Coating processes – Optical element produced – Transparent base
Reexamination Certificate
2000-07-12
2002-05-07
Parker, Fred J. (Department: 1762)
Coating processes
Optical element produced
Transparent base
C427S180000, C427S202000, C427S355000
Reexamination Certificate
active
06383558
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a monolayer powder film by embedding powders in an adhesive layer consisting of acrylic type adhesive previously formed on the surface of a base material, so that part of the powder is exposed. Additionally, the present invention relates to a production method for a filler lens which is suitable for use in displays such as LCDs, ELs, FEDs, etc., and which in particular, yields superior effects in which nonuniformity of luminance in these displays is avoided and contrast therein is improved.
As a general conventional method in which powders are adhered to a base material, (1) flowing and soaking methods in which powders are sprayed on a base material preheated to above the melting point of the powder and are adhered by melting; (2) electrostatic spray method in which powders are charged and sprayed on a base material by air spraying; (3) electrostatic flowing and soaking method in which a base material is soaked in a powder coating material fluidized by charged air and powders are adhered to the base material by electrostatic attraction; and (4) electrodeposition method in which charged powders are dispersed into solution and are supported on a base material by applying voltage; etc., can be used.
As a powder coating method proposed in Japanese Patent Application Publications, etc., (5) a method in which an adhesive layer consisting of uncured resin is previously formed on the surface of a base material, powder coating materials adhered to the surface of film forming media are embedded in the adhesive layer by using external force such as vibration, procedures in which powders are further embedded in the adhesive pushed out on the surface in the above embedding procedure by the film forming media are repeated, and then a powder film is completely formed at which pushing out of the adhesive is stopped, is disclosed in Japanese Unexamined Patent Publication No. 5-302176. In addition, (6) methods in which an adhesive layer is formed on a base material, transparent microspheres are placed on the adhesive layer, the surface thereof is leveled by skizing, and then the transparent microspheres are embedded in the adhesive layer by presses, pressure rollers, etc., are disclosed in Japanese Unexamined Patent Publications No. 9-318801 and No. 11-95004.
However, film forming methods of the above (1) to (4) are methods for adhering powders on the surface of a base material in multilayers, and the methods theoretically cannot form a monolayer powder film in which powders are uniformly filled in the planar direction at high density.
In contrast, according to the coating method (5), since uncured liquid resin is used as an adhesive layer, the adhesive oozes from spaces and is adhered to the powders and a powder adhered layer is formed as a multilayer. In addition, in this coating method, if the film forming media and the base material are not vibrated or stirred at the same time, the film forming media adhere to the surface of the adhesive layer. Therefore, it was unsuitable for coating base materials having a large area such as film or sheet materials.
Furthermore, in the coating method (6), filling density of the powders in the planar direction is often not uniform, and dense regions and sparse regions of the powders in filling density are easily formed. In addition, in this method, it was also difficult to embed the powders to a uniform depth in the adhesive layer. That is, pressure differences partially occur, depending on partial bending of pressure rollers or presses, dispersion of thicknesses in an adhesive layer, dispersion of thicknesses in a film, etc. At a place at which a large pressure is applied, an adhesive layer is easily formed as a multilayer because powders are deeply embedded, adhesive oozes from openings adhered to the powders, and other powders are adhered thereon. In contrast, at a place at which a slight pressure is applied, defects such as powder coming out easily occur in washing processes for surplus powder, etc., because powders have not been sufficiently embedded in the adhesive layer. This phenomenon is pronounced in the case in which a large area is coated or in the case in which the volume average particle diameter of powders to be used is 15 &mgr;m or less. In particular, in the case in which the volume average particle diameter of powders to be used is 15 &mgr;m or less, since the specific surface area of the powders is increased and the fluidity of the powders is substantially deteriorated by effects of interparticle forces such as van der Waals forces, electrostatic attraction such as frictional electrostatic charging, etc., it was difficult for powders to be adhered uniformly to the surface of the adhesive layer at high densities. Furthermore, if powders in which volume average particle diameter is 15 &mgr;m or less are used, since the pressure from pressure rollers disperses and the pressure applied to each powder is lowered, other powders cannot be embedded to uniform depth in spaces between the powder particles already adhered on the adhesive layer. Therefore, the filling density of the powders is low, and dispersion of embedding depths of the powders in the adhesive layer is also increased by the above partial dispersion of pressure.
Additionally, there has been remarkable progress in displays such as LCDs, ELs, FEDs, etc., recently. In particular, the LCD has spread through numerous fields such as notebook-size personal computers, portable type terminals, etc., and this is anticipated to continue in the future. LCDs may be divided into reflecting types and transmitting types, depending on the manner in which illuminating light is taken into the liquid crystal panel. The reflecting type uses a method in which a reflecting plate on which an aluminum film, etc., is adhered having a high reflectivity is arranged in the back of a liquid crystal panel; external light transmitted from a surface side of the display is reflected by the reflecting plate; the liquid crystal panel is illuminated; and a liquid crystal image is obtained. In contrast, the transmitting type uses a method in which a liquid crystal panel is illuminated by a back light unit arranged in the back of the liquid crystal panel. In the reflecting type, in order to prevent loss of contrast in which the native color of the aluminum appears, the background color is made to closely resemble paper white color by inserting a medium which moderately diffuses the light between the liquid crystal panel and the reflecting plate. In addition, the back light unit in the transmitting type is generally provided with a light source such as an acrylic light conducting board having a cold cathode tube and a light diffusing board diffusing light from the light source, and is a composition in which uniform planar light illuminates the liquid crystal panel.
Thus, in either of the methods used in the reflecting type and transmitting type, a medium having a light diffusivity (hereinafter referred to as “light diffusion material”) is used. As this light diffusion material, for example, a material in which adhesive resin dispersed fillers having light diffusivity is laminated on one surface of a transparent resin film, can be employed. Such conventional light diffusion materials have been produced by a method in which a coating material is prepared by dispersing fillers in a solution dissolved solvent in adhesive resin, and this coating material is coated on a film by a spray or a coater. In
FIG. 17
, a light diffusion material obtained by such a production method is schematically shown, and an adhesive layer
22
is formed on a film
21
by curing adhesive resin solution and fillers
23
are dispersed in this adhesive layer
22
.
With respect to total light diffusion transmittance and total light diffusion reflectance in the above conventional light diffusion material, these values in a direction of incident light in which light is transmitted from a filler side are almost similar to these values in a direction from a film side, and
Fujiwara Akira
Mitani Shuji
Murata Chikara
Arent Fox Kintner Plotkin & Kahn
Parker Fred J.
Tomoegawa Paper Co. Ltd.
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