U.S. patent application number 11/866521 was filed with the patent office on 2008-03-27 for high refractive index monomers for optical applications.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Emily S. Goenner, Brant U. Kolb, Roger A. Mader, Joan M. Noyola, Christopher B. JR. Walker, Sharon Wang.
Application Number | 20080075959 11/866521 |
Document ID | / |
Family ID | 36217510 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080075959 |
Kind Code |
A1 |
Walker; Christopher B. JR. ;
et al. |
March 27, 2008 |
HIGH REFRACTIVE INDEX MONOMERS FOR OPTICAL APPLICATIONS
Abstract
The present invention includes optical coatings containing
ultraviolet curable monomers employing a bromine substituted
fluorene structure. The fluorene backbone of the monomers of the
present invention may also be functionalized with one or more
polymerizable or reactive functionalities, and most readily at the
9 position. Compositions of the present invention include the
reactive bromosubstituted fluorenes combined with inorganic
nanoparticles, particularly nanoparticles with reactive surface
modifiers exhibiting polymerizable functionality. Reactive high
index nanoparticles such as surface modified zirconia are
contemplated.
Inventors: |
Walker; Christopher B. JR.;
(St. Paul, MN) ; Mader; Roger A.; (Stillwater,
MN) ; Goenner; Emily S.; (Shoreview, MN) ;
Kolb; Brant U.; (Afton, MN) ; Wang; Sharon;
(St. Paul, MN) ; Noyola; Joan M.; (Maplewood,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
36217510 |
Appl. No.: |
11/866521 |
Filed: |
October 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11026674 |
Dec 30, 2004 |
7297810 |
|
|
11866521 |
Oct 3, 2007 |
|
|
|
Current U.S.
Class: |
428/421 ;
106/287.24; 428/411.1; 522/183; 524/467 |
Current CPC
Class: |
C07C 69/653 20130101;
Y10T 428/256 20150115; Y10T 428/3154 20150401; Y10T 428/31504
20150401; G02B 1/111 20130101; G02B 1/10 20130101; C07C 2603/18
20170501; G02B 1/14 20150115 |
Class at
Publication: |
428/421 ;
106/287.24; 428/411.1; 522/183; 524/467 |
International
Class: |
B01F 17/00 20060101
B01F017/00; B32B 27/00 20060101 B32B027/00; C08F 2/46 20060101
C08F002/46 |
Claims
1. An optical coating comprising: a monomer containing a
substituted fluorene structure wherein said fluorene structure is a
bromo-substituted fluorene; and surface modified inorganic
nanoparticles dispersed within said fluorene, wherein said optical
coating has a refractive index of at least 1.58.
2. The coating of claim 1 wherein said bromo-substituted fluorene
is selected from the group of monomers defined by the following
formulas: ##STR2##
3. The coating of claim 2 wherein said bromo substituted fluorene
monomer is selected from the group consisting of acrylic acid
3-[9-(3-acryloyloxy-propyl)-2,3,7-tribromo-9H-fluoren-9-yl]-propyl
ester, acrylic acid
3-{9-[3-acyloyloxy-propoxy)-propyl]-2,3,7-tribromo-9H-fluoren-9-yl}-propy-
l ester,
3-[9-(3-acryloyloxy-propyl)-2,7-dibromo-9H-fluoren-9-yl]-propyl
ester, and
2-[9-(2-acryloyloxy-ethyl)-2,7-dibromo-9H-fluoren-9-yl]-ethyl
ester.
4. The coating of claim 1 wherein said bromo-substituted fluorene
is functionalized with one or more polymerizable
functionalities.
5. A display system comprising the coating of claim 1.
6. The display system of claim 5 further comprising a
photoinitiator within said coating.
7. The coating of claim 1 wherein said surface modified inorganic
nanoparticle comprises nanoparticles selected from the group
consisting of titanium, antimony, silica, zirconia, mixed metal
oxides, and mixtures thereof.
8. The coating of claim 1 wherein said nanoparticles are selected
from the group consisting of surface modified crystalline zirconia,
surface modified amorphous zirconia, and functionalized silica.
9. A nanocomposite coating comprising: a polymer matrix formed from
bromo-substituted fluorene; and surface modified zirconia
nanoparticles dispersed within said polymer matrix.
10. A coating comprising: a polymeric substrate; a hard coat layer
fixed to the polymeric substrate; a high refractive index optical
layer fixed to the hard coat layer, said high refractive index
optical layer comprising a bromine substituted fluorene structure;
and an optional low refractive index optical layer fixed to the
high refractive index optical layer, wherein said high refractive
index optical layer has a refractive index of at least 1.6 and said
optional low refractive index layer has a refractive index less
than 1.5.
11. The coating of claim 10 wherein said fluorene structure is
bromine substituted at one or more of the 2, 3, and 7
positions.
12. The coating of claim 10 wherein said high refractive index
optical layer further comprises surface modified zirconia
nanoparticles.
13. The coating of claim 10 wherein said high refractive index
optical layer further comprises surface modified inorganic
nanoparticles selected from the group consisting of nanoparticles
formed from titanium, antimony, silica, zirconia, mixtures of metal
oxides, and mixtures thereof.
14. The coating of claim 10 wherein said high refractive index
optical layer further comprises a photoinitiator prior to
curing.
15. The coating of claim 10 wherein said high refractive index
optical layer comprises a polymer containing a bromine fluorene
monomer substituted with a polymerizable functionality.
16. The coating of claim 15 wherein said polymerizable
functionality is an acrylate group substituted at the 9-position of
the fluorene monomer.
17. A display system comprising the coating of claim 10.
Description
RELATED APPLICATION DATA
[0001] This application is a divisional application of U.S. Ser.
No. 11/026,674, filed Dec. 30, 2004, now allowed.
BACKGROUND OF THE INVENTION
[0002] The development of films or coatings as protective films for
display devices such as a CRT screen is well documented in the art.
These include antireflective coatings, hardcoats, optical coatings,
and the like. Nevertheless, there continues to be a need for
further improvement in the development of polymerizable high index
materials for optical applications. Exemplary applications include
antireflective coatings, hardcoats, and brightness enhancement film
materials. Many polymerizable films have a refractive index of 1.5
or less. Because of the optical advantages, however, an increase of
the refractive index to 1.58 or more would be a desirable
improvement. Furthermore, there is a need for durable, inexpensive,
and yet high quality antireflective coatings that exhibit a
relatively low reflectance, that is less than 1%.
SUMMARY OF THE INVENTION
[0003] The above-referenced concerns are resolved by the
development of new ultraviolet curable monomers employing a
substituted fluorene structure. Bromine is readily substituted at
the 2 position in the mono brominated derivative, the 2 and 7
positions in the dibrominated derivative and the 2, 3, and 7
positions in the tribrominated derivative. The fluorene backbone of
the monomers of the present invention may also be functionalized
with one or more polymerizable or reactive functionalities, and
most readily at the 9 position. In particular, preferred
embodiments incorporate reactive, pendant acrylate groups.
[0004] Compositions of the present invention include the reactive
bromosubstituted fluorenes combined with inorganic nanoparticles,
particularly nanoparticles with reactive surface modifiers
exhibiting polymerizable functionality. Reactive high index
nanoparticles such as zirconia are preferred, although other high
index nanoparticles such as titania are acceptable. Photoinitiators
may also be employed in the present compositions thereby enhancing
free radical curing by ultraviolet light for example.
[0005] One advantage of the monomers of the present invention is
the copolymerizability and high refractive index of the monomers. A
second advantage is the compatibility of the monomers with the
solvents employed in dispersing functionalized nanoparticles
thereby forming stable coating formulations. Another advantage of
the high refractive index monomers is that antireflective coatings
including the high refractive index monomers within high index
optical layer(s) may be provided, thereby enhancing the optical
properties of the antireflective coating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates an antireflective coating construction
containing an optical coating, in accordance with the present
invention.
[0007] FIG. 2 illustrates a fluorene structure and the nine
positions referred to throughout the specification.
[0008] FIG. 3 illustrates the structures of Examples 1-4 and
Comparative Example
[0009] FIG. 4 illustrates a typical display device in accordance
with the present invention.
DETAILED DESCRIPTION
[0010] The present invention includes the development of
bromosubstituted fluorenes as a coating matrix. The incorporation
of bromine is believed to raise the refractive index and is readily
substituted at the 2 position in the mono brominated derivative,
the 2 and 7 positions in the dibrominated derivative and the 2, 3,
and 7 positions in the tribrominated derivative. The substituted
polymers are also functionalized with one or more polymerizable
functionalities along the fluorene backbone, and preferably at the
9 position. FIG. 2 illustrates a fluorene structure that may be
substituted about the positions shown. The functional groups
particularly emphasized include reactive, pendant acrylate groups.
Co-polymers may be made from other acrylates and methacrylates, and
from monofunctional derivatives represented by the generic
structure shown below. Pendant acrylate groups include those
selected from the group of acrylate, methacrylate, polyacrylate,
polymethacrylate, and polymethylmethacrylate compounds formed from
acrylic acid, methacrylic acid, trimethoxysilylpropylmethacrylate,
and trimethoxysilylpropylacrylate, for example.
[0011] The use of the new monomers of the invention are envisioned
in combination with other monomers, multifunctional acrylates,
crosslinking monomers, fillers, nanoparticles, adhesion promoters,
slip agents, initiators, photoinitiators, dyes, and solvents, and
are given in weight percent ranges relative to the total weight of
the optical coating composition. The weight percents of each
constituent are given relative to the total weight of the
compositions, absent the solvent used in the processing thereof.
For UV curable formulations, the photoinitiators may be employed
between 0.05% and 10%, although preferably between 1-4%. For the
films of the invention, the nanoparticles were provided at 20-60 wt
% and even more preferably in a range of 30-38.5 wt %, whereby the
weight percents given reflect the weight of nanoparticles not yet
surface modified. In accordance with the present invention, the
nanoparticle surface modifier weight percent ratio preferably
ranges from about 2.70:1 to 6:1. Stated another way, the weight
percent range for nanoparticles with surface modifiers is the sum
of the two. To illustrate, example 12 has 30% ZrO2+11.1% surface
modifier, so that the weight percent of the surface modified
particles is 41.1%. Similarly, example 16 exhibits a 35.32% wt % of
surface modified nanoparticles, wherein the wt % is also relative
to the total compositional weight. Table 1 below gives exemplary
nanoparticle/surface modifier combinations of the present
invention. TABLE-US-00001 TABLE 1 Wt % SM Total wt % Wt % SM Total
wt % Wt % at 2.70:1 at 2.70:1 at 6:1 at 6:1 ZrO2 nano:SM nano:SM
nano:SM nano:SM 20 7.41 27.41 3.33 23.33 30 11.11 41.11 5 36 38.5
14.26 52.76 6.42 44.92 60 22.22 82.22 10 70
[0012] The bromosubstituted monomers of the invention were
generally provided at about 25-60 wt % and more preferably at about
31-58 wt %. The multifunctional acrylates or crosslinkers are
generally provided at about 25-50 wt %. ##STR1##
[0013] Two classes of bromo-substituted fluorene monomers are
characterized by the structures illustrated above. Examples 1-4,
illustrated in FIG. 3, exemplify molecules that may be formed as
given above. As such, a preferred group of bromo substituted
fluorene monomers may be selected from the group including acrylic
acid
3-[9-(3-acryloyloxy-propyl)-2,3,7-tribromo-9H-fluoren-9-yl]-propyl
ester, acrylic acid
3-{9-acyloyloxy-propoxy)-propyl)-2,3,7-tribromo-9H-fluoren-9-yl}-propyl
ester,
3-[9-(3-acryloyloxy-propyl)-2,7-dibromo-9H-fluoren-9-yl]-propyl
ester, and
2-[9-(2-acryloyloxy-ethyl)-2,7-dibromo-9H-fluoren-9-yl]-ethyl
ester. It has been found that the bromosubstituted monomers of the
present invention as exemplified by this preferred group, possess a
high refractive index (greater than or about 1.58 to 1.6), good
solubility, good miscibility with the nanoparticles, and reasonable
durability after curing, especially when formulated with zirconia
nanoparticles.
[0014] Polymerizable compositions of the present invention
incorporating the bromosubstituted fluorene described above may be
characterized as nanocomposites. Nanocomposites are defined as a
polymer matrix that contains well-dispersed nanoparticles.
Nanoparticles are defined as particles that are smaller than 100
nanometers. U.S. Pat. No. 5,385,776 exemplifies the current
understanding of nanocomposites incorporated within polyamides and
is herein incorporated by reference. A nanoparticle is generally an
inorganic particle such as a metal, metal oxide, metal nitride,
metal carbide or metal chloride. In accordance with the present
invention, the use of high index nanoparticles increases the
refractive index of compositions incorporating the same. Preferred
nanoparticles include crystalline zirconia, although other high
index nanoparticles such as titania, antimony, mixtures of metal
oxides, and mixed metal oxides are acceptable. Crystalline zirconia
is preferred over amorphous zirconia due to the greater refractive
index of compositions containing crystalline zirconia.
Functionalized silica nanoparticles may be used for added
reinforcement, although it lowers the refractive index of the cured
coating. Examples of useful zirconia are those described in U.S.
Pat. No. 6,376,590, and examples of titania are described in U.S.
Pat. No. 6,432,526, both incorporated by reference in their
entirety.
[0015] Surface modification of the nanoparticles relates to the
reaction of specific molecules on the surface of particles, and is
useful in achieving good dispersion within the polymer matrix.
Accordingly, the nanoparticles are preferably treated with surface
modifying agents such as carboxylic acids, silanes and/or
dispersants to help compatibilize them with the polymer matrix.
U.S. Pat. No. 6,329,058 exemplifies typical surface modifiers and
is herein incorporated by reference. In essence, it is believed
that surface modification prevents particle agglomeration thereby
facilitating particle dispersion within the monomers and resins,
and therefore enhancing the transparency of the coating. Preferred
surface modifiers are carboxylic acids and silanes including
methoxyethoxyethoxyacetic acid (MEEAA) and A1230 (a polyethersilane
or PEG-silane). The use of surface modifiers with high refractive
index is also preferred and includes naphthyl acetic acid and
trimethoxy phenyl silane.
[0016] The nanoparticles of the present invention may also be
surface modified by reactive surface modifiers. Reactive surface
modification means that surface modifiers are employed that include
functional groups that facilitate polymerization in addition to
functionality that can either adsorb or covalently bond with the
particle surface. When a coating of the present invention is
polymerized (or cured), it forms a nanocomposite having particles
covalently linked to the polymer matrix. When employing mixtures of
nanoparticles, a combination of benefits may be realized. For
example, surface modified zirconia may be added to raise the
refractive index, while surface modified silica may be added to
further enhance durability.
[0017] Compositions of the present invention may further contain
any of the well known Type I and Type II UV photoinitiators, such
as the substituted acetophenones, benzoins, phosphine oxides,
benzophenone/amine combinations, and other photoinitiator classes
well known to those in the art. Exemplary photoinitiators include
Irgacure.TM. 819, Darocure.TM. 1173, or TPO supplied for example by
Ciba Geigy of Tarrytown, N.Y. It is believed that radical
photoinitiators cleave in the presence of ultraviolet light to form
radicals that initiate the polymerization of the acrylate and
methacrylate functional groups in the formulation to form the
crosslinked nanocomposite. Known types and classes of radical
photoinitiators may be employed as described in, "Chemistry and
Technology of UV & EB Formulation For Coatings, Inks, &
Paints" of Volume 3 of Photoinitiators for Free Radical Cationic
Polymerization, published by SITA Technology Ltd., Gardiner House,
Broomhill Road, LONDON SW18184JQ ENGLAND, herein incorporated by
reference.
[0018] Specific photoinitiators which are useful in the
compositions of the invention include onium salts as described in
U.S. Pat. No. 5,545,676, herein incorporated by reference. Onium
salts have been found to be useful as coinitiators in high speed
visible light curing of free radically polymerizable systems.
Photoinitiators are typically employed from about 0.05 wt % to
about 10 wt %, and more preferably at about 1 to 4 wt %.
[0019] The invention is further illustrated, but not thereby
limited, by the Examples given below. In particular, the examples
given provide a template for production of a class of compounds
characterized as bromo-substituted fluorene monomers, and also
polymerizable compositions containing the same.
EXAMPLE 1
[0020] Preparation of Acrylic Acid
3-[9-(acryloyloxy-propyl)-2,7-dibromo-9H-fluoren-9-yl]-propyl ester
(DBFDA): There are various suppliers that are known in the art that
may provide the various chemical constituents of the present
invention. Because of the availability, as known to one of ordinary
skill, further discussion is abbreviated. Aldrich Chemical Co. of
Milwaukee, Wis. exemplifies one of many known chemical
suppliers.
[0021] A mixture containing 47 grams of 2,7-dibromofluorene,
provided by Alfa Aesar for example, 3.3 grams of
benzyltriethylammonium chloride, and 29 grams of 50% aqueous sodium
hydroxide in 470 ml of dimethylsulfoxide was stirred and to it was
added 50.8 grams of 3-bromo-1-propanol, provided by Aldrich
Chemical for example. An exothermic reaction occurred and the
temperature was controlled at 50.degree. C. by means of an ice
bath. After the exothermic reaction was complete the mixture was
maintained at 35.degree. C. for one hour and then cooled to
23.degree. C. and added to 200 ml of water. The solid obtained was
recrystallized from methanol/water to give a crude material which
was further purified by recrystallization from ethyl acetate/hexane
to yield 23.5 grams of
3-[2,7-Dibromo-9-(3-hydroxypropyl)-9H-fluorene-9-yl]-propane-1-ol.
[0022] A solution containing 15 grams of
3-[2,7-Dibromo-9-(3-hydroxypropyl)-9H-fluorene-9-yl]-propane-1-ol
and 18.7 grams of diisopropylethylamine in 150 ml of
tetrahydrofuran was cooled to 10.degree. C., and to it was slowly
added a solution of 7.7 grams of acryloyl chloride in 18 ml of
tetrahydrofuran. The temperature was maintained at 10.degree. C.
during the addition. After stirring at 10.degree. C. for one hour
the mixture was poured into a mixture containing 100 ml of 2%
aqueous HCl and 100 ml of ethyl acetate. The organic phase was
separated and dried over anhydrous sodium sulfate. The solvent was
removed and the residue purified by column chromatography on silica
gel eluted with 15% ethyl acetate in hexane to give 8.5 grams of
acrylic acid
3-[9-(acryloyloxy-propyl)-2,7-dibromo-9H-fluoren-9-yl]-propyl
ester. This product was verified by NMR analysis to be present and
pure.
EXAMPLE 2
Preparation of Acrylic Acid
2-[9-(2-acryloyloxy-ethyl)-2,7-dibromo-9H-fluoren-9-yl]-ethyl
ester(4) (DBFDC2A)
[0023] A solution containing 50 grams of 2-bromoethanol (Aldrich)
and 0.1 gram of p-toluene sulfonic acid was stirred and to it was
added slowly with cooling 33.6 grams of dihydropyran. After the
addition was complete the mixture was cooled to room temperature.
This gave the tetrahydropyranyl ether of 2-bromoethanol which was
used without further purification.
[0024] A mixture containing 5.0 grams of 2,7-dibromofluorene, 3.1
grams of sodium hydroxide and 0.35 grams of Benzyltriethylammonium
chloride in 50 ml of dimethylsulfoxide was stirred and to it was
added 9.7 grams of the tetrahydropyranyl ether of 2-bromoethanol.
The temperature rose slowly to 50.degree. C. The temperature was
maintained at 35.degree. C. for 1 hr after which the mixture was
added to 100 ml of water and 50 ml of ethyl acetate and 50 ml
hexane. The organic layer was removed washed 2.times. with 100 ml
of water and dried over sodium sulfate. The solvent was removed and
150 ml of ethanol added followed by 0.5 grams p-toluene sulfonic
acid. The mixture was stirred at 70.degree. C. for 30 min. The
mixture was cooled and treated with aqueous potassium carbonate to
pH8. The solvent was removed and the residue treated with 50 ml of
1:1 ethyl acetate:hexane and 25 ml of water the solid was filtered
and washed with water. Recrystallization from 1:1 ethyl acetate
hexane to give 4.5 grams of
2-[2,7-dibromo-9-(2-hydroxy-ethyl)-9H-fluoren-9-yl]-ethanol which
was esterified by the process described in example 1 to give 3.8
grams of Acrylic acid
2-[9-(2-acryloyloxy-ethyl)-2,7-dibromo-9H-fluoren-9-yl]-ethyl
ester(4). This product was verified by NMR analysis to be present
and pure.
EXAMPLE 3
Preparation of acrylic acid
3-{9-[3-(3-acryloyloxy-propoxy)-propyl}-2,3,7-tribromo-9H-fluoren-9-yl}-p-
ropyl ester(3) (WTBFDA)
[0025] A mixture containing 60 grams of fluorene and 1.17 grams of
ferric chloride in 700 ml of chloroform was stirred at 25.degree.
C. and to it was slowly added 173 grams of bromine. The temperature
rose to 24.degree. C. during the addition. After the addition was
complete the mixture was stirred for 30 minutes then 500 ml of
water added. The solid was filtered and washed with acetone. After
drying overnight the solid was slurried in 600 ml of acetone at
reflux then cooled and filtered to give 110 grams of
2,3,7-tribromofluorene.
[0026] A mixture containing 40 grams of 2,3,7-tribromofluorene,
19.9 grams of sodium hydroxide and 2.3 grams of
benzyltriethylammonium chloride in 400 ml of dimethylsulfoxide were
stirred and to it was added 51.4 grams of 3-bromo-1-propanol in
increments. The temperature rose slowly to 30 C. The temperature
was maintained at 30 C for one hour after which the mixture was
added to 500 ml of water. The mixture was extracted with 500 ml of
ethyl acetate. The organic phase was washed three times with 300 ml
of water. After drying over sodium sulfate the solvent was removed
giving a crude product which was purified by column chromatography
on silica gel eluted first with 1:1 ethyl acetate:hexane followed
by 3:2 ethyl acetate hexane and finally ethyl acetate. This gave 13
grams of
3-{2,3,7-tribromo-9-[3-(3-hydroxy-propoxy)-propyl]-9H-flouren-9-yl}-propa-
n-1-ol in the second fraction. A 10.1 gram sample of this was
esterified by the process described in example 1 to give 6.4 grams
of acrylic acid
3-{9-[3-(3-acryloyloxy-propoxy)-propyl}-2,3,7-tribromo-9H-fluoren-9-yl}-p-
ropyl ester(3). This product was verified by NMR analysis to be
present and pure.
EXAMPLE 4
Preparation of
3-[9-(3-acryloyloxy-propyl)-2,3,7-tribromo-9H-fluoren-9-yl]-propyl
ester(2) (TBFDA)
[0027] A mixture containing 30 grams of 2,3,7-tribromofluorene, 1.7
grams of benzyltriethylammonium chloride, and 14.9 gram of sodium
hydroxide in 300 ml of dimethylsulfoxide was stirred and to it was
added 26.1 grams of 3-bromo-1-propanol. The temperature rose slowly
to 50 C, was allowed to cool to 35oC and was maintained at 35 C for
one hour after which the mixture was added to 200 ml of water. The
solid which formed was filtered and recrystallized from
methanol/water to give 25 grams of solid. After drying this was
recrystallized from ethyl acetate/hexane to give 14.4 grams of
3-[2,3,7-tribromo-9-(3-hydroxy-propyl)-9H-fluoren-9-yl]-propan-1-
-ol. A 7.6 grams sample of this material was esterified using the
procedure described in example 1 to give 4.2 grams of
3-[9-(3-acryloyloxy-propyl)-2,3,7-tribromo-9H-fluoren-9-yl]-propyl
ester(2). This product was verified by NMR analysis to be present
and pure.
[0028] Examples 1-4 provide a basic template of the formation of
the bromo-substituted monomers in accordance with the present
invention.
EXAMPLE 5
Surface Modification of Zirconia Nanoparticles
[0029] The following exemplifies surface modification of any
suitable nanoparticle and in particular relates to the preparation
of a silane-modified zirconia nanoparticle dispersion. 400.0 grams
of Nalco.TM. zirconia sol and 26.57 grams of MEEAA (Sigma-Aldrich,
Milwaukee, Wis.) were charged to a 1 L round bottom flask. The
water and acetic acid were removed via rotary evaporation at
80.degree. C. The powder thus obtained was redispersed in 398 grams
of D.I. water. 416.56 grams of the particles dispersed in water was
charged to a 2 L beaker. While stirring the particle dispersion,
800 grams of 1-methoxy-2-propanol, 45.0 grams of Silane A-174.TM.,
and 29.21 grams of Silquest A-1230.TM., supplied for example by OSI
Specialties, a Crompton Corporation, of Greenwich, Conn. This
mixture was slowly added to the beaker. This mixture was then
poured into two quart-sized jars, sealed and heated to 90.degree.
C. for three hours. The contents of the jars were removed and
concentrated via rotary evaporation to 40.43 wt % zirconia. 1268.0
grams of deionized water and 42.0 grams concentrated aqueous
ammonia (29% ammonia) were charged to a 4 L beaker. The
concentrated dispersion was added slowly to the beaker while
stirring. The white precipitate thus obtained was isolated via
vacuum filtration and washed with additional deionized water. The
damp solids were dispersed in methylethylketone (MEK). The
resultant silane modified zirconia dispersion contained 14.89%
zirconia. U.S. Pat. No. 6,800,378, herein incorporated by
reference, further describes other inorganic oxide particles useful
as nanoparticles, and, aqueous, organic, and mixed sols that may be
employed when surface modifying the nanoparticles of the present
invention. Mixed oxides containing more than one type of inorganic
atom may also be employed as described in U.S. Patent Application
No. US2003/0165680, herein incorporated by reference. Accordingly,
in some embodiments, Ti/Sb mixed oxide nanoparticles may be
combined with additional nanoparticles having a different elemental
composition (e.g., silica, zirconia, alumina, titania, antimony
pentoxide). Desirably, such additional nanoparticles, if present,
have an average particle size comparable to that of the Ti/Sb mixed
oxide nanoparticles. Such nanoparticles may be commercially
obtained, for example, from Nalco Chemical Co. (Naperville, Ill.)
or Nyacol Nano Technologies, Inc. (Ashland, Mass.). Exemplary
additional nanoparticles are also described in U.S. Pat. Nos.
5,037,579; and 6,261,700; which disclosures are incorporated herein
by reference.
EXAMPLES 6-10
[0030] To develop a solvent-based system, solubility studies were
conducted. Examples 1-4 and Comparative Example 1 were solubilized
as indicated in Table 2 given below and are respectively identified
as Examples 6-10. As shown, each monomer was soluble in one or more
of the commonly employed solvents (MEK, acetone, toluene, and ethyl
acetate). The comparative example was not soluble in these
acceptable solvents. The comparative example is, however, soluble
in methylene chloride, but is not considered useful given the
hazardous nature of methylene chloride. TABLE-US-00002 TABLE 2
Example State R.I. Solubility (Ex. 1 monomer) Solid 1.615 MEK,
Acetone, Toluene, Ethyl Acetate (Ex. 4 monomer) Solid 1.6237 Ethyl
Acetate, Acetone, MEK (Ex. 3 monomer) Liquid 1.5802 MEK, Acetone,
Toluene, Ethyl Acetate (Ex. 2 monomer) Solid 1.6198 MEK, Ethyl
Acetate 10 (Comp. Ex. 1) Solid CH.sub.2Cl.sub.2 Example 1 = DBFDA
Example 2 = DBFDC2A Example 3 = WTBFDA Example 4 = DBFDC2A SR399 =
dipentaerythritolpentaacrylate from Sartomer, Exton, PA.
EXAMPLES 11-12
[0031] UV curable formulations identified below as Examples 11 and
12 in the table below, were prepared by mixing the solution of
surface modified zirconia nanoparticles with acrylate
functionalized fluorene (DBFDA, Example 1), a photoinitiator
(Irgacure 819, provided by Ciba Specialty Chemicals, Tarreytown,
N.Y.), and optionally SR295, a mixture of pentaerythritol tri and
tetracrylates available from SARTOMER of Exton, Pa. were prepared
as shown in Table 3. The zirconia employed in both examples 11 and
12 is described in Example 5. MEK was added to the formulations
until the % solids was 5%. TABLE-US-00003 TABLE 3 wt % wt % Wt % NP
ZrO2 S.M. S.M. resin Resin(s) P.I. Ex. Nalco 30.0 3:1 11.1 57.9
DBFDA 1.0% 11 ZrO2 A174:A1230 819 Ex. Nalco 30.0 3:1 11.1 57.9
50:50 1.0% 12 ZrO2 A174:A1230 DBFDA:SR295 819
[0032] Examples 11 and 12 (as 5% solids, 95% MEK), were coated,
dried, and UV cured with a Fusion Systems UV source (employing a
"D" bulb) to a nominally 80 nm thickness on a 5 um film of 906
hardcoat on top of a polyester substrate. Example 3 of U.S. Pat.
No. 6,299,799, herein incorporated by reference in its entirety,
describes an exemplary hardcoat employed in the present invention.
First surface reflection measurements were obtained using an MPC
3100 spectrophotometer in accordance with standardized testing
method, First Surface Total and CP Reflection Measurement Using the
Shimadzu Spectrophotometer. The thickness of the single high index
optical layer on 906 hardcoated PET can be calculated from the
following relationship: [0033] t=.lamda./4.eta. [0034] where:
[0035] t=thickness (nm) [0036] .lamda.=wavelength (nm) [0037]
.eta.=refractive index
[0038] Ideally, the samples will reflect maximally at 550 nm. The
higher reflection at the peak of Example 11v. Example 12 occurs due
to the addition of the low refractive index multifunctional
acrylate PETA in Example 12. Tables 3 and 4 given below illustrate
coated and cured samples, UV-VIS measurement correlating to
thickness, and the abrasion resistance results to date. The cured
samples were evaluated for durability through: [0039] Rubbing with
cheesecloth using 2 kg weight on top of 6 mm wide "stylus". [0040]
Linear scratch testing--with 100 g and 750 g styli.
[0041] Cheesecloth testing with 1'' diameter pin and 1018 kg
weight--
[0042] Refractive indices were calculated on the basis of a volume
average of the RI of the individual components. The refractive
index of neat liquid materials was measured on a Zeiss
refractometer. Solids were melted and then measured promptly.
Refractive index of a coating is often found to increase 0.01-0.02
after UV curing, as a consequence of increasing coating density.
TABLE-US-00004 TABLE 4 Calc. R.I. Fusion uncured nominal max. in %
R at Lamp Solution Sample thickness UV/VIS peak Ex. 11 D 5% MEK
1.639 80 560 8.49% Ex. 12 D 5% MEK 1.589 80 560 7.84%
[0043] The UV data shows that the target thicknesses were reached,
as the reflection is centered near 550 nm, the middle of the
visible spectrum. The high % reflection, confirms the high
refractive index nature of the coatings. TABLE-US-00005 TABLE 5 Wt
% calc Example nano Nanos SM Wt % SM Wt % R Resins and ratios RI
Solvent Ex 11 Nalco ZrO2 30 3:1 A174:A1230 11.1 57.9 DBFDA 1.639 5%
MEK Ex 12 Nalco ZrO2 30 3:1 A174:A1230 11.1 57.9 50:50 DBFDA:SR295
1.589 5% MEK Ex 13 Nalco ZrO2 29.99 3:1 A174:A1230 11.09 57.92
28.96:28.96 DBFDA, 1.585 5% in Acetone SR295 Ex 14 Nalco ZrO2 29.99
3:1 A174:A1230 11.09 57.92 28.96:28.96 DBFDA, 1.587 5% in Acetone
SR399 Ex 15 3M ZrO2 30 3:1 A174:A1230 5.32 63.68 31.84:31.84 1.596
7.5% in TBFDA:SR399 acetone Ex 16 3M ZrO2 30 3:1 A174:A1230 5.32
63.68 31.84:31.84 1.596 7.5% in DBFDC2A:SR399 acetone Ex 17 99
50:50 TBFDA:S399 1.551 7.5% in MEK
[0044] Each of the compositions of Examples 11-17 include 1 wt-%
"Irgacure 819" photoinitiator.
Table of Examples 11, 12 and 13-17.
[0045] Examples 13-17 were prepared in the same way as examples 11
and 12 with the same surface modified zirconia and resins, and at
the wt % ranges and with the solvent listed in the table. It should
be emphasized that although the refractive index of Examples 12-16
are below 1.6, when cured, the refractive index of compositions
formed in accordance with the present invention generally rises to
an index at or above 1.6.
[0046] The cured samples were evaluated for durability by
mechanically rubbing the sample with a 6 mm "stylus" wrapped with
24 layers of cheesecloth with a 2.2 kg weight onto the stylus (plus
the weight of the stylus) and noting how many passes or "rubs" were
performed without damage being observed and at how many passes or
"rubs" damage was observed. The results are given in an X/Y format,
where the number X indicates the number of passes where the sample
remained unchanged visually from the abrasion. The number Y
represents the point at which damage was observed. Unacceptable
abrasion resistance is defined as failure below 25 rubs. The
samples are examined at 25, 50, 150, and 200 rubs, but not in
between. TABLE-US-00006 TABLE 6 Stylus Stylus scratch scratch
Durability Testing test/100 g test/750 g Nominal UV-VIS UV 80 nm
samples 2 kg/ probe probe thickness max (nm) lamp cheesecloth
linear linear apprx UVVIS UV 2 kg, 6 mm pin scratch scratch EX.
thickness max lamp cheesecloth 100 g, 750 g Ex 11 80.00 560 D 25/50
(5.times.), 50/100 GOOD 2/2 (1.times.) 0/2 scratched Ex 12 80.15
480 D 50/100, 25/50 (5.times.) 6 GOOD GOOD times 0/3 0/2 Ex 13 450
D 25/50 Ex 14 525 D 25/50 (3.times.), 50/100 Ex 15 86.80 600 D
25/50 Ex 16 120.00 625 D 100/150, Ex 17 85.86 491 D 50/100
[0047] It can therefore be concluded that exemplary compositions
with acrylate functionalized zirconia and polymerizable resins have
achieved durable coating with a refractive index equal to or
greater than 1.58. It has been found that compositions of the
present invention, as exemplified in the tables when cured will
typically exhibit a refractive index of about 1.6 or more.
EXAMPLE 18
Preparation of 3M Zirconia with Surface Modifiers
3M ZrO.sub.2 75/25 methacrylaoxypropyltrimethoxy silane/A1230
[0048] The ZrO2 sol (279.85 g, 40.05% solids, 36.02% ZrO2) was
charged to a 1 qt jar. De-ionized water (150 g) was charged with
stirring. Methoxypropanol (455 g), Methacryloxypropyl trimethoxy
silane (26.33 g) and A1230 (17.8) were charged to a 1 liter beaker
with stirring. The methoxypropanol mixture was then charged to the
ZrO2 sol with stirring. The jar was sealed and heated to 90 C for 4
hr. After heating the mixture was stripped to 350 g via rotary
evaporation. U.S. Pat. No. 7,241,437, describes exemplary 3M
zirconia particles and is hereby incorporated by reference. Nalco
and Buhler also provide zirconia particles in accordance with the
present invention.
[0049] De-ionized water (1287 g) and Concentrated NH3 (28.34, 29 wt
%) were charged to a 4 lt beaker. The above concentrated sol was
added to this with minimal stirring. A white precipitate was
obtained. The precipitate was isolated as a damp filter cake via
vacuum filtration. The damp solids (240 g) were dispersed in
methoxypropanol (500 g). The mixture was then concentrated (383 g)
via rotary evaporation. Methoxypropanol (220 g) was added and the
mixture concentrated (261 g) via rotary evaporation.
Methoxypropanol was charged (150 g) and the mixture was
concentrated via rotary evaporation. The final product 257 g was
isolated at 45.49% solids. The mixture was filtered with a 1 um
filter. Methoxypropanol (150 g) was added and the mixture
concentrated (363 g) via rotary evaporation.
[0050] Other additives may be included in the present compositions.
For example, UV sensitizers, oxygen scavengers, and other
components useful in free radical curing may be employed as known
in the art.
[0051] Films made in accordance with the present invention may be
coupled, layered, laminated, and/or otherwise coupled to other
films or display devices in accordance with the present invention.
U.S. Pat. No. 6,800,378, herein incorporated by reference,
describes a process of bonding layers of film together and also of
bonding the an antireflective film, for example, upon a display
device. The same process may be employed in accordance with the
present invention. Known techniques of preparing multilayer films
may be employed to include spin coating, knife coating, and the
like.
[0052] In yet another aspect of the invention, the optical films
described above are included within an antireflective film
construction. As shown in FIGS. 1 and 4, a coating 10, and
preferably an antireflective coating, contains a substrate 12
formed from PET or polycarbonate, or any other material recognized
for its utility as a substrate in antireflective films. An optional
adhesive 14 may be provided on one side of the substrate 12 whereby
the substrate 12 is coupled to a display device 16 and also to a
juxtaposed layer outwardly oriented from the substrate 12. In
accordance with the present invention, a hardcoat layer 18 is
coupled to and layered over or otherwise fixed to substrate 12 in a
known manner thereby forming an outwardly oriented layer in
physical contact with substrate 12. An optical layer 20 having a
relatively high refractive index of at least 1.6, formed as
described above, is next coupled to and/or layered over hardcoat
layer 18. If desired, the construct 10 may include other layers
typically used in antireflective film such as a relatively lower
refractive index layer 22, or an anti-smudge layer (not shown) as
known in the art.
[0053] The low index layer 20 may be formed as known in the art.
U.S. Pat. No. 6,723,423 exemplifies the known understanding of
forming a low refractive index layer and is herein incorporated by
reference, although not by way of limitation. An exemplary low
index layer may be formed from low refractive index fluoropolymer
compositions and derived from an interpenetrating polymer network
or semi-interpenetrating polymer network which includes a reactive
fluoroplastic and/or a fluoroelastomer (i.e. the functional
fluoropolymer phase) blended with multi-functional acrylates (i.e.
the acrylate phase) such as trimethylolpropane triacrylate (TMPTA)
and optionally additional fluorinated mono-functional acrylates or
multi-functional fluorinated acrylates which can be coated and
cured by ultraviolet light or by thermal means. The presence of an
acrylate crosslinker provides a composition with both low
refractive index and improved adhesion to high index polymer
substrates such as polyethylene terephthalate ("PET") or hard
coated PET films. The low index coating mixture preferably
describes a reactive high molecular weight fluoropolymer(s) that
can participate in the crosslinking reactions between the monomeric
multi-functional acrylates. This enhances the crosslinkability of
the fluoropolymer phase to the forming polyacrylate phase and
produces a co-crosslinked, interpenetrating or
semi-interpenetrating polymer network with enhanced interfacial
contact between the high index layer and the low index layer and
thereby improves durability and low refractive index.
[0054] Various optional permanent and removable grade adhesive
compositions 14 may be coated on the opposite side of the substrate
12 (i.e. to that of the hardcoat 18) so the article 10 can be
easily mounted to a display surface. Typically, the adhesive 14,
substrate 12, and hard coating layer 18 are prepackaged as a film
19 having a release layer (not shown) attached to the adhesive 14.
The release layer is then removed and the adhesive layer 14 coupled
to a housing or other area of the display 16 to form the optical
display 16.
[0055] Suitable optional adhesive compositions 14 include (e.g.
hydrogenated) block copolymers such as those commercially available
from Kraton Polymers, Westhollow, Tex. under the trade designation
"Kraton G-1657", as well as other (e.g. similar) thermoplastic
rubbers. Other exemplary adhesives include acrylic-based,
urethane-based, silicone-based and epoxy-based adhesives. Preferred
adhesives are of sufficient optical quality and light stability
such that the adhesive does not yellow with time or upon weather
exposure so as to degrade the viewing quality of the optical
display. The adhesive can be applied using a variety of known
coating techniques such as transfer coating, knife coating, spin
coating, die coating and the like. Exemplary adhesives are
described in U.S. Patent Application Publication No. 2003/0012936,
herein incorporated by reference. Several of such adhesives are
commercially available from 3M Company, St. Paul, Minn. under the
trade designations 8141, 8142, and 8161. The substrate layer 12 may
consist of any of a wide variety of non-polymeric materials, such
as glass, or polymeric materials, such as polyethylene
terephthalate (PET), bisphenol A polycarbonate, cellulose
triacetate, poly(methyl methacrylate), and biaxially oriented
polypropylene which are commonly used in various optical
devices.
[0056] It is contemplated that the present invention will find
primary application in optical coatings and films including
antireflective film, for example. However, it is not limited
thereto. It will also be understood that the foregoing description
of an embodiment of the present invention is for illustrative
purposes only. As such, the various structural and operational
features herein disclosed are susceptible to a number of
modifications commensurate with the abilities of one of ordinary
skill in the art, none of which departs from the scope of the
present invention as defined in the appended claims.
* * * * *