Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-28
2002-04-23
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C106S287190, C106S450000, C252S363500, C423S608000, C516S090000, C522S081000, C523S117000
Reexamination Certificate
active
06376590
ABSTRACT:
BACKGROUND
This invention relates to zirconia sols and to methods of making zirconia sols.
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.
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
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.
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.
In another aspect, the present invention provides a method of making 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.
In a preferred embodiment of the process, step (a) comprises:
(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
(b) optionally, removing at least a portion of the free acid.
In a preferred embodiment, the step of removing at least the free acid comprises:
(a) drying an 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.
Preferred zirconium salts for use as starting materials in the formation of a polyether acid zirconium salt have the general formula:
ZrO
(4−n/2)
(X)
n
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.
Preferred polyether carboxylic acids for use in the process of the present invention have the general formula:
CH
3
—[O—(CH
2
)
y
]
x
—X
2
—CH
2
)
n
—COOH
where X
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.
Examples of particularly preferred polyether carboxylic acids include 2-[2-(2-methoxyethoxy)ethoxy]acetic acid and 2-(2-methoxyethoxy) acetic acid.
In another aspect, the present invention provides 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.
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.
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.
As used herein, with respect to the present invention, the terms listed below shall have the following meanings.
“associated particles” as used herein refers to a grouping of two or more primary particles that are aggregated and/or agglomerated.
“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.
“agglomeration” as used herein is descriptive of a weak association of primary particles which may be held together by charge or polarity.
“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.
“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).
“primary particle size” as used herein refers to the size of a non- associated single crystal zirconia particle.
“sol” as used herein refers to a dispersion or suspension of colloidal particles in an aqueous phase.
“zirconia” as used herein refers to ZrO
2
and may also be known as zirconium oxide and as zirconium dioxide.
DETAILED DESCRIPTION
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.
Chien Bert T.
Kolb Brant U.
3M Innovative Properties Company
Lovering Richard D.
Pribnow Scott R.
LandOfFree
Zirconia sol, process of making and composite material does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Zirconia sol, process of making and composite material, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zirconia sol, process of making and composite material will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2819666