Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-11-20
2002-04-30
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S332000, C428S336000, C428S339000, C427S164000
Reexamination Certificate
active
06379788
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an antireflection film comprising a polymeric substrate bearing a polymeric antireflection layer, and to a process for producing such an antireflection film.
It has long been known that it is advantageous to provide various articles, for example lenses, cathode ray tubes, flat panel displays, window films and windshields, with antireflection films which reduce the amount of light reflected from the surface of the article and thus reduce or eliminate “ghost” images formed by such reflected light For example, U.S. Pat. Nos. 5,106,671; 5,171,414 and 5,234,748 describe antireflection films which are placed on the inside surface of automobile windshields to reduce the intensity of the image of the instrument panel caused by light reflected from the inside surface of the windshield.
Antireflection coatings on a substrate typically comprise a plurality of inorganic layers, for example a metal or metal oxide layer and a silica layer. (The term “silica” is used herein in accordance with its normal meaning in the antireflection art to mean a material of the formula SiO
x
where x is not necessarily equal to two. As those skilled in the art are aware, such silica layers are often deposited by chemical vacuum deposition or sputtering of silicon in an oxygen atmosphere, so that the material deposited does not precisely conform to the stoichiometric formula SiO
2
of pure silica.) Typically, one surface of a silica layer is exposed, and this exposed surface, which has a high surface energy, as shown by its low contact angle with water, is highly susceptible to fingerprints and other marks. Such marks are extremely difficult to clean, often requiring the use of chemical cleaners.
Perhaps the most effective antireflection film available commercially is that sold by Southwall Technologies, 1029 Corporation Way, Palo Alto, Calif. 94303. This material comprises a 180 &mgr;m poly(ethylene terephthalate) substrate provided with an abrasion-resistant hard coat, and then successively with a 17 nm indium tin oxide (ITO) layer, a 23 nm silica layer, a 95 nm ITO layer, an 84 nm silica layer and finally a thin “lubrication” layer, which is formed from a fluoropolymer and is stated to improve the scratch resistance and the susceptibility of the surface to marking.
This complex film possesses excellent antireflection characteristics, but is so expensive (approximately US$10 per square foot, US$100 m
−2
) as to preclude its use in many applications where antireflection films are desirable. Much of the high cost of this film can be attributed to the 95 nm ITO layer and 84 nm silica layer; since these layers are typically formed by sputtering, and the cost of a sputtered layer is directly proportional to its thickness. Furthermore, if it is desired to produce large quantities of such a complex film on a production line basis, the need for four separate sputtering stations, all of which must be maintained under high vacuum, results in a complex and costly apparatus.
For example, the aforementioned multilayer antireflection coatings are too expensive for use on photographic images. It has long been known that the appearance of photographs and other images can be improved by providing an antireflection coating over the image. For example, U.S. Pat. Nos. 3,793,022 and 3,925,081 describe peel-apart diffusion transfer photographic units in which the surface of the image-receiving element through which the final photograph is viewed (hereinafter called the “viewing surface”) is provided with an antireflection layer comprising a fluorinated polymer. Preferably the fluorinated polymer also includes an isocyanate to improve the abrasion resistance of the antireflection layer. Similarly, U.S. Pat. No. 4,047,804 describes peel-apart diffusion transfer photographic units in which the viewing surface is provided with an antireflection layer comprising a fluorinated polymer incorporating a polydimethylsiloxane. U.S. Pat. Nos. 4,904,525 and 4,940,602 describe an optical article comprising a transparent plastic substrate; a hard coat film formed on a surface of the substrate, the film having an index of refraction of not less than 1.52; and a fluorine-containing organopolysiloxane-based film with a thickness of 10 nm to 500 nm, which has an index of refraction lower than that of the hard coat film by not less than 0.02, and which is formed on the hard coat film.
U.S. Pat. Nos. 5,061,769; 5,178,955; and 5,225,244 describe solid bodies having a reflective surface and provided with an antireflection coating of a terpolymer composition derived from (a) perfluoroalkylalkyl acrylate or methacrylate, (b) acrylic, methacrylic or itaconic acid, and (c) hydroxyl-containing acrylate or methacrylate. Among the solid bodies mentioned in these patents are optical lenses; eyeglasses, both plastic and glass; windows, glass as well as polymeric windows, such as windows of clear polymeric vinyl (including copolymers thereof), styrene, acrylics or polycarbonate; clear polymer films such as vinyl (including copolymers), nylon, polyester, and the like; the exterior viewing surface of liquid crystal displays, cathode ray tubes (e.g. video display tubes for televisions and computers); and the like; and the surface of glossy displays and pictures, such as glossy prints and photographs.
The selection of materials for use in antireflection coatings on plastic films and similar substrates is affected by numerous factors. The antireflection coating needs to have a lower refractive index than the plastic substrate in order to reduce surface reflections substantially. However, the antireflection coating must also adhere firmly to the substrate, be sufficiently transparent that it, does not affect the appearance of the underlying image, and have good scratch resistance and impact resistance. In addition, it is highly desirable that the antireflection coating have good anti-static properties, be flexible so that it does not affect the mechanical properties of the substrate and be resistant to water and common solvents to which it may be exposed. Some of these desirable characteristics of antireflection coatings tend to conflict with one another; for example, highly fluorinated coatings have low refractive indices, but tend to be too soft and lack sufficient adherence to other polymers for optimum performance as antireflection coatings.
The aforementioned parent application Ser. No. 09/026,271 describes multilayer antireflection coatings comprising one or more inorganic antireflection layers and a top layer of a polymer having a refractive index not greater than about 1.53 over the wavelength range of 400 to 700 nm and a thickness of from about 20 to about 200 nm. In a preferred embodiment of this multilayer antireflection coating, the polymer layer is formed from a terpolymer comprising repeating units derived from a fluoroalkene, an alkyl acrylate or methacrylate and a polyfunctional acrylate monomer. It has now been found that this terpolymer can be used alone, without an inorganic antireflection layer, to provide a low cost, but effective, antireflection coating on polymeric and other transparent substrates. The resultant antireflection coatings have desirable properties and are especially useful on polymeric films used in the image-receiving elements of diffusion transfer photographic units.
SUMMARY OF THE INVENTION
Accordingly, this invention provides an antireflection film comprising a substantially transparent substrate bearing a polymeric antireflection layer, which forms one outer surface of the antireflection film. The antireflection layer has a refractive index at least about 0.02 less than that of the substrate over the wavelength range of 400 to 700 nm. The antireflection layer is formed from a cured polymer comprising repeating units derived from a fluoroalkene, an alkyl acrylate or methacrylate and a polyfunctional acrylate monomer; there is no inorganic antireflection layer present between the substrate and the polymeric antireflection layer.
This invention also provides a process
Choi Hyung-Chul
Jones Robert L.
Nagarkar Pradnya V.
Smyth William K.
3M Innovative Properties Company
Dixon Merrick
Kirkpatrick & Lockhart LLP
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