U.S. patent application number 11/143141 was filed with the patent office on 2006-06-08 for low-reflection glass article and method for manufacturing.
This patent application is currently assigned to Nippon Sheet Glass Co., Ltd.. Invention is credited to Tetsuro Kawahara, Hideki Okamoto, Toshifumi Tsujino.
Application Number | 20060121190 11/143141 |
Document ID | / |
Family ID | 26579747 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060121190 |
Kind Code |
A1 |
Tsujino; Toshifumi ; et
al. |
June 8, 2006 |
Low-reflection glass article and method for manufacturing
Abstract
A low reflection film comprising silica fine particles and a
binder in a weight ratio proportion of 60:40 to 95:5 is obtained by
mixing starting fine particles comprising at least non-aggregated
silica fine particles with a mean particle size of 40-1000 nm
and/or linear (chain-like) aggregated silica fine particles with a
mean primary particle size of 10-100 nm, a hydrolyzable metal
compound, water, and a solvent, hydrolyzing the hydrolyzable metal
compound in the presence of the starting fine particles, and then
coating the prepared coating solution onto a glass base substrate
and subjecting it to heat treatment. The obtained low reflection
film is a single-layer low reflection film with low reflectivity,
excellent abrasion resistance, high film strength and excellent
contamination removal property, and coating of the low reflection
film onto glass base substrates can give low reflection glass
articles.
Inventors: |
Tsujino; Toshifumi;
(Osaka-fu, JP) ; Okamoto; Hideki; (Osaka-fu,
JP) ; Kawahara; Tetsuro; (Osaka-fu, JP) |
Correspondence
Address: |
INTELLECTUAL PROPERTY LAW GROUP LLP
12 SOUTH FIRST STREET
SUITE 1205
SAN JOSE
CA
95113
US
|
Assignee: |
Nippon Sheet Glass Co.,
Ltd.
|
Family ID: |
26579747 |
Appl. No.: |
11/143141 |
Filed: |
June 1, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09928836 |
Aug 11, 2001 |
6921578 |
|
|
11143141 |
Jun 1, 2005 |
|
|
|
PCT/JP00/08778 |
Dec 12, 2000 |
|
|
|
09928836 |
Aug 11, 2001 |
|
|
|
Current U.S.
Class: |
427/226 |
Current CPC
Class: |
H01L 31/02168 20130101;
C03C 19/00 20130101; G02B 1/12 20130101; C03C 17/007 20130101; C03C
17/42 20130101; Y10T 428/26 20150115; C03C 2218/113 20130101; Y02E
10/50 20130101; C03C 2217/42 20130101; C03C 2218/116 20130101; C03C
1/008 20130101; G02B 1/11 20130101; F24S 80/52 20180501; Y02E 10/40
20130101; Y10T 428/2993 20150115; C03C 2217/213 20130101; C03C
2217/478 20130101; Y10T 428/25 20150115 |
Class at
Publication: |
427/226 |
International
Class: |
B05D 3/02 20060101
B05D003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 1999 |
JP |
11/352970 |
Dec 26, 2000 |
JP |
2000/16860 |
Claims
1. A method for manufacturing coated glass articles, the method
comprising: adding a hydrolyzable metal compound (1) in a state
before hydrolyzation, to a mixture of starting fine particles (2)
comprising non-aggregated silica fine particles with a mean
particle size of 40-1000 nm and/or linear (chain-like) aggregated
silica fine particles with a mean primary particle size of 10-100
nm, water (3), and a solvent (4), hydrolyzing the hydrolyzable
metal compound in the presence of the starting fine articles to
prepare a coating solution, the coating solution undergoing a
condensation reaction between a product of the hydrolysis and a
silanol present on said silica fine particles, coating a glass base
substrate with the coating solution, and heating the coating
solution.
2. The method for manufacturing coated glass articles according to
claim 1, wherein said hydrolyzable metal compound includes at least
one type of metal alkoxide selected from the group consisting of
silicon alkoxides, aluminum alkoxides, titanium alkoxides,
zirconium alkoxides and tantalum alkoxides.
3. The method for manufacturing coated glass articles according to
claim 1, wherein said coating solution has a starting compositional
ratio of 100 parts by weight of said metal compound (in terms of
the metal oxide), 150-1900 parts by weight of said starting fine
particles, 0-200 parts by weight of a catalyst, 50-10,000 parts by
weight of said water and 1000-500,000 parts by weight of said
solvent.
4. The method for manufacturing coated glass articles according to
claim 2, wherein said coating solution has a starting compositional
ratio of 1 00 parts by weight of said metal compound (in terms of
the metal oxide), 150-1900 parts by weight of said starting fine
particles, 0-200 parts by weight of a catalyst, 50-10,000 parts by
weight of said water and 1000-500,000 parts by weight of said
solvent.
5. A method for manufacturing coated glass articles, the method
comprising: adding a hydrolyzable metal compound (1) in a state
before hydrolyzation, to a mixture of starting fine particles (2)
comprising non-aggregated silica fine particles with a mean
particle size of 40-1000 nm and/or linear (chain-like) aggregated
silica fine particles with a mean primary particle size of 10-100
nm, water (3), and a solvent (4), wherein the starting fine
particles and the metal compound are present in a weight ratio
proportion of 60:40 to 95:5 with the metal compound in terms of
metal oxide, hydrolyzing the hydrolyzable metal compound in the
presence of the starting fine articles to prepare a coating
solution, the coating solution undergoing a condensation reaction
between a product of the hydrolysis and a silanol present on the
silica fine particles, coating a glass base substrate with the
coating solution, and heating the coating solution.
6. The method for manufacturing coated glass articles according to
claim 5, wherein hydrolyzing the hydrolyzable metal compound is
conducted in the presence of an acid catalyst, the acid catalyst
being added before or after the addition of the hydrolysable metal
compound to the starting fine particles.
7. The method for manufacturing coated glass articles according to
claim 5, wherein said hydrolyzable metal compound includes at least
one type of metal alkoxide selected from the group consisting of
silicon alkoxides, aluminum alkoxides, titanium alkoxides,
zirconium alkoxides and tantalum alkoxides.
8. The method for manufacturing coated glass articles according to
claim 6, wherein said hydrolyzable metal compound includes at least
one type of metal alkoxide selected from the group consisting of
silicon alkoxides, aluminum alkoxides, titanium alkoxides,
zirconium alkoxides and tantalum alkoxides.
9. The method for manufacturing coated glass articles according to
claim 6, wherein the coating solution has a starting compositional
ratio of 100 parts by weight of the metal compound (in terms of the
metal oxide), 150-1900 parts by weight of the starting fine
particles, 0-200 parts by weight of the catalyst, 50-10,000 parts
by weight of the water and 1000-500,000 parts by weight of the
solvent.
Description
CROSS REFERENCE
[0001] This is a divisional of U.S. application Ser. No.
09/928,836, filed on Aug. 11, 2001, which is hereby incorporated
herein by reference. Application Ser. No. 09/928,836 is a
continuation of International Application PCT/JP00/08778, with an
international filing date of Dec. 12, 2000 and now abandoned.
BACKGROUND
[0002] The present invention relates to a method for manufacturing
low reflection glass articles such as automobile glass windows,
construction glass, show windows, displays, solar cell glass base
substrates, solar water heater glass panels, optical glass parts
and the like.
[0003] Coating of glass base substrates with films for low
reflection treatment to reduce visible light reflectivity of glass
base substrates is widely known. An example of a method of
utilizing the light interference effect obtained by lamination of
two or more films on a glass sheet to realize low reflectivity is
the invention of Japanese Unexamined Patent Publication No.
Hei-4-357134, which discloses automobile reflection-reducing glass
with a two-layer construction, characterized in that a thin-film
layer with a refractive index of n1=1.8-1.9 and a film thickness of
700-900 angstroms is coated on at least one surface of a
transparent glass sheet as the first layer from the glass side, and
then a thin-film layer with a refractive index of n2=1.4-1.5 and a
film thickness of 1100-1300 angstroms is coated on the first
thin-film as a second layer, whereby the reflectivity on the
thin-film coated layer side is reduced by 4.5-6.5% for visible
light on the film side entering at an incident angle of 50.degree.
to 70.degree. with respect to the normal to the surface. The
invention of Japanese Unexamined Patent Publication No.
Hei-4-357135 also proposes glass with a low reflection film
composed of three layers.
[0004] On the other hand, as a method of forming a single layer
film on glass to reduce reflection with the film, such as the
invention of Japanese Unexamined Patent Publication No.
Sho-63-193101 for example, discloses an anti-reflection film
obtained by coating and drying an alcohol solution of Si(OR).sub.4
(where R is an alkyl group) containing SiO.sub.2 fine particles
onto the surface of glass, to attach SiO.sub.2 fine particles and
an SiO.sub.2 thin-film coating it onto the glass surface.
[0005] The invention described in Japanese Unexamined Patent
Publication No. Sho-62-17044 discloses an anti-reflection film
obtained by mixing a metal alcoholate such as tetraethoxysilane
with colloidal silica with a particle size of 5-100 nm in a
proportion of 1 mole of the metal alcoholate to 1 mole of the
colloidal silica, hydrolyzing a mixed solution obtained by
dissolving it in an organic solvent such as alcohol, and coating
the partially condensed sol solution onto an optical element
surface, and heat treating it.
[0006] Also, the invention described in Japanese Unexamined Patent
Publication No. Hei-11-292568 discloses visible light low
reflection glass obtained by forming a low reflection film with a
thickness of only 110-250 nm, containing linear silica fine
particles and silica at 5-30 wt % with respect thereto.
[0007] It is known, as described in Optical Engineering, Vol. 21,
No. 6, (1982), page 1039-, that such low reflection films which are
single-layer low refractive index layers have low incident angle
dependence of reflectivity, and that their low wavelength
dependence of reflectivity results in a wide wavelength region of
low reflection.
[0008] The method of coating a glass base substrate with a coating
comprising two or more laminated film layers can reliably provide
low reflection of visible light, but since the film thickness must
be strictly specified to satisfy the interference conditions and
the coating must be performed at least twice, the production costs
are undesirably increased. Moreover, films of two or more layers
have higher incident angle dependence of reflectivity, and
therefore the reflectivity is not always lowered outside of the
designed incident angle range. In this respect, coating a glass
base substrate with a single-layer low reflection film with a low
refractive index results in a wider wavelength range of low
reflectivity.
[0009] With the anti-reflection films disclosed in Japanese
Unexamined Patent Publications No. Sho-62-17044 and No.
Sho-63-193101, the anti-reflection performance provided is
insufficient. Also, the visible light low reflection glass
disclosed in Japanese Unexamined Patent Publication No.
Hei-11-292568, while being a single-layer low reflection film that
realizes low reflectivity and exhibits sufficient film strength in
evaluation by surface abrasion such as a back-and-forth abrasion
test, is also associated with the problem of inadequate film
strength in most stringent abrasion resistance tests such as the
Taber abrasion test. In addition, in the case of oil adhesion which
cannot be removed by wiping with a dry or wet cloth, the problem of
increased reflectivity occurs.
[0010] It is an object of the present invention to provide a low
reflection film for visible light or infrared light, which exhibits
low reflectivity with a single layer, has high film strength as
evaluated by anti-abrasion tests, and exhibits excellent
contamination resistance.
SUMMARY
[0011] The present invention relates to a method for manufacturing
a low reflection glass article obtained by forming a low reflection
film composed of silica fine particles and a binder on a glass base
substrate, the low reflection glass article being characterized in
that the low reflection film contains the silica fine particles and
the binder in a weight ratio proportion of 60:40 to 95:5, and in
that the low reflection film is formed by coating a coating
solution onto the glass base substrate and subjecting it to heat
treatment, said coating solution being prepared by mixing
[0012] (1) starting fine particles comprising non-aggregated silica
fine particles with a mean particle size of 40-1000 nm and/or
linear (chain-like) aggregated silica fine particles with a mean
primary particle size of 10-100 nm,
[0013] (2) a hydrolyzable metal compound,
[0014] (3) water, and
[0015] (4) a solvent
[0016] and then hydrolyzing the hydrolyzable metal compound in the
presence of the starting fine particles.
[0017] The silica fine particles used for the invention may be
produced by any production method, and are typically silica fine
particles synthesized by reacting a silicon alkoxide by a sol-gel
method in the presence of a basic catalyst such as ammonia,
colloidal silica prepared from a sodium silicate starting material,
or fumed silica synthesized in a gas phase as an example. The
structure of the resulting low reflection film can be widely varied
based on the particle size of the silica fine particles. If the
particle size of the silica fine particles is too small, the pores
produced between the particles in the low reflection film will be
too small which will increase capillary force, making it difficult
to remove adhered contamination, while moisture and organic
substances in the air gradually become incorporated into the pores
thereby increasing the reflectivity as time progresses.
Furthermore, since an upper limit is placed on the amount of binder
used for adhesion between the silica fine particles and between the
silica fine particles and the glass base substrate, as will be
described below, too small a particle size of the silica fine
particles will mean a relative increase in the fine particle
surface area, such that the amount of binder reacting with the
surface will be insufficient and the adhesive force of the film
will as a result be weaker. Also, if the silica fine particle size
(primary particle size) is too small, the apparent refractive index
will increase with the lower irregularity roughness value of the
formed film surface or the internal void volume of the film (the
proportion between the non-binder-filled space between the silica
fine particles with respect to the film volume).
[0018] Consequently, the mean primary particle size of the silica
fine particles (refractive index: approximately 1.45) is preferably
at least 40 nm and more preferably at least 50 nm, in order to (1)
facilitate removal of contamination on the low reflection film, (2)
increase the film strength and (3) reduce the apparent refractive
index to approach the square root (approximately 1.22) of the
refractive index (approximately 1.5) of the glass base substrate on
which the low reflection film is coated.
[0019] If the particle size of the silica fine particles is too
large, light scattering is intensified and adhesion with the glass
base substrate is weakened. For uses which require visual
transparency, i.e. uses for which a low haze value, such as a haze
value of 1% or lower, is desired, for example, in automobile and
construction windows, the mean particle size of the silica fine
particles is preferably no greater than 500 nm, and more preferably
no greater than 300 nm. A more preferred mean particle size range
for the silica fine particles is 50-200 nm, and even more
preferably 70-160 nm.
[0020] On the other hand, for uses which do not require visual
transparency and do not demand very high film strength, for
example, in solar cell glass base substrates, it is important to
increase the transmittance by lowering the reflectivity. In order
to increase the sunlight absorption efficiency in the silicon film
provided in contact with the glass base substrate, it is
advantageous to lengthen the optical path length in the silicon
film for sunlight incident to the silicon film. Light passing
through the low reflection film can be separated into rectilinear
transmitted light and scattered transmitted light, and increasing
the amount of scattered transmitted light with respect to the
amount of rectilinear transmitted light increases the haze value.
When compared to using a low reflection film wherein the total
light transmittance is identical (and therefore the reflectivity is
identical), a low reflection film which increases the amount of
scattered transmitted light of the light passing through the low
reflection film, i.e. a low reflection film with a high haze value,
such as a low reflection film with a haze value of 10-80%, for
example, is preferred for the aforementioned lengthening of the
optical path. For a low reflection film with such a large haze
value it is preferred to use silica fine particles with a mean
particle size of 100-1000 nm.
[0021] The mean particle size of the silica fine particles used as
the starting fine particles is defined as the value d averaged for
a given number of fine particles (n=100) according to the following
formula (1), based on measurement of the diameters (averages of
long and short diameters) of the actual primary particles
(individual primary particles in cases where they aggregate to form
linear secondary particles) in the planar visual field with a
transmission electron microscope at 10,000-50,000 magnification.
This measured value therefore differs from the particle size
determined by the BET method used for colloidal silica and the
like. The sphericity of the silica fine particles is represented by
the ratio of the long axis length and the short axis length of each
of the particles, and is averaged among 100. The standard deviation
which represents the particle size distribution of the fine
particles is determined from the diameters according to the
following formulas (2) and (3). In each of the formulas (1) to (3),
n=100. d = ( i = 1 n .times. .times. d i ) / n ( 1 ) .sigma. = i =
1 n .times. .times. ( d - d i ) 2 n - 1 ( 2 ) Standard .times.
.times. deviation = ( d + .sigma. ) / d ( 3 ) ##EQU1##
[0022] The sphericity of the silica fine particles is preferably
1.0-1.2, because a low reflection film with an increased degree of
fine particle packing will be formed, thereby increasing the
mechanical strength of the film. The sphericity is even more
preferably 1.0-1.1. Also, using silica fine particles with a
uniform particle size can increase the voids between the fine
particles, thereby lowering the apparent refractive index of the
film and lowering the reflectivity. Thus, the standard deviation of
the particle size indicating the particle size distribution of the
silica fine particles is preferably 1.0-1.5, more preferably
1.0-1.3 and most preferably 1.0-1.1.
[0023] As suitable non-aggregated silica fine particles with a mean
particle size of 40-1000 nm there may be mentioned the commercially
available products "SNOWTEX OL", "SNOWTEX YL" and "SNOWTEX ZL" by
Nissan Chemical Co., and "SEAHOSTAR KE-W10", "SEAHOSTAR KE-W20",
"SEAHOSTAR KE-W30", "SEAHOSTAR KE-W50", "SEAHOSTAR KE-E70",
"SEAHOSTAR KE-E90", etc. by Nippon Shokubai Co., Ltd. Silica fine
particles are preferably in the form of a silica fine particle
dispersion in a solvent, for ease of handling. The dispersion
medium may be water, an alcohol, a cellosolve, a glycol or the
like, and silica fine particle dispersions in these dispersion
media are commercially available. Silica fine particle powder may
also be used in the form of dispersions in these dispersion
media.
[0024] When several of the fine particles aggregate to form
aggregated fine particles (secondary fine particles), the mean
particle size of each of the individual fine particles (primary
particles) composing these aggregated fine particles is defined as
the mean primary particle size. If the aggregates of the fine
particles have aggregated in a non-branched linear or branched
linear fashion (linear (chain-like) aggregated fine particles),
each of the fine particles is fixed in that aggregated state during
the film formation, resulting in a highly bulky film, and the
irregularity roughness value of the formed film surface and the
film interior void volume increase with respect to the
non-aggregated silica fine particles having a mean particle size
equivalent to the mean primary particle size of the
linear(chain-like) aggregated fine particles. Thus, the linear
(chain-like) aggregated silica fine particles used may be linear
(chain-like) aggregated silica fine particles having a mean primary
particle size of less than 40 nm or a mean primary particle size d
of 10-100 nm. The linear (chain-like) aggregated silica fine
particles preferably have an average length (L) of 60-500 nm and an
average length to mean primary particle size ratio (L/d) of 3-20.
Examples of such linear (chain-like) aggregated silica fine
particles include "SNOWTEX OUP" and "SNOWTEX UP", by Nissan
Chemical Co.
[0025] The coating solution for formation of the low reflection
film is prepared by hydrolysis of a hydrolyzable metal compound in
the presence of the silica fine particles, and the mechanical
strength of the resulting film is thereby drastically improved.
When the metal compound is hydrolyzed in the presence of the silica
fine particles, a condensation reaction between the product of
hydrolysis and the silanol present on the fine particle surfaces
occurs almost simultaneously with the hydrolysis, and (1) the
condensation reaction with the binder component improves the
reactivity of the fine particle surfaces, while (2) as the
condensation reaction proceeds, the silica fine particle surfaces
become coated with the binder, so that the binder can be
effectively utilized to enhance the adhesion between the silica
fine particles and the glass base substrate.
[0026] On the other hand, hydrolysis of the metal compound in the
absence of fine particles leads to high molecular formation of the
binder component by condensation reaction between the hydrolysis
products. When the high molecular binder component and the silica
fine particles are combined to prepare a coating solution, (1)
almost no condensation reaction occurs between the binder component
and silica fine particles, resulting in poor reactivity of the fine
particle surfaces, and (2) the silica fine particle surfaces are
almost uncovered with the binder. Consequently, when it is
attempted to increase the adhesion between the glass and silica
fine particles in the manner described above, a much larger amount
of binder is required.
[0027] A scanning electron microscope (SEM) at 100,000
magnification was used to compare a film B (comparative example)
fabricated using a coating solution prepared by mixing colloidal
silica (mean particle size: 50 nm, "SNOWTEX OL" by Nissan Chemical
Co.) and pre-hydrolyzed tetraethoxysilane at a solid ratio of
80:20, and then further adding a hydrolyzing catalyst, water and a
solvent, and a film A (present invention) fabricated using a
coating solution prepared by mixing the colloidal silica and
tetraethoxysilane at a solid ratio of 80:20, and then further
adding the hydrolyzing catalyst, water and a solvent and stirring
at 25.degree. C. for 24 hours for hydrolysis of the
tetraethoxysilane in the presence of the colloidal silica. FIGS. 1
and 2 show, respectively, SEM photographs of the edge sections
(cross-sections) of films A and B as seen from an upper slant angle
of 30.degree. from the film plane. Both of the films have silica
fine particles layered on glass base substrates. The 11 white dots
at the lower right indicate a distance of 300 nm from both ends of
the line of dots.
[0028] In FIG. 2 (film B), a rather thick film-like adhesion can be
seen covering the surface of several of the silica fine particles
aligned adjacent to the film surface. The film-like adhesion is
believed to be the binder component from the tetraethoxysilane, and
therefore in FIG. 2 (film B), the amount of binder that ought to
work for effective adhesion between the fine particles and between
the fine particles and the base substrate is thought to be lower
due to the film-like adhesion. If the tetraethoxysilane content is
increased to increase the amount of binder that ought to work for
effective adhesion, then the spaces between the fine particles and
the spaces between the fine particles and the base substrate
surface are reduced thus increasing the apparent refractive index
of the film, and making it difficult to lower the reflectivity.
[0029] In FIG. 1 (film A), such film-like adhesion is either
unobservable or does not exist, and it is therefore surmised that
all of the binder component uniformly covers the surfaces of the
silica fine particles, so that the binder effectively acts for
adhesion between the fine particles and between the fine particles
and the base substrate.
[0030] The preparation method for film A allows the binder
component content to be decreased while maintaining film strength,
and can achieve a lower apparent refractive index of the film, thus
resulting in both supported film strength and reduced reflectivity
of the film. According to the method for film A, even if the binder
amount is reduced to half, it is possible to achieve equivalent
film strength compared to film B prepared using a coating solution
with silica fine particles mixed with the pre-hydrolyzed
binder.
[0031] The judgment standard for the film strength was based on the
results of determining the residual film with a Taber abrasion test
according to JIS-R3212 and JIS-R3221 using a CS-10F rotating wheel,
with 1000 rotations at a load of 500 g (JIS-R3212) or 200 rotations
at a load of 500 g (JIS-R3221), and measuring the haze value before
and after the Taber abrasion test.
[0032] The binder of the invention is composed of a metal oxide,
and it is preferred to use at least one metal oxide selected from
the group consisting of silicon oxides, aluminum oxides, titanium
oxides, zirconium oxides and tantalum oxides. The weight ratio of
the silica fine particles and binder forming the low reflection
film is in the range of 60:40 to 95:5. If the binder amount is
above this range, the fine particles become embedded in the binder
which reduces the fine particle-based irregularity roughness value
or the film void volume, thus reducing the anti-reflection effect.
If the binder amount is below this range, the adhesive force
between the fine particles and between the glass base substrate and
fine particles is reduced, leading to weak mechanical strength of
the film. Considering the balance between the reflectivity and the
film strength, the weight ratio of the silica fine particles and
the binder is more preferably 65:35 to 85:15. The binder preferably
covers the entire surfaces of the silica fine particles, and the
coating thickness is preferably 1-100 nm which is 2-9% of the mean
particle size of the silica fine particles.
[0033] The hydrolyzable metal compound as the binder starting
material is suitably a metal alkoxide of Si, Al, Ti, Zr, Ta or the
like, for film strength and chemical stability. Of these metal
alkoxides it is preferred to use silicon tetraalkoxides, aluminum
trialkoxides, titanium tetraalkoxides and zirconium tetraalkoxides,
with methoxides, ethoxides, propoxides and butoxides being
particularly preferred. For films with particularly high binder
component contents, the refractive index of the binder component
will affect the reflectivity, and therefore silicon alkoxides and
especially silicon tetraalkoxides or oligomers thereof, which have
low refractive indexes, are most suitable. The binder component
used may also be a combination of more than one of these metal
alkoxides. Other than metal alkoxides, there are no particular
restrictions so long as a reaction product of M(OH).sub.n is
obtained by hydrolysis, and for example, there may be mentioned
metal halides and metal compounds with isocyanate groups, acyloxy
groups, aminoxy groups and the like. In addition, compounds
represented by R.sup.1.sub.nM(OR.sup.2).sub.4-n (where M is a
silicon atom, R.sup.1 is an organic functional group such as an
alkyl group, amino group, epoxy group, phenyl group or methacryloxy
group, R.sup.2 is, for example, an alkyl group, and n is an integer
of 1-3), which are a type of silicon alkoxide, may also be used as
binder starting materials. Using such compounds represented by
R.sup.1.sub.nM(OR.sup.2).sub.4-n leaves an organic residue on the
gel film after coating, and therefore if this is used for all of
the binder starting material the organic residue portions become
fine pores on the nanometer level after heat treatment, and the
small size of the fine pores increases the capillary force, making
it difficult to remove adhered contaminants and causing other
problems such as inclusion of contaminants and water in the fine
pores which results in change in the reflectivity over time, while
the film strength is also weakened; compounds represented by
R.sup.1.sub.nM(OR.sup.2).sub.4-n are therefore preferably not used
in large amounts, and are limited to, for example, within 50 wt %
in terms of the metal oxide with respect to the total binder.
[0034] The haze value of the low reflection film-coated glass
article is the total of the haze value of the glass base substrate
itself and the haze value of the low reflection film, and the glass
base substrate used for the invention should have as small a haze
value as possible, such as a haze value of no greater than 0.1%.
Thus, the haze value of a low reflection glass article of the
invention is approximately equal to the haze value of the low
reflection film. The haze value of the low reflection film is
preferably adjusted to the optimum range which will differ
depending on the use. For example, for an automobile window, a
lower haze value is preferred from the standpoint of safety, while
the haze value for low reflection glass articles is no greater than
1%, and preferably no greater than 0.5%.
[0035] On the other hand, for solar cell glass base substrates
which require effective utilization of solar energy, increased
multiple reflection in a film of polycrystalline silicon,
monocrystalline silicon, amorphous silicon or the like formed close
to the glass sheet to lengthen the optical path can allow more
effective utilization of incident light for enhanced transformation
efficiency. For this purpose, as mentioned above, a low reflection
film with a high degree of scattered transmitted light, i.e. a low
reflection film with a high haze value, is most suited.
[0036] A solar cell glass sheet with lowered reflectivity and
increased scattered transmission is effective to raise the total
light transmittance (total light transmittance of rectilinear
transmitted light and scattered transmitted light) and lengthen the
optical path in the silicon, and a most notable effect is achieved
with a haze value of 10% or higher. If the haze value exceeds 80%,
the effect of lowered reflectivity (increased transmittance) is
almost eliminated. Thus, a solar cell glass sheet according to the
invention preferably has a haze value of 10-80%.
[0037] However, the haze value may exceed 80% in cases where an
increase in scattered light intensity is desired instead of a high
total light transmittance or in cases where the outer appearance is
important, such as for reduced front reflection (to prevent mirror
image reflection). When high film strength is demanded, the haze
value for a solar cell glass sheet is typically no greater than
30%. A method of achieving both anti-reflection performance and
light scattering transmission is to use two types of fine particles
with different mean particle sizes as the non-aggregated silica
fine particles used in the low reflection film coating solution,
namely (1) 70-95 wt % of a first type of non-aggregated silica fine
particles with a mean particle size of 40-200 nm and (2) 5-30 wt %
of a second type of non-aggregated silica fine particles with a
mean particle size of more than 200 nm to 3000 nm or less and at
least 100 nm larger than the mean particle size of the first type
of non-aggregated silica fine particles.
[0038] In the low reflection film obtained using these
non-aggregated silica fine particles, 30-90% of the area seen from
above the film is occupied by fine particles with a mean particle
size of 40-200 nm, while no more than 50% and preferably 1-30% of
the area is occupied by fine particles with a mean particle size of
200-3000 nm. The occupied area is the area occupied by the fine
particles per unit area of the film as seen from the normal to the
glass surface.
[0039] When the fine particles overlap, the occupied area is
determined by the area of the uppermost fine particles. There is no
need for all of the surface section of the base substrate to be
occupied by fine particles. Anti-reflection performance is obtained
in the fine particle-occupied sections in the former case, while
light scattering transmission performance is obtained in the fine
particle-occupied sections in the latter case. It is thus possible
to increase the haze value to 30% while maintaining low
reflectivity.
[0040] When non-aggregated fine particles of a uniform particle
size are arranged in one level on the glass base substrate, the
relationship between the fine particle sizes and the haze value may
be indicated as follows with a fine particle content of 80 wt % and
a binder content of 20 wt %: the haze value is about 10% for a film
formed with fine particles of particle size 200 nm alone, about 20%
for 300 nm, about 55% for 500 nm and about 70% for fine particles
with a particle size of 700 nm. For fine particles with a particle
size of 900 nm or greater, the haze value exceeds 70%.
[0041] A greater low reflection effect enhances the safety for
automobiles and increases the usable light energy for solar cell
base substrates, and therefore the reflectivity is preferably lower
with a reflectivity from the film side of no greater than 2%,
preferably no greater than 1% and more preferably no greater than
0.7%.
[0042] The structure of the low reflection film is preferably such
that the silica fine particles covered with the binder on their
surfaces (hereunder referred to simply as fine particles) almost
totally cover the surface of the glass base substrate, for reduced
reflectivity of the film. When fine particles of exactly the same
particle size are packed to maximum density in one layer on the
glass base substrate, the area occupied by the fine particles as
seen from above is theoretically about 90%. For a low reflection
film with only a single layer of fine particles, the occupied area
is 50% or greater, and preferably 70% or greater, in order to
achieve low reflection performance. If the occupied area is less
than 50%, exposure of the glass base substrate surface results in
strong reflection due to the difference in refractive indexes of
the glass and air, such that reflection cannot be reduced.
[0043] The structure of the low reflection film may be such that
the fine particles are arranged in a single layer on the upper
glass surface, or that the fine particles are layered in multiple
levels. With either a single layer or multilayer structure, the
pores corresponding to the fine particle size are formed by the
gaps between the glass base substrate and fine particles or the
gaps between the fine particles themselves, and these spaces are
effective for lowering the apparent refractive index. When the film
is observed with an electron microscope from directly above the
film, the total number of the fine particles aligned in a planar
fashion on the uppermost surface of the film and the fine particles
located under the uppermost surface fine particles but slightly
visible between the gaps between the uppermost surface fine
particles is 30-3000 in a 1 .mu.m 1 .mu.m square area, when using
non-aggregated silica fine particles with a mean particle size of
40-500 nm as the starting fine particles, and these fine particles
preferably have a mean particle size of 40-500 nm. The total number
is more preferably from 100 to 1000.
[0044] When using non-aggregated silica fine particles with a mean
particle size of 100-1000 nm as the starting fine particles, the
total number of the fine particles is 10-50,000 in a 10
.mu.m.times.10 .mu.m square area, and the fine particles preferably
have a mean particle size of 100-1000 nm. The total number is more
preferably from 20 to 25,000.
[0045] The fine particle density depends on the sizes of the fine
particles, with a larger fine particle size resulting in a smaller
number, and a smaller fine particle size resulting in more
particles. Rather than having the fine particles simply held on the
glass base substrate, it is preferred for increased film strength
to employ a structure wherein the fine particles are in dense
contact and bonded together by the binder. For example, when the
mean particle size of the fine particles is D nm, the number of
fine particles in a 10 .mu.m.times.10 .mu.m square film observed
using an electron microscope directly above the film is preferably
from 5,000,000/D.sup.2 to 10,000,000/D.sup.2.
[0046] The average thickness of the low reflection film of the
invention is defined below. An image of a cross-section of the film
as observed with an electron microscope at 50,000.times.
magnification is prepared. A 10 cm (actually 2 .mu.m) length of the
electron microscope image is taken, and after selecting 12
locations in order from the largest height, the average thickness
is determined as the average height value from the base substrate
surface among the 10 heights from the 3rd to 12th ones counting
from the highest one. If 12 heights cannot be selected because the
sizes of the fine particles are large or the particles are sparsely
dispersed, the magnification of the electron microscope is
gradually decreased from 50,000, and the average thickness is
determined by the above-mentioned method when 12 heights can be
selected.
[0047] A film with an average thickness in the range of 90 to 180
nm has the lowest reflectivity in the visible light region. The
value of the physical thickness (d) defined by the optical
thickness (nd) is smaller than the average thickness, and the
physical thickness (d) corresponding to the average thickness of
90-180 nm is 80-140 nm. This is in order to satisfy the
interference conditions for reflected light at the glass/film
interface and film/air interface. The interference conditions are
established even at 2 n-1 times the thickness mentioned above
(where n is a natural number), and therefore although the
reflectivity reduces even with a thickness of 3 times or greater,
this is undesirable since the film loses strength.
[0048] On the other hand, considering the region spanning both
visible light (400-780 nm) and infrared light (780 nm-1.5 .mu.m) as
the region in which reflectivity is to be reduced, the average
thickness of the low reflection film is preferably from 90 nm to
350 nm. This corresponds to a physical thickness d of 80 nm to 300
nm.
[0049] Particularly for automobile window seals, since the mounting
angle (the inclination angle from the vertical surface) is around
60.degree., a film design corresponding to the method of use is
necessary. The surface reflectivity (not including the back side
reflection) of soda lime glass which has a refractive index of 1.52
is 4.2% with an incident angle of 12.degree., but the surface
reflectivity with an incident angle of 60.degree. (the incident
angle corresponds to the angle of incidence of light from the
horizontal direction with respect to the window seal mounted on the
automobile) reaches 9% or greater.
[0050] The low reflection film composed of the fine particles and
binder approaches the porous single layer film with the average
refractive index, but low reflection performance is achieved by
utilizing the interference effect of the reflected light at the
glass/low reflection film interface and reflected light at the low
reflection film/air interface, to shift the half-wavelength of the
optical path difference between the reflected light. When the
incident angle to the low reflection film-formed glass is
increased, the optical path difference tends to become smaller, so
that it becomes necessary to increase the optical thickness (nd) of
the low reflection film compared to vertical incident reflection.
In order to reduce the reflectivity with 60.degree. incidence, the
optical thickness is preferably designed to be about 140-250
nm.
[0051] The surface reflectivity with an incident angle of
60.degree. depends largely on the apparent refractive index and
optical thickness of the low reflection film, and is no greater
than 6%, preferably no greater than 5% and more preferably no
greater than 4%.
[0052] According to the invention, the coating solution for the low
reflection film is obtained by hydrolyzing a mixture of silica fine
particles, a hydrolyzable metal compound, a catalyst for
hydrolysis, water and a solvent. For example, reaction is conducted
at room temperature for 1-24 hours while stirring, or else reaction
may be conducted at a temperature higher than room temperature,
such as 40-80.degree. C., for 10-50 minutes while stirring. The
resulting coating solution may also be diluted with an appropriate
solvent depending on the coating method to be used.
[0053] The hydrolysis catalyst is most effectively an acid
catalyst, examples of which include mineral acids such as
hydrochloric acid and nitric acid, or acetic acid, etc. With an
acid catalyst, the condensation polymerization reaction rate is
slower than the hydrolysis reaction rate of the hydrolyzable metal
compound, such as a metal alkoxide, and the hydrolysis reaction
product M(OH).sub.n is produced in a large amount, which is
preferred to allow efficient action as a binder. With a basic
catalyst, the condensation polymerization reaction rate is faster
than the hydrolysis reaction rate, and therefore the metal alkoxide
becomes a fine particulate reaction product and is used for
particle size growth of the originally present silica fine
particles, which results in a lower effect of the metal alkoxide as
a binder. The catalyst content is preferably 0.001-4 in terms of
molar ratio with respect to the metal compound as the binder.
[0054] The amount of water necessary for hydrolysis of the metal
compound may be 0.1-100 as the molar ratio with respect to the
metal compound. If the water is added at less than 0.1 in terms of
the molar ratio, the hydrolysis of the metal compound will not
proceed adequately, whereas if it is greater than a molar ratio of
100, the stability of the solution will tend to be undesirably
reduced.
[0055] When a chloro group-containing compound is used as the metal
compound, addition of a catalyst will not always be necessary. The
chloro group-containing compound can undergo hydrolysis reaction
even without a catalyst. However, there is no problem with further
addition of an acid.
[0056] The solvent may basically be any one which can substantially
dissolve the metal compound, but most preferred are alcohols such
as methanol, ethanol, propanol and butanol, cellosolves such as
ethylcellosolve, butylcellosolve and propylcellosolve, and glycols
such as ethylene glycol, propylene glycol and hexylene glycol. If
the concentration of the metal compound dissolved in the solvent is
too high, although the amount of dispersed silica fine particles is
also a factor, sufficient gaps may not be produced between the fine
particles, and therefore the content is preferably no greater than
20 wt % and more preferably 1-20 wt %. The proportion of the amount
of silica fine particles and the metal compound (in terms of the
metal oxides SiO.sub.2, Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2 or
Ta.sub.2O.sub.5) in the coating solution is preferably 60:40 to
95:5 and more preferably 65:35 to 85:15, in terms of weight.
[0057] A preferred starting material mixing ratio for the coating
solution of the invention is listed in table 1 below.
TABLE-US-00001 TABLE 1 Hydrolyzable metal compound 100 parts by
weight (in terms of metal oxide) Starting fine particles 150-1900
parts by weight comprising either or both non-aggregated silica
fine particles of mean particle size 40-1000 nm and
linear(chain-like) aggre- gated silica fine particles of mean
primary particle size 10-100 nm Water 50-10,000 parts by weight
Acid catalyst 0-200 parts by weight, preferably 0.01-200 parts by
weight Solvent 1000-500,000 parts by weight
[0058] The coating solution is coated onto a glass base substrate
and heated for dehydration condensation reaction of the metal
compound hydrolysate and gasification and combustion of the
volatile components, to form a low reflection film on the glass
base substrate.
[0059] The coating method is not particularly limited and may be
any publicly known technique, and methods using such apparatuses as
spin coaters, roll coaters, spray coaters and curtain coaters,
methods such as dip coating, flow coating and the like or printing
methods such as screen printing, gravure printing, curve printing
or the like may be used. Glycols are effective solvents in coating
methods requiring high-boiling-point solvents, for example, in
printing methods such as flexo printing and gravure printing, and
while the reason is not fully understood, glycols are suitable
solvents because they suppress aggregation of the fine particles
and form low reflection films with low haze values. The weight
proportion of the glycol in the coating solution may be from
5-80%.
[0060] Depending on the glass base substrate it may not be possible
to achieve uniform coating due to repellence of the coating
solution, but this can be improved by washing the base substrate
surface or carrying out surface modification. As methods of washing
or surface modification there may be mentioned degreasing washing
with an organic solvent such as alcohol, acetone, hexane or the
like, washing with an alkali or acid, methods of surface polishing
with polishing agents, or methods such as ultrasonic washing,
ultraviolet irradiation treatment, ultraviolet ozone treatment,
plasma treatment, etc.
[0061] The heating treatment after the coating is effective to
increase the adhesion of the film composed of the silica fine
particles and binder with the glass base substrate. The treatment
temperature is preferably a maximum temperature of 200.degree. C.
or higher, preferably 400.degree. C. or higher and more preferably
600.degree. C. or higher, up to 1800.degree. C. At 200.degree. C.
or higher, the solvent component in the coating solution
evaporates, leading to gelling of the film and increased adhesive
force. At 400.degree. C. or higher, the organic components
remaining in the film are almost completely removed by combustion.
At 600.degree. C. or higher, the residual unreacted silanol groups
and hydrolyzed groups of the metal compound hydrolysates undergo
almost complete condensation reaction, leading to densification of
the film and improved film strength. The heating time is preferably
from 5 seconds to 5 hours, and more preferably from 30 seconds to
one minute.
[0062] The low reflection film of the invention may be formed on
one side or on both sides of the glass base substrate. When both
sides of the glass sheet are to be used against a medium such as
air or a gas with a refractive index of nearly 1, formation of the
film on both surfaces of the glass base substrate can give a better
anti-reflection effect. However, when one surface of the glass base
substrate is to be used against a medium with a refractive index
near the refractive index of the glass base substrate, for example,
with sandwich glass wherein two glass base substrates are bonded
via a transparent resin layer such as polyvinylbutyral, visible
light reflection at the interface between the glass sheet and
transparent resin layer can be ignored, and therefore the low
reflection film may be formed only on the outer surface of each
glass sheet, instead of being formed on the glass base substrate
surfaces facing the transparent resin layer.
[0063] When a low reflection glass article of the invention is to
be used in an automobile, for example, the glass sheet coated with
the low reflection film may be further coated on the surface with a
water-repellent film or anti-fogging film. Coating a
water-repellent film can provide water-repellent performance, as
well as enhanced contamination removal in the case of adhesion of
contaminants. The water-repellency obtained by coating a
water-repellent film on the low reflection film of the invention
exhibits more excellent water-repellent function than when a
water-repellent agent is used on an untreated glass base substrate
surface. Coating an anti-fogging film can provide anti-fogging
performance, as well as enhanced contamination removal in the case
of adhesion of contaminants. The low reflection film may be coated
on both sides of the glass sheet (or sandwich glass sheet) with the
water-repellent film coated thereover, or the low reflection film
may be coated on one surface of the glass sheet and the
water-repellent film coated over both the low reflection film side
and the untreated glass surface, or on either side.
[0064] Likewise, the low reflection film may be coated on both
sides of the glass sheet (or sandwich glass sheet) with the
anti-fogging film coated thereover, or the low reflection film may
be coated on one surface of the glass sheet (or sandwich glass
sheet) and the anti-fogging film coated over both the low
reflection film side and the untreated glass surface, or on either
side.
[0065] Preferably, the low reflection film is coated on both
surfaces of the glass sheet (or sandwich glass sheet), an
anti-fogging film coated on one surface of the film (car interior
or room interior side), and a water-repellent film coated on the
other side of the film (car exterior or room exterior side), and
more preferably, the low reflection film is coated onto only one
surface (car interior or room exterior side) of the glass sheet (or
sandwich glass sheet), an anti-fogging film coated on the surface
of that film, and a water-repellent film coated on the other
surface of the glass base substrate (car exterior or room exterior
side). The reflectivity is virtually unchanged even when such an
anti-fogging film and water-repellent film are coated on the low
reflection film, and therefore low reflectivity is maintained.
[0066] The transparent glass base substrate of the invention is
preferably a transparent glass article with a refractive index of
1.47-1.53, and preferably there may be used a colorless glass base
substrate or a green- or bronze-colored glass sheet with a
composition of, for example, soda-lime silicate glass, borosilicate
glass or aluminosilicate glass, a glass sheet with a function of
blocking ultraviolet light or heat rays, or a transparent glass
base substrate made of a glass material in a different shape than a
sheet, but still provided with the aforementioned composition,
coloring or performance, having a thickness of 0.2-5.0 mm, a
visible light transmittance Ya of 70% or greater, and a haze value
of no greater than 0.1%. When it is to be used as a front glass
sheet for a solar cell panel, or as a solar cell glass base
substrate such as a base glass base substrate for a solar cell, the
thickness is preferably 0.2-5.0 mm, the visible light transmittance
Ya 85% or greater and most preferably 90% or greater, and the haze
value no greater than 0.1%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] FIG. 1 is an electron microscope image of the structure of a
low reflection film according to an example of the invention.
[0068] FIG. 2 is an electron microscope image of the structure of a
low reflection film of a comparative example.
[0069] FIG. 3 is an electron microscope image of the structure of a
low reflection film according to another example of the
invention.
[0070] FIG. 4 is an electron microscope image of the structure of a
low reflection film according to yet another example of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0071] Examples of the invention will now be explained in detail,
with the understanding that the invention is in no way limited by
these examples.
[0072] In the following examples and comparative examples, the
optical properties were measured according to JIS-R3106 for the
reflectivity and reflection color tone, and according to the
following methods for the surface roughness, abrasion resistance
and contamination resistance.
[0073] Film reflectivity 1: The reflectivity for incident light
from the film side at an incident angle of 12.degree. was measured
according to JIS-R3106 with respect to standard light A specified
by JIS-Z8720, as the reflectivity including no reflection from the
glass back side. The terms "reflectivity" and "film reflectivity"
refer to this film reflectivity 1.
[0074] Film reflectivity 2: The reflectivity for incident light
from the film side at an incident angle of 12.degree. was
measured,. as reflectivity including reflection on the glass back
side.
[0075] Total light transmittance and haze value: An integrating
sphere light transmittance meter ("HGM-2DP", product of Suga Test
Instruments Co., Ltd., C-light source, light incident from film
side) was used for measurement of the total light transmittance and
haze value by the haze value measuring method described in JIS
K7105-1981 (Plastic Optical Properties Test).
[0076] Reflection color tone (a, b): A C-light source was used
incident at an angle of 12.degree. from the film side, and the
reflected color of the reflection light including the reflection on
the glass back side was measured according to JIS-Z8729, and
expressed as the Hunter color coordinate value.
[0077] Taber abrasion 1: Following the standard of JIS-R3221, a
CS-10F rotating wheel was used for 200 rotations under a load of
500 g, and then the presence or absence of film was examined. The
symbol "O" was used to denote film remaining over the entire
surface, ".DELTA." was used to denote film partially remaining, and
"x" was used to denote absolutely no film. The values in
parentheses indicate the increase in haze value after the Taber
abrasion (value of "[haze value (%) after Taber abrasion
test]-[haze value (%) before Taber abrasion test]").
[0078] Taber abrasion 2: Same as Taber abrasion 1, except that
evaluation was made under conditions with a 500 g load and 1000
rotations.
[0079] Fastness: The results with a dry flannel fabric traverse
tester ("HEIDON-18", product of Shinto Kagaku Co., 500 g/cm.sup.2
load, 1000 passes) were evaluated based on the haze value and total
light transmittance before and after the test. The Taber abrasion
1, Taber abrasion 2 and fastness are all evaluations of the film
abrasion resistance, with the Taber abrasion 2 being the most
stringent abrasion resistance test, followed by the Taber abrasion
1 and the fastness test. The Taber abrasion 1 and Taber abrasion 2
are suitable abrasion resistance evaluations for uses such as
automobile and building windows, while the fastness is a suitable
abrasion resistance evaluation for uses such as solar cell glass
base substrates.
[0080] Surface roughness (Ra): The surface roughness Ra was
measured with an atomic force microscope (AFM, "SPI3700" by Seiko
Electronics) in a measuring range of 2 .mu.m.times.2 .mu.m.
[0081] Contamination resistance: A finger was pressed against the
film side of the glass to create a fingerprint, and this was
subjected to exhaled breath and wiped with tissue paper. After
again subjecting it to exhaled breath, the condition of the
fingerprint residue was observed and the change in reflectivity
before and after creating the fingerprint and wiping with tissue
paper was judged according to the following scale.
Scale:
[0082] O: No shape of fingerprint visible, no change in
reflectivity before and after wiping
[0083] .DELTA.: Shape of fingerprint visible, but no change in
reflectivity before and after wiping
[0084] x: Shape of fingerprint visible, and change in reflectivity
before and after wiping
EXAMPLE 1
[0085] While stirring 40 g of a silica fine particle dispersion
("SNOWTEX OL" by Nissan Chemical Co., mean particle size: 50 nm,
particle size standard deviation: 1.4, average ratio of long axis
length to short axis length: 1.1, solid portion: 20%), there were
added thereto 52.1 g of ethylcellosolve, 1 g of concentrated
hydrochloric acid and 6.9 g of tetraethoxysilane in that order, and
after further stirring for 120 minutes, the mixture was stationed
for 120 hours for reaction. A 6 g portion of ethylcellosolve was
then added to 4 g of this sol for dilution to prepare a coating
solution with a solid portion of 4%.
[0086] This coating solution was used to form a film by spin
coating onto one side of a green-colored float glass base substrate
having a composition of soda lime silicate glass and a thickness of
3.4 mm (refractive index=1.52, visible light transmittance
Ya=81.3%, total light transmittance=81.1%, sunlight transmittance
Tg=60.8%, ultraviolet transmittance Tuv(iso)=26.9%, visible light
reflectivity=7.4%, Hunter color coordinate transmitted color
L=90.7, a=-4.5, b=0.8, reflected color L=27.3, a=-1.3, b=-0.4), and
then it was placed in a 700.degree. C. electric oven for 2 minutes
to obtain a low reflection glass sheet coated with a low reflection
film with an average thickness of 128 nm. The maximum temperature
reached by heating in the electric oven was 630.degree. C. The
image of the edge section (cross-section) of the film of the
resulting film-formed glass sheet taken with an electron microscope
(100,000.times. magnification) as seen from an inclination of
30.degree. from the film plane was the same as in FIG. 1 explained
above.
EXAMPLE 2
[0087] The same procedure was followed as in Example 1, except that
the average film thickness was 105 nm. The average film thickness
was adjusted to satisfy conditions for minimum visible light
reflectivity. The average film thickness was similarly adjusted in
the following Examples 3-5 and Comparative Examples 1-7.
EXAMPLE 3
[0088] While stirring 21.3 g of a silica fine particle dispersion
("SNOWTEX YL" by Nissan Chemical Co., mean particle size: 70 nm,
particle size standard deviation: 1.3, average ratio of long axis
length to short axis length: 1.1, solid portion: 40%), there were
added thereto 21.3 g of water, 51.3 g of ethylcellosolve, 1 g of
concentrated hydrochloric acid and 5.2 g of tetraethoxysilane in
that order, and reaction was conducted for about 4 hours. A 6 g
portion of ethylcellosolve was then added to 4 g of this sol to
prepare a coating solution. A film was formed on a 2.0 mm thick
glass base substrate having the same composition as the base
substrate used in Example 1 (visible light transmittance Ya=85.3%,
total light transmittance=85.4%, sunlight transmittance Tg=71.0%,
ultraviolet transmittance Tuv(iso)=61.6%, visible light
reflectivity=7.6%, Hunter color coordinate transmitted color
a=-2.9, b=0.4, reflected color a=-0.1, b=-0.8), and heat treatment
was carried out in the same manner as Example 1. The average
thickness of the resulting film was 123 nm. The image of the edge
section (cross-section) of the film of the resulting film-formed
glass sheet taken with an electron microscope (100,000
magnification) as seen from an inclination of 30.degree. from the
film plane is shown in FIG. 3.
EXAMPLE 4
[0089] While stirring 50.0 g of a silica fine particle dispersion
("SEAHOSTAR KE-W10" by Nippon Shokubai Co., Ltd., mean particle
size: 110 nm, particle size standard deviation: 1.1, average ratio
of long axis length to short axis length: 1.03, solid portion:
15%), there were added thereto 40.3 g of ethanol, 8.7 g of
tetraethoxysilane and 1.0 g of concentrated nitric acid in that
order, and reaction was conducted for 3 hours. After adjusting the
solid portion to 3%, a film was formed on one side of a colorless
transparent (clear) 2.8 mm thick float glass base substrate having
a composition of soda lime silicate glass (refractive index=1.52,
visible light transmittance Ya=89.9%, total light
transmittance=89.7%, sunlight transmittance Tg=84.3%, ultraviolet
transmittance Tuv(iso)=61.3%, visible light reflectivity=8.0%,
Hunter color coordinate transmitted color L=94.9, a=-1.0, b=0.2,
reflected color L=28.3, a -0.4, b=-0.6). The coated glass was
subjected to 30 minutes of heat treatment in an electric oven
heated to 500.degree. C. The average thickness of the resulting
film was 163 nm. The image of the edge section (cross-section) of
the film of the resulting film-formed glass sheet taken with an
electron microscope (100,000 magnification) as seen from an
inclination of 30.degree. from the film plane is shown in FIG.
4.
EXAMPLE 5
[0090] A coating solution was prepared by mixing 53.3 g of a
linear(chain-like) aggregated silica fine particles dispersion
("SNOWTEX OUP" by Nissan Chemical Co., Ltd., mean primary particle
size: 25 nm, average length: 100 nm, solid portion: 15%), 38.8 g
ethanol, 1 g of 3 mole/L hydrochloric acid and 6.9 g of
tetraethoxysilane and reacting the mixture for 12 hours. This
coating solution was used to form a film by spin coating onto one
side of the same type of glass base substrate as in Example 1, and
then it was placed in a 600.degree. C. electric oven for 10 minutes
to obtain a low reflection glass sheet coated with a low reflection
film with an average thickness of 120 nm. The maximum temperature
reached by heating in the electric oven was 590.degree. C.
[0091] Table 2 lists the silica fine particle form (as either
non-aggregated fine particles or linear aggregated fine particles,
or listed as "mixed" when two types of fine particles are
combined), the mean particle size of the silica fine particles (or
the mean primary particle size in the case of linear (chain-like)
aggregated silica fine particles), the binder content in the film
(wt %), the silica fine particle content (wt %), the final film
thickness (average film thickness), whether the silicon alkoxide
was hydrolyzed in the presence of the silica fine particles during
preparation of the coating solution ("hydrolysis with particles"),
the number of fine particles in the film in a 1 .mu.m.times.1 .mu.m
square area as observed from above the film using an electron
microscope (fine particle density), and the type of glass base
substrate (color and thickness (mm)) for Examples 1 to 5 above, as
well as the evaluation results for the film reflectivity 1, film
reflectivity 2, haze value (%), reflection color tone a/b, Taber
abrasion 1, Taber abrasion 2, surface roughness Ra (nm) and
contamination removal property for the resulting low reflection
glass sheets. The values for the reflected light hue
[(a.sup.2+b.sup.2).sup.1/2] calculated from the reflection color
tone were 4 or less in all the examples. TABLE-US-00002 TABLE 2
Example 1 Example 2 Example 3 Example 4 Example 5 Silica fine
particles Non- Non- Non- Non- Linear aggregated aggregated
aggregated aggregated (chain-like) aggregated Mean particle size 50
nm 50 nm 70 nm 110 nm 25 nm Binder content 20% 20% 15% 25% 20%
Silica fine particle content 80% 80% 85% 75% 80% Average film
thickness 128 nm 105 nm 123 nm 163 nm 120 nm Hydrolysis with
particles yes yes yes yes yes Fine particle density 800 750 500 180
2700 (1 .mu.m square) Base substrate (color, Green Green Green
Clear Green thickness mm) 3.4 3.4 2.0 2.8 3.4 Film reflectivity 1
1.3% 0.9% 0.6% 0.3% 0.4% Film reflectivity 2 4.7% 4.3% 4.0% 4.3%
3.6% Haze value (%) 0.1 0.2 0.1 0.2 0.1 Reflection color tone a/b
-1.3/-3.5 -1.2/-1.1 -1.0/-1.9 -1.5/-2.1 -1.1/-1.4 Taber Abrasion 1
.smallcircle. (1.3) .smallcircle. (1.2) .smallcircle. (1.0)
.smallcircle. (1.3) .smallcircle. (1.9) Taber Abrasion 2
.smallcircle. (1.8) .smallcircle. (1.6) .smallcircle. (1.5)
.smallcircle. (1.5) .smallcircle. (2.4) Ra (nm) 10.1 7.8 12.5 19.6
5.8 Contamination .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. removal property
[0092] As seen from Table 2, the low reflection glass of Examples 1
to 5 had a low value of 0.3-1.3% for the film reflectivity and
particularly for the film reflectivity 1 (reflectivity not
including the back side reflection), and a small haze value of
0.1-0.2 and thus excellent through visibility, while also
exhibiting excellent abrasion resistance and contamination removal
property.
[0093] When the reflectivity and reflection color tone were
measured after the manufactured low reflection glass of Examples 1
to 5 had been allowed to stand outdoors for 2 months, all of the
examples exhibited excellent durability, with no change in the
measured values before and after standing outdoors.
[0094] The low reflection glass obtained in Example 4 (with the low
reflection film facing outside) and the glass base substrate used
in Example 4 prior to coating of the low reflection film were each
used as the front cover glass for a polycrystalline solar cell (3
serially connected 57 mm 28 mm modules; characteristic values:
Pmax(W)=0.57, Voc(V)=1.7, Isc(mA)=450 AM 1.5, 100 mW/cm.sup.2,
25.degree. C.), for comparative measurement of the current values
generated in cloud-free weather. The current value of the former
was 397 mA and the current value of the latter was 387 mA, thus
indicating an approximately 3% increase in conversion efficiency by
the low reflection glass.
[0095] A water-repellent film was also coated onto the low
reflection film obtained in Example 4, in the following manner.
After dissolving 1 g of
CF.sub.3(CF.sub.2).sub.7(CH.sub.2).sub.2Si(OCH.sub.3).sub.3
(heptadecafluorodecyltrimethoxysilane, product of Toshiba Silicone)
in 98 g of ethanol, 1.0 g of 0.1 N hydrochloric acid was further
added and the mixture was stirred for one hour to obtain a
water-repellent treatment agent.
[0096] A cotton cloth was wetted with 3 ml of the water-repellent
treatment agent and was used to coat the surface of the low
reflection film of the low reflection glass sheet, after which the
excess attached water-repellent treatment agent was wiped off with
a unused cotton cloth, to obtain water-repellent treated glass.
[0097] The static water droplet contact angle of the
water-repellent treated glass with a 2 mg water droplet weight was
measured using a contact angle meter (CA-DT, product of Kyowa
Kaimen Kagaku Co.). The value of the contact angle was
approximately 125.degree., which was a larger value than the
approximately 105.degree. contact angle obtained by water-repellent
treatment of the untreated glass sheet surface in the same manner
as described above and exhibited excellent in water-repellency. The
anti-reflection performance and conversion efficiency of the low
reflection glass treated with the water-repellent agent were
excellent.
[0098] All of the film surfaces of Examples 1 to 5 had water
contact angles of 5.degree. or less as measured using a contact
angle meter (CA-DT, product of Kyowa Kaimen Kagaku Co.) with a 2 mg
water droplet weight, thus exhibiting excellent hydrophilicity.
[0099] The following examples (Examples 6-10) are applications to
solar cell glass sheets.
EXAMPLE 6
[0100] There were mixed 32.0 g of a first silica fine particle
dispersion ("SNOWTEX OL" by Nissan Chemical Co., Ltd., mean
particle size: 50 nm, solid portion: 20%) and 8.0 g of a second
silica fine particle dispersion ("SEAHOSTAR KE-W30" by Nippon
Shokubai Co., Ltd., mean particle size: 300 nm, particle size
standard deviation: 1.1, average ratio of long axis length to short
axis length: 1.02, solid portion: 20%) at a proportion of 4:1 in
terms of solid ratio, to obtain 40.0 g of a silica fine particle
dispersion (mean particle size: 50 nm, almost equivalent to mean
particle size of first silica fine particles). After then adding
52.6 g of ethanol, 0.5 g of 3 mole/L hydrochloric acid and 6.9 g of
tetraethoxysilane, the mixture was reacted for 12 hours to prepare
a coating solution. The coating solution was spin coated onto the
surface of a colorless transparent (clear) 4.0 mm thick float glass
base substrate having a composition of soda lime silicate glass
(visible light transmittance Ya=88.5%, total light
transmittance=88.5%, sunlight transmittance Tg=79.6%, ultraviolet
transmittance Tuv(iso)=52.0%, visible light reflectivity=7.7%,
Hunter color coordinate transmitted color L=94.3, a=-1.7, b=0.2,
reflected color L=27.8, a=-0.5, b=-0.6), and then held for 10
minutes in an electric oven at 500.degree. C., to obtain a low
reflection glass sheet coated with a low reflection film (average
film thickness: 250 nm) having a haze value of 5.1%.
EXAMPLE 7
[0101] While stirring 40 g of a silica fine particle dispersion
("KE-W50" by Nippon Shokubai Co., Ltd., mean particle size: 550 nm,
particle size standard deviation: 1.1, average ratio of long axis
length to short axis length: 1.02, solid portion: 20%), there were
added thereto 52.1 g of ethylcellosolve, 1 g of concentrated
hydrochloric acid and 6.9 g of tetraethoxysilane in that order, and
reaction was conducted while stirring for 240 minutes to obtain a
sol. A 3 g portion of ethylcellosolve and 4 g of hexyleneglycol
were then added to 3 g of this sol for dilution to prepare a
coating solution with a solid portion of 3%.
[0102] This coating solution was used to form a film by spin
coating onto one side of a float glass base substrate with the same
composition and thickness as in Example 4, and then it was placed
in a 700.degree. C. electric oven for 2 minutes to obtain a low
reflection glass sheet coated with a low reflection film with a
haze value of 51.7% (average thickness: 560 nm). The maximum
temperature reached by heating in the electric oven was 630.degree.
C.
EXAMPLE 8
[0103] While stirring 40 g of a silica fine particle dispersion
("KE-E70" by Nippon Shokubai Co., Ltd., mean particle size: 740 nm,
particle size standard deviation: 1.1, average ratio of long axis
length to short axis length: 1.02, solid portion: 20%), there were
added thereto 52.1 g of ethylcellosolve, 1 g of concentrated
hydrochloric acid and 6.9 g of tetraethoxysilane in that order, and
reaction was conducted while stirring for 240 minutes. A 4 g
portion of hexyleneglycol was then added to 6 g of this sol for
dilution to prepare a coating solution with a solid portion of 6%.
This coating solution was used to form a film by spin coating onto
one side of a float glass base substrate with the same composition
and thickness as in Example 7, and then it was placed in a
700.degree. C. electric oven for 2 minutes to obtain a low
reflection glass sheet coated with a low reflection film with a
haze value of 69.5% (average thickness: 750 nm).
EXAMPLE 9
[0104] While stirring 35 g of a silica fine particle dispersion
("KE-W30" by Nippon Shokubai Co., Ltd.,.mean particle size: 300 nm,
solid portion: 20%), there were added thereto 52.1 g of
ethylcellosolve, 1 g of concentrated hydrochloric acid and 10.4 g
of tetraethoxysilane in that order, and reaction was conducted
while stirring for 300 minutes. A 4 g portion of hexyleneglycol was
then added to 3 g of this sol for dilution to prepare a coating
solution with a solid portion of 3%. This coating solution was used
to form a film by spin coating onto one side of a float glass base
substrate with the same composition and thickness as in Example 7,
and then it was placed in a 700.degree. C. electric oven for 2
minutes to obtain a low reflection glass sheet coated with a low
reflection film with a haze value of 18.2% (average thickness: 320
nm).
EXAMPLE 10
[0105] A mixture of 16 g of the fine particle-containing hydrolyzed
solution used in Example 4 (mean particle size: 1 10 nm), 24 g of
the fine particle-containing hydrolyzed solution used in Example 7
(mean particle size: 550 nm), 20 g of ethylcellosolve and 40 g of
hexyleneglycol was prepared to obtain a coating solution. This
coating solution was coated by gravure coating onto the surface of
the same type of glass base substrate used in Example 6, and then
it was placed in a. 500.degree. C. electric oven for 10 minutes to
obtain a low reflection glass sheet coated with a low reflection
film with a haze value of 27.2% (average thickness: 570 nm).
[0106] There was no change in the reflectivities and reflection
color tones of the low reflection glass of Examples 6 to 10 upon
remeasurement after 2 months, and the measured values were all
within the range of instrument error.
[0107] Table 3 lists the silica fine particle form (as either
non-aggregated fine particles or linear (chain-like) aggregated
fine particles, or listed as "mixed" when two types of fine
particles are combined), the silica fine particle dimensions (mean
particle size), the binder content in the film (wt %), the silica
fine particle content (wt %), the. final film thickness (average
film thickness), whether the silicon alkoxide was hydrolyzed in the
presence of the silica fine particles during preparation of the
coating solution ("hydrolysis with particles"), the number of fine
particles in the film in a 100 square .mu.m area (10 .mu.m.times.10
.mu.m) as observed from above the film using an electron microscope
(fine particle density), and the type of glass sheet of the base
substrate(color and thickness (mm)) for Examples 6 to 10 above, as
well as the evaluation results for the film reflectivity 1 and 2,
reflection color tone a/b, contamination removal property, initial
haze value (%), initial total light transmittance (%) and the haze
value (%) and total light transmittance (%) after a fastness test
(1000 passes with load of 500 g/cm.sup.2) for the resulting low
reflection glass sheets. The values for the reflected light hue
[(a.sup.2+b.sup.2).sup.1 /2] calculated from the reflection color
tone were 4 or less in all the examples. As seen in Table 3, the
low reflection glass sheets obtained in Examples 6 to 8 and Example
10 had higher total light transmittance than the total light
transmittance of the glass base substrates, while the low
reflection glass sheet obtained in Example 9 had total light
transmittance roughly equivalent to the total light transmittance
of the glass sheet base substrate. The low reflection glass of
Examples 6 to 10 had high haze values and were therefore not very
suitable as window glass for automobiles or construction, but they
could be suitably used as solar cell base substrate glass sheets or
solar water heater glass sheets. TABLE-US-00003 TABLE 3 Example 6
Example 7 Example 8 Example 9 Example 10 Silica fine particles Non-
Non- Non- Non- Non- aggregated/ aggregated aggregated aggregated
aggregated/ mixture mixture Mean particle size 50 nm 550 nm 740 nm
300 nm 160 nm Binder content 20% 20% 20% 30% 22% Silica fine
particle content 80% 80% 80% 70% 78% Average film thickness 250 nm
560 nm 750 nm 320 nm 570 nm Hydrolysis with particles yes yes yes
yes yes Fine particle density 650 100 30 300 6500 (10 .mu.m square)
Base substrate (color, Clear Clear Clear Clear Clear thickness mm)
4.0 2.8 2.8 2.8 4.0 Film reflectivity 1 0.5% 0.2% 0.2% 0.3% 0.2%
Film reflectivity 2 4.3% 2.6% 2.9% 3.9% 3.4% Reflection color tone
a/b -1.9/0 1.0/-1.3 -0.3/0.8 -0.8/-0.8 -0.1/0.9 Contamination
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. removal property Initial haze value (%) 5.1 51.7 69.5
18.2 27.1 Initial total light 91.5 91.2 90.5 89.5 91.4
transmittance (%) After fastness test Haze value (%) 5.3 52.6 70.8
19.0 28.5 Total light transmittance (%) 91.4 91.3 90.7 89.5
91.2
[0108] In Examples 6 to 10, the changes in the film reflectivities
1 and 2 and the reflection color tones were within the measuring
error ranges for the spectrophotometer, and no change was found in
the optical thickness. After the fastness test, the haze values
increase slightly,. but the total light transmittances were
virtually unchanged, and therefore since there was no decrease in
diffused transmitted light due to scattering of light by the fine
particles, this demonstrated that the fine particles had adhered
firmly to the glass base substrates.
COMPARATIVE EXAMPLE 1
[0109] After adding 45 g of ethanol, 8.67 g of tetraethoxysilane
and g of concentrated hydrochloric acid in that order to 12.5 g of
a silica fine particle dispersion ("SNOWTEX OL" by Nissan Chemical
Co., mean particle size: 50 nm, solid portion: 20%), the mixture
was stirred for 24 hours for hydrolysis reaction. This was further
diluted with ethylcellosolve to obtain a coating solution
(containing silica fine particles and ethyl silicate in a weight
ratio of 1:1 in terms of silica).
COMPARATIVE EXAMPLE 2
[0110] After mixing 36.8 g of ethanol and 7.2 g of 3 mole/L
hydrochloric acid to 15.2 g of tetramethoxysilane, the mixture was
reacted for 12 hours to hydrolyze the tetramethoxysilane. This
hydrolyzed solution was then mixed with 160 g of a
linear(chain-like) aggregated silica fine particle dispersion
("SNOWTEX-OUP" by Nissan Chemical Co., mean primary particle size:
25 nm, solid portion: 15%) to prepare a coating solution.
COMPARATIVE EXAMPLE 3
[0111] After adding 29 g of ethylcellosolve and 10 g of 1 mole/L
hydrochloric acid to 21 g of tetraethoxysilane while stirring, the
mixture was reacted for 12 hours. A 3.3 g portion of this reaction
solution was mixed with 3.3 g of a silica fine particle dispersion
("SNOWTEX OL", by Nissan Chemical Co., mean particle size: 50 nm,
solid portion: 20%) and diluted with ethylcellosolve to obtain a
coating solution.
COMPARATIVE EXAMPLE 4
[0112] After adding 74.53 g of ethanol, 3.47 g of tetraethoxysilane
and 2 g of concentrated hydrochloric acid in that order to 20 g of
a silica fine particle dispersion ("SNOWTEX O" by Nissan Chemical
Co., mean particle size: 30 nm, solid portion: 20%), the mixture
was stirred for 18 hours for hydrolysis reaction. This was further
diluted with ethylcellosolve to obtain a coating solution
(containing silica fine particles and ethyl silicate in a weight
ratio of 4:1 in terms of silica).
COMPARATIVE EXAMPLE 5
[0113] Twenty grams of a silica fine particle dispersion ("SNOWTEX
O" by Nissan Chemical Co., mean particle size: 30 nm, solid
portion: 20%) and g of a hydrolyzed polycondensate of ethyl
silicate (trade name: HAS-10 by Colcoat Co., Ltd., Sio.sub.2 10 wt
% content) were added in that order to 70 g of ethanol to prepare a
coating solution (containing silica fine particles and ethyl
silicate in a weight ratio of 4:1 in terms of silica).
COMPARATIVE EXAMPLE 6
[0114] After mixing 8.4 g of tetramethoxysilane, 53.8 g of ethanol
and 4.5 g of 3 mole/L hydrochloric acid, the mixture was reacted
for 24 hours to obtain a hydrolyzed solution. After further adding
33.3 g of a silica fine particle dispersion ("SNOWTEX OL", by
Nissan Chemical Co., mean particle size: 50 nm, solid portion:
20%), ethylcellosolve was added for dilution to obtain a coating
solution.
COMPARATIVE EXAMPLE 7
[0115] After mixing 8.4 g of tetramethoxysilane, 57.3 g of ethanol
and 1.0 g of 3 mole/L hydrochloric acid with 33.3 g of a silica
fine particle dispersion ("SNOWTEX O", by Nissan Chemical Co., mean
particle size: 30 nm, solid portion: 20%), the mixture was reacted
for 12 hours for hydrolysis of the tetramethoxysilane to prepare a
coating solution. This was used for coating, drying and heat
treatment in the same manner as Example 1 using the same type of
glass base substrate as in Example 1 (green colored, 3.4 mm
thickness) to obtain a glass sheet having a silica irregular film
with a thickness of 125 nm formed on each surface thereof.
[0116] The coating solutions prepared in Comparative Examples 1 to
7 were used for the same coating and heat treatment as in Example
1, using the same type of glass base substrate used in Example 1
(green colored, 3.4 mm thickness), except that the heat treatment
was carried out for 10 minutes in a 600.degree. C. electric oven
instead of the heat treatment for 2 minutes in the 700.degree. C.
electric oven in Example 1, to obtain glass coated with silica
irregular films having the thicknesses shown in Tables 4 and 5. The
evaluation results for the glass sheets are shown in Tables 4 and
5. The indication "undetermined" under the column "Fine particle
density" means that the fine particles were embedded in the binder
so that the number of fine particles could not be counted.
[0117] The results in Table 4 demonstrate the following for each of
the comparative examples. The film reflectivity was higher in
Comparative Example 1 in which the binder content exceeded 40%. The
abrasion resistance and contamination removal property were
inferior in Comparative Examples 2 and 5 in which the mean particle
size of the non-aggregated silica fine particles was less than 40
nm and no "hydrolysis with silica fine particles" had been carried
out. The film reflectivity was also higher and the abrasion
resistance inferior in Comparative Example 3 in which no
"hydrolysis with silica fine particles" had been carried out. In
Comparative Example 4 in which the mean particle size of the
non-aggregated silica fine particles was less than 40 nm, the film
reflectivity, and especially the film reflectivity 1 not including
the back side reflectivity, was high and the contamination removal
property was inferior. The abrasion resistance was inferior in
Comparative Example 6 in which the binder content exceeded 40% and
no "hydrolysis with silica fine particles" had been carried out.
The film reflectivity was high in Comparative Example 7 in which
the mean particle size of the non-aggregated silica fine particles
was less than 40 nm and the binder content exceeded 40%.
TABLE-US-00004 TABLE 4 Compar- Compar- Compar- Compar- ative ative
ative ative Example 1 Example 2 Example 3 Example 4 Silica fine
Non- Linear Non- Non- particles aggre- (chain-like) aggre- aggre-
gated aggregated gated gated Mean particle 50 nm 25 nm 50 nm 30 nm
size Binder content 50% 20% 33% 20% Silica fine 50% 80% 67% 80%
particle content Average film 125 nm 110 nm 120 nm 110 nm thickness
Hydrolysis with yes no no yes particles Fine particle 850 2800 650
2500 density (1 .mu.m square) Base substrate Green Green Green
Green (color, 3.4 3.4 3.4 3.4 thickness mm) Film reflec- 2.4 0.5
1.9 1.9 tivity 1 (%) Film reflec- 5.8 3.8 5.3 5.3 tivity 2 (%) Haze
value (%) 0.1 5.1 0.4 0.1 a/b -1.2/-1.0 -1.5/-0.5 -1.4/-0.1
-1.1/-1.0 Taber abrasion 1 .smallcircle. (1.5) x x .smallcircle.
(1.2) Taber abrasion 2 .smallcircle. (1.6) x x .smallcircle. (1.40
Contamination .smallcircle. x .smallcircle. .DELTA. removal
property
[0118] TABLE-US-00005 TABLE 5 Comparative Comparative Comparative
Example 5 Example 6 Example 7 Silica fine particles Non- Non- Non-
aggregated aggregated aggregated Mean particle size 30 nm 50 nm 30
nm Binder content 20% 67% 67% Silica fine particle 80% 33% 33%
content Average film 110 nm 130 nm 120 nm thickness Hydrolysis with
no no yes particles Fine particle density 2300 800 undetermined
Base substrate Green Green Green (color, thickness mm) 3.4 3.4 3.4
Film reflectivity 1 (%) 1.9 1.6 3.3 Film reflectivity 2 (%) 5.4 4.9
6.7 Haze value (%) 0.1 0.2 0.1 a/b -1.2/0.1 -1.4/-0.6 -1.1/-1.0
Taber abrasion 1 x x .smallcircle. (1.2) Taber abrasion 2 x x
.smallcircle. (1.4) Contamination x .smallcircle. .smallcircle.
removal property
COMPARATIVE EXAMPLE 8
[0119] One side of a float glass base substrate with the same
composition and thickness as the one used in Example 4 was rubbed
with #100 polishing sand to prepare surface-roughened frosted
glass. The haze value and total light transmittance of the frosted
glass were measured with a haze meter. The haze value was 82.6% and
the total light transmittance was 75.4%. The mechanical strength of
the frosted glass fell to about 40% of the original glass
strength.
COMPARATIVE EXAMPLE 9
[0120] Frosted glass was prepared in the same manner as Comparative
Example 8 except that # 1000 polishing sand was used instead of the
#100 polishing sand in Comparative Example 8, and the haze value
and total light transmittance thereof were measured. The haze value
was 81.4% and the total light transmittance was 83.0%. The
mechanical strength of the frosted glass fell to about 50% of the
original glass strength.
INDUSTRIAL APPLICABILITY
[0121] According to the present invention, a coating solution
obtained by hydrolysis of a hydrolyzable metal compound in the
presence of silica fine particles is used, with relatively large
silica fine particles or with a specified proportion of silica fine
particles and binder, to obtain much lower reflectivity and high
film strength, while improving contamination removal and
eliminating changes in reflectivity with time.
[0122] Also according to the present invention, warping of the
glass due to film contraction is completely eliminated even when
the glass base substrate is heated at above the softening
temperature. This is because the film is composed of mainly silica
fine particles that undergo almost no contraction, and therefore
the bond between the film and glass is reduced and the contact
between the particles is minimal. Particularly in the case of a
film obtained by co-hydrolysis, the binder concentration on the
surfaces of the silica fine particles increases, such that the
binder forms no film on the glass base substrate surface and the
contraction force of the binder does not act as easily on the
glass. Consequently, even with formation into a curved shape such
as for automobile glass, for example, the same working may be
carried out as for film-free glass, and production costs may
therefore be reduced. It is suitable also for uses such as solar
cell base substrates and building windows as well, since the
flatness of the glass can be maintained even when high temperature
treatment is carried out for enhanced film strength.
[0123] Also according to the present invention, the uppermost
surface of the low reflection glass has an irregular shape, so that
the hydrophilicity of the silicon dioxide is improved and the glass
surface is more resistant to fogging by moisture adhesion. Even
when water droplets adhere, the contact angle is small and the
surface is highly hydrophilic, and therefore contamination such as
dust is easily washed off. Since the water droplets do not easily
remain, the glass has a contamination resistant property whereby
contamination such as water tracks are less prone to form on the
surface.
[0124] A single layer low reflection film according to the
invention not only is less costly to manufacture than a multilayer
film, but its reflectivity performance also provides lower
reflection across a wide wavelength range and less increase in
reflectivity with respect to the incident angle, while the degree
of reflected light hue is also smaller. Such performance is useful
particularly for automobile window and solar cell glass sheets. The
lower reflection increases light transmittance and thus offers
suitability for glass of solar cells that convert light to other
forms of energy, while it is possible to obtain low reflection
glass articles having total light transmittance that is equivalent
to or higher than the total light transmittance of the glass base
substrates used, and particularly total light transmittance of 88%
or greater.
[0125] The low reflection glass articles of the invention can be
used for window glass of vehicles such as automobiles, trains and
the like that require particularly good through visibility and
recognizability with low reflection of objects inside the vehicles;
for front glass sheets of building windows, show windows, image
display devices and the like or optical glass articles; for front
glass sheets of solar water heaters; and for glass sheets in solar
cells such as the front glass sheets of solar cell panels or the
glass sheets use for solar cell base substrates.
* * * * *