U.S. patent application number 13/422015 was filed with the patent office on 2012-07-05 for coating composition for low-refractive index anti-reflection film.
This patent application is currently assigned to NATIONAL CENTRAL UNIVERSITY. Invention is credited to Anthony Shiaw-Tseh Chiang, Shiao-Yi Li.
Application Number | 20120167800 13/422015 |
Document ID | / |
Family ID | 40953907 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120167800 |
Kind Code |
A1 |
Chiang; Anthony Shiaw-Tseh ;
et al. |
July 5, 2012 |
Coating Composition for Low-Refractive Index Anti-Reflection
Film
Abstract
A coating composition comprising zeolite nanocrytals, a zeolite
precursor solution, and wetting agents in a mixture of solvents is
provided. The coating composition can be used to form a transparent
layer having a low refractive index on a substrate for
antireflection effect.
Inventors: |
Chiang; Anthony Shiaw-Tseh;
(Jhongli City, TW) ; Li; Shiao-Yi; (Hualien City,
TW) |
Assignee: |
NATIONAL CENTRAL UNIVERSITY
Jhongli City
TW
|
Family ID: |
40953907 |
Appl. No.: |
13/422015 |
Filed: |
March 16, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12388613 |
Feb 19, 2009 |
8157907 |
|
|
13422015 |
|
|
|
|
Current U.S.
Class: |
106/286.4 ;
106/286.5; 977/773 |
Current CPC
Class: |
C08K 3/34 20130101; C09D
7/67 20180101; C09D 7/45 20180101; G02B 5/02 20130101; C09D 7/42
20180101; C09D 7/61 20180101; C09D 1/00 20130101 |
Class at
Publication: |
106/286.4 ;
106/286.5; 977/773 |
International
Class: |
C09D 1/02 20060101
C09D001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2008 |
TW |
97105673 |
Claims
1. A method for preparing a coating composition that produces low
refractive index anti-reflection film, comprising the following
steps: preparing a zeolite precursor sol; preparing a zeolite
nanocrystals colloid containing a plurality of zeolite
nanocrystals; mixing the zeolite nanocrystals with the zeolite
precursor sol to form a coating mixture.
2. The method according to the claim 1, further comprising adding a
solvent into the coating mixture after the mixing step.
3. The method according to the claim 1, wherein the zeolite
precursor sol is prepared by adding tetraalkoxysilanes to an
aqueous solution of tetraalkylammonium hydroxide.
4. The method according to the claim 1, wherein the molar ratio of
tetraalkylammonium hydroxide to tetraalkoxysilanes is 0.17-0.6.
5. The method according to the claim 1, further comprising
concentrating the zeolite precursor sol to a solid content of
20%-40% by weight after the step of preparing the zeolite precursor
sol.
6. The method according to the claim 5, further comprising heating
the concentrated zeolite precursor sol at 40-100.degree. C. after
the concentrating step.
7. The method according to the claim 5, further comprising diluting
the concentrated zeolite precursor sol after the concentrating
step.
8. The method according to the claim 1, wherein the zeolite
nanocrystals have a particle size of from 40 nm to 100 nm.
9. The method according to the claim 1, wherein the step of
preparing the zeolite nanocrystals colloid comprises a heating
process at a temperature of 150.degree. C. to 250.degree. C.
10. The method according to the claim 1, wherein the zeolite
nanocrystals are selected from the group consisting of silica
zeolite, aluminum silicate zeolite and titanium silicate zeolite
having MFI or BEA zeolite structure.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. application
Ser. No.12/388,613, filed on Feb. 19, 2009 which claims priority to
Taiwan Application Serial Number 97105673, filed Feb. 19, 2008. The
entire disclosures of the above applications are hereby
incorporated by reference herein.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The invention relates to a stable composition comprising
zeolite nanocrystals and zeolite precursor nanoparticles for
producing an abrasion-resistant anti-reflection layer, having a
refractive index close to the optimum refractive index of 1.22, on
substrates, preferably glass, and to a process for the preparation
of such composition. The anti-reflection layer reduces the
reflection of light over a broad spectrum, which is particularly
suitable for protective cover of flat panel display or photovoltaic
solar panels.
[0004] 2. Description of Related Art
[0005] Anti-reflective (AR) film is generally disposed on an
outermost surface of an image display device, such as the
polarizing film for a liquid crystal display (LCD), the front plate
of a touch panel (PET substrate), the front plate of a projection
television (PC substrate), the front plate of a cathode ray tube
display or plasma display panel (glass substrate), to reduce
reflectance and prevent optical interference or image glare caused
by external light or enhancing the visibility of image. It is also
needed in the solar panel covering glass to enhance the penetration
of incident light.
[0006] There are several approaches to produce the desired
anti-reflection effect. The first approach is to coat a
multiple-layered stack with alternating high and low refractive
index materials. To achieve the desired anti-reflection effect, a
tight thickness control of each layer is needed, so that the
destructive interference occurred at the target wavelength range.
However, the processing of multilayer is cumbersome and thus the
productivity is low. There are increasing needs to find an easier
alternative.
[0007] Another alternative may be to create a gradient refractive
index along the thickness of the coated film. Such gradient index
is known to produce a broadband anti-reflection effect.
Particularly, a single-layer antireflective film having a gradient
refractive index can be obtained by various methods, such as
etching, sol-gel, phase separation, micro-imprinting, or molding.
In the extreme case, a single layer of .about.110 nm silica
particle electrostatically anchored to the substrate via
polyelectrolyte had been reported to reduce >90% of reflection
in visible range (H. Hattori, Adv. Mater. 2001, 13, 51-54).
[0008] Besides the conventional multiple coatings and gradient
refractive index layer, it is also possible to generate an
anti-reflection action by means of a single coating. The simplest
design of an single layer AR film would be just a monolayer with a
refractive index (n) of n=(n.sub.o*n.sub.sub).sup.1/2, where
n.sub.o is the refractive index of air and n.sub.sub is the
refractive index of the substrate, and with an optical thickness of
.lamda./4, where .lamda. is the wavelength where the reflection is
to be minimized. For glass substrate with a refractive index of
1.52, this means a refractive index of 1.23, and a thickness of 110
nm to reach zero reflection at .about.540 nm. The most-used
anti-reflection monolayer of this type is a .lamda./4 layer of
MgF.sub.2 having a refractive index of 1.38 applied by vapor
deposition.
[0009] To achieve a refractive index below 1.3, the only
possibility is to using porous materials. Typically, a porous AR
coating is made of silica sol-gel with sacrificed porogen to create
nano-proes, such as that disclosed in U.S. Pat. Nos. 6,918,957 and
7,128,944. In these inventions, a hybrid sol comprising surfactants
and 10-60 nm sized silicon oxide hydroxide nanoparticles was coated
on glass. Subsequent removal of the organics at 600.degree. C.
produces a porous layer capable of anti-reflection effect. To
improve the abrasion resistance, U.S. Pat. No. 7,241,505 further
described the partitioning of these silicon oxide hydroxide
nanoparticles into two size fractions with specific weight ratios.
In the above-mentioned patents, the silicon oxide hydroxide
nanoparticles were made from a process where tetraalkoxysilane was
added to an aqueous-alcoholic ammoniacal hydrolysis mixture.
[0010] For porous silica film to achieve the desired refractive
index, roughly 58% porosity is needed. The mechanical strength
would be impaired if the skeleton is not strong enough. Zeolite, a
crystalline tectosilicates having a low refractive index of
.about.1.3 (S. Nair, M. Tsapatsis, Micropor. Mesopor. Mater. 2003,
58 81-89) and an elastic modulus above 30 GPa (Z. J. Li, M. C.
Johnson, M. W. Sun, E. T. Ryan, D. J. Earl, W. Maichen, J. I.
Martin, S. Li, C. M. Lew, J. Wang, M. W. Deem, M. E. Davis, Y. S.
Yan, Angew. Chem. Int. Edn 2006, 45 6329-6332.), would be an ideal
porous silica to be used for AR coating.
[0011] U.S. Pat. No. 7,381,461 described an antireflective
transparent zeolite hardcoat, comprising a zeolite nanostructure
made of zeolite nanocrystals vertically stacked into a porous
structure on a substrate, wherein the porosity increases with
structure height, thereby providing a smooth refractive index
transition.
[0012] In order to obtain a transparent layer of zeolite, U.S. Pat.
No. 7,253,130 described a method of preparing a precursor sol
capable of forming zeolite, coating the precursor sol to a surface
of a substrate, and heating the coated substrate under a
temperature between about 120.degree. C. and about 250.degree. C.
under a humidity less than a saturation to convert the precursor
sol to a transparent zeolite film. However, the conversion of
zeolite precursors into zeolite via heating in humidity is rather
time consuming.
SUMMARY
[0013] The present invention has been made in view of the
above-mentioned drawbacks. The inventors of the present invention
have found that it is much more effective if a part of the coating
composition is zeolite nanocrystals, while the remaining part
contains the zeolite precursors that serve as glue to bind the
zeolite nanocrystals together and as a reactant to transform into
zeolite under heating. Such a coating composition can be directly
applied on the desired object and be converted to an effective
zeolite anti-reflection film upon heat treatment.
[0014] An embodiment of the present invention provides a
composition useful as a low refractive index anti-reflection
coating and a method for forming the composition. The composition
comprises a mixture of zeolite nanocrystals, having a particle size
of 40-100 nm, and a zeolite precursor sol, prepared from the
hydrolytic polycondensation of tetraalkoxysilanes in an aqueous
solution of tetraalkylammonium hydroxide, in a mixture of solvents.
When such a composition is coated onto substrate, it can be
converted to a zeolite layer after only a short period of heating.
The abrasive resistance can be adjusted by the ratio of the zeolite
nanocrystals and the zeolite precursors in the sol.
[0015] These and other features, aspects, and advantages of the
present invention will become better understood with reference to
the following description and appended claims. It is to be
understood that both the foregoing general description and the
following detailed description are by examples, and are intended to
provide further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a graph showing XRD patterns of the powder
obtained from the zeolite precursor sol and the zeolite
nanocrystals.
[0017] FIG. 2 is a graph showing FTIR spectra of the powder
obtained from the zeolite precursor sol and the zeolite
nanocrystals.
[0018] FIG. 3 is a graph showing the reflection spectra obtained
from the composition prepared in comparative example 1.
[0019] FIG. 4 is a graph showing the reflection spectra obtained
from the compositions prepared in comparative example 2 with
different amount of Tween 20.
[0020] FIG. 5 is a graph showing the reflection spectra obtained
from the compositions prepared in comparative example 2 with
different amount of Tween 80.
[0021] FIG. 6 is a graph showing the reflection spectra obtained
from the compositions prepared in comparative example 2 with
different amount of P123.
[0022] FIG. 7 is a graph showing the reflection spectra obtained
from the compositions prepared in example, with different
percentage of zeolite nanocrystals in combination with the zeolite
precursor sol.
[0023] FIG. 8 is a representative SEM picture illustrating the AR
coating surface prepared in example 3.
DETAIL DESCRIPTIONS
[0024] According to an embodiment of this invention, a coating
composition for low refractive index anti-reflection layer is
disclosed. The coating composition comprises zeolite nanocrystals,
a zeolite precursor sol, and a solvent mixture. The zeolite
nanocrystals has a particle size of 40-100 nm. The zeolite
precursor sol is obtained from the hydrolytic polycondensation of
tetraalkoxysilanes in an aqueous solution of tetraalkylammonium
hydroxid. Optionally, the coating composition can further comprises
a wetting agent, such as a surfactant, for better wetting a
substrate to be coated by the coating composition. The
concentrations of the zeolite nanocrystals, the zeolite precursor,
and the wetting agent are respectively 0.3-4% by weight, 0.3-4% by
weight, and 0.03-0.2% by weight, and the composition has a pH of
from 7 to 11.
[0025] In particularly, the zeolite precursor sol is prepared by
heating a concentrated solution made from the hydrolysis of
tetraalkoxysilane. The tetraalkoxysilane is added into an aqueous
solution of tetraalkylammonium hydroxide. Preferably, the molar
ratio of tetraalkylammonium hydroxide to tetraalkoxysilanes is
0.17-0.6. Upon the hydrolysis of the tetraalkoxysilane, the alcohol
and the excess water was removed by vacuum evaporation until the
silica concentration reaches about 20-40 wt %. The concentrated sol
was then heated at a temperature of 40 to 100.degree. C. for a
period of 2-200 hours, but before the occurrence of strong Rayleigh
scattering, as described by C. Y. Hsu, A. S. T. Chiang, R. Selvin,
R. W. Thompson (J. Physical Chemistry B, 2005,109 18804-18814). The
silica concentration in the concentrated zeolite precursor sol is
better about 20-40 wt %. Since it is not easy to transform zeolite
precursor into zeolite having a uniform size when the silica
concentration is too low. But the concentrated sol becomes too
sticky as the silica concentration is higher than 40 wt % and thus
is unfavorable to the following process. The term of "zeolite
precursor" in the present invention refers to the solid portion
containing silica, without the liquid portion in the "zeolite
precursor sol".
[0026] The zeolite nanocrystals having a particle size of 40-100 nm
could be produced from a process similar to the above, by prolonged
the heating of the concentrated sol after the occurrence of strong
Rayleigh scattering, or by subjecting the concentrated sol that
already showing strong Rayleigh scattering to a 150 to 250.degree.
C. hydrothermal condition to accelerate the zeolite
crystallization, or any other method know to the art of zeolite
nanocrystals preparation. In the present invention, there is no
special limitation to the material of the zeolite. Silica zeolite,
aluminum silicate zeolite or titanium silicate zeolite can be used.
The type of crystal structure of zeolite is also non-limited, but
MFI or BEA zeolite structure is preferred because of ease to form
particles in nano size. The molar ratios of tetraalkylammonium
hydroxide to tetraalkoxysilanes, in preparing the zeolite precursor
sol, are preferably between 0.17 to 0.4 and 0.3 to 0.6 for MFI
zeolite structure and BEA zeolite structure respectively. More
preferably, the molar ratios of tetraalkylammonium hydroxide to
tetraalkoxysilanes are 0.17-0.25 and 0.3-0.4 for MFI zeolite
structure and BEA zeolite structure respectively.
[0027] Upon mixing the zeolite nanocrystals with the zeolite
precursor sol, the composition is further diluted with solvents
such as water and/or alcohols, preferably having less than 4
carbons.
[0028] The above-described composition can be coated on glass with
any known method, such as spin, dip, spray, micro-gravure,
meniscus, web tension coating. The coated object is then subjected
to low temperature (<200.degree. C.) curing and high temperature
(400-600.degree. C.) calcination to remove the organics (i.e.
tetraalkylammonium hydroxide), after which the coated film is
converted to a strongly adhered, low refractive index, abrasive
resistant anti-reflection film.
[0029] As it is clear from the above description, the present
invention is different from that disclosed in U.S. Pat. No.
7,253,130, where the zeolite precursor sol is the sole source of
silica that eventually converted into a zeolite film.
[0030] Since zeolite nanocrystals and zeolite precursor sol
prepared from the hydrolytic polycondensation of tetraalkoxysilanes
in tetraalkylammonium hydroxide aqueous solution was used in the
present invention, it is also different from U.S. Pat. Nos.
6,918,957, 7,128,944 and 7,241,505, where the coating composition
was a mixture of amorphous silicon oxide hydroxide nanoparticles,
produced in an aqueous-alcoholic ammoniacal solution.
[0031] The method according to the present invention is elucidated
in detail with reference to the following exemplary
embodiments.
Preparation of the Glass Substrates
[0032] Chemical strengthen glasses were cleaned in 0.1 N sodium
hydroxide solution, washed with water, then again cleaned with
Merck cleaning solution (Extran MA-02), further rinsed with water
for three times before stored for coating use.
Preparation of Zeolite Precursor Sol
[0033] In a 1000 mL PP bottle, 67.7 g of TPAOH (tetrapropyl
ammonium hydroxide) solution (40%, V.P. chemicals, India), 223.4 g
of water and 138.7 g of TEOS (tetraethylorthosilicate, 99.9%) were
added. The mixture becomes a clear solution after stirring for 30
min. The ethanol produced from the hydrolysis of TEOS and excess
water was removed by rotary evaporator at 80.degree. C. until a
final viscose sol of 127 g was obtained. The product was heated at
80.degree. C. for 24 hours to obtain the zeolite precursor sol.
Preparation of Zeolite Nanocrystal Colloid
[0034] The above preparation was repeated once more. However, this
time the viscose sol was heated at 80.degree. C. for 48 hours.
Afterward, the product was transferred to a Teflon lined autoclave
and further reacted at 230.degree. C. for 2 hours. A white colloid
containing 67 nm MFI zeolite nanocrystals is obtained.
Preparation of the Coatings
[0035] Different compositions were prepared from the above zeolite
precursor sol and zeolite nanocrystals. The coating on glass
substrates was made with a laboratory dip coater, at a pulling rate
of 61 mm/min. After coating, the substrate was cured at 100.degree.
C. for 10 min, and then calcined, with 20.degree. C./min heating
rate, at 550.degree. C. for 30 min to remove the organics.
Characterization
[0036] The size of the particles in the zeolite precursor sol and
the zeolite nanocrystal colloid was analyzed by dynamic light
scattering (DLS; Nano-ZS from Malvern, 4 mW He--Ne laser at 173
scattering angle). Powder samples were prepared from the respective
sol (colloid) by flash drying on hot glass plate and subjected to
Powder X-ray diffraction (XRD) measurements on a Shimadzu
LAB-X-6000 diffractometer. FT-IR spectra were measured using the
KBr wafer technique (1% w/w) in a Jasco-410 FT-IR spectrometer.
[0037] The difference between the zeolite precursor particles and
zeolite nanocrystals is clearly showed by the DLS analysis results
of the zeolite precursor sol and the zeolite nanocrystal colloid
given in table 1.
TABLE-US-00001 TABLE 1 DLS analysis results of the zeolite
precursor sol and colloidal zeolite nanocrystals Z-Average Peak
Sample (d nm) PDI Count (d nm) Zelite precursor sol 37.4 1.330
233.8 47.3 Zeolite nanocrystals 66.7 0.042 278.0 68.9
[0038] The zeolite precursor sol had a much larger polydispersity
index (PDI) compared to the zeolite nanocrystal colloid. The very
small PDI value of the zeolite nanocrystal colloid suggests that
the zeolite nanocrystals are very uniform in size. The XRD patterns
of the two materials are given in FIG. 1, where the crystallinity
of the zeolite nanocrystals is clearly exhibited. The zeolite
precursor particles, on the other hand, is practical amorphous.
However, the zeolite precursor particles are not the same as silica
oxide hydroxide particles obtained by other preparation. As
indicated in the IR spectrum given in FIG. 2, the zeolite precursor
particles exhibit a small absorption peak at the 559 cm.sup.-1.
According to the optical density ratio (about 0.37) of the about
559 cm.sup.-1 peak over the 450 cm.sup.-1 peak, one can judge that
around 70% of the silica had formed double ring structures that
eventually will lead to zeolite, but was not yet converted to
zeolite, as evident from the absence of strong zeolite peaks in
FIG. 1. (Coudurier, G.; Naccache, C.; Vedrine, J. C., J. Chem.
Soc., Chem. Comm., 1982, 1413-1415). By comparison, the optical
density ratio of these peaks is 0.7 for zeolite nanocrystals,
indicating again their good crystallinity.
COMPARATIVE EXAMPLE 1
Comparing Characteristics of the AR Coatings Made of Zeolite
Precursors and Zeolite Nanocrvstals
[0039] Two coating compositions were prepared in this example.
Composition 1A is prepared by diluting the zeolite precursor sol
with 95% ethanol to an equivalent silica content of 4 wt %.
Composition 1B is done similarly using the zeolite nanocrystal
colloid. AR coatings on glass substrates were prepared according to
the procedures described above.
[0040] The reflection of the coated glass was measured by Hitachi
U-400 spectroscope using an incidence angle of 5 degrees. The
strength of the coating was tested according to ASTM D3363-92a
pencil hardness method. The results are given in FIG. 3 and Table
2.
TABLE-US-00002 TABLE 2 The characteristics of the AR coating
prepared in comparative example 1 Composition 1A 1B Wavelength at
minimum reflection (nm) 450 858 Minimum Reflection (%) 4.8 1
Thickness (nm) 91 188 Refractive index 1.43 1.128 Porosity 0.24 0.8
Hardness 3H H
[0041] We found that composition 1A did not lead to a good
anti-reflection effect. The refractive index calculated from the
spectrum was only slightly lower than expected from pure silica.
The composition 1B prepared from zeolite nanocrystals, on the other
hand, lead to an excellent reduction of the reflection. The
refractive index calculated was even lower than the optimized value
of 1.22. Unfortunately, the film coated with composition 1B was
very weak. The pencil hardness was only H at the best.
Comparatively, the composition 1A gave much stronger coating.
COMPARATIVE EXAMPLE 2
Comparing Characteristics of the AR Coatings Made of Zeolite
Precursors Combined with Various Amounts of Sacrificed Porogen
[0042] The zeolite precursor sol, which leads to a stronger
coating, was combined with different amounts of sacrificed porogen,
hoping to increase the porosity of the coated layer. The sacrificed
porogens used were Tween 20 (polyoxyethylene.sub.20 sorbitan
monostearate), Tween 80 (polyoxyethylene sorbitan monolaurate), and
P123 (EO.sub.20PO.sub.70EO.sub.20 tri-block copolymer) in Table 3,
4, and 5, respectively. The AR coating was prepared as described
similar to above. In addition to the pencil hardness, the adhesion
of the coated layer was also tested according to ASTM D3359
(Cross-cut/Tape Test) standard method. The results were listed in
Table 3 to 5 and the spectra given in FIGS. 4 to 6.
TABLE-US-00003 TABLE 3 AR coatings prepared from compositions
containing zeolite precursor sol and porogen Tween 20.
Porogen/Silica ratio by weight 0.1 0.3 0.5 0.7 Wavelength at
minimum 530 530 540 620 reflection (nm) Minimum Reflection (%) 1.9
1.7 1.1 1.3 Refractive index 1.347 1.343 1.324 1.324 Thickness (nm)
97 101 102 116 Porosity 0.406 0.414 0.451 0.451 Adhesion 5B 5B 5B
5B Hardness 3H 3H 3H H
TABLE-US-00004 TABLE 4 AR coatings prepared from compositions
containing zeolite precursor sol and porogen Tween 80.
Porogen/Silica ratio by weight 0.1 0.3 0.5 0.7 Wavelength at
minimum 515 550 620 Broadband reflection (nm) Minimum Reflection
(%) 1.15 0.75 0.7 0.25 Refractive index 1.319 1.301 1.298 ~
Thickness (nm) 98 102 119 ~ Porosity 0.46 0.495 0.451 ~ Adhesion 5B
5B 5B 5B Hardness <H <H <H <H
TABLE-US-00005 TABLE 5 AR coatings prepared from compositions
containing zeolite precursor sol and porogen P123. Porogen/Silica
ratio by weight 0.1 0.3 0.5 Wavelength at minimum 440 450 530
reflection (nm) Minimum Reflection (%) 2.7 1.3 0.4 Refractive index
1.376 1.326 1.271 Thickness (nm) 81 85 102 Porosity 0.348 0.447
0.454 Adhesion 5B 5B 5B Hardness <H <H <H
[0043] It was found that the addition of sacrificed porogen did
lead to certain increase of the porosity, and consequently a
reduction of the refractive index. However, except for the case of
adding Tween 20, the coatings became very soft, and cannot be used
for practical purpose. Even in the case with adding Tween 20, the
refractive index is still higher than the desired value, and the
average reflection between 400 to 800 nm remained higher than
desired.
EXAMPLE
AR Coatings Made of Zeolite Precursors Combined with Various
Amounts of Zeolite Nanocrystals
[0044] In order to increase the porosity of the coated layer,
compositions were prepared with different ratios of the zeolite
nanocrystals in combination with the zeolite precursor. In all
cases, an amount of a wetting agent, Tween 20 surfactant, at 1 wt %
to that of silica was added for better wetting. AR coatings were
prepared from these compositions, and following the same procedures
of curing and calcination. The reflection spectra were presented in
FIG. 7. The SEM picture of the surface of the sample prepared is
given in FIG. 8. In addition to the adhesion and hardness tests,
the boiling water test and Cycle Humidity Oven/Crosshatch Adhesion
(CHOCA) test were also done according to Colts Laboratories Real
Life Simulation Test SOP. The results of these tests were collected
in Table 6. Here, the NC/(ZP+NC) is a weight ratio of zeolite
nanocrystal to the sum of zeolite nanocrystal and zeolite
precursor.
TABLE-US-00006 TABLE 6 Results on AR coatings prepared from
composition containing both the zeolite precursor (ZP) and zeolite
nanocrystals (NC). NC/(ZP + NC) 0.5 0.54 0.6 0.65 0.8 Wavelength at
minimum 602 644 626 583 687 reflection (nm) Minimum Reflection (%)
0.26 0.71 0.31 0.34 0.09 Average Reflection (%) 1.05 1.52 1.17 0.93
1.61 Average transmittance 96.13 96.41 96.4 95.95 96.48 (%)
Thickness (nm) 121 126 123 113 136 Refractive index 1.269 1.3 1.272
1.275 1.251 Porosity 0.555 0.497 0.549 0.544 0.588 Hardness 4H 4H
4H 3H 2H Average Reflection 1.62 0.92 1.24 0.83 1.77 after CHOCA
(%) Average Reflection 1.55 1.23 1.26 0.92 1.69 after Boiling Water
(%)
[0045] Clearly, with the combination of zeolite nanocrystals and
zeolite precursors, the quality of the antireflection layer is much
better. A pencil hardness could higher then 4 H can be achieved,
and even after CHOCA test and boiling water treatment, the average
reflection can still remain below 1.5%. In particular, while the
weight ratio of the zeolite nanocrystals to the zeolite precursor
in the range of from 3:7 to 7:3, the abrasive resistance of the
anti-reflection film is sufficient for commercial application. In
addition, the surface of the anti-reflection film according to the
present invention is super-hydrophilic, thereby preventing the
surface from fingerprints by touching. In the present invention,
the zeolite precursors transform into zeolite under heating, and
serves as glue to bind the zeolite nanocrystals together and also
bind the zeolite nanocrystals with the substrate. Therefore, the
abrasive resistance of the anti-reflection film is improved.
Further, the zeolite nanocrystals have already been formed in the
coating composition, thereby decreasing the time period of
calcination.
* * * * *