U.S. patent application number 09/428374 was filed with the patent office on 2002-01-10 for zirconia sol, process of making composite material.
Invention is credited to CHIEN, BERT T., KOLB, BRANT U..
Application Number | 20020004544 09/428374 |
Document ID | / |
Family ID | 23698626 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020004544 |
Kind Code |
A1 |
KOLB, BRANT U. ; et
al. |
January 10, 2002 |
ZIRCONIA SOL, PROCESS OF MAKING COMPOSITE MATERIAL
Abstract
A zirconia sol comprising an aqueous phase having dispersed
therein a plurality of single crystal zirconia particles having an
average primary particle size less than about 20 nm. The zirconia
sols are substantially non associated having a dispersion index
ranging from about 1-3 and are highly crystalline exhibiting a
crystallinity index of about 0.65 or greater. Of the crystalline
phase, about 70% or greater exists in combined cubic and tetragonal
crystal lattice structures without a crystal phase stabilizer. Also
described is a hydrothermal method of making zirconia sols having
substantially non-associated zirconia particles and composite
materials made from the zirconia sols.
Inventors: |
KOLB, BRANT U.; (AFTON,
MN) ; CHIEN, BERT T.; (MINNEAPOLIS, MN) |
Correspondence
Address: |
SCOTT R PRIBNOW
OFFICE OF INTELLECTUAL PROPERTY COUNSEL
3M INNOVATIVE PROPERTIES COMPANY
P O BOX 33427
ST PAUL
MN
551333427
|
Family ID: |
23698626 |
Appl. No.: |
09/428374 |
Filed: |
October 28, 1999 |
Current U.S.
Class: |
524/413 |
Current CPC
Class: |
C01G 25/02 20130101;
C08K 3/22 20130101; C01P 2004/64 20130101; B01J 13/0008 20130101;
C08K 2003/2244 20130101; B82Y 30/00 20130101; C01P 2004/62
20130101 |
Class at
Publication: |
524/413 |
International
Class: |
C08L 001/00 |
Claims
What is claimed is:
1. A zirconia sol comprising: an aqueous phase having dispersed
therein a plurality of substantially non-associated single crystal
zirconia particles having an average primary particle size about 20
nm or less and a dispersion index ranging from about 1-3, wherein
the zirconia particles have a crystallinity index of about 0.65 or
greater and about 70% or greater combined cubic and tetragonal
crystal lattice structure in the absence of an effective amount of
a crystal phase stabilizer.
2. The zirconia sol of claim 1, wherein the zirconia sol has an
optical transmission of about 70% or greater at about 1.28 wt. %
ZrO.sub.2.
3. The zirconia sol of claim 1, wherein the zirconia sol has an
optical transmission of about 20% or greater at about 10 wt. %
ZrO.sub.2.
4. The zirconia sol of claim 1, wherein the dispersion index ranges
from about 1-2.5.
5. The zirconia sol of claim 1, wherein the dispersion index ranges
from about 1-2.
6. The zirconia sol of claim 1, wherein the zirconia particles have
an average primary particle size ranging from about 7-20 nm.
7. The zirconia sol of claim 1, wherein the zirconia particles have
about 75% or greater combined cubic and tetragonal crystal lattice
structure.
8. The zirconia sol of claim 1, wherein the zirconia particles have
about 85% or greater combined cubic and tetragonal crystal lattice
structure.
9. The zirconia sol of claim 1, wherein the zirconia particles
comprise less than about 1 wt. % of a crystal phase stabilizer.
10. The zirconia sol of claim 1, wherein the pH of the sol is less
than about 7.
11. The zirconia sol of claim 1, wherein the pH of the sol ranges
from about 1-4.5.
12. The zirconia sol of claim 1, wherein the zirconia particles
each have an outer surface and wherein a plurality of polyether
carboxylic acid molecules are adsorbed onto the outer surface.
13. The zirconia sol of claim 12, wherein the polyether carboxylic
acid has the general formula:
CH.sub.3--[O--(CH.sub.2).sub.y].sub.x--X.sub.2---
(CH.sub.2).sub.n--COOH wherein X.sub.2 is selected from the group
consisting of --O--, --S--, --C(O)O-- and --C(O)NH; n ranges from
about 1-3; x ranges from about 1-10; and y ranges from about
1-4.
14. The zirconia sol of claim 14, wherein the polyether carboxylic
acid is selected from the group consisting of
2-[2-(2-methoxyethoxy)ethoxy] acetic acid and 2-(2-methoxyethoxy)
acetic acid.
15. The zirconia sol of claim 1 further including a polyether
carboxylic acid wherein at least a portion of the polyether
carboxylic acid is adsorbed onto the zirconia particles.
16. The zirconia sol of claim 1, wherein the aqueous phase
comprises a mixture of water and at least one carboxylic acid.
17. The zirconia sol of claim 1, wherein the zirconia particles
have a cube-like shape.
18. A process for preparing a zirconia sol comprising the steps of:
(a) providing an aqueous solution comprising a polyether acid
zirconium salt; and (b) hydrolyzing the aqueous solution of the
polyether acid zirconium salt by heating the solution at a
temperature and a pressure sufficient to convert the polyether acid
zirconium salt into crystalline zirconia particles.
19. The process for preparing a zirconia sol of claim 18, wherein
step (a) comprises: (a) reacting an aqueous solution or sol of a
zirconium salt with a polyether carboxylic acid to form an aqueous
solution comprising a polyether acid zirconium salt and a free
acid; and (b) optionally, removing at least a portion of the free
acid.
20. The process for preparing a zirconia sol of claim 19, wherein
step (b) comprises: (a) drying the aqueous solution of the
polyether acid zirconium salt; and (b) dispersing the dried acid
polyether acid zirconium salt in water to form an aqueous
solution.
21. The process for preparing a zirconia sol of claim 19, wherein
the polyether carboxylic acid has the general formula:
CH.sub.3--[O--(CH.sub.2).sub.y].sub.x--X.sub.2--(CH.sub.2).sub.n--COOH
wherein X.sub.2 is selected from the group consisting of --O--,
--S--, --C(O)O-- and --C(O)NH; n ranges from about 1-3; x ranges
from about 1-10; and y ranges from about 1-4.
22. The process for preparing a zirconia sol of claim 19, wherein
the polyether carboxylic acid is selected from the group consisting
of 2-[2-(2-methoxyethoxy)ethoxy] acetic acid and
2-(2-methoxyethoxy) acetic acid.
23. The process for preparing a zirconia sol of claim 19, wherein
the zirconium salt has the general formula:
ZrO.sub.(4-n/2)(X).sub.n wherein X is a carboxylic acid
displaceable counterion selected from the group consisting of
formate, propionate, nitrate, chloride, carbonate and a combination
thereof, and wherein n ranges from 0.5-4.
24. The process for preparing a zirconia sol of claim 19, wherein
the zirconium salt is zirconium acetate.
25. The process for preparing a zirconia sol of claim 18, wherein
the temperature ranges from about 140-250.degree. C.
26. The process for preparing a zirconia sol of claim 18, wherein
the pressure ranges from about 1-30 bars.
27. A zirconia sol prepared according to the process of claim
18.
28. The zirconia sol of claim 1 prepared according to the process
of claim 18.
29. A composite material comprising: an organic matrix material
having dispersed therein a plurality of single crystal zirconia
particles having an average primary particle size less than about
20 nm and having a dispersion index ranging from about 1-3, wherein
the zirconia particles have a crystallinity index of about 0.65 or
greater and about 70% or greater combined cubic and tetragonal
crystal lattice structure in the absence of an effective amount of
a crystal phase stabilizer.
30. The composite material of claim 29 having an index of
refraction of about 1.6 or greater.
31. The composite material of claim 29 having an index of
refraction of about 1.75 or greater.
32. The composite material of claim 29, wherein the organic matrix
material is a monomer, oligomer, polymer or a mixture thereof.
33. The composite material of claim 29, wherein the organic matrix
material is selected from the group consisting of acrylates,
methacrylates, epoxies, styrenes and mixtures thereof.
34. The composite material of claim 29, wherein the organic matrix
material is selected from the group consisting of polyolefins,
polyesters, polyurethanes, polymethylmethacrylates, polystyrenes,
polycarbonates, polyimides and mixtures thereof.
Description
BACKGROUND
[0001] This invention relates to zirconia sols and to methods of
making zirconia sols.
[0002] The incorporation of zirconia sols into organic matrix
materials (e.g., polymers) can provide optically transparent or
translucent materials having high x-ray opacity and high refractive
index. The degree to which the x-ray opacity and/or refractive
index of the organic matrix may be increased is a function of the
loading limit of the sol in the organic matrix and the x-ray
scattering capability or refractive index of the zirconia
particles.
[0003] The characteristics of the zirconia sol (e.g., degree of
crystallinity of the zirconia particles, crystal lattice structure,
particle size and degree of primary particle association) govern
the optical transmission, x-ray opacity, refractive index and the
loading limit of the zirconia sol in an organic polymer. Condensed
crystalline zirconia is a high refractive index material having a
large x-ray scattering capability whereas amorphous hydrous
zirconium salts have a lower refractive index and lower x-ray
scattering capability. Optical transmission of a zirconia sol is a
function of the size of the zirconia particles in the sol. As the
primary particle size increases and/or the degree of association
between primary particles increases the optical transmission is
reduced. Loading limit of a zirconia sol in an organic matrix
material is a function of both particle association and particle
aspect ratio. As particle association in a zirconia sol increases,
the loading limit of the zirconia sol in an organic matrix
decreases. Similarly, as the aspect ratio of the zirconia particles
in a sol increases, the loading limit of the zirconia particles in
an organic matrix decreases. Accordingly, zirconia particles having
a low aspect ratio are preferred when it is desired to incorporate
high loadings of the particles in organic matrix materials. In this
respect, zirconia particles having cubic and/or tetragonal crystal
phases are preferred over those having a monoclinic crystal
phase.
SUMMARY
[0004] The present invention provides zirconia sols and methods for
making zirconia sols wherein the sols comprise crystalline zirconia
particles having a small primary particle size and substantially
non-associated form. Sols of the present invention may be added to
organic matrix materials (e.g., monomer, oligomers and polymers) to
provide transparent or translucent zirconia filled composite
materials having high index of refraction and high x-ray
opacity.
[0005] In one aspect, the present invention provides zirconia sols
comprising an aqueous phase having dispersed therein a plurality of
single crystal zirconia particles having an average primary
particle size less than about 20 nm, preferably ranging from about
7-20 nm. The zirconia sols of the present invention are
substantially non associated (i.e., non aggregated and non
agglomerated) having a dispersion index ranging from about 1-3,
more preferably ranging from 1-2.5 and most preferably ranging from
about 1-2. The zirconia sols of the present invention are highly
crystalline exhibiting a crystallinity index of about 0.65 or
greater, more preferably about 0.75 or greater and most preferably
about 0.85 or greater. Of the crystalline phase, about 70% or
greater, more preferably about 75% or greater and most preferably
about 85% or greater exists in combined cubic and tetragonal
crystal lattice structures.
[0006] In another aspect, the present invention provides a method
of making a zirconia sol comprising the steps of:
[0007] (a) providing an aqueous solution comprising a polyether
acid zirconium salt; and
[0008] (b) hydrolyzing the aqueous solution of the polyether acid
zirconium salt by heating the solution at a temperature and a
pressure sufficient to convert the polyether acid zirconium salt
into crystalline zirconia particles.
[0009] In a preferred embodiment of the process, step (a)
comprises:
[0010] (a) reacting an aqueous solution of a zirconium salt with a
polyether carboxylic acid to form an aqueous solution comprising a
polyether acid zirconium salt and a free acid; and
[0011] (b) optionally, removing at least a portion of the free
acid.
[0012] In a preferred embodiment, the step of removing at least the
free acid comprises:
[0013] (a) drying an aqueous solution of the polyether acid
zirconium salt; and
[0014] (b) dispersing the dried acid polyether acid zirconium salt
in water to form an aqueous solution.
[0015] Preferred zirconium salts for use as starting materials in
the formation of a polyether acid zirconium salt have the general
formula:
ZrO.sub.(4-n/2)(X).sub.n
[0016] where X is a carboxylic acid displaceable counterion
selected from the group consisting of formate, propionate, nitrate,
chloride, carbonate and a combination thereof; and wherein n ranges
from 0.5-4. A particularly preferred starting material is zirconium
acetate.
[0017] Preferred polyether carboxylic acids for use in the process
of the present invention have the general formula:
CH.sub.3--[O--(CH.sub.2).sub.y].sub.x--X.sub.2--(CH.sub.2).sub.n--COOH
[0018] where X.sub.2 is selected from the group consisting of:
[0019] --O--, --S--, --C(O)O-- and --C(O)NH;
[0020] n ranges from about 1-3;
[0021] x ranges from about 1-10; and
[0022] y ranges from about 1-4.
[0023] Examples of particularly preferred polyether carboxylic
acids include 2-[2-(2-methoxyethoxy)ethoxy] acetic acid and
2-(2-methoxyethoxy) acetic acid.
[0024] In another aspect, the present invention provides a
composite material comprising:
[0025] an organic matrix material having dispersed therein a
plurality of single crystal zirconia particles having an average
primary particle size less than about 20 nm and having a dispersion
index ranging from about 1-3, wherein the zirconia particles have a
crystallinity index of about 0.65 or greater and about 70% or
greater combined cubic and tetragonal crystal lattice structure in
the absence of an effective amount of a crystal phase
stabilizer.
[0026] In a preferred embodiment, the composite material has an
index of refraction of about 1.6 or greater, more preferably about
1.66 or greater and most preferably about 1.75 or greater.
[0027] In a preferred embodiment the organic matrix material is a
monomer, oligomer or polymer, for example, acrylates,
methacrylates, epoxies, styrenes, polyolefins, polyesters,
polyurethanes, polymethylmethacrylates- , polystyrenes,
polycarbonates, polyimides and mixtures thereof.
[0028] As used herein, with respect to the present invention, the
terms listed below shall have the following meanings.
[0029] "associated particles" as used herein refers to a grouping
of two or more primary particles that are aggregated and/or
agglomerated.
[0030] "aggregation" as used herein is descriptive of a strong
association between primary particles which may be chemically bound
to one another. The breakdown of aggregates into smaller particles
is difficult to achieve.
[0031] "agglomeration" as used herein is descriptive of a weak
association of primary particles which may be held together by
charge or polarity.
[0032] "dispersion index" as used herein refers to the hydrodynamic
particle size of the zirconia particles in the sol divided by the
primary particle size of the zirconia particles. Theoretically, the
dispersion index for non-associated particles equals 1 with the
dispersion index increasing as the degree of association between
primary particles increases.
[0033] "hydrodynamic particle size" refers to the weight average
particle size of the zirconia particles in the aqueous phase as
measured by Photon Correlation Spectroscopy (PCS).
[0034] "primary particle size" as used herein refers to the size of
a non-associated single crystal zirconia particle.
[0035] "sol" as used herein refers to a dispersion or suspension of
colloidal particles in an aqueous phase.
[0036] "zirconia" as used herein refers to ZrO.sub.2 and may also
be known as zirconium oxide and as zirconium dioxide.
DETAILED DESCRIPTION
[0037] The zirconia sols and zirconia particles of the present
invention possess several advantageous characteristics. For
example, the zirconia particles have a small average primary
particle size and are highly crystalline. Of the crystalline
portion of the zirconia particles the predominate crystal lattice
structures are cubic and tetragonal with the balance being
monoclinic. Cubic and tetragonal crystal lattice structures promote
the formation of low aspect ratio primary particles having a
cube-like shape when viewed under an electron microscope. In the
sol the primary particles exist in a substantially non-associated
(i.e., non aggregated and non-agglomerated) form. The particle
size, crystalline nature of the particles and freedom from
association of the particles allows the production of high
refractive index, high x-ray opacity transparent composite
materials when the sols of the present invention are incorporated
into organic matrix materials, for example, monomers, oligomers
and/or polymers.
[0038] Primary Particle Size:
[0039] Zirconia sols of the present invention comprise a plurality
of single crystal zirconia particles having an average primary
particle size of about 20 nm or less, more preferably, having an
average primary particle size ranging from about 7-20 nm. As used
herein, the term "primary particle size" refers to the size of a
non-associated single crystal zirconia particle. Primary particle
size is determined by x-ray diffraction as described in Test
Procedure 3.
[0040] Crystallinity:
[0041] Zirconia sols of the present invention comprise zirconia
particles which are highly crystalline in nature. This is important
in that crystalline zirconia has a higher refractive index and
higher x-ray scattering capability than amorphous zirconia.
Crystallinity of zirconia particles may be quantified, for example,
using a crystallinity index. Crystallinity index is calculated by
dividing the x-ray scattering intensity of the sample material by
the x-ray scattering intensity of a known crystalline standard
material, for example, calcium stabilized zirconium oxide. A
specific test procedure for determining the crystallinity index of
zirconia particles is set forth herein in Test Procedure 4. In
zirconia sols of the present invention the zirconia particles have
a crystallinity index of about 0.65 or greater as measured using
Test Procedure 4. More preferably, the zirconia particles having a
crystallinity index of about 0.75 or greater, most preferably about
0.85 or greater as measured using Test Procedure 4.
[0042] Of the crystalline portion of the zirconia particles, the
predominate crystal lattice forms are cubic and tetragonal with a
minor amount of monoclinic phase also being present. Due to the
difficulty in separately quantifying cubic and tetragonal crystal
lattice structures using x-ray diffraction, the two have been
combined and are reported herein as combined cubic and tetragonal.
Specifically, the zirconia particles comprise about 70% or greater
combined cubic and tetragonal crystal lattice structure. More
preferably, the zirconia particles comprise about 75% or greater
combined cubic and tetragonal crystal lattice structure, and most
preferably comprise about 85% or greater combined cubic and
tetragonal crystal lattice structure. In each instance, the balance
of the crystalline phase is in the monoclinic crystal lattice
structure.
[0043] Due to their very small size, the zirconia particles exist
in predominately cubic and tetragonal crystal lattice phases
without need for an effective amount of a crystal phase stabilizer.
As used herein the term "crystal phase stabilizer" refers to a
material which may be added to stabilize zirconia in the cubic
and/or tetragonal crystal lattice structure. Specifically, crystal
phase stabilizers function to suppress transformation from the
cubic and/or tetragonal phase to the monoclinic phase. Crystal
phase stabilizers include, for example, alkaline-earth oxides such
as MgO and CaO, rare earth oxides (i.e., lanthanides) and
Y.sub.2O.sub.3. As used herein the term "an effective amount"
refers to the amount of crystal phase stabilizer necessary to
suppress transformation of zirconia from the cubic and/or
tetragonal phase to the monoclinic phase. In a preferred
embodiment, the zirconia particles comprise less than about 1 wt. %
of a crystal phase stabilizer, more preferably less than about 0.1
wt. % of a crystal phase stabilizer.
[0044] Dispersion Index:
[0045] In zirconia sols of the present invention, the primary
particles of zirconia exist in a substantially non-associated
(i.e., non-aggregated and non-agglomerated) form. A quantitative
measure of the degree of association between the primary particles
in the sol is the dispersion index. As used herein the "dispersion
index" is defined as the hydrodynamic particle size divided by the
primary particle size. The primary particle size is determined
using x-ray diffraction techniques as described in Test Procedure
3. Hydrodynamic particle size refers to the weight average particle
size of the zirconia particles in the aqueous phase as measured by
Photon Correlation Spectroscopy (PCS) (see, Test Procedure 5). If
the primary particles are associated, PCS provides a measure of the
size of the aggregates and/or agglomerates of primary particles in
the zirconia sol. If the particles are non-associated, PCS provides
a measure of the size of the primary particles. Accordingly, as the
association between primary particles in the sol decreases the
dispersion index approaches a value of 1. In zirconia sols of the
present invention the primary zirconia particles exist in a
substantially non-associated form resulting in a zirconia sol
having a dispersion index ranging from about 1-3, more preferably
ranging from about 1-2.5, and most preferably ranging from about
1-2.
[0046] Optical Transmission:
[0047] Zirconia sols of the present invention may be characterized
in part as having a high optical transmission due to the small size
and non-associated form of the primary zirconia particles in the
sol. High optical transmission of the sol is an important
characteristic in preparing transparent or translucent
zirconia-filled composite materials. As used herein, "optical
transmission" refers to the amount of light that passes through a
sample (e.g., a zirconia sol of the present invention) divided by
the total amount of light incident upon the sample and may be
calculated using the following equation:
%Transmission=(I/I.sub.O)
[0048] where:
[0049] I is the light intensity passing though the sample; and
[0050] I.sub.O is the light intensity incident on the sample.
[0051] Optical transmission may be determined using an
ultraviolet/visible spectrophotometer such as that commercially
available as Model 6-550 Pye Unicam (from Pye Unicam Ltd.,
Cambridge England).
[0052] For zirconia sols of the present invention having a percent
zirconia of about 1.28 wt. %, the optical transmission is
preferably about 70% or greater, more preferably about 80% or
greater, and most preferably about 90% or greater when tested in
accordance with Test Procedure 2. For zirconia sols of the present
invention having a percent zirconia of about 10 wt. %, the optical
transmission is preferably about 20% or greater, more preferably
about 50% or greater, and most preferably about 70% or greater when
tested in accordance with Test Procedure 2.
[0053] Method of Making Zirconia Sols:
[0054] Zirconia Precursor:
[0055] Suitable starting materials for preparing polyether acid
zirconium salts include basic zirconium salts such as zirconium
carboxylates and basic zirconium salts having counterions that may
be displaced with carboxylic acids. Representative examples of
basic zirconium salts having counterions that may be displaced with
carboxylic acids include zirconium oxynitrate, zirconium
oxychloride and zirconium carbonates. Basic zirconium salts are
salts of zirconium wherein at least a portion of the cationic
charge on the zirconium is compensated by hydroxide or an O.sup.2-
anion. Because it is difficult in practice to determine whether the
oxygen content in basic zirconium salts arises from bound hydroxide
or O.sup.2-, it is common to represent this oxygen content as
simply oxygen. Thus, formula (1) set forth below is presented with
bound water excluded for simplicity and represents a general
formula for zirconium compounds that may be suitable as starting
materials for preparing polyether acid zirconium salts.
ZrO.sub.(4-n/2)(X).sub.n (1)
[0056] where:
[0057] X is a carboxylic acid displaceable counterion; and
[0058] n ranges from 0.5 to 4.
[0059] Representative examples of carboxylic acid displaceable
counterions include carboxylates such as acetates, formates and
propionates and other counterions such as nitrate, chloride,
carbonate or a combination thereof. Zirconium alkoxides, although
not formally zirconium salts, may be used as starting materials in
the formation of the polyether acid zirconium after initial
reaction with a suitable acid to form a basic zirconium salt.
[0060] A preferred starting material is an aqueous solution or sol
of basic zirconium acetate having the general formula
ZrO.sub.(4-n/2)(CH.sub.3COO).sub.n. where n ranges from about 1-2.
In aqueous solutions, zirconium acetate probably exists as complex
polynuclear zirconium cation. Processes for making zirconium
acetate are well known in the art (see, for example, W. B.
Blumenthal, "The Chemical Behavior of Zirconium", D.Van Nostrand
Company, Princeton, N.J., pp. 311-338). Suitable zirconium acetate
solutions comprise from about 5-40 wt. % as ZrO.sub.2 and range
from about 5-40 wt. % acetate. A preferred zirconium acetate sol
starting material comprises ZrO.sub.1.25(C.sub.2H.s-
ub.3O.sub.2).sub.1.5 at 20 wt. % ZrO.sub.2 and is commercially
available under the trade designation "Nyacol ZrO.sub.2(Ac)" from
Nyacol Products Corporation, Ashland, Mass.
[0061] Polyether Carboxylic Acid:
[0062] In a preferred process of the present invention a polyether
acid zirconium salt is prepared by reacting, in an aqueous
solution, a zirconium salt with a polyether carboxylic acid. As
presently understood, the polyether carboxylic acid is believed to
function to prevent association (i.e., agglomeration and/or
aggregation) of the zirconia particles as they are formed during
the hydrolysis reaction. In this way, the zirconia particles
produced according to the process of the present invention are
substantially non-associated.
[0063] Polyether carboxylic acids suitable for use as modifiers in
the present invention are water soluble monocarboxylic acids (i.e.,
containing one carboxylic acid group per molecule) having a
polyether tail. The polyether tail comprises repeating difunctional
alkoxy radicals having the general formula --O--R--. Preferred R
groups have the general formula --C.sub.nH.sub.2n-- and include,
for example, methylene, ethylene and propylene (including
n-propylene and i-propylene) or a combination thereof. Combinations
of R groups may be provided, for example, as random, or block type
copolymers.
[0064] A preferred class of monovalent polyether radicals may be
represented generally by formula (3):
CH.sub.3--[O--(CH.sub.2).sub.y].sub.x--X--COOH (3)
[0065] where:
[0066] X is a divalent organic linking group;
[0067] x ranges from about 1-10; and
[0068] y ranges from about 1-4.
[0069] Representative examples of X include
--X.sub.2--(CH.sub.2).sub.n-- where X.sub.2 is --O-- --S--,
--C(O)O--, --C(O)NH-- and wherein n ranges from about 1-3.
[0070] Examples of preferred polyether carboxylic acids include
2-[2-(2-methoxyethoxy)ethoxy] acetic acid having the chemical
structure CH.sub.3O(CH.sub.2CH.sub.2O).sub.2CH.sub.2COOH (hereafter
MEEAA) and 2-(2-methoxyethoxy) acetic acid having the chemical
structure CH.sub.3OCH.sub.2CH.sub.2OCH.sub.2COOH (hereafter MEAA).
MEAA and MEEAA are commercially from Aldrich Chemical Co.,
Milwaukee, Wis. as catalog numbers 40,701-1 and 40,700-3,
respectively. It is also within the scope of this invention to
utilize a mixture of more than one polyether carboxylic acid.
[0071] Reaction of the polyether carboxylic acid with a zirconium
salt following reaction sequence (1):
ZrO.sub.(4-n/2)(X).sub.n+aR.sub.2--COOH.fwdarw.ZrO.sub.(4-n/2)(X).sub.n-a(-
R.sub.2COO).sub.a+aHX (1)
[0072] results in the formation of a polyether acid zirconium salt
having the general formula
ZrO.sub.(4-n/2)(X).sub.n-a(R.sub.2COO).sub.a and liberates (i.e.,
releases) approximately a stochiometric amount of an acid having
the general formula HX. By way of example, when the zirconium salt
comprises zirconium acetate
(ZrO.sub.(4-n/2)(C.sub.2H.sub.3O.sub.2).- sub.n) a near
stochiometric amount of acetic acid (C.sub.2H.sub.3O.sub.2H) is
released as a result of the formation of the polyether acid
zirconium salt (see, reaction sequence 1a).
ZrO.sub.(4-n/2)(C.sub.2H.sub.3O.sub.2).sub.n+aR.sub.2--COOH.fwdarw.ZrO.sub-
.(4-n/2)(C.sub.2H.sub.3O.sub.2).sub.n-a(R.sub.2COO).sub.a+aC.sub.2H.sub.3O-
.sub.2H (1a)
[0073] Salts of zirconium with carboxylic acids are not dissociated
in the aqueous phase as the acid is bound to the zirconium atom.
The carboxylic acid effects the water solubility of the salt.
Attachment of hydrophobic acids (e.g., alkyl acids) to the
zirconium causes the salts to be insoluble in water. In fact, even
the addition of small acids such as propionic acid and acrylic acid
cause the salt to be insoluble in water. In contrast, the polyether
acids used in the present invention allow higher molecular weight
acids to be used while maintaining the water solubility of the
polyether acid zirconium salt. This in turn allows hydrothermal
treatment of the dissolved polyether acid zirconium salt in the
aqueous phase.
[0074] Typically, relative to the zirconium salt starting material,
the polyether carboxylic acid is added in an amount ranging from
about 2.5-5.0 millimoles per gram equivalent of ZrO.sub.2 in the
zirconium salt. For the preferred zirconium acetate starting
material (i.e., Nyacol ZrO.sub.2(Ac)), this range results in the
displacement of about 20-50% of the acetate groups. Preferably, the
amount of polyether carboxylic acid added should be limited to the
minimum amount necessary to prevent association of the resulting
zirconia particles. In this way, the amount of acid released during
formation of the polyether acid zirconium salt is kept to a
minimum. The amount of polyether carboxylic acid added may depend
upon such factors as, for example, the molecular weight of the
polyether carboxylic acid, the concentration, time and temperature
during the hydrolysis reaction.
[0075] Typically, the polyether carboxylic acid is added to an
aqueous solution of the zirconium salt and the resulting solution
is stirred at room temperature for about 30-60 minutes. The
polyether carboxylic acid molecules react with the zirconium salt
displacing and substituting for at least a portion of the acid
groups bound to the zirconium salt. The displaced acid groups are
released into the solution as free acid. It will ordinarily be
preferred to remove at least a portion of the acid, more preferably
substantially all of the acid released during the formation of the
polyether acid zirconium salt. It should be noted that removal of
the acid may function to shift the reaction equilibrium towards
formation of the polyether acid zirconium salt. Suitable techniques
for removing the excess acid are known in the art and include, for
example, drying or distillation. When the liberated acid has a low
boiling point (e.g., < about 175.degree. C.), it may be removed
by heating the solution until the aqueous phase evaporates leaving
a residue of the polyether acid zirconium salt. The polyether acid
zirconium salt must then be dissolved in water prior to
hydrolysis.
[0076] Hydrolysis:
[0077] After formation of the polyether acid zirconium salt and,
preferably, removal of the liberated acid, the next step is to
hydrolyze an aqueous solution of the polyether acid zirconium salt
under conditions sufficient to convert the polyether acid zirconium
salt into crystalline zirconia particles. By way of example, when
the polyether acid zirconium salt is derived from the acetate salt
(see, reaction sequence 1a), the hydrolysis step follows general
reaction sequence (2a):
ZrO.sub.(4-n/2)(C.sub.2H.sub.3O.sub.2).sub.n-a(R.sub.2COO).sub.a.fwdarw.ac-
id modified ZrO.sub.2+(n-a)C.sub.2H.sub.3O.sub.2H+aR.sub.2COOH
(2a)
[0078] The hydrolysis reaction forms acid modified zirconia
particles and also produces free carboxylic acids (i.e.,
C.sub.2H.sub.3O.sub.2H and R.sub.2COOH) as a by product. Therefore,
the resultant zirconia sol comprises the acid modified zirconia
particles and a mixture of two carboxylic acids in water. By acid
modified zirconia particles it is meant that at least a fraction of
the acids are adsorbed to the surface of the zirconia
particles.
[0079] The hydrolysis reaction of the polyether acid zirconium salt
solution may take place in any suitable reaction vessel. Since the
reaction is typically performed under high temperatures and
pressures, an autoclave will generally be the preferred type of
reaction vessel. One example of a preferred reaction vessel is
commercially available as Pressure Reactor Series #4520" from Parr
Instruments Co., Moline, Ill.
[0080] In operation, an aqueous solution of the polyether acid
zirconium salt is first charged into a reaction vessel. The
concentration of the polyether acid zirconium salt solution is
typically in the range of 0.5-3 wt. % ZrO.sub.2, preferably in the
range of 1-2 wt. % ZrO.sub.2. However, the concentration may be
varied through a wider range depending upon the other reaction
conditions. The polyether acid zirconium salt solution is then
heated to a temperature sufficient to convert it into zirconia
particles. Preferred hydrolysis temperatures range from about
140-250.degree. C., more preferably ranging from about
150-200.degree. C. Typically the reaction vessel is heated to the
desired hydrolysis temperature over a period of several hours.
Among other considerations, a suitable hydrolysis temperature or
temperature range, may be selected in order to minimize degradation
and/or decomposition of the polyether carboxylic acid. The pressure
maintained in the reaction vessel may be the autogenous pressure
(i.e., the vapor pressure of water at the temperature of the
reaction) or, preferably, the reaction vessel may be pressured, for
example, with an inert gas such as nitrogen. Preferred pressures
range from about 1-30 bars, more preferably 2-20 bars.
Pressurization of the reaction vessel is believed to reduce or
eliminate refluxing of the polyether acid zirconium salt solution
within the reaction vessel which may deleteriously affect the
properties of the resulting zirconia sol. The time of hydrolysis is
typically a function of the hydrolysis temperature and the
concentration of the salt solution. Heat is typically applied until
the hydrolysis reaction is substantially complete. Generally, the
time involved is in the range of about 16-24 hours at a temperature
of about 175.degree. C., however, longer or shorter times may also
be suitable. The reaction may be monitored by examining the
resulting zirconia particles using x-ray diffraction or by
examining the amount of free acid in the water phase using IR
spectroscopy or HPLC. Upon completion of the hydrolysis, the
pressure vessel is allowed to cool and the resulting zirconia sol
is removed from the reaction vessel. Although the procedure
described above is a batchwise process, it is also within the scope
of this invention to conduct the hydrolysis in a continuous
process.
[0081] Post-Treatment of Zirconia Sols:
[0082] Zirconia sols of the present invention may be concentrated
by removing at least a portion of the liquid phase using techniques
well known in the art, for example, evaporation or
ultra-filtration. In a preferred method the zirconia sols are
concentrated to about 10-40 wt. % ZrO.sub.2 using a rotary
evaporator.
[0083] Zirconia sols prepared in accordance with the method of the
present invention typically contain an excess of acid over that
normally desired (see, reaction sequence 2a). When it is desired to
combine a zirconia sol of the present invention with an organic
matrix material, for example, an organic monomer, it will
ordinarily be necessary to remove at least a portion of, more
preferably substantially all of, the free acid present in the sol.
Typically, the acid may be removed by such conventional methods as
drying, dialysis, precipitation, ion exchange, distillation or
diafiltration.
[0084] Due to the formation of free acid during the hydrolysis
reaction, the pH of the as prepared zirconia sols typically ranges
from about 1.8-2.2. Dialysis may be used to increase the pH of the
sols. Dialyzed sols typically have a pH ranging about 1-4.5, or
greater, depending upon the extent of the dialysis. The pH of the
sols may also be adjusted by the addition of acids (e.g.,
concentrated HCl and glacial acetic) and/or base (e.g., aqueous
ammonia). Addition of aqueous ammonia has resulted in clear sol to
at least pH 6-7.
[0085] Dialysis, ion exchange and diafiltration methods may be used
to remove the free acid without substantially changing the ratio of
the acids adsorbed to the surface of the zirconia particles.
Alternatively, removal of excess acid and concentration of the sol
may be achieved by first evaporating the water and free acid from
the sol to obtain a dry powder. The dry powder may then be
redispersed in a desired amount of water to obtain a concentrated
sol substantially free of excess acid. It should be noted, however,
that this technique may change the ratio of the acids adsorbed to
the surface of the zirconia particles in such a way that the ratio
of the higher boiling acid to the lower boiling acid is
increased.
[0086] Optionally, after formation of the zirconia sol, the
polyether carboxylic acid groups may be removed or displaced from
the zirconia particles of the sol. Removal of the polyether
carboxylic acid groups may be advantageous, for example, when the
polyether groups would be incompatible with an organic matrix
material to which it is desired to add the zirconium sol.
Displacement of the polyether carboxylic acid groups may be
accomplished, for example, by displacing the polyether acid from
the zirconia particles with a carboxylic acid, for example, acetic
acid. The carboxylic acid displaces and substitutes for the
polyether carboxylic acid groups on the zirconia particles. After
displacement, the free polyether carboxylic acid may be removed
from the sol using techniques known in the art, for example,
dialysis or diafiltration.
[0087] Surface Modification:
[0088] In some instance it may be desirable to combine a zirconia
sol of the present invention with an organic matrix material, for
example a monomer, oligomer and/or polymer. The zirconia particles
may be added to a organic matrix materials to provide matrix
materials having increased index of refraction and increased
radiopacity. Specifically, the zirconia particles may provide
increased index of refraction and/or increased radiopacity without
detrimentally affecting the optical transmission of the organic
matrix.
[0089] Generally it will be necessary to surface modify the
zirconia particles in order to provide compatibility with an
organic matrix material. Surface modification involves reacting the
zirconia particles with a surface modification agent or combination
of surface modification agents that attach to the surface of the
zirconia particles and which modify the surface characteristics of
the zirconia particles to provide increased compatibility with the
organic matrix material.
[0090] Surface modification agents may be represented by the
formula A-B where the A group is capable of attaching to the
surface of a zirconia particle, and where B is a compatibilizing
group which may be reactive or non-reactive with the organic
matrix. Groups capable of attaching, via adsorption, to the surface
of a zirconia particle include, for example, acids such as
carboxylic acids, sulfonic acids, phosphonic acids and the like.
Compatibilizing groups B which impart polar character to the
zirconia particles include, for example, polyethers.
[0091] Representative examples of polar modifying agents having
carboxylic acid functionality include MEEAA, MEAA and
mono(polyethylene glycol)succinate. Compatibilizing groups B which
impart non-polar character to the zirconia particles include, for
example, linear or branched aromatic or aliphatic hydrocarbons.
Representative examples of non-polar modifying agents having
carboxylic acid functionality include octanoic acid, dodecanoic
acid and oleic acid. Modifying agents reactive with the organic
matrix include, for example, acrylic acid, methacrylic acid and
mono-2-(methacryloxyethyl)succinate. A useful surface modification
agent which imparts both polar character and reactivity to the
zirconia particles is mono(methacryloxypolyethyleneglycol)
succinate. This material may be particularly suitable for addition
to radiation curable acrylate and/or methacrylate organic matrix
materials.
[0092] Generally, the surface modification may be accomplished by
simple addition of a surface modifying agent to a zirconia sol of
the present invention. Optionally, a water miscible cosolvent may
be used to increase the solubility of the surface modifying agent
and/or compatibility of the surface modified particles in the
aqueous phase. Suitable cosolvents include water-miscible organic
compounds, for example, methoxy-2-propanol or N-methyl pyrrolidone.
When the surface modification agents are acids, the modification of
the zirconia particles typically does not require elevated
temperatures.
[0093] Various methods may be employed to combine the zirconia sol
of the present invention with an organic matrix material. In one
aspect, a solvent exchange procedure may be utilized. In the
solvent exchange procedure the organic matrix material is first
added to the surface modified sol. Optionally, prior to addition of
the organic matrix material, a cosolvent such as methoxy-2-propanol
or N-methyl pyrolidone may be added to the zirconia sol to help
miscibilize the organic matrix material in the water. After
addition of the organic matrix material, the water and cosolvent
(if used) are removed via evaporation, thus leaving the zirconia
particles dispersed in the organic matrix material. The evaporation
step may be accomplished for example, via distillation, rotary
evaporation or oven drying.
[0094] Alternatively, another method for incorporating a zirconia
sol of the present invention into an organic matrix material
involves drying of the zirconia particles to produce a powder
followed by the addition of the organic matrix material into which
the particles are dispersed. The drying step may be accomplished by
conventional means such as oven drying or spray drying. In another
aspect, conventional oven drying can be performed at between about
70.degree. C. to 90.degree. C. for about 2 to 4 hours.
[0095] Alternatively, another method of incorporating a zirconia
sol of the present invention into an organic matrix material
involves first surface treating the zirconia particles with a
non-polar carboxylic acid, for example, oleic acid. The non-polar
acid surface modifies the zirconia particles causing them to flock
into a filterable mass. The particles may then be separated from
the liquid phase via filtration, optionally dried, and combined
with the organic matrix material.
[0096] In yet another method the surface modified particles can be
extracted into a water immiscible solvent or monomer, for example,
toluene, hexane, ethyl acetate or styrene.
[0097] The sols of the present invention may be combined with
organic matrix materials, for example, monomers, oligomers and
polymers by the various techniques discussed above. The resultant
composite material can have the properties of optical clarity, high
refractive index and high radiopacity combined with high modulus,
hardness, and the processibility and flexibility of the polymer
matrix. Suitable materials for incorporated zirconia sols of the
present invention include, for example, dental materials as
described in Attorney Docket Nos. 55117USA2A "Dental Materials With
Nano-Sized Silica Particles" (filed on Oct. 28, 1999) and
55118USA1A "Radiopaque Dental Materials With Nano-Sized Particles"
(filed on Oct. 28, 1999), the disclosures of which are incorporated
herein by reference. In general, the refractive index of a
composite material increases linearly with volume fraction of the
zirconia particles in the organic matrix. To obtain a high index of
refraction, an organic matrix material having a high index of
refraction is generally preferred. Zirconia particles from the
zirconia sol of the present invention may be used to further
increase the refractive index of the organic matrix. When combined
with an organic matrix material the resulting composite materials
may achieve a refractive index of about 1.6 or greater, more
preferably about 1.66 or greater and most preferably about 1.75 or
greater.
[0098] Representative examples of polymerizable monomers include
acrylates, methacrylates, styrenes, epoxies and the like. Also,
reactive oligomers such as acrylated or methacrylated polyesters,
polyurethanes or acrylics may also be used. The resulting composite
material may be shaped or coated and then polymerized, for example,
via a free-radical photopolymerization mechanism.
Photopolymerization may be initiated by the use of a photoinitiator
such as that commercially available under the trade designation
"IRGACURE 184" (Ciba Specialty Chemicals, Tarrytown, N.Y.). The
sols of the present invention may also be combined with other types
of polymers, for example, polyolefins, polyesters, polyurethanes,
polymethylmethacrylates, polystyrenes, polycarbonates and
polyimides. Suitable techniques for combining the sol with a
thermoplastic polymer include, for example, extrusion, milling or
brabender mixing. Surface modification agents should be selected to
be stable at the desired processing temperature.
EXAMPLES
[0099] Test Procedure 1: Percent ZrO.sub.2
[0100] The weight percent zirconia, in the sols of the present,
invention was determined by gravimetric analysis using a TA
Instruments 2950 TGA (Thermogravimetric analyzer). Analysis were
completed by heating a 30 to 60 mg sample of the sample sol in an
air to 900.degree. C. to volatilize all organic materials, leaving
only the inorganic ZrO.sub.2. Alternatively the total solids
content (ZrO.sub.2 and adsorbed acid) was determined by solids dry
down at 80 C for 16 hr, followed by TGA of the dried solids to
determine the ZrO.sub.2 content of the solids. The weight loss of
the samples was essentially complete between 500-600.degree. C.
[0101] Test Procedure 2: Optical Transmission
[0102] Optical transmission of the sol sample was determined by
measuring the transmission of a of a known wt. % ZrO.sub.2 solution
of the sol in deionized water at 600 nm, using a standard
polystyrene cuvette (1 cm path length) in a Model 6-550 Pye Unicam
UV/V spectrophotometer (available from Pye Unicam Ltd (Cambridge,
England). The % transmission was adjusted to 100% using a cuvette
filled with deionized water. The reported optical transmission
measurement is transmission relative to distilled water.
[0103] The optical transmission of free standing films was
determined by measuring the transmission through a film sample of
known thickness at 600 nm using a Model 6-550 Pye Unicam UV/V
spectrophotometer. The spectrophotometer was first calibrated to
100% transmission against air.
[0104] Test Procedure 3: Crystallite Particle Size and Crystal Form
Content
[0105] Particle size of dried zirconia sample was reduced by hand
grinding using an agate mortar and pestle. A liberal amount of the
sample was applied by spatula to a glass microscope slide on which
a section of double coated tape had been adhered and pressed into
the adhesive on the tape by forcing the sample against the tape
with the spatula blade. Excess sample was removed by scraping the
sample area with the edge of the spatula blade, leaving a thin
layer of particles adhered to the adhesive. Loosely adhered
materials remaining after the scraping were remove by forcefully
tapping the microscope slide against a hard surface. In a similar
manner, corundum (Linde 1.0 .mu.m alumina polishing powder, Lot
Number C062, Union Carbide, Indianapolis, Ind.) was prepared and
used to calibrate diffractometer for instrumental broadening.
[0106] X-ray diffraction scans were obtained from by use of a
diffractometer employing copper K.sub..alpha. radiation and Inel
CPS120 (Inel Inc, Stratham, N.H.) position sensitive detector
registry of the scattered radiation. The detector has a nominal
angular resolution of 0.03 degrees (2.theta.) and received
scattering data from 0 to 115 degree (2.theta.). The X-ray
generator was operated at a setting of 40 kV and 10 mA and fixed
incident beam slits were used. Data was collected for 60 minutes at
a fixed take-off (incident) angle of 6 degrees. Data collections
for the corundum standard were conducted on three separate areas of
several individual corundum mounts. Data was collected on three
separate areas of the thin layer sample mount.
[0107] Observed diffraction peaks were identified by comparison to
the reference diffraction patterns contained within the ICDD powder
diffraction database (sets 1-47, International Center for
Diffraction Data, Newton Square, Pa.) and attributed to either
cubic/tetragonal (C/T) or monoclinic (M) forms of zirconia. The
amounts of each zirconia form were evaluated on a relative basis
and the form of zirconia having the most intense diffraction peak
was assigned the relative intensity value of 100. The strongest
line of each of the remaining crystalline zirconia forms were
scaled relative to the most intense line and given a value between
1 and 100.
[0108] Peak widths for the observed diffraction maxima due to
corundum were measured by profile fitting. The relationship between
mean corundum peak widths and corundum peak position (2.theta.) was
determined by fitting a polynomial to these data to produce a
continuous function used to evaluate the instrumental breadth at
any peak position within the corundum testing range. Peak widths
for the observed diffraction maxima due to zirconia were measured
by profile fitting observed diffraction peaks. The following peak
widths were evaluated depending on the zirconia phase found to be
present:
[0109] cubic/tetragonal (C/T): (1 1 1)
[0110] monoclinic (M): (-1 1 1), and (1 1 1)
[0111] Peak widths were found as the peak full width at half
maximum (FWHM) having units of degrees using a Pearson VII peak
shape model, with K.sub..alpha.1 and K.sub..alpha.2 wavelength
components accounted for, and linear background model. The profile
fitting was accomplished by use of the capabilities of the JADE
(version 3.1, Materials Data Inc., Livermore, Calif.) diffraction
software suite. Sample peak widths were evaluated for the three
separate data collections obtained for the same thin layer sample
mount.
[0112] Sample peaks were corrected for instrumental broadening by
interpolation of instrumental breadth values from corundum
instrument calibration and corrected peak widths converted to units
of radians. Corrected sample peak width (.beta.) were used to
evaluate primary crystal (crystallite) size by application of the
Scherrer equation. The arithmetic mean of the cubic/tetragonal
(C/T) and monoclininc phases (M) were calculated.
.beta.=[calculated peak FWHM-instrumental breadth](converted to
radians)
Crystallite Size (D)=K.lambda./.beta.(cos .theta.)
[0113] where:
[0114] K=form factor (here 0.9);
[0115] .lambda.=wavelength (1.540598 .ANG.);
[0116] .beta.=calculated peak width after correction for
instrumental broadening (in radians); and
[0117] .theta.=1/2 the peak position (scattering angle).
Cubic/Tetragonal Mean Crystallite Size=[D(1 1 1).sub.area 1+D(1 1
1).sub.area 2+D(1 1 1).sub.area 3]/3
Monoclinic Mean Crystallite Size=[D(-1 1 1).sub.area 1+D(-1 1
1).sub.area 2+D(-1 1 1).sub.area 3+D(1 1 1).sub.area 1+D(1 1
1).sub.area 2+D(1 1 1).sub.area 3]/6
[0118] The crystallite size is reported in the format:
[C/T crystallite size](parts C/T)+[M crystallite size](parts M)
Weighted average=[(% C/T)(C/T size)+(% M)(M size)]/100
[0119] where:
[0120] %C/T=the percent crystallinity contributed by the cubic
and
[0121] tetragonal crystallite content of the ZrO.sub.2 sol;
[0122] C/T size=the size of the cubic and tetragonal
crystallites;
[0123] % M=the percent crystallinity contributed by the monoclinic
crystallite content of the ZrO.sub.2 sol; and
[0124] M size=the size of the monoclinic crystallites.
[0125] Test Procedure 4: Crystallinity Index
[0126] Particle size of the phase standard (zirconium oxide,
calcium stabilized Z-1083 Lot Number 173077-A-1, CERAC Inc,
Milwaukee, Wis.) was reduced by ball milling and/or hand grinding
using a boron carbide mortar and pestle to pass 325 mesh sieve.
Individual mixtures were prepared consisting of 0.400 grams of
sample and 0.100 grams of mass standard, a material incorporated
into samples being evaluated for crystallinity index to normalize
X-ray intensity values based on amount of material present in a
sample. Tungsten metal powder (<3 .mu.m) was the mass standard
used. Mixtures of the samples were blended under ethanol using an
agate mortar and pestle and allowed to dry under flowing nitrogen.
A similar mixture composed of the phase standard was also prepared
to serve as the crystallinity index reference. The dried mixtures
were removed from the mortar and pestle by spatula and fine brush
and subsequently transferred to individual sample containers.
Portions of each sample were prepared as ethanol slurries on sample
holders containing flush mounted glass inserts. Multiple X-ray
diffraction scans (a minimum or 10 scans for both sample and
standard) were obtained from each sample and phase standard mixture
by use of a vertical Bragg-Bretano diffractometer (constructed by
Philips Electronic Instruments, Mahwah, N.J.) employing copper
K.sub..alpha. radiation, variable incident slit, fixed exit slit,
graphite diffracted beam monochromator, and proportional counter
registry of the scattered radiation. Scans were conducted from
25-55 degree (2.theta.) employing a 0.04 degree step size. A 8
second dwell time was used for standard mixture while a 20 second
dwell time was employed for sample mixtures to improve counting
statistics. The X-ray generator (Spellman High Voltage Electronics
Corporation, Hauppage, N.Y.) was operated at a setting of 40 kV and
20 mA. Peak areas for the observed diffraction maxima due to
zirconia and tungsten phases were measured by profile fitting
observed diffraction peaks within the 25-55 degree (2.theta.)
scattering angle range. The following peak areas were evaluated
depending on the zirconia phase found to be present:
1 cubic (C) (1 1 1), (2 0 0), and (2 2 0) tetragonal (T) (1 0 1),
(0 0 2)/(1 1 0), and (1 1 2)/(2 0 0) monoclinic (M) (-1 1 1), (1 1
1), (0 0 2), (0 2 0), and (2 0 0)
[0127] The X-ray scattering of internal mass standard was evaluated
by measurement of cubic tungsten (1 1 0) peak area. A Pearson VII
peak shape model and linear background model were employed in all
cases. The profile fitting was accomplished by use of the
capabilities of the JADE (version 3.1, Materials Data Inc.
Livermore, Calif.) diffraction software suite. The peak areas of
zirconia peaks outlined above were summed to produce a total
zirconia scattered intensity value [(Zirconia Area).sub.sample] for
each sample as well as standard [(Zirconia Area).sub.standard].
These total zirconia scattered intensity values were divided by
respective cubic tungsten (1 1 0) peak areas to produce the ratio
[R.sub.sample] for each sample as well as the phase standard
[R.sub.standard]. The arithmetic mean of R.sub.sample and
R.sub.standard are calculated using individual values obtained from
the multiple runs of sample and standard, respectively. The
crystallinity index [X.sub.c] for each sample was calculated as the
ratio of R.sub.sample(mean) to R.sub.standard (mean).
R.sub.sample (i)=[(Total Zirconia Area).sub.sample]/[(Tungsten
Area).sub.sample]
R.sub.standard (i)=[Total Zirconia Area).sub.standard]/[(Tungsten
Area).sub.standard]
R.sub.sample (mean)=[.SIGMA.R.sub.sample (i)]/N.sub.sample
[0128] where N.sub.sample=number of sample scans
R.sub.standard (mean)=[.SIGMA.R.sub.standard
(i)]/N.sub.standard
[0129] where N.sub.standard=number standard scans
X.sub.c=R.sub.sample (mean)/R.sub.standard (mean)
[0130] Test Procedure 5: Photon Correlation Spectroscopy
[0131] The weight average mean particle diameter of the zirconia
particles was determined by Photon Correlation Spectroscopy using a
Coulter N4 Submicron Particle Sizer (available from Coulter
Corporation, Miami Fla.). Dilute zirconia sol samples were filtered
through a 0.45 .mu.m filter using syringe-applied pressure into a
glass cuvette. The remaining volume of the cuvette was filled with
water, covered, and repeatedly inverted to remove air bubbles. The
cuvette was wiped down to remove fingerprints and dust prior to
taking any measurements. Light scattering intensity was measured to
ensure that an appropriate concentration of sol was sampled. If the
intensity was too high, a portion of the cuvette's contents was
removed and the remaining contents diluted with water. If the
intensity was too low, several more drops of filtered sol were
added to the sample and the solution mixed by repeatedly inverting
the cuvette. Prior to starting data acquisition the temperature of
the sample chamber was allowed to equilibrate for 5 minutes at
25.degree. C. The supplied software was used to do a SDP analysis
(1.0 nm-1000 nm) with an angle of 90.degree.. The analysis was
performed using 25 data bins. The following values were used in the
calculations: refractive index of water=1.333, viscosity of water
0.890 cP, and referactive index for zirconia particles=1.9. Data
acquisition immediately ensued for a period of 3:20 minutes. The
reported PCS number is the mean diameter based on weight analysis
that results from this procedure.
[0132] Test Procedure 6: Refractive Index
[0133] The refractive index of the zirconia containing materials
were measured on an Abbe refractometer, commercially available from
Fisher Scientific, Pittsburgh, Pa.
[0134] Test Procedure 7: Diametral Tensile Strength (DTS) and
Compressive Strength (CS) Testing
[0135] DTS and CS measurements were made according to ADA
("American Dental Association") specification No. 9 and ADA
specification No. 27 respectively of ISO-test procedure 4049
(1988). Specifically, for determination of compressive strength
("CS") and diametral tensile strength ("DTS"), the composition was
packed into a 4 mm inside diameter glass tube, capped with silicone
rubber plugs and axially compressed at about 0.28 MPa for 15
minutes, then light cured for 80 seconds by exposure to two
oppositely-disposed Visilux units. Each sample was then irradiated
for 90 seconds using a Dentacolor XS unit (Kulzer, Inc., Germany).
Hardened samples were cut on a diamond saw to form cylindrical
plugs 8 mm long for measurement of CS and 2 mm long for measurement
of DTS. The plugs were stored in distilled water at 37.degree. C.
for 24 hours. CS and DTS values for each composition were measured
using a force testing apparatus available under the trade
designation "INSTRON" (Instron 4505, Instron Corp. Canton,
Mass.).
[0136] The compressive strength (CS) of these samples was tested on
an Instron with 10 kN load cell. A total of 5 cylinders of hardened
composite with about 8 mm length and 4 mm diameter were
prepared.
[0137] The Diametral Tensile Strength (DTS) of these samples was
tested on an Instron with 10 kN load cell. A total of 5 cylinders
of hardened composite with about 2.2 mm length and 4 mm diameter
were prepared.
[0138] Test Procedure 8: Visual Opacity & Radopacity
Determination
[0139] Disc-shaped 1 mm thick by 20 mm diameter samples of the
composite were cured by exposing them to illumination from an
Visilux 2.TM. (3M Co , St. Paul, Minn.) curing light for 60 seconds
on each side of the disk at a distance of 6 mm. The hardened
composite samples were then evaluated for visual opacity and
radiopacity as follows.
[0140] Hardened composite samples were measured for direct light
transmission by measuring transmission of light through the
thickness of the disk using a MacBeth transmission densitometer
Model TD-903 equipped with a visible light filter, available from
MacBeth (MacBeth., Newburgh & NY).
[0141] For radiopacity evaluation, the procedure used followed the
ISO-test procdeure 4049 (1988). Specifically, hardened composite
samples were exposed to radiation using a Gendex GX-770 dental
X-ray (Milwaukee, Wis.) unit for 0.73 seconds at 7 milliamps and 70
kV peak voltage at a distance of about 400 mm. The X-ray negative
was developed using a Air Techniques Peri-Pro automatic film
processor. (Hicksville, N.Y.).
[0142] Material List
[0143] Nyacol ZrO.sub.2(Ac): a zirconium acetate sol with a Zr:AcOH
ratio 1:1.5, (20 wt. % as zirconia in water) available from Nyacol
Products Corporation an affiliate of the PQ Corporation (Ashland,
Mass.).
[0144] MEEAA: 2[2-(2-methoxyethoxy)ethoxy]acetic acid commercially
available from Aldrich Chemical Co., Milwaukee, Wis. under catalog
number 40,701-7.
[0145] MEAA: 2-(2-methoxyethoxy)acetic acid commercially available
from Aldrich Chemical Co., Milwaukee, Wis. under catalog number
40,700-3.
Example 1
[0146] A polyether acid zirconium salt was prepared as follows:
[0147] Nyacol ZrO.sub.2(Ac) (150 g) and MEEAA (26.95 g, 5 mmole/g
ZrO.sub.2) were charged into a liter beaker and the resulting
mixture stirred at room temperature (approximately 22.degree. C.)
for 30 minutes. Water and excess acetic acid were removed and the
polyether acid zirconium salt was isolated as a dry solid (67.15 g)
by allowing the reaction mixture to evaporate at room temperature
for 2 days in an evaporating dish, followed by drying in a
circulating air oven maintained at approximately 90.degree. C. for
approximately 5 hours. A portion of the polyether acid zirconium
salt (45 g) was dissolved in deionized water (1455 g) to produce a
clear polyether acid zirconium salt solution (1500 g). A portion of
the polyether acid zirconium salt solution (1354 g) was poured into
a 2 liter, unstirred, stainless steel Parr Reactor (available from
Parr Instrument Company, Ill.) and the autoclave pressurized to
about 2.75 bars (40 psi) with nitrogen to keep the liquid contents
from refluxing during the subsequent heating cycle. The autoclave
was subsequently heated to 100.degree. C. in approximately 30
minutes, then to 150.degree. C. over a period of approximately two
hours, and finally to 175.degree. C. (12 bars) and maintained at
that temperature for 24 hours, after which the autoclave was cooled
and depressurized over a period of 2-3 hr. The zirconia sol of the
present invention was obtained as a clear liquid with an opalescent
blue color with no sediment.
[0148] The X-ray diffraction spectrum (Test Procedure 3) of the
zirconia particles showed [ZrO.sub.2 (C,T) (9.0
nm)]100+[ZrO.sub.2(M)(9.0 nm)]13 and Photon Correlation
Spectroscopy (Test Procedure 5) gave a weight average mean particle
diameter of 13.1 nm. Additional properties of the zirconia sol are
presented in Table 1.
[0149] The sol of Example 1 was also concentrated to about 20 wt. %
ZrO.sub.2. Excess MEEAA was first removed from the sample by
dialysis using Spectra/Por membrane tubing (MWCO of 3500, available
from Fisher Scientific (Pittsburgh, Pa.). The zirconia sol was
poured into a 25-30 cm length of the tubing, the ends of tube
clipped to prevent leaking, and the tube immersed in a beaker of
deionized water. The water was changed every hour. Free acid
removal, which was tracked using IR measurements, required
approximately 6 hours of dialysis. The dialyzed sol which was
subsequently concentrated to 37 wt. % ZrO.sub.2 by vacuum
distillation and its optical transmission (Test Procedure 2)
determined to be 70%.
[0150] A portion of the as prepared sol was dried at 85.degree. C.
for approximately 16 hours in a circulating air oven. The ZrO.sub.2
content of the solid was determined to be 87.16 wt. % ZrO.sub.2,
evaluated by TGA to 600.degree. C., the remainder of the weight
being surface adsorbed acids. The X-ray scattering intensity for
this material, measured according to Test Procedure 4 produced a
value of 1.751/0.8716=2.0089. The ratio of this to the value of
2.340 obtained for the standard material (see, Test Procedure 4)
was used to determine the crystallinity index of 0.8585.
Example 2
[0151] A polyether acid zirconium salt was prepared as follows:
[0152] Nyacol ZrO.sub.2(Ac) (150 g) and MEAA (20.22 g, 5 mmole/g
ZrO.sub.2) were charged to a 1 liter beaker and the resulting
mixture stirred at room temperature (approximately 22.degree. C.)
for 60 minutes. The mixture was poured into two large
crystallization dishes and dried at room temperature for about 18
hr to remove water and excess acetic acid, producing a dry solid. A
portion of the polyether acid zirconium salt (40.6 g) was dissolved
in deionized water (1459.4 g) to produce a clear polyether acid
zirconium salt solution (1500 g). A portion of the polyether acid
zirconium salt solution (1329.8 g) was poured into a 2 liter,
unstirred stainless steel Parr Reactor and the autoclave
pressurized to about 2.75 bars (40 psi) with nitrogen. The
autoclave was subsequently heated to 100.degree. C. in
approximately 40 minutes and then to 175.degree. C. (12 bars) and
maintained at that temperature for about 21 hr. The autoclave was
cooled and depressurized over a period of 1-3 hr. The resultant
zirconia sol of the present invention was obtained as a clear
liquid with an opalescent blue color.
[0153] The sol was concentrated to about 20 wt. % ZrO.sub.2 by
rotary evaporation (.about.85.degree. C.) to obtain a clear stable
sol. The X-ray diffraction spectrum (Test Procedure 3) of the
zirconia particles showed [ZrO.sub.2 (C,T) (10.5
nm)]100+[ZrO.sub.2(M)(12 nm)]31 and Photon Correlation Spectroscopy
(Test Procedure 5) gave a weight average mean particle diameter of
18.4 nm. Additional properties of the zirconia sol are presented in
Table 1.
Example 3
[0154] A polyether acid zirconium salt was prepared as follows:
[0155] Nyacol ZrO.sub.2(Ac) (150 g) and MEEAA (13.44 g, 2.5 mmole/g
ZrO.sub.2) were charged to a 1 liter round bottom flask and the
resulting mixture stirred at room temperature (approximately
22.degree. C.) for 30 minutes. Water and excess acetic acid were
removed by rotary evaporation at 85.degree. C. for 2.5 hr producing
a dry solid (60.99 g). The polyether acid zirconium salt (60.99 g)
was dissolved in deionized water (2282.7 g) to produce a clear
polyether acid zirconium salt solution (2343.7 g).
[0156] A portion of the polyether acid zirconium salt solution
(1339.6 g) was poured into a 2 liter, unstirred, stainless steel
Parr Reactor and the autoclave pressurized to about 2.75 bars (40
psi) with nitrogen. The autoclave was subsequently heated to
100.degree. C. in approximately 30 minutes, to 150.degree. C. over
a period of approximately 1.5 hours, and finally to 175.degree. C.
(12 bars) and maintained at that temperature for 19 hours. The
autoclave was cooled and depressurized over a period of 2-3 hr. The
zirconia sol of the present invention was obtained as a clear
liquid with an opalescent blue color and a slight white haze.
[0157] The sol was concentrated to about 20 wt. % ZrO.sub.2 by
rotary evaporation (.about.85.degree. C.) to obtain a clear stable
sol. The X-ray diffraction spectrum (test Procedure 3) of the
zirconia particles showed [ZrO.sub.2 (C,T) (9.0
nm)]100+[ZrO.sub.2(M)(9.0 nm)]22 and Photon Correlation
Spectroscopy (Test Procedure 5) gave a weight average mean particle
diameter of 21.7 nm. Additional properties of the zirconia sol are
presented in Table 1.
Example 4
[0158] A polyether acid zirconium salt was prepared as follows:
[0159] Nyacol ZrO.sub.2(Ac)) (200 g) and MEAA (13.52 g, 2.5 mmole/g
ZrO.sub.2) were charged to a 1 liter beaker and the resulting
mixture stirred at room temperature (approximately 22.degree. C.)
for 30 minutes. Water and excess acetic acid were removed and the
polyether acid zirconium salt was isolated as a dry solid (73.87 g)
by allowing the reaction mixture to evaporate in an evaporation
dish in a circulating air oven maintained at 85.degree. C. for
about 24 hr. The polyether acid zirconium salt (73.87 g) was
dissolved in deionized water (3051.9 g) to produce a clear
polyether acid zirconium salt solution (3125.8 g). A portion of the
polyether acid zirconium salt solution, prepared above, (1672.6 g)
was poured into a 2 liter, unstirred, stainless steel Parr Reactor
and the autoclave pressurized to about 2.75 bars (40 psi) with
nitrogen. The autoclave was subsequently heated to 100.degree. C.
in approximately 2 hr, to 150.degree. C. over a period of
approximately two hours, and finally 175.degree. C. (12 bars) and
maintained at that temperature for about 19 hours. The autoclave
was cooled and depressurized over a period of 2-3 hr. The zirconia
sol of the present invention was obtained as a clear liquid with an
opalescent blue color and a slight white haze.
[0160] The sol was concentrated to about 20 wt. % ZrO.sub.2 by
rotary evaporation (.about.85.degree. C.) to obtain a clear stable
sol. The X-ray diffraction spectrum (Test Procedure 3) of the
zirconia particles showed [ZrO.sub.2 (C,T) (11.4
nm)]100+[ZrO.sub.2(M)(13.5 nm)]33 and Photon Correlation
Spectroscopy (test Procedure 5) gave a weight average mean particle
diameter of 22.6 nm. Additional properties of the zirconia sol are
presented in Table 1.
Comparative Example C-1
[0161] The sol of this comparative example was prepared as
follows:
[0162] Nyacol ZrO.sub.2(Ac) (100 g) and deionized water (1463.3 g)
were charged to a 1 liter beaker and the resulting mixture stirred
at room temperature for about 30 min. A portion of the salt
solution (1559 g) was poured into a 2 liter, unstirred, stainless
steel Parr Reactor and the autoclave pressurized to about 2.75 bar
(40 psi) with nitrogen. The autoclave was subsequently heated to
100.degree. C. in approximately 70 min, to 150.degree. C. over a
period of approximately two hours, and finally to 175.degree. C.
(12 bars) and maintained at that temperature for about 18.5 hours.
The autoclave was cooled and depressurized over a period of 2-3 hr.
The zirconia sol was obtained as a dull white sol with a fair
amount of sediment. X-ray diffraction (Test Procedure 3) of the
zirconia particles showed [ZrO.sub.2 (C,T) (11
nm)]100+[ZrO.sub.2(M)(15 nm)]49 and Photon Correlation Spectroscopy
(Test Procedure 5) gives a weight average mean particle diameter of
49.8 nm. Additional properties of the zirconia sol are presented in
Table 1.
Comparative Example C-2
[0163] Comparative Example C-2 is commercially available zirconia
sol having an average particle size of about 100 nm, available from
Nyacol Products Inc., Ashland, Mass. under the trade designation
"Zr 100/20".
Comparative Example C-3
[0164] Comparative Example C-3 is commercially available zirconia
sol having an average particle size of about 50 nm, available from
Nyacol Products Inc. under the trade designation "Zr 50/20".
2TABLE 1 Zirconia Sol Properties Acid Average Ex- Modifier Parts
Cubic Cubic & Parts Crystallite % T % T am- (mmole/g &
Tetragonal Mono- % Cubic & Size Dispersion PCS (1.28% (10% ple
ZrO.sub.2) Tetragonal Size (nm) clinic Tetragonal (nm) Index pH
(nm) Appearance solids) solids) 1 MEEAA 100 9 13 88 9 1.455 1.9
13.1 Clear sol, blue tint 93.1 86.6 5 mmole/g 2 MEEAA 100 10.5 31
76 10.85 1.695 1.9 18.4 Clear sol, blue tint 89.1 47.2 2.5 mmole/g
3 MEAA 100 9 22 82 9 2.411 2.2 21.7 Clear sol, blue tint, 80.8 52.8
5 mmole/g slightly white 4 MEAA 100 11.4 33 75 11.92 1.895 1.9 22.6
Clear sol, blue tint, 70.2 38.7 2.5 mmole/g slightly white C-1 None
100 9 49 67 12.31 4.044 1.9 49.8 Hazy white/blue sol 25 1.1 C-2
None 0 -- 100 0 5.6 17.857 1.9 100 Milky white 0 0 C-3 None 0 --
100 0 5.15 9.709 2.2 50 Hazy white/blue sol, 13 0 slightly
milky
[0165] A comparison of the data in Table 1 shows that the particles
of examples 1-4 have much closer match between the crystallite size
and the aggregate size as is evidenced by the dispersion index
being close to 1. The dispersion index of Comparative Examples C-1
through C-3 generally show small average monoclinic crystal sizes,
but significantly higher PCS values as well as higher dispersion
indices, indicative of aggregation. Also, the data suggests that
higher modifier acid levels (approximately 5 mmole/g ZrO.sub.2) and
longer modifier acid length tend to produce smaller agglomerate
size and more transparent sols. Comparative example C-1 shows the
results of the control reaction where no acid modifier was added
and the resulting significant increase in the agglomerate size
under these conditions. It should be noted that the acid length and
amount charged can have a substantial effect on the amount of
cubic/tetragonal phase present.
Example 5
[0166] A polyether acid zirconium salt was prepared as follows:
[0167] Nyacol ZrO.sub.2(Ac) (96 g) and MEEAA (17.2 g, 5 mmole/g
ZrO.sub.2) were charged into a liter beaker and the reaction
mixture stirred at room temperature (approximately 22.degree. C.)
for 30 minutes. Water and excess acetic acid were removed and the
polyether acid zirconium salt was isolated as a dry solid by
allowing the reaction mixture to evaporate in an evaporation dish
placed in a circulating air oven maintained at approximately
80.degree. C. for approximately 18 hours. The polyether acid
zirconium salt was dissolved in deionized water to produce a clear
polyether acid zirconium salt solution (1500 g total wt), the
solution poured into a 2 liter, unstirred, stainless steel Parr
Reactor and the autoclave pressurized to about 2.75 bars (40 psi)
with nitrogen. The autoclave was subsequently heated to 100.degree.
C. in approximately 50 minutes, to 150.degree. C. over a period of
approximately 45 min, and finally to 175.degree. C. (12 bars) and
maintained at that temperature for about 22 hours. The autoclave
was cooled and depressurized over a period of 2-3 hr. The zirconia
sol of the present invention was obtained as a clear liquid with an
opalescent blue color with no sediment.
[0168] The sol was concentrated via rotary evaporation to a stable
clear blue sol of about 10 wt. % ZrO.sub.2. The free acid was
removed via multiple dialysis runs in 3 liter of water
substantially as described in Example 1. The first three dialysis
were 1-2 hr in duration and the forth dialysis was run overnight.
The dialyzed sample was dried at 80.degree. C. overnight to give
14.6 wt. % solids. Thermal gravimetric analysis of the resultant
powder showed that it was 87.2 wt. % ZrO.sub.2. Simple calculation
shows that the starting sol was 12.71 wt. % ZrO.sub.2. A portion of
the dialyzed sol (5.04 g) was charged to a 25 ml round bottom flask
and methoxy-2-propanol (7.0 g, available from Aldrich Chemical
Co.), oleic acid (0.022 g, available from Aldrich Chemical Co.),
acrylic acid (0.027 g, available from Aldrich Chemical Co.), MEEAA
(0.021 g, available form Aldrich Chemical Co.) and
phenoxyethylacrylate (0.46 g, available from Aldrich Chemical Co.)
were charged to the flask in that order. Water and alcohol were
removed from the reaction mixture via rotary evaporation followed
by trap to trap distillation to produce a clear blue organosol in
phenoxyethylacrylate with a refractive index of 1.5915 (refractive
index of phenoxyethylacrylate is 1.518). Irgacure 184
photoinitiator (approximately 1 wt. %, Ciba Specialty Chemicals,
Tarrytown, N.Y.) was added to the sol. A thin coating (0.1-0.2 g)
of the mixture was cast between two PET liners and was cured using
low pressure Hg lamps for 10 minutes. The resulting cured film was
opaque white in appearance. Additional acrylic acid (0.018 g) was
added to the remaining sol and the resulting mixture was cast
between two PET liners and was cured using a low pressure Hg lamps
for 10 minutes. The resulting cured film was clear, flexible and
free standing. The refractive index of the film was measured to be
1.616 using Test Procedure 6.
[0169] A second portion of the dialyzed sol (5.0 g) was charged to
a 25 ml round bottom flask and methoxy-2-propanol (7.19 g), oleic
acid (0.022 g), acrylic acid (0.065 g), MEEAA (0.022 g) and
phenoxyethylacrylate (0.525 g) were charged to the flask in that
order. Water and alcohol were removed via rotary evaporation
followed by trap to trap distillation to produce a clear blue
organosol in phenoxyethylacrylate with a refractive index of 1.581
(refractive index of phenoxyethylacrylate is 1.518). Irgacure 184
(.about.1 wt. %) was added to the sol. The resulting mixture was
cast between two PET liners separated by a 180 .mu.m spacer and was
cured using a low pressure Hg lamps for 10 minutes. The resulting
cured film was clear, flexible and free standing. The refractive
index of the film was determined to be 1.6155 using Test Procedure
6. The percent transmission at 600 nm of the 180 .mu.m film was
84.2% (Test Procedure 2). A control was prepared as described above
except that the zirconia sol was not added to the mixture. The
percent transmission at 600 nm of the control was 82.19%. The
ZrO.sub.2 content of the film was determined to be 42.85 wt. %
(Test Procedure 1).
[0170] A third portion of the dialyzed sol (15.0 g) was charged to
a 100 ml round bottom flask and methoxy-2-propanol (21 g), oleic
acid (0.066 g), acrylic acid (0.144 g), MEEAA (0.065 g) and
phenoxyethylacrylate (0.885 g) were charged to the flask in that
order. Water and alcohol were removed via rotary evaporation
followed by trap to trap distillation to produce a clear blue
organosol in phenoxyethylacrylate with a refractive index of 1.609.
Irgacure 184 (.about.1 wt. %) was added to the sol. The resulting
mixture was cast between two PET liners separated by a 180 .mu.m
spacer and was cured using a low pressure Hg lamps for 10 minutes.
The resulting cured film was clear, flexible and free standing. The
refractive index of the film was determined to be 1.6345 using Test
Procedure 6. The percent transmission at 600 nm of the 180 .mu.m
film was 83% (Test Procedure 2). A control was prepared as
described above except that the zirconia sol was not added to the
mixture. The percent transmission at 600 nm of the control was
82.1%. The ZrO.sub.2 content of the film was determined to be 53.9
wt. % (Test Procedure 1).
Example 6
[0171] A polyether acid zirconium salt was prepared as follows:
[0172] Nyacol ZrO.sub.2(Ac) (182.09 g) and MEAA (24.42 g, 5 mmole/g
ZrO.sub.2) were charged to a liter beaker and the reaction mixture
stirred at room temperature (approximately 22.degree. C.) for 30
minutes. Water and excess acid were removed and the polyether acid
zirconium salt was recovered as a dry solid (74.1 g) by allowing
the reaction mixture to evaporate in an evaporation dish placed in
a circulating air oven maintained at approximately 85.degree. C.
for approximately 24 hours. The polyether acid zirconium salt (74.1
g) was dissolved in deionized water (2771 g) to produce a clear
polyether acid zirconium salt solution (2845.1 g total wt). A
portion of the solution (1402.7 g) was poured into a 2 liter,
unstirred, stainless steel Parr Reactor and the autoclave
pressurized to about 2.75 bars (40 psi) with nitrogen. The
autoclave was subsequently heated to 100.degree. C. in
approximately 40 minutes and then to 175.degree. C. (12 bars) and
maintained at that temperature for about 24 hours. The autoclave
was cooled and depressurized over a period of 2-3 hr. The zirconia
sol of the present invention was obtained as a clear liquid with an
opalescent blue color with no sediment.
[0173] The sol was concentrated via rotary evaporation to a stable
clear blue sol of about 15 wt. % ZrO.sub.2. The free acid was
removed via dialysis substantially as described in Example 1 except
that the sample was dialyzed twice with 1 liter of water, each
dialysis having a 1-2 hr. duration. A sample of the dialyzed sol
was dried overnight at 80.degree. C. to give 17.54 wt. % solids.
Thermal gravimetric analysis of the resultant powder showed the
powder was 89.99 wt. % ZrO.sub.2. Simple calculation shows that the
starting dialyzed sol was 15.78 wt. % ZrO.sub.2. This sol was added
to a NMP/Polyimide solution as described below and films were cast
to obtain clear high refractive index composite materials.
[0174] A 10 wt. % stock solution (Stock Solution A) of a soluble
polyimide, (polymer # 17, prepared-as described in U.S. Pat. No.
5,750,641) in N-methyl pyrrolidone was prepared. A portion of stock
solution A (2.0 g) was charged to a 25 ml round bottom flask
followed by N-methyl pyrrolidone (5.0 g, available from Aldrich
Chemical Co.), ZrO.sub.2 sol (1.93 g, described above), N-methyl
pyrrolidone (1 g), and stock solution A (0.45 g), in that order.
Water was removed by rotary evaporation to produce a clear blue
fluid organosol. The weight % of ZrO.sub.2 in the composite film
(PI6A) was approximately 55.42%.
[0175] A second portion of stock solution A (2.51 g) was charged to
a 25 ml round bottom flask followed by N-methyl pyrrolidone (12 g)
and ZrO.sub.2 sol (2.52 g), in that order. Water was removed by
rotary evaporation followed by trap to trap distillation to obtain
a clear blue fluid organosol. The weight % of ZrO.sub.2 in the
composite film (PI6B) was approximately 61.4 wt. %.
[0176] A third portion of stock solution A (2.518 g) was charged to
a 25 ml round bottom flask followed by N-methyl pyrrolidone (12.06
g) and ZrO.sub.2 sol (3.71 g), in that order. Water was removed by
rotary evaporation to produce a clear blue fluid organosol. The
weight % of ZrO.sub.2 in the composite film (PI6C) was
approximately 68.8 wt. %.
[0177] An 8.8 wt. % stock solution (Stock Solution B) of a soluble
polyimide (polymer # 1, prepared-as described in U.S. Pat. No.
5,750,641) in N-methyl pyrrolidone was prepared. A portion of stock
solution B (2.85 g) was charged to a 25 ml round bottom flask
followed by N-methyl pyrrolidone (12 g) and the ZrO.sub.2 sol (2.5
g), in that order. Water was removed via rotary evaporation
followed by trap to trap distillation to obtain a clear blue fluid
organosol. The weight % of ZrO.sub.2 in the composite film (PI6D)
was approximately 61.28 wt. %.
[0178] A second portion of stock solution B (2.85 g) was charged to
a 25 ml round bottom flask. To this was charged N-methyl
pyrrolidone (19 g) and ZrO.sub.2 sol (3.78 g) in that order. The
water was removed via rotary evaporation followed by trap to trap
distillation to obtain a clear blue fluid organosol. The weight %
of ZrO.sub.2 in the composite film (PI6E) was approximately 68.8
wt. %.
[0179] Composite films were prepared from polyimide stock solutions
A and B as well as polyimide/zirconia nanoparticle organosols
PI6A-PI6E in the following manner. Each solution was cast on glass
and allowed to dry at 60.degree. C. in nitrogen to produce clear,
colorless films after approximately 4 hours drying. Residual
solvent was removed by drying the films in a vacuum oven at
125.degree. C. overnight. The solid films were then removed from
the glass substrates by dipping the glass/film substrate in water.
After dipping the film/substrates in water to delaminate the film
from the glass substrates. The free standing films were uniformly
thick, with sample to sample thickness ranging from 25 to 50
microns. The final films retained good optical clarity and were
colorless.
[0180] The in-plane and out-of-plane refractive index of each of
the films was measured with a Metricon 2010 Prism Coupler at 632.8
nm (helium-neon laser source). The results are listed in Table 2.
The % transmission for the films was also measured at 600 nm (Test
Procedure 2).
3TABLE 2 Film Refractive Index and Transmission Data In-plane
Out-of-plane Sample/Zirconia weight % index index Transmission
Stock Soln. A 1.5600 1.5550 89.6 (0 wt. % ZrO.sub.2) PI6A (55 wt. %
ZrO.sub.2) 1.6804 1.6755 84.4 PI6B (61.4 wt. % ZrO.sub.2) 1.6998
1.6939 83.0 PI6C (68.8 wt. % ZrO.sub.2) 1.7281 1.7270 82.5 Stock
Soln B (0 wt. % ZrO.sub.2) 1.6520 1.6420 88.2 PI6D (61.3 wt. %
ZrO.sub.2) 1.7330 1.7300 85.0 PI6E (68.8 wt. % ZrO.sub.2) 1.7708
1.7696 83.5
Example 7
[0181] Mono(methacryloxypolyethyleneglycol)succinate (MMPS)
Preparation
[0182] Polyethyleneglycol methacrylate (16.00 g, available from
Aldrich Chemical Co.) and succinic anhydride (4.15 g, available
from Aldrich Chemical Co.) were heated to 80.degree. C. with
shaking for a period of 24 hours. A clear, somewhat viscous liquid
was obtained which had an IR spectra consistent with the reaction
with succinic anhydride. The compound was named
mono(methacryloxypolyethyleneglycol)succinate (hereinafter "MMPS")
having the structure indicated below:.
CH.sub.2.dbd.C(CH.sub.3)C(O)OCH.sub.2CH.sub.2[OCH.sub.2CH.sub.2].sub.nOC(O-
)CH.sub.2CH.sub.2CO.sub.2H
[0183] where n=6-8.
[0184] Surface Modified Colloidal Silica
[0185] A surface modified silica filler was prepared by thoroughly
mixing Nalco 2329, (250 g, a colloidal SiO.sub.2, 40 wt. % solids
in water containing a sodium counter ion, H=8.4, and particle size
75 nm. available from Nalco Naperville, Ill.), methoxy-2-propanol
(281.0 g, available from Aldrich Chemical Co.), and A174 (3.72 g,
gammamethacryloxypropyltrimethoxysilane, available from Witco Osi
Specialties, Danbury, Conn.). The Nalco 2329 silica sol was weighed
into a 2L beaker and a premixed solution of the silane coupling
agent A-174 in the methoxy-2-propanol slowly added to the silica
with swirling (1-2 min). The resultant mixture was heated at
80.degree. C. for 16 hr to produce a modified silica sol. Water (1
kg) was added to the modified silica sol and the resulting mixture
spray-dried using a Buchi spray drier at 200.degree. C. inlet
temperature and an 85-100.degree. C. outlet temperature
[0186] Resin System Preparation
[0187] A resin system comprising
2,2-bis[4-(2-hydroxy-3-methacryloyloxy-pr- opoxy)phenyl]propane
(24.18 g, available from Aldrich Chemical Co.), diurethane
dimethacrylate, CAS No. 41137-60-4, (33.85 g, commercially
available as Rohamere 6661-0 from Rohm Tech, Inc., Malden, Mass.),
ethoxylated (6 mole ethylene oxide) bisphenol A dimethacrylate,
commercially available as Sartomer CD541 from Sartomer Inc, Exton,
Pa.)., triethyleneglycol dimethacrylate (4.84 g, available from
Aldrich Chemical Co.), camphorquinone (0.2 g, available from
Aldrich Chemical Co.), diphenyl iodonium hexafluorophosphate (0.5
g, available from Aldrich Chemical Co.), ethyl
4-dimethylaminobenzoate (1.0 g, available from Aldrich Chemical
Co.), 2,6-di-tert-butyl-4-methylphenol (0.1 g, available from
Aldrich Chemical Co.), and
2-(2'-hydroxy-5'-methacryloxyethylphenyl)- -H-benzotriazole (1.5 g,
CAS 96478-09-0, available from Janssen Pharmaceutica, Titusville,
Pa.) was prepared by adding the above components in the specified
amounts and mixing until a uniform blend of the components as
obtained.
[0188] ZrO.sub.2 Sol Preparation
[0189] A polyether acid zirconium salt was prepared as follows.
[0190] Nyacol ZrO.sub.2(Ac) (200.04 g) and MEEAA (17.8 g, 2.5
mmole/g ZrO.sub.2) were charged to a liter beaker and the resulting
mixture stirred at room temperature (approximately 22.degree. C.)
for 30 minutes. Water and excess acetic acid were removed and the
polyether acid zirconium salt was recovered as a dry solid (78.17
g) by allowing the reaction mixture to evaporate in an evaporating
dish placed in a circulating air oven maintained at approximately
85.degree. C. for approximately 18 hours. The polyether acid
zirconium salt was dissolved in deionized water (3047.4 g) to
produce a clear polyether acid zirconium salt solution (3125.6 g),
which was poured into a 2 liter, unstirred, stainless steel Parr
Reactor, and the autoclave pressurized to about 2.75 bars (40 psi).
The autoclave was subsequently heated to 100.degree. C. in
approximately 2 hr, to 150.degree. C. over a period of
approximately 1.5 hours, and finally to 175.degree. C. (12 bars)
and maintained at that temperature for 15 hours. The autoclave was
cooled and depressurized over a period of 2-3 hr. The zirconia sol
of the present invention was obtained as a clear liquid with an
opalescent blue/white color with no sediment.
[0191] The sol was concentrated to approximately 20 wt. % ZrO.sub.2
by distillation of the water to obtain a clear stable sol. Photon
Correlation Spectroscopy (Test Procedure 5) gave a weight average
mean particle diameter of 19.2 nm. The sol was dialyzed against
deionized water substantially as described in Example 1 except that
5 dialysis treatments using 2 liters of deionized water were used.
The IR spectrum showed no free acid. The sol was then dialyzed
against 5 g acetic acid in 2 liters of water for three days. IR
analysis confirmed exchange of a majority of the MEEAA for acetic
acid. The resultant sol was stable (11.72 wt. % ZrO.sub.2).
[0192] Composite 7A
[0193] Acetic acid dialyzed ZrO.sub.2 sol (10 g, preparation
described above) was added to a 100 ml beaker and 2-methoxypropanol
(18 g), MMPS acid modifier (0.15 g, preparation described above)
and resin (1.75 g, preparation described above) were added to the
ZrO.sub.2 sol, in that order, with stirring. Surface modified
colloidal silica (2.6 g, preparation described above) was then
added to the mixture, with stirring, to produce a uniform
dispersion. The resultant dispersion/mixture was poured into a
glass petri dish and dried at 80.degree. C. for 2-3 hours. The
material was molded and cured as described in the DTS/CS and visual
opacity and radioopacity test procedures (Test Procedure 8). The
visual opacity, radioopacity and diametral tensile strength (Test
Procedure 7) were determined and are reported in the Table 3.
[0194] Composite 7B
[0195] Acetic acid dialyzed ZrO.sub.2 sol (15 g, preparation
described above) was added to a 100 ml beaker and 2-methoxypropanol
(27 g), MMPS acid modifier (0.487 g, preparation described above)
and resin (2.84 g, preparation described above) were added to the
zirconia sol, in that order, with stirring. Surface modified
colloidal silica (3 g, preparation described above) was added to
the mixture, with stirring, to produce a uniform dispersion. The
resultant dispersion/mixture was poured into a glass petri dish and
dried at 80.degree. C. for 2-3 hr. The material was molded and
cured as described in the DTS/CS and visual opacity and
radioopacity test procedures (Test Procedure 8). The visual
opacity, radioopacity and diametral tensile strength (Test
Procedure 7) were determined and are reported in the Table 3.
[0196] Composite 7C
[0197] Acetic acid dialyzed ZrO.sub.2 sol (15 g, preparation
described above) was added to a 100 ml beaker and 2-methoxypropanol
(27 g), MMPS acid modifier (0.3896 g, preparation described above),
acetic acid (0.05 g, available from Aldrich Chemical Co.), and
resin (2.84 g, preparation described above) were added to the
zirconia sol, in that order, with stirring. Surface modified
colloidal silica (3 g, preparation described above) was then added
to the mixture with stirring, to produce a uniform dispersion. The
resultant dispersion/mixture was poured into a glass petri dish and
dried at 80.degree. C. for 2-3 hr. The material was molded and
cured as described in the DTS/CS and visual opacity and
radioopacity test procedures (Test Procedure 8). The visual
opacity, radioopacity and diametral tensile strength (Test
Procedure 7) were determined and are reported in the Table 3.
[0198] Composite 7D
[0199] Acetic acid dialyzed ZrO.sub.2 sol (15 g, preparation
described above) was added to a 100 ml beaker and 2-methoxypropanol
(27 g), MMPS acid modifier (0.3896 g, preparation described above),
acetic acid (0.105 g) and resin (2.84 g, preparation described
above) were added to the zirconia sol, in that order, with
stirring. Surface modified colloidal silica (3 g, preparation
described above) was then added to the mixture, with stirring, to
produce a uniform dispersion. The resultant mixture was poured into
a glass petri dish and dried at 80.degree. C. for 2-3 hr. The
material were molded and cured as described in the DTS/CS and
visual opacity and radioopacity test procedures (Test Procedure 8).
The visual opacity, radioopacity and diametral tensile strength
(Test Procedure 7) were determined and are reported in the Table
3.
4TABLE 3 Cured Resin Properties Material Acid Modifier loading
Visual DTS after 24 # on ZrO.sub.2 Opacity Radiopacity hours (Mpa)
7A MMPS, 0.22 mmol/g 0.18 1.60 59.03 7B MMPS, 0.44 mmol/g 0.16 1.58
63.86 7C MMPS, 0.35 mmol/g 0.16 1.56 65.66 and Acrylic Acid, 0.33
mmol/g 7D MMPS 0.35 mmol/g and 0.17 1.5 63.38 Acrylic Acid, 0.66
mmol/g
[0200] The complete disclosures of all patents, patent applications
and publications are incorporated herein by reference as if
individually incorporated. Various modifications and alterations of
this invention will become apparent to those skilled in the art
without departing from the scope and spirit of this invention, and
it should be understood that this invention is not to be unduly
limited to the illustrative embodiments set forth herein.
* * * * *