Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
2001-06-21
2004-01-20
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C423S339000
Reexamination Certificate
active
06680040
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fine particle prepared by coating a surface of a porous composite oxide particle with a silica-based inorganic oxide layer. Also the present invention relates to a sol prepared by dispersing said fine particles in a dispersion medium and a production method for the same as well as to a substrate with an anti-reflection coating film containing said fine particles formed on the surface thereof.
BACKGROUND TECHNOLOGY
The present inventors previously made an invention of silica sol as well as of composite oxide sol such as silica-alumina sol and silica-zirconia sol in which fine and porous particles each having a large specific surface area are dispersed (Japanese Patent Laid-Open Publication No. HEI 5-132309). The composite oxide sol is used by making use of its porosity for various applications such as a binder, an absorbent, a filler having low refractive index and others, in addition to its use as a catalyst.
Further to prevent reflection on a surface of a substrate such as glass or plastic sheet, there has been known the technology for forming an anti-reflection coating film on the surface, and for instance, a coating film made from a low refractive index substance such as a fluorine resin or fluoride magnesium is formed on a surface of a glass or plastic sheet by means of the coating method, the evaporation method, or the CVD method. These methods are, however, expensive in the cost, and the durability is not so high.
There has been known also the method in which an anti-reflection coating film having fine and uniform convex and concave sections is made from fine particles of silica by applying a coating liquid containing fine particles of silica on a surface of a glass sheet. In this method, the reflection is prevented by making use of the effect that normal reflection is reduced by random reflection of light on an irregular surface made from fine particles of silica, or by making use of an air layer in clearance between the fine particles, but it is difficult to fix the particles on the surface of the substrate or to form a single layer coating film, so that it is not easy to control the refractive index on the surface.
Further the present inventors have proposed a sol in which fine particles of composite oxide with low refractive index prepared by completely coating surfaces of porous fine particles with silica is dispersed (Refer to Japanese Patent Laid-Open Publication No. HEI 7-133105). To coat the fine particles completely, however, the step of coating the particles repeatedly or the step of subjecting the fine particles to heat processing is required, and further as a solvent such as water or alcohol is sealed in the coated particles, so that there is a limit in reduction of the refractive index. In addition, it has been found that a film or a resin plate obtained by dispersing the particles in resin or the like has weak adhesion between the resin and the particles, and further that also strength of the anti-refection film prepared with such the material as described above is rather low.
The present inventors disclosed the fact that silica particles each having an organic group directly bonded to silicon have high affinity with organic solvents or resins and are easily monodispersed in water. With the silica particles, particles hardly drop off from a mold prepared by mixing the silica particles in a resin, but it is impossible to completely prevent the particles from dropping off from the mold. Further particles with low refractive index, which can be used as a filler for adjusting a refractive index, have not been obtained.
Further even if a coating film is formed on a substrate such as glass or plastic sheet using a substance having a low refractive index such as silica fluorine resin or magnesium fluoride, when there is no mutual solubility (affinity) between the coating film made from the low refractive index substance and the substrate, the adhesiveness with the substrate is often low. In addition, the capability of preventing reflection may be insufficient according to used substrates.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a variety of fine particles having a structure wherein a porous composite oxide particle is coated with a porous silica-based inorganic oxide layer. It is also an object of the present invention to provide a sol with said fine particles, method for preparing the sol, and a substrate having a coating film comprising the fine particles thereon, which has a low refractive index and excellent in adhesion with a resin or the like, strength, the ability to reduce reflection and the like.
Fine particles according to the present invention are porous fine particles of composite oxide comprising silica and an inorganic oxide other than silica, wherein said fine particles are coated with a porous silica-based inorganic oxide layer having a thickness from 0.5 to 20 nm.
The maximum pore diameter of said silica-based inorganic oxide layer is preferably in the range from 0.5 to 5 nm.
The molar ratio (MO
x
/SiO
2
) is preferably in the range from 0.0001 to 0.2, when silica is expressed by SiO
2
and the inorganic oxide other than silica is expressed by MO
x
.
The pore volume of said fine particles is preferably in the range from 0.1 to 1.5 cc/g and the particles further comprise a second silica coating film layer coated thereon preferably.
The fine particles include preferably an organic group directly bonded to silicon, and S
R
/S
T
, the ratio of the molar amount of silicon having the organic group directly bonded thereto (S
R
) vs the molar amount of the total silicon (S
T
), is preferably in the range from 0.001 to 0.9.
A method of producing fine particle dispersion sol according to the present invention comprises the steps of:
(a) preparing a dispersion liquid of core particle precursor by concurrently adding an aqueous solution of a silicate and/or an acidic silicate solution, a hydrolyte of an organic silicon compound expressed by the formula (1), and a solution of an alkali-soluble inorganic compound to an alkaline aqueous solution with the pH value of 10 or more, or to an alkaline aqueous solution with the pH value of 10 or more in which species particles are dispersed, if necessary;
(b) forming a first silica-based coating film layer on the core particle precursor by adding a silica source or an aqueous solution of the silica source and any inorganic salt other than silica to said dispersion liquid of core particle precursor; and
(c) selectively removing at least a portion of elements other than silicon and oxygen from among those constituting said core particle precursor by adding an acid to said dispersion liquid;
R
n
SiX
(4−n)
(1)
[wherein R indicates a non-substituted or substituted hydrocarbon comprising 1 to 10 carbon elements; X indicates an alkoxy group containing 1 to 4 carbon elements, a silanol group, halogen, or hydrogen, and n indicates a number from 1 to 3].
The producing method according to the present invention further comprises preferably the step of forming a second silica coating film layer on said fine particles by adding an alkaline aqueous solution, an organic silicon compound expressed by the formula (2) and/or a partial hydrolyte thereof to the fine particle dispersion sol prepared in the step (c).
R
n
SiX
(4−n)
(2)
[wherein R indicates a not-substituted or substituted hydrocarbon comprising 1 to 10 carbon elements; X indicates an alkoxy group containing 1 to 4 carbon elements, a silanol group, halogen, or hydrogen, and n indicates a number from 0 to 3]
Said method further comprises preferably the step of eliminating pores in the second silica coating film layer by heating the fine particle dispersion sol under the temperature from 50° C. to 350° C.
A substrate with a coating film according to the present invention is characterized in that said coating film contains the above-mentioned fine particles and a matrix for forming a coating film.
The refractive index of said
Komatsu Michio
Nakai Mitsuru
Nishida Hiroyasu
Yoshitome Hiroo
Catalysts & Chemicals Industries Co. Ltd.
Johnson Edward M.
Kanesaka & Takeuchi
Silverman Stanley S.
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