Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2001-08-27
2004-03-30
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S328000, C428S330000, C428S331000, C428S402000, C428S409000, C428S143000, C428S148000, C428S149000, C428S206000, C428S212000, C428S217000, C106S286600, C106S286300
Reexamination Certificate
active
06713170
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to transparent hard coating materials comprising silica-magnesium fluoride hydrate composite colloidal particles and a UV-curable or heat-curable resin suitable for use as antireflection coating materials for lenses, transparent plastics, plastic films and surface of display screens such as cathode ray tubes or liquid crystal displays, and more specifically to hard coating materials for conferring scratch resistance and chemical resistance on the surfaces of films or sheets of plastics such as polyesters, acrylics, polycarbonates, TAC (triacetate) or glasses and forming a hard coating layer with high transparency and low refractivity.
BACKGROUND OF THE INVENTION
Generally, the surfaces of lenses, transparent plastics, plastic films and surface of display screens such as cathode ray tubes or liquid crystal displays are subjected to antireflection treatments to reduce reflection of external light such as sunlight or electric light and increase light transmittance. Antireflection treatments are typically effected by a vacuum deposition method or a coating method, in which a low refractive material such as magnesium fluoride or silica is used for the outermost layer. In this case, magnesium fluoride sols and silica sols are known to be effective as microfillers for antireflection coating materials.
Magnesium fluoride sols have been reported as follows. JP 64041149A proposes a method for conferring antireflective properties by coating the screen panel of a cathode ray tube with a sol liquid comprising magnesium fluoride microparticles having a particle diameter of 100-200 angstroms. However, no processes for preparing this sol are described. JP 2026824A proposes aqueous and organo magnesium fluoride sols having a light transmittance of 50% or more, coated products obtained by applying and drying said sols on the surface of a substrate as well as a process for preparing an aqueous magnesium fluoride sol comprising the steps of reacting an aqueous solution of a magnesium salt with an aqueous solution of a fluoride by a simultaneous addition method to produce gel-like precipitates followed by heating and aging the resulting reaction solution and then removing electrolytes in the solution. Colloidal particles of magnesium fluoride obtained by this process have a very small particle diameter of 100-120 angstroms. However, sols obtained by adding an aqueous solution of potassium fluoride to an aqueous solution of magnesium chloride are reported to be opaque white and have a colloidal particle diameter of 100-300 angstroms and a transmittance of 20% or less. JP 7069621A discloses a magnesium fluoride hydrate sol and a process for the process thereof as well as the use thereof as an antireflection coating material.
Many proposals have been made about silica sols, and JP 80122501A discloses antireflection film having a low refractive index which comprises a silica sol having a particle diameter of 5-30 nm and a hydrolyzate of alkoxysilane. However, a silica-magnesium fluoride composite sol has not been reported to date.
When the magnesium fluoride and magnesium fluoride hydrate colloidal particles described above are used as antireflection coating materials, an organic or inorganic binder is needed because the bond strength of the coating materials is weak. Magnesium fluoride and magnesium fluoride hydrate sols have a low refractive index, but their bond strength to binders is weak so that the resulting films have an insufficient strength. Silica sols have a sufficient bond strength, but their refractive index is not sufficiently low so that the films prepared by combining them with an organic binder have a high strength but not a low refractive index. Therefore, there is a demand for the development of a composition for conveniently providing an antireflection coating having a lower refractive index and a good film strength.
DISCLOSURE OF THE INVENTION
As a result of our earnest investigations to solve the above problems, we accomplished the present invention. Accordingly, the present invention relates to:
(1) a transparent hard coating material comprising a UV-curable resin having one or more (meth)acryloyl groups in one molecule or a heat-curable resin and silica-magnesium fluoride hydrate composite colloidal particles such that the transparent film obtained by curing said transparent hard coating material has a refractive index of 1.48 or less;
(2) the transparent hard coating material as defined in (1) wherein the silica-magnesium fluoride hydrate composite colloidal particles have an average particle diameter of 0.5 &mgr;m or less;
(3) the transparent hard coating material as defined in (1) or (2) wherein the silica-magnesium fluoride hydrate composite colloidal particles are obtained from a sol of silica-magnesium fluoride hydrate composite colloidal particles having a ratio of silica to magnesium fluoride hydrate (MgF
2
.nH
2
O where n is 0.25-0.5) of 0.01-5 in an SiO
2
/MgF
2
weight ratio, and a primary particle diameter of 5-50 nm;
(4) the transparent hard coating material as defined in (3) wherein the sol of silica-magnesium fluoride hydrate composite colloidal particles is an organosol;
(5) the transparent hard coating material as defined in (4) wherein the organosol of silica-magnesium fluoride hydrate composite colloidal particles is obtained by the steps of:
(a) adding an aqueous solution of fluorides to a mixture of a silica sol having a primary particle diameter of 3-20 nm and an aqueous solution of magnesium salts in an F/Mg molar ratio of 1.9-2.1 to produce a slurry comprising aggregates of silica-magnesium fluoride hydrate composite colloidal particles,
(b) removing by-produced salts in the slurry obtained in step (a), and
(c) replacing water of the aqueous sol obtained in step (b) with an organic solvent; and
(6) a film having a hard coating layer obtained by applying and curing the transparent hard coating material as defined in any one of (1) to (5).
BEST EMBODIMENT FOR CARRYING OUT THE INVENTION
The present invention is explained in detail below.
The transparent hard coating materials of the present invention comprises a UV-curable resin having one or more (meth)acryloyl groups in one molecule acting as a UV-curable resin binder or a heat-curable resin acting as a heat-curable resin binder and silica-magnesium fluoride hydrate composite colloidal particles. These transparent hard coating materials can be cured by irradiation with UV light or heating to form a transparent cured film having a refractive index of 1.48 or less.
UV-curable resins having one or more (meth)acryloyl groups in one molecule used in the invention preferably have a refractive index as low as possible, for example, that lower than about 1.48. For example, in order to primarily increase the strength of the coating film such as scratch resistance and solvent resistance, polyfunctional acrylates having two or more (meth)acryloyl groups are preferable. These UV-curable resins function as a binder resin for binding between silica-magnesium fluoride hydrate composite colloidal particles and between the particles and a substrate.
Specific examples of UV-curable resins having one (meth)acryloyl groups in one molecule include, for example, trifluoroethyl acrylate, trifluoromethyl acrylate, phenylglycidyl acrylate, hydroxyethyl (meth)acrylate, tetrahydrofurfuryl acrylate, acryloyl morpholine, N-vinylpyrrolidone and N-vinyl-&egr;-caprolactam.
Polyfunctional acrylates having two or more (meth)acryloyl groups include, for example, polyol poly(meth)acrylates such as neopentylglycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate; epoxy (meth)acrylates such as di(meth)acrylate of bisphenol A diglycidyl ether, di(meth)acrylate of neopentylglycol diglycidyl ether, di(meth)acrylate of 1,6-hexanediol diglycidyl ether; polyester (meth)acrylates obtained by esterifying a pol
Kaneko Shoichi
Koyama Yoshinari
Suzuki Keitaro
Takahashi Takeshi
Tanegashima Osamu
Nields & Lemack
Nippon Kayaku Kabushiki Kaisha
Rickman Holly
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