Stock material or miscellaneous articles – Composite – Of fluorinated addition polymer from unsaturated monomers
Reexamination Certificate
1998-06-10
2001-06-12
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of fluorinated addition polymer from unsaturated monomers
C428S447000, C428S448000, C428S480000, C428S688000
Reexamination Certificate
active
06245428
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to low reflective transparent polyermic film.
2. Discussion of Prior Art
The transparency of windows, show cases, glass, viewers or video screens can be effected by glass, reflective light sources, or the reflection of surrounding scenery. In order to ameliorate the problem with glare and reflections, anti-reflective coatings have been developed which are typically applied to a surface by vapour deposition or sputtering methods.
Another method for depositing anti reflective coatings is disclosed in U.S. Pat. No. 4,687,707 in which the coating is formed from a thin layer of a reaction product containing a metal oxide e.g. SiO
2
or TiO
2
. Such a product results from the condensation of titanium tetra-alkoxides, titanium chelates or tetraalkoxy silanes. To this layer, is added a second layer of a condensation product containing a fluorine compound such as fluorine containing silane compounds. This multi layer construction bringing about an improvement in the reduction of reflectance.
U.S. Pat. No. 4,966,812 discloses the deposition of a low refractive index anti-reflective coating on plastics material using sol-gel techniques. U.S. Pat. No. 5,109,080 discloses a high refractive index ceramic/polymer material which is made from a sol-gel synthesis of a metal alkoxide with an alkoxysilane-capped poly(arylene ether) polymeric component.
EP 0166363 discloses the use of at least two thin layers as a low reflective coating, a first layer containing metal oxide and having a refractive index in the range of 1.65-2.10, and a second over layer comprising a fluorine-containing silicon compound making a low refractive index having a refractive index of about 1.4.
SUMMARY OF THE INVENTION
The present invention provides a transparent polymeric film having an anti-reflective coating, the coating being a novel coating.
According to the invention there is provided an anti-reflective film comprising a transparent polymeric film substrate coated with at least two polymeric layers, the two layers being an exposed outer polymeric layer comprising a fluorine containing polymer and an inner organometallic reflective layer adjacent the exposed layer and comprising the condensation product of a metal alkoxide and a polymer reactive with the metal alkoxide.
Preferably the inner organometallic polymeric layer has a refractive index of at least 1.6, more preferably 1.7 and the outer layer has a refractive index not greater than 1.45, and preferably not greater than 1.4.
Additional optically active layers of a desired refractive index may be coated onto the film substrate between said substrate and said inner layer and said additional layer or layers may be the same as the inner and outer layers, or different as is required.
Also according to the invention there is provided an anti-reflective film comprising a transparent polymeric film substrate, an exposed outer polymeric layer comprising fluorine containing polymers having a refractive index not greater than 1.45 and a thickness in the order of ¼ wavelength, and an inner polymeric layer adjacent the exposed outer layer containing metal oxide and having a refractive index of at least about 1.6 and a thickness of about ¼ wavelength.
The polymeric film may comprise at least one of cellulose acetate, polyamide, acrylic, polyester, and polycarbonate films.
For the purpose of the present invention the wave length of light is taken as substantially the middle of the visible range that is about 550 nm in air, and the wave length in a particular layer is related to the refractive index of the material of that layer by the formula=
λ
mat
=
λ
air
η
material
where &lgr;=wavelength and &eegr;=refraction index
Preferably the inner polyermic layer comprises the reaction production of a titanium alkoxide, preferably titanium isopropoxide, and a silane containing polymer which can undergo the sol-gel reaction. Suitable polymers are &agr; &ohgr; dihydroxypolysiloxanes poly(methyl phenyl siloxane), poly (dimethylsiloxane), and silane modified polyesters.
Preferably the second layer is a fluorine containing polymer which is crosslinkable, preferably using one of the known curing techniques for example ultra violet light, thermal cure, electron beam, free radical and cationic initiation. Preferably the fluorine containing polymer is an acrylate, conveniently an acrylate modified perfluoropolyether. Alternatively the fluorine containing polymer may be a vinyl ether which is crosslinked by a cationic initiator.
The invention also provides a method of manufacture of an anti reflective film in which method fine particles of metal oxide are dispersed in a liquid polymeric material, and the liquid polymeric material is coated onto a polymeric film substrate and cured to give a transparent inner polymeric layer having a refractive index of at least about 1.60 and a thickness of about ¼ wavelength, and the inner polymeric layer is overcoated by an outer polymeric layer of fluorine containing polymer which is cured to give an exposed outer polymeric layer having a refractive index no greater than 1.45 and a thickness of substantially ¼ wavelength.
The invention also provides a further method of manufacture of an anti-reflective film in which method a reaction mixture of a metal alkoxide and a silane modified polymer is coated onto a transparent film substrate and cured to form an inner polymeric layer, and a second layer of a fluorine containing polymer is coated over the inner layer, and is cured to form an exposed outer polymeric layer.
The outer layer can be coated onto the inner layer by either vacuum deposition, or by overcoating the inner layer with a solution of the fluorine containing polymer, followed by removal of the solvent.
Preferably the first layer is a reaction mixture of a metal alkoxide and a silane modified polyester, and the mixture is cured at 180° C. for at least one minute to form said inner layer, and the outer layer is a fluorine containing polymer which is coated over the inner layer directly in contact therewith. Preferably the outer layer is curable on exposure to ultra violet light.
Preferably the metal alkoxide is a titanium or zirconium alkoxide.
Preferably up to 10% by weight of a silane coupling agent, preferably a carbodiimide functional silane, is added as a crosslinking agent to the sol-gel reaction mixture, more preferably about 4% carbodiimide.
Alternatively the inner polymeric layer may be formed from polymerisable monomers such as acrylates, methacrylates, vinyl ether, epoxies, or other monomers containing unsaturated bonds, or from a mixture of polymerisable monomers preferably a triacrylate, or a tetraacrylate and acrylic acid and photo initiators into which fine metal mineral powder is dispersed. Preferably the mineral powder is a colour imparting powder such as a metal oxide, and the particles are sufficiently small that the layer is transparent. Preferably the metal oxide is an iron oxide, preferably haematite which has been ground to a particle size having an average equivalent diameter of less than 100 nm (100×10
−9
m) and preferably less than 50 nm (50×10
−9
m).
The invention also relates to a method of making a multi layer anti reflective polymeric film comprising a polymer film substrate and having as one of its layers a layer comprising particles of metal oxide, preferably iron oxide, dispersed in a curable polymeric resin, the particles having an average equivalent diameter of less than 100×10
−9
m. The presence of the metal oxide powder especially coloured powder, such as iron oxide, colours the polymer film layer which absorbs some light and thereby reduces reflection to given an improved anti-reflectance.
If it is desired to reduce the coloration due to the pigment a dye may be added to the film substrate or other layer to produce an overall neutral colour e.g. grey by the addition of blue and red dye
Barth Steven Allen
Enniss James P.
Packer Elizabeth Jean
Parnandi Aravinda
Port Anthony Brian
CPFilms Inc.
Hess Bruce H.
Nixon & Vanderhye P.C.
Shewareged B.
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