Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Primarily organic continuous liquid phase
Reexamination Certificate
1999-12-07
2001-09-18
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Primarily organic continuous liquid phase
C106S286600, C106S287340, C516S079000, C516S084000
Reexamination Certificate
active
06291535
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sols comprising silica-magnesium fluoride hydrate composite colloidal particles which are suitably used in anti-reflection coating materials for forming anti-reflection coatings onto substrates such as lenses, transparent plastics, plastic films, and display surfaces of cathode ray tubes, liquid crystal display devices as well as a process for their preparation.
PRIOR ARTS
In general, lenses, transparent plastics, plastic films, and display surfaces of cathode ray tubes, liquid crystal display devices are subjected to anti-reflection treatments in order to reduce reflection of external lights such as a sunlight and a lamplight and increase their optical transmittance. The anti-reflection treatment is effected by a vacuum deposition method or a coating method. A substance having a low refractive index such as magnesium fluoride or silica is used in an outermost layer of a coating.
Especially, it has been known that a magnesium fluoride sol and a silica sol are effective as microfillers for anti-reflection coating materials.
Reports concerning the magnesium fluoride sols are set forth below.
JP 64041149A proposes prevention of reflection by coating a screen panel of a cathode ray tube with a sol liquid comprising fine particles of magnesium fluoride having a particle size of 100 to 200 Angstroms. However, it does not describe a process for the preparation of the sol liquid.
JP 2026824A proposes aqueous and orcano magnesium fluoride sols, each having an optical transmittance of 50% or more, a coated product obtained by coating a substrate surface with the sol and drying, and a process for the preparation of the aqueous magnesium fluoride sol comprising the steps of simultaneously adding and reacting an aqueous magnesium salt solution and an aqueous fluoride solution to produce a gel-like precipitates, heating and aging the resultant reaction liquid and then removing an electrolyte remaining in the liquid. It describes that magnesium fluoride colloid particles obtained by the above process have very small particle size ranging from 100 to 120 Angstroms. While, it describes that a sol obtained by adding an aqueous potassium fluoride solution to an aqueous magnesium chloride solution has a colloidal particle size of 100 to 300 Angstroms, an opaque milky color and an optical transmittance of 20% or lower.
JP 7069621A describes a magnesium fluoride hydrate sol and a process for its preparation. And, it describes that the sol is used in an anti-reflection coating material.
Many other silica sols have also beer. proposed. For example, JP 8122501A describes an anti-reflection coating of a low refractive index comprising a silica sol having a particle size of 5 to 30 nm and a hydrolysate of alkoxysilane.
However, a silica-magnesium fluoride composite sol has not been reported.
Problems to be Solved by the Invention
Since the above-mentioned magnesium fluoride and magnesium fluoride hydrate colloidal particles themselves are inferior in bond strength, they should be combined with organic or inorganic binders to provide an anti-reflection coating material. The magnesium fluoride and magnesium fluoride hydrate sols have low refractive indexes, but they are weakly bound to binders so that a coating prepared therefrom does not have sufficient bond strength. On the other hand, the silica sol has sufficient bond strength, but its refractive index is not low. A coating prepared from the silica sol together with an organic binder does not have a low refractive index although it has high bond strength.
A sol having both a low refractive index inherent in magnesium fluoride and a bonding property inherent in silica sol and a process for easily preparing the same are desired.
An object of the present invention is to provide a novel silica-magnesium fluoride hydrate composite sol used in an anti-reflection coating for reducing reflection of an external light and increasing an optical transmittance as well as a process for easily preparing the sol.
[Method for Solving Problems]
The present invention relates to a sol comprising silica-magnesium fluoride hydrate composite colloidal particles having a primary particle size of 5 to 50 nm and a ratio of silica to magnesium fluoride hydrate MgF
2
.nH
2
O, n being in the range between 0.25 to 0.5, in terms of a SiO
2
/MgF
2
weight ratio of from 0.01 to 5.
A process for the preparation of an aqueous sol comprising silica-magnesium fluoride hydrate composite colloidal particles of the present invention comprises the following steps (a) and (b):
(a) adding an aqueous fluoride solution to a mixture liquid of a silica sol having a primary particle size of 3 to 20 nm and an aqueous magnesium salt solution such that a F/Mg molar ratio ranges from 1.9 to 2.1 to produce a slurry of an agglomerate comprising silica-magnesium fluoride hydrate composite colloidal particles; and
(b) removing the salts thus-formed as by-products from the slurry of the agglomerate comprising silica-magnesium fluoride hydrate composite colloidal particles obtained from the step (a).
And, a process for the preparation of an organosol comprising silica-magnesium fluoride hydrate composite colloidal particles of the present invention comprises the above steps (a) and (b) and the following step (c): (c) replacing water in the aqueous sol comprising silica-magnesium fluoride hydrate composite colloidal particles obtained from the step (b) with an organic solvent.
DETAILED DESCRIPTION OF THE INVENTION
A silica sol having a primary particle size of 3 to 20 nm used in the present invention can be prepared by any one of the known methods including a method using water glass as a starting material such as ion-exchanging, heating, spherizing and concentrating and a method of hydrolyzing ethyl or methyl silicate. It is also commercially available. Primary particle size is determined by the BET method, the Shears method or the electron-microscopic method. The above silica sol has generally a pH of 2 to 10, but any other sol can be used.
Magnesium salt used in the present invention is a water-soluble salt, including magnesium chloride, magnesium nitrate, magnesium sulfate, magnesium sulfamate, magnesium acetate, magnesium formate. The magnesium salt may be used alone or in combination. It may be used in the form of a normal salt or an acid salt.
Fluoride used in the present invention is a water soluble salt, including sodium fluoride, potassium fluoride, cesium fluoride, rubidium fluoride, ammonium fluoride, guanidine fluoride, quaternary ammonium fluoride, acidic ammonium fluoride, hydrogen fluoride. The fluoride may be used alone or in combination.
In the preparation of the silica-magnesium fluoride hydrate composite sol of the present invention, it is important that an aqueous fluoride solution should be added to a mixture liquid of a silica sol having a primary particle size of 3 to 20 nm and an aqueous magnesium salt solution with a mixing ratio in terms of a F/Mg molar ratio of from 1.9 to 2.1.
Simultaneous addition of an aqueous fluoride solution and a mixture liquid of a silica sol and an aqueous magnesium salt solution in such stoichiometric amounts of the magnesium salt and the fluoride as to produce magnesium fluoride and addition of a mixture liquid of a silica sol and an aqueous magnesium salt solution to an aqueous fluoride solution are not efficient processes for preparing a desired silica-magnesium fluoride hydrate sol.
The addition and mixing of the aqueous fluoride solution into the mixture liquid of the silica sol and the aqueous magnesium salt solution in the step (a) of the process of the present invention can be carried out with stirring using an apparatus such as a Satake type impeller, a Pfaudler type impeller, a disper and a homogenizer at the temperature of 0 to 100° C. for 0.1 to 10 hours.
Preferably, a concentration of the silica-magnesium fluoride hydrate composite colloid resulting from the step (a) is adjusted within the range between 0.1 and 10% by weight.
In the step (a), silica colloidal particles having
Koyama Yoshinari
Suzuki Keitaro
Tanegashima Osamu
Watanabe Yoshitane
Lovering Richard D.
Nissan Chemical Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Silica-magnesium fluoride hydrate composite sols and process... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Silica-magnesium fluoride hydrate composite sols and process..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silica-magnesium fluoride hydrate composite sols and process... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2519319