a silicon atom
originating from the alkoxysilane compound having three bonds to an
oxygen atom further bonded to silicon atoms. At least one of the
silicon atoms is a silicon atom on a particle. The sites are
represented by the formula (II):
R--Si(OSi--P.sup.1)(OS.sup.1--P.sup.2)(OS.sup.1--P.sup.3) wherein
the group R is as herein defined for the alkoxysilane compound and
wherein P.sup.1, P.sup.2, and P.sup.3 independently represent a
bond to a silicon atom on a particle surface and/or a silicon atom
of another silane-containing molecule. Si atoms corresponding to T3
sites have been correlated with the resonance signals with chemical
shifts in the range from -65 ppm to -69 ppm in the CP/MAS .sup.29Si
NMR spectrum, wherein the chemical shift in ppm is measured
relative to the standard tetramethylsilane.
[0030] As defined herein, T2 is the integrated intensity of a peak
having a chemical shift in the CP/MAS.sup.29Si NMR spectrum
centered within the range of -56 ppm to -59 ppm. T3 is the
integrated intensity of a peak having a chemical shift in the
CP/MAS.sup.29Si NMR spectrum centered within the range of -65 ppm
to -69 ppm. The intensity of a peak refers to the maximum peak
height of the signal at that approximate location or the area of
the peak occurring within the recited ranges, as calculated using
standard calculation methods well known to those skilled in the
art.
[0031] The hydrophobic metal oxide particles preferably have a
ratio of T3 to T2 (i.e., T3:T2), based on the integrated area of
the peaks, of about 1.5 or more (e.g., about 2 or more, about 2.5
or more, about 3 or more, or about 3.5 or more), wherein T2 and T3
are as defined herein.
[0032] The hydrophobic metal oxide particles can be formulated as a
dry particle composition (e.g., a dry powder) or as a wet particle
composition (e.g., dispersion) comprising the hydrophobic metal
oxide particles. The dispersion can comprise any suitable
dispersant, preferably water alone or with a co-solvent, treating
agents, or additives of any type commonly used in dispersions of
hydrophobic metal oxide particles.
[0033] The hydrophobic metal oxide particles can be used for many
different applications including but not limited to toner
compositions, antiblocking agents, adhesion modifiers, polymer
additives (e.g., for elastomers and rubbers, such as silicone
rubbers), abrasion-resistant coatings and films, delustering
coatings and films, reological control agents (e.g., for epoxies or
liquid polymers), and mechanical/optical control agents (e.g., for
composites and plastics). The hydrophobic metal oxide particles are
especially useful in toner compositions. In that regard, the
invention provides a toner composition comprising toner particles
and metal oxide particles surface-treated with at least one
alkoxysilane compound, which metal oxide particles are hydrophobic,
non-aggregated, and have a tap density of about 110 g/l to about
420 g/l or less and a BET surface area of about 200 m.sup.2/g or
less.
[0034] All aspects of the hydrophobic metal oxide particles used in
the toner composition are as described with respect to the particle
composition of the invention.
[0035] The tribocharge of toner compositions containing the treated
metal oxide particles can be either positive or negative. The
tribocharge of a toner composition containing the inventive treated
metal oxide particles is affected by the presence of the treated
particles. Without wishing to be bound by a particular theory, it
is thought that the presence of the treated metal oxide particles
stabilizes and increases the positive or negative tribocharge of
toner compositions containing the metal oxide particles.
[0036] Toner compositions containing the treated metal oxide
particles can be formulated, for example, by mixing 4 wt. % of the
treated particles in a laboratory blender with pulverized styrene
acrylate toner particles free of any external additives and having
an average diameter of 9 .mu.m. Toner compositions containing the
treated particles can be developed, for example, by rolling for 30
minutes at a 2/98 wt. % toner/carrier ratio in glass jars. The
carrier can be 70 .mu.m Cu--Zn ferrite coated with silicone resin.
Samples can be conditioned in a standard humidity chamber at either
a high humidity and high temperature (30.degree. C. and 80%
relative humidity) or at a low humidity and low temperature
(18.degree. C. and 15% relative humidity) overnight.
[0037] The tribocharge of toner compositions containing the treated
metal oxide particles can be either positive or negative.
Tribocharge measurements can be made using suitable techniques and
equipment known in the art (e.g., Vertex T-150 tribocharger).
Measurements can be made after conditioning the toner particles
overnight in a standard humidity chamber at 30.degree. C. and 80%
relative humidity (HH) and at 18.degree. C. and 15% relative
humidity (LL). The toner particles (e.g., of a toner composition
comprising about 4 wt. % treated metal oxide particles) preferably
have a tribocharge at HH conditions of about -40 .mu.C/g to about
+15 .mu.C/g (e.g., about -40 .mu.C/g to about -20 .mu.C/g, about
-40 .mu.C/g to about 0 .mu.C/g, about -5 .mu.C/g to about +10
.mu.C/g, about 0 .mu.C/g to about +5 .mu.C/g, or about +5 .mu.C/g
to about +10 .mu.C/g). The toner particles preferably have a
tribocharge at LL conditions of about -100 .mu.C/g to about +25
.mu.C/g (e.g., about -80 .mu.C/g to about -50 .mu.C/g, about -80
.mu.C/g to about 0 .mu.C/g, about -5 .mu.C/g to about +10 .mu.C/g,
about +5 .mu.C/g to about +35 .mu.C/g, or about +10 .mu.C/g to
about +25 .mu.C/g).
[0038] The free flow of a toner composition containing the
inventive treated metal oxide particles is affected by the presence
of the treated particles. Without wishing to be bound by a
particular theory, it is thought that the presence of the treated
metal oxide particles, especially particles which have been jet
milled, improves the free flow of toner compositions containing the
metal oxide particles due to the lower tap and pour densities of
the treated particles. In the context of the invention, free flow
is the percentage of toner discharged from a grounded metal role
tube of 25 mm diameter and 350 mm in length, with seven 0.5 mm
discharge holes, that contains 40 g of the toner composition and is
rotated at 30 rpm for one minute for a total of 30 rotations. The
toner composition can have a free flow of about 0.5 wt. % loss or
more (e.g., about 1 wt. % loss or more, about 1.5 wt. % loss or
more, about 2 wt. % loss or more, or about 3.5 wt. % loss or more).
The free flow of the toner composition typically will be about 8
wt. % loss or less (e.g., about 6 wt. % loss or less, about 5 wt. %
loss or less, about 4 wt. % loss or less, or about 3 wt. % loss or
less). Preferably, the free flow of the toner composition is about
0.5 wt. % loss to about 8 wt. % loss (e.g., about 1 wt. % loss to
about 6 wt. % loss, about 1.5 wt. % loss to about 5 wt. % loss, or
about 2 wt. % loss to about 4.5 wt. % loss).
[0039] The hydrophilic metal oxide particles that are treated with
the alkoxysilane compound are in an aqueous dispersion. The aqueous
dispersion of metal oxide particles preferably is colloidally
stable. The colloidal stability of the dispersion prevents any
substantial portion of the particles from irreversibly
agglomerating or gelling, or from settling out of the dispersion
during use. The aqueous dispersion of metal oxide particles used in
conjunction with the invention preferably has a degree of colloidal
stability such that the average overall particle size of the silica
in dispersion, as measured by dynamic light scattering, does not
change over a period of 1 hour or more (e.g., about 8 hours or
more, or about 24 weeks or more), more preferably 2 weeks or more
(e.g., about 4 weeks or more, or about 6 weeks or more), most
preferably 8 weeks or more (e.g., about 10 weeks or more, or about
12 weeks or more), or even about even 16 weeks or more.
[0040] The invention provides a method of preparing hydrophobic
metal oxide particles comprising (a) providing an aqueous
dispersion of hydrophilic metal oxide particles, (b) combining the
dispersion with at least one alkoxysilane treating agent to provide
a reaction mixture, wherein the reaction mixture is basic, and (c)
drying the reaction mixture to provide hydrophobic metal oxide
particles. According to one aspect of the invention, the
hydrophobic metal oxide particles have a tap density of about 110
g/l to about 420 g/l and a BET surface area of less than about 200
m.sup.2/g. According to another aspect of the invention, the
agglomerate size of the hydrophobic metal oxide particles can be
reduced by jet milling or hammer milling.
[0041] The aqueous dispersion containing the hydrophilic metal
oxide particles can be a commercially available metal oxide
dispersion, as described herein. Alternatively, the aqueous
dispersion can be prepared by any suitable technique. In one
embodiment, the metal oxide particles can be prepared via a wet
process, such as by mixing a metal oxide with water and a
water-soluble organic solvent. The water-soluble organic solvent
can be any suitable water-soluble organic solvent, such as an
alcohol (e.g., methanol, ethanol, n-propanol, 2-propanol,
n-butanol, isobutanol, sec-butanol, tert-butanol, n-propanol,
ethylene glycol, and propylene glycol), ketone (e.g., acetone and
2-butanone), ether (e.g., tetrahydrofuran and 1,2-dimethoxyethane),
and combinations thereof. The water and water-soluble organic
solvent can be added in any order. For example, the water can be
added before the water-soluble organic solvent, or vice versa.
Although not wishing to be bound by a particular theory, it is
thought that adding the water before the water-soluble organic
solvent prevents the dispersion from gelling. Typically, the
reaction mixture will comprise no more than about 50 wt. % of
organic solvent, and preferably will comprise not more than about
40 wt. % of organic solvent.
[0042] The water-soluble organic solvent to water volume ratio can
be any suitable ratio. The ratio typically is less than about 10
(e.g., about 8 or less, about 6 or less, about 5 or less, about 3
or less, or about 2 or less). The ratio can be about 0.05 or more
(e.g., about 0.1 or more, about 0.5 or more, about 0.7 or more,
about 1 or more, or about 1.2 or more). The ratio can be, for
example, from about 0.05 to about 10 (e.g., from about 0.1 to about
5, or from about 0.2 to about 2).
[0043] The aqueous dispersion containing the hydrophilic metal
oxide particles can contain any suitable amount of metal oxide
particles. The aqueous dispersion typically comprises about 30 wt.
% or less (e.g., about 25 wt. % or less, about 20 wt. % or less,
about 15 wt. % or less, about 10 wt. % or less, or about 5 wt. % or
less) metal oxide particles. The aqueous dispersion can comprise
about 5 wt. % or more (e.g., about 10 wt. % or more, about 15 wt. %
or more, about 20 wt. % or more, about 25 wt. % or more, or about
30 wt. % or more) metal oxide particles. Thus, the aqueous
dispersion can comprise, for example, from about 5 wt. % to about
30 wt. % (e.g., from about 10 wt. % to about 25 wt. %, or from
about 15 wt. % to about 20 wt. %) metal oxide particles.
[0044] The aqueous dispersion containing the hydrophilic metal
oxide particles can be combined with at least one alkoxysilane
treating agent to provide a reaction mixture in any suitable
manner. The dispersion can be acidic or basic, and the pH of the
dispersion can be altered by the addition of the at least one
alkoxysilane treating agent.
[0045] The amount of the at least one alkoxysilane compound that is
added to the aqueous dispersion containing the hydrophilic metal
oxide particles can be any suitable amount. The amount of the at
least one alkoxysilane compound typically comprises less than about
50 .mu.mole/m.sup.2 metal oxide particles (e.g., about 25
pnaole/m.sup.2 metal oxide particles or less, about 15
.mu.mole/m.sup.2 metal oxide particles or less, about 10
.mu.mole/m.sup.2 metal oxide particles or less, or about 5
.mu.mole/m.sup.2 metal oxide particles or less). The amount of the
at least one alkoxysilane compound can comprise about 0.1
pmole/m.sup.2 metal oxide particles or more (e.g., about 0.5
.mu.mole/m.sup.2 metal oxide particles or more, about 1
.mu.mole/m.sup.2 metal oxide particles or more, or about 2
.mu.mole/m.sup.2 metal oxide particles or more). Thus, the amount
of the at least one alkoxysilane compound can comprise, for
example, from about 0.1 .mu.mole/m.sup.2 metal oxide particles to
about 50 .mu.mole/m.sup.2 metal oxide particles (e.g., from about
0.5 .mu.mole/m.sup.2 metal oxide particles to about 25
.mu.mole/m.sup.2 metal oxide particles, or from about 2
.mu.mole/m.sup.2 metal oxide particles to about 15 .mu.mole/m.sup.2
metal oxide particles).
[0046] The pH of the aqueous dispersion can be any suitable pH
before the at least one alkoxysilane is added to the dispersion.
Regardless of whether the starting dispersion is acidic, basic, or
neutral, the reaction mixture should have a basic pH, i.e., a pH of
about 7 or more. The pH of the reaction mixture can be, for
example, about 7 or more (e.g., about 8 or more, about 9 or more,
about 10 or more, about 11 or more, or about 12 or more).
Generally, the pH of the reaction mixture will be from about 7 to
about 12 (e.g., from about 8 to about 11, from about 9 to about
10.5, or from about 9.5 to about 10.5).
[0047] The reaction between the aqueous dispersion containing the
metal oxide particles and the alkoxysilane compound can occur at
any suitable temperature and for any suitable amount of time that
allows the alkoxysilane compound to react completely, or to any
extent desired, with the aqueous dispersion of metal oxide
particles. Generally, the reaction mixture is maintained at a
temperature of about 20.degree. C. to about 100.degree. C. (e.g.,
about 30.degree. C. to about 70.degree. C., or about 45.degree. C.
to about 75.degree. C.) for about 5 minutes or longer (e.g., about
30 minutes or longer, about 1 hour or longer), or even about 2
hours or longer (e.g., about 3 hours or longer, or about 4 hours or
longer). Longer reaction times (e.g., 5 hours or more, 10 hours or
more, or even 20 hours or more) may be required depending on the
particular reaction conditions (e.g., temperature and concentration
of reagents).
[0048] Additional alkoxysilanes, silazanes, or other treating
agents can be added (e.g., a second, third, or fourth alkoxysilane,
silazane, or treating agent) at any suitable time before or after
the addition of the first alkoxysilane compound. After the addition
of another treating agent, the temperature of the reaction mixture
can be adjusted to any suitable temperature for any suitable amount
of time that allows the additional alkoxysilane compound to react
completely, or to any extent desired, with the aqueous dispersion
of metal oxide particles.
[0049] Preferably, the reaction mixture containing the hydrophobic
metal oxide particles is dried to form a powder. The drying of the
reaction mixture can be effected in any suitable manner. For
example, spray drying can be used to dry the hydrophobic metal
oxide particles. Spray drying involves spraying the reaction
mixture, or some portion thereof, comprising the hydrophobic metal
oxide particles as a fine mist into a drying chamber, wherein the
fine mist is contacted with hot air causing the evaporation of
volatile components of the reaction mixture. The temperature chosen
for the hot air will depend, at least in part, on the specific
components of the reaction mixture that require evaporation.
Typically, the drying temperature will be about 40.degree. C. or
higher (e.g., about 50.degree. C. or higher) such as about
70.degree. C. or higher (e.g., about 80.degree. C. or higher) or
even about 120.degree. C. or higher (e.g., about 130.degree. C. or
higher). Thus, the drying temperatures generally can be within the
range of about 40-250.degree. C. (e.g., about 50-200.degree. C.),
such as about 60-200.degree. C. (e.g., about 70-175.degree. C.), or
about 80-150.degree. C. (e.g., about 90-130.degree. C.).
[0050] The hydrophobic metal oxide particles can be isolated from
the reaction mixture prior to drying, or the hydrophobic metal
oxide particles can be dried directly from the reaction mixture.
Any suitable method can be used to isolate the hydrophobic metal
oxide particles from the reaction mixture. Suitable methods include
filtration and centrifugation.
[0051] The hydrophobic metal oxide particles can be dried after
isolation from the reaction mixture, or directly from the reaction
mixture, by any suitable technique, e.g., by evaporating the
volatile components of the reaction mixture from the hydrophobic
metal oxide particles. Evaporation of the volatile components of
the reaction mixture can be accomplished using any suitable
techniques, e.g., heat and/or reduced atmospheric pressure. When
heat is used, the hydrophobic metal oxide particles can be heated
to any suitable drying temperature, for example, by using an oven
or other similar device. The temperature can be as recited for the
spray drying embodiment of the invention.
[0052] The hydrophobic metal oxide particles can be dried at any
pressure that will provide a useful rate of evaporation. When
drying temperatures of about 120.degree. C. and higher (e.g., about
120-150.degree. C.) are used, drying pressures of about 125 kPa or
less (e.g., about 75-125 kPa) are desirable. At drying temperatures
lower than about 120.degree. C. (e.g., about 40-120.degree. C.),
drying pressures of about 100 kPa or less (e.g., about 75 kPa or
less) are desirable. Of course, reduced pressure (e.g., pressures
of about 100 kPa or less, 75 kPa or less, or even 50 kPa or less)
can be used as a sole method for evaporating the volatile
components of the reaction mixture.
[0053] Alternatively, the hydrophobic metal oxide particles can be
dried by lyophilization, wherein the liquid components of the
reaction mixture are converted to a solid phase (i.e., frozen) and
then to a gas phase by the application of a vacuum. For example,
the reaction mixture comprising the hydrophobic metal oxide
particles can be brought to a suitable temperature (e.g., about
-20.degree. C. or less, or about -10.degree. C. or less, or even
-5.degree. C. or less) to freeze the liquid components of the
reaction mixture, and a vacuum can be applied to evaporate those
components of the reaction mixture to provide dry hydrophobic metal
oxide particles.
[0054] The hydrophobic metal oxide particles can be washed prior to
or after isolation and/or drying from the reaction mixture. Washing
the hydrophobic metal oxide particles can be performed using a
suitable washing solvent, such as water, a water-miscible organic
solvent, a water-immiscible solvent, or a mixture thereof. The
washing solvent can be added to the reaction mixture and the
resulting mixture suitably mixed, followed by filtration,
centrifugation, or drying to isolate the washed hydrophobic metal
oxide particles. Alternatively, the hydrophobic metal oxide
particles can be isolated from the reaction mixture prior to
washing. The washed hydrophobic metal oxide particles can be
further washed with additional washing steps followed by additional
filtration, centrifugation, and/or drying steps.
[0055] The hydrophobic metal oxide particles have an overall
particle size that is dependent, at least in part, on the overall
particle size of the metal oxide particles in the initial
dispersion. The average overall particle size of the hydrophobic
metal oxide particles can be determined by any suitable method,
many of which methods are known in the art, such as dynamic light
scattering. Preferred average particle sizes of the hydrophobic
metal oxide particles prepared in accordance with the method of the
invention are as described with respect to the treated metal oxide
particles of the invention. Desirably, the average particle size of
the hydrophobic, non-aggregated particle prepared in accordance
with the method of the invention is within about 50%, preferably
within about 30% (e.g., within about 20%, about 15%, about 10%, or
even about 5%) of the average particle size of the metal oxide
particle of the starting dispersion. Preferably, the average
particle size of the hydrophobic metal oxide particles is further
reduced after drying. The agglomerate size of the hydrophobic metal
oxide particles is also preferably reduced after drying. Suitable
processes for the reduction of the particle size and agglomerate
size of the hydrophobic metal oxide particles include but are not
limited to wet or dry grinding, hammer milling, and jet
milling.
[0056] The carbon content of the hydrophobic metal oxide particles
can be used as an indicator of the level of treatment of the
hydrophobic metal oxide particles and, thus, as an indicator of the
degree of hydrophobicity. The carbon content of the treated
particles can be determined using commercially available carbon
analyzers (e.g., Leco C-200). The hydrophobic metal oxide particles
prepared in accordance with the invention desirably have a carbon
content of about 0.1 wt. % or more (e.g., about 0.2 wt. % or more,
about 0.3 wt. % or more, about 0.4 wt. % or more, about 0.5 wt. %
or more, or about 0.8 wt. % or more). The carbon content of the
treated metal oxide particles typically comprises less than about
10 wt. % (e.g., about 8 wt. % or less, about 7 wt. % or less, about
6 wt. % or less, or about 5 wt. % or less). Thus, the carbon
content of the treated metal oxide particles can be, for example,
from about 0.01 wt. % to about 10 wt. % (e.g., from about 0.05 wt.
% to about 8 wt. %, from about 0.1 wt. % to about 7 wt. %, from
about 0.3 wt. % to about 7 wt. %, or from about 0.5 wt. % to about
6 wt. %).
[0057] The following examples further illustrate the invention but,
of course, should not be construed as in any way limiting its
scope.
Example 1
[0058] This example illustrates the preparation of hydrophobic
metal oxide particles by treating colloidal silica particles with
an alkoxysilane compound.
[0059] The reactor was charged with 41.6 kg of 40 wt. % colloidal
silica in an aqueous solution at a pH of 9.4 (SNOWTEX MP-1040,
Nissan Chemical Co.). 2.5 kg of deionized water and 27 kg of
2-propanol were added to the colloidal silica solution while
continually agitating the mixture with a stirrer. The ratio of
2-propanol to water was 1.24 v/v.
[0060] 1.44 kg of OTES (octyltriethoxysilane) was added to the
reaction mixture, and the mixture was heated to about 72.degree. C.
After the addition of the OTES, the agitation of the mixture
continued, and the mixture was re-circulated through a homogenizer
for about 8 hours. The mixture was then held in the reactor and
allowed to cool to room temperature while stirring overnight. The
mixture was spray dried the following day at a temperature of about
110.degree. C. (dryer exit temperature). The inlet temperature to
the dryer was 230.degree. C. The resulting powder was collected
from the cyclone collector. After drying, the powder was jet milled
and packaged.
[0061] .sup.29Si CP/MAS NMR spectra of the inventive particles
described in this example (bottom spectrum) and untreated silica
particles (top spectrum) are shown in FIG. 1. The change of the
relative intensities of the Q3 and Q4 peaks in the spectra
indicates that some of the single silanol groups present on the
surface of treated silica particles are reacted with OTES. The T2
and T3 peaks in the spectrum of the treated silica are due to the
Si atoms of the OTES molecules, which became immobilized on the
surface of the silica particles. T3 is about 4 to about 5 times
more intense that T2, suggesting that octyltrisilanols are well
cross-linked on the surface.
[0062] The effect of jet milling on the agglomerate size
distribution of the inventive particles described in this example
is shown in FIG. 2. As is apparent from FIG. 2, jet milling results
in significantly less agglomerated material, which is preferred for
toner applications.
[0063] The amount of extractable carbon was determined by
extracting 0.5-2 g treated silica with 100 ml toluene and boiling
for three hours using the soxhlet method.
[0064] The toner was formulated by mixing 4 wt. % of the treated
silica particles in a laboratory blender with a pulverized styrene
acrylate black toner free of any external additives. The average
diameter of toner particles was 9 .mu.m. The toner was developed by
rolling for 30 minutes at a 2/98 wt. % toner/carrier ratio in glass
jars. The carrier was 70 .mu.m Cu--Zn ferrite coated with silicone
resin. Samples were conditioned in a standard humidity chamber at
either a high humidity and high temperature (30.degree. C. and 80%
relative humidity) or at a low humidity and low temperature
(18.degree. C. and 15% relative humidity) overnight. Tribocharge
measurements were done using a Vertex T-150 tribo charger.
[0065] Free flow was calculated using a perforated grounded metal
role tube by measuring the amount of toner discharged from the tube
upon rotation. Measurements were taken after 30, 60, and 90
seconds, which were then averaged. The role tube was 25 mm in
diameter, 350 mm in length, had seven 0.5 mm discharge holes, and
was rotated at 30 rpm. The initial charge to the tube was 40 g.
[0066] The properties of the treated silica particles are shown in
Table 1.
TABLE-US-00001 TABLE 1 Carbon content (wt. %) 2.7 Carbon content
after extraction (wt. %) 1.78 BET surface area (m.sup.2/g) 28 Tap
density (3000 taps) (g/l) 257 Tribocharge at high humidity &
-13 temperature (.mu.C/g) T3:T2 ratio 4.7 Tribocharge at low
humidity & -36 temperature (.mu.C/g) Free flow (wt. % loss)
1.57
Example 2
[0067] This example illustrates the preparation of hydrophobic
metal oxide particles by treating colloidal silica particles with
an alkoxysilane compound.
[0068] The reactor was charged with 48.3 kg of 40 wt. % colloidal
silica in an aqueous solution at a pH of 9.4 (SNOWTEX MP-1040,
Nissan Chemical Co.). 10.1 kg of deionized water and 44.7 kg of
2-propanol were added to the colloidal silica solution while
continually agitating the mixture with a stirrer. The ratio of
2-propanol to water was 1.45 v/v.
[0069] 1.78 kg of OTES was added to the reaction mixture and the
mixture was heated to about 65.degree. C. After the addition of the
OTES, the agitation of the mixture continued, and the mixture was
re-circulated through a homogenizer for about 7 hours. The mixture
was then held in the reactor and allowed to cool to room
temperature while stirring overnight. The mixture was spray dried
the following day at a temperature of about 115.degree. C. (dryer
exit temperature). The inlet temperature to the dryer was
230.degree. C. Composition 2A was dried in a cyclone drier, and
composition 2B was dried in a baghouse drier. After drying, the
powder was jet milled and packaged.
[0070] The amount of extractable carbon and tribocharge were
measured as described in Example 1 for each of compositions 2A and
2B. The pour density was determined by obtaining a sample of the
treated silica particles of composition 2A, pouring the treated
silica particles into a calibrated container, and weighing
them.
[0071] The properties of the treated silica particles are shown in
Table 2.
TABLE-US-00002 TABLE 2 Composition 2A Composition 2B Carbon content
(wt. %) 2.41 2.07 Carbon content after 1.83 1.79 extraction (wt. %)
Pour density (g/l) 234 not determined Tribocharge at high humidity
& -18 -19 temperature (.mu.C/g) Tribocharge at low humidity
& -38 -45 temperature (.mu.C/g)
Example 3
[0072] This example illustrates the preparation of hydrophobic
metal oxide particles by treating colloidal silica particles with
an alkoxysilane compound.
[0073] A reactor (compositions 3A-3E) or a 3 L 3-neck flask
(composition 3F) was charged with 40 wt. % colloidal silica in an
aqueous solution at a pH of about 9 to about 10 (SNOWTEX XL, Nissan
Chemical Co.) in the amount indicated in Table 3. Deionized water
and 2-propanol were added to the colloidal silica solution while
continually agitating the mixture with a stirrer.
[0074] OTES alone or both OTES and APS
((3-aminopropyl)triethoxysilane) were added to the reaction
mixture, and the mixture was heated to about 68.degree. C. to about
72.degree. C. After the addition of the OTES alone or both OTES and
APS, the agitation of the mixture continued, and the mixture was
re-circulated through a homogenizer for about 5 hours to about 9
hours. The mixture was then held in the reactor or flask and
allowed to cool to room temperature while stirring overnight. The
mixture was spray dried the following day at a temperature of about
118.degree. C. to about 127.degree. C. (dryer exit temperature).
The inlet temperature to the dryer was 235.degree. C. After drying,
the resulting powder was jet milled and packaged. Compositions 3B
and 3D were dried in a cyclone drier, and compositions 3C and 3E
were dried in a baghouse drier. Composition 3F was dried in an oven
at 120.degree. C.
[0075] The amount of extractable carbon, tribocharge, and free flow
of each composition were measured as described in Example 1. The
pour density of composition 3A was measured as described in Example
2.
[0076] The properties of the treated silica particles are shown in
Table 3.
TABLE-US-00003 TABLE 3 Comp. 3A Comp. 3B Comp. 3C Comp. 3D Comp. 3E
Comp. 3F Silica (kg) 39 60.3 60.3 35.7 35.7 0.9 OTES (kg) 2.92 3.51
3.51 1.83 1.83 .052 APS (kg) -- -- -- 0.283 0.283 .0024 IPA/water
1.25 (2.9 0.72 (30 0.72 (30 0.74 (30 0.74 (30 -- (750 ratio (v/v)
kg water, kg water, kg water, kg water, kg water, g water, 24.2 kg
37.5 kg 37.5 kg 30.1 kg 30.1 kg 750 g IPA) IPA) IPA) IPA) IPA) IPA)
Carbon 3.12 2.55 2.3 4.3 3.03 4.2 content (wt. %) Carbon 2.76 2.5
2.3 2.51 2.41 3.31 content after extraction (wt. %) BET surface
45.9 -- -- -- -- -- area (m.sup.2/g) Pour density 230 -- -- -- --
-- (g/l) Tap density -- 269 254 -- -- -- (g/l) Tribocharge -19 -24
-26 -11 -16 -17 at high humidity & temperature (.mu.C/g)
Tribocharge -44 -59 -58 -16 -21 -31 at low humidity &
temperature (.mu.C/g) Free flow 1.88 4.42 4.04 4.6 4.57 -- (wt. %
loss)
Example 4
[0077] This example illustrates the preparation of hydrophobic
metal oxide particles by treating colloidal silica particles with
an alkoxysilane compound.
[0078] A 500 ml 3-neck round bottom flask with an overhead stirring
motor and condenser was charged with 137 g of 40 wt. % colloidal
silica in an aqueous solution at a pH of 9.2 (SNOWTEX YL, Nissan
Chemical Co.). 87 g of 2-propanol was added to the colloidal silica
solution while continually agitating the mixture with a
stirrer.
[0079] 6.2 g of OTES was added to the reaction mixture, and the
mixture was heated to about 70.degree. C. for about 3.5 hours. The
mixture was then held in the flask and allowed to cool to room
temperature. The mixture was transferred to a Pyrex tray and dried
at a temperature of about 120.degree. C.
[0080] The tribocharge and free flow of the resulting treated
silica particles were measured as described in Example 1.
[0081] The properties of the treated silica particles are shown in
Table 4.
TABLE-US-00004 TABLE 4 Tribocharge at high humidity & -20
temperature (.mu.C/g) Tribocharge at low humidity & -60
temperature (.mu.C/g) Free flow (wt. % loss) 1.2
Example 5
[0082] This example illustrates the preparation of hydrophobic
metal oxide particles by treating two different types of colloidal
silica particles with an alkoxysilane compound.
[0083] A 500 ml 3-neck round bottom flask with an overhead stirring
motor and condenser was charged with either 100 g of 40 wt. %
colloidal silica in an aqueous solution at a pH of 9.2 (SNOWTEX XL,
Nissan Chemical Co.) to which 50 ml of deionized water and 65 g of
2-propanol were added, or 75 g of 40 wt. % colloidal silica in an
aqueous solution (NYACOL9950, Eka Chemicals), to which 75 ml of
deionized water and 65 g of 2-propanol were added. Both
compositions were continually agitated with a stirrer.
[0084] 5.8 g of OTES was added to each reaction mixture. The pH of
the composition containing the SNOWTEX silica was 10.1, and the pH
of the composition containing the NYACOL9950 silica was 9.7. The
mixtures were heated to about 70.degree. C. for about 5.5 hours.
The mixtures were allowed to cool to room temperature, then dried
in an oven at a temperature of about 125.degree. C. The dried
mixtures were then milled using an IKA A 11 laboratory grinder.
[0085] The amount of extractable carbon and free flow of each
composition were measured as described in Example 1.
[0086] The properties of the treated silica particles are shown in
Table 5.
TABLE-US-00005 TABLE 5 SNOWTEX XL NYACOL9950 silica silica Carbon
content (wt. %) 3.9 3.4 Carbon content after 3.7 3.4 extraction
(wt. %) BET surface area (m.sup.2/g) 49 54 T3:T2 ratio 2.6 5.2 Free
flow (wt. % loss) 2.5 1.9
Comparative Example 6
[0087] This example illustrates the preparation of hydrophobic
metal oxide particles by treating colloidal silica particles with
an alkoxysilane compound.
[0088] A 500 ml 3-neck round bottom flask with an overhead stirring
motor and condenser was charged with 113 g of 35 wt. % colloidal
silica in an aqueous solution (PL-8L, Fuso Co.). 37 ml of deionized
water and 65 g of 2-propanol were added to the colloidal silica
solution while continually agitating the mixture with a
stirrer.
[0089] 4.5 g of OTES was added to the reaction mixture. The pH of
the reaction mixture was about 7.5. The mixture was heated to about
70.degree. C. for about 5.5 hours. The mixture was allowed to cool
to room temperature, then dried in an oven at a temperature of
about 125.degree. C. The dried mixture was then milled using an IKA
A 11 laboratory grinder.
[0090] The amount of extractable carbon and free flow of the
resulting treated silica particles were measured as described in
Example 1.
[0091] The properties of the treated silica particles are shown in
Table 6.
TABLE-US-00006 TABLE 6 Carbon content (wt. %) 0.27 Free flow (wt. %
loss) 0.6 T3:T2 ratio Not detected
[0092] As is apparent from the data presented in Table 6, the
carbon content of the treated particles was very low and the T3:T2
ratio could not be measured, indicating that treatment was
unsuccessful.
Example 7
[0093] This example illustrates the preparation of hydrophobic
metal oxide particles by treating colloidal silica particles with
an alkoxysilane compound.
[0094] Three different compositions containing hydrophobic
colloidal silica particles were prepared as described herein. The
reactor was charged with 40 wt. % colloidal silica in a basic
aqueous solution (Nissan Chemical Co.) in the amounts indicated in
Table 7. Deionized water and 2-propanol (IPA) were added to the
colloidal silica solutions while continually agitating the mixtures
with a stirrer in the amounts indicated in Table 7.
[0095] OTES was added to the reaction mixtures in the amounts
indicated in Table 7, and the mixtures were heated to about
64.degree. C. After the addition of the OTES, the agitation of the
mixtures continued, and the mixtures were re-circulated through a
homogenizer for about 8-9 hours. The mixtures were then held in the
reactor and allowed to cool to room temperature while stirring
overnight. The mixtures were spray dried the following day at a
temperature of about 119.degree. C. to about 125.degree. C. (dryer
exit temperature). The inlet temperature to the dryer was
235.degree. C. The powder was collected from the cyclone collector.
After drying, the powder was jet milled and packaged.
[0096] The properties of the treated silica particles are shown in
Table 7.
TABLE-US-00007 TABLE 7 Tap Density IPA/water ratio OTES (3000 taps)
Composition Silica (v/v) (kg) (g/l) 7A 40 kg 1.38 (0.8 kg 2.3 271
SNOWTEX water, 27.1 XL kg IPA) 7B 39 kg 1.68 (0.8 kg 1.47 265
SNOWTEX water, 32.1 MP-1040 kg IPA) 7C 79.1 kg 0.75 (40.9 kg 4.65
220 SNOWTEX water, 51.5 XL kg IPA)
Example 8
[0097] This example illustrates the preparation of hydrophobic
metal oxide particles by treating colloidal silica particles with
an alkoxysilane compound.
[0098] A 5 L 3-neck round bottom flask with an overhead stirring
motor and condenser was charged with 1829 g of 41 wt. % colloidal
silica in an aqueous solution stabilized with NaOH (NEXSIL 86, Eka
Chemicals). 895 g of deionized water and 1136 g of 2-propanol were
added to the colloidal silica solution while continually agitating
the mixture with a stirrer.
[0099] 103.7 g of OTES was added to the reaction mixture, and the
mixture was heated to about 70.degree. C. for about 6 hours. The
mixture was then held in the flask overnight and allowed to cool to
room temperature. The mixture was agitated to homogenize it, then
the solid phase was separated by centrifugation and dried at a
temperature of about 60.degree. C. overnight, then again at a
temperature of about 120.degree. C. overnight. After drying, the
resulting powder was jet milled and packaged.
[0100] The tap density of the colloidal silica particles, after 0,
300, 600, 1250, and 3000 taps, is shown in Table 8.
TABLE-US-00008 TABLE 8 Tap Density (0 taps) (g/l) 214 Tap Density
(300 taps) (g/l) 277 Tap Density (600 taps) (g/l) 287 Tap Density
(1250 taps) (g/l) 296 Tap Density (3000 taps) (g/l) 299
Comparative Example 9
[0101] This example illustrates the tap density of hydrophobic
fumed silica particles.
[0102] The tap density of commercially available fumed silica
particles treated with OTES (AEROSIL R 805, Degussa) was measured
after 0, 300, 600, 1250, and 3000 taps with a tap volumeter.
[0103] The tap density of the fumed silica particles is shown in
Table 9.
TABLE-US-00009 TABLE 9 Tap Density (0 taps) (g/l) 51 Tap Density
(300 taps) (g/l) 51 Tap Density (600 taps) (g/l) 55 Tap Density
(1250 taps) (g/l) 59 Tap Density (3000 taps) (g/l) 63
Example 10
[0104] This example illustrates the effect of jet milling a powder
comprising hydrophobic metal oxide particles on pour density.
[0105] The reactor was charged with 40 wt. % colloidal silica in a
basic aqueous solution (Nissan Chemical Co.) in the amounts
indicated in Table 10. Deionized water and 2-propanol (IPA) were
added to the colloidal silica solutions while continually agitating
the mixtures with a stirrer in the amounts indicated in Table
10.
[0106] OTES was added to the reaction mixtures in the amounts
indicated in Table 10, and the mixtures were heated to about
65.degree. C. to about 70.degree. C. After the addition of the
OTES, the agitation of the mixtures continued, and the mixtures
were re-circulated through a homogenizer for about 8-9 hours. The
mixtures were then held in the reactor and allowed to cool to room
temperature while stirring overnight. The mixtures were spray dried
the following day at a temperature of about 110.degree. C. to about
125.degree. C. (dryer exit temperature). The inlet temperature to
the dryer was 235.degree. C. The powder was collected from either
the cyclone collector or the bag filter. After collection, the
powder was jet milled.
[0107] The pour density was measured as described in Example 2.
[0108] The properties of the treated silica particles are shown in
Table 10.
TABLE-US-00010 TABLE 10 Colloidal Unmilled pour Unmilled tap Milled
pour Milled tap silica Water IPA OTES density (3000) density
density (3000) density Sample particle (kg) (kg) (kg) (g/l) (g/l)
(g/l) (g/l) 10A 41.6 kg 2.5 27 1.44 293 379 194 257 SNOWTEX MP-1040
10B 39 kg 0.8 32 1.47 342 478 190 265 SNOWTEX MP-1040 10C 59 kg 31
38 1.77 204 271 165 234 SNOWTEX MP-1040 10D 40 kg 0.8 27.1 2.3 354
508 185 271 SNOWTEX XL 10E 79 kg 41 52 4.65 206 265 150 220 SNOWTEX
XL
[0109] As is apparent from the data presented in Table 10, the pour
density of the powder is significantly reduced by jet milling.
[0110] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0111] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0112] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *