BACKGROUND OF THE INVENTION
1. Field of the Invention:
[0001] The present invention relates to a light-transmissible plastic plate which shields
electromagnetic waves. More particularly, the present invention relates to a light-transmissible
plate capable of effectively shielding deleterious electromagnetic waves which are
generated from a display or a Braun tube etc. Moreover, the present invention relates
to a light-transmissible plate having durability and the function of reducing reflection.
2. Description of the Prior Art:
[0002] Displays of office automation equipment, for example word processors or computers
etc., or Braun tubes of game machines or television sets generate deleterious electromagnetic
waves. There are some problems due to the electromagnetic waves, which are often pointed
out, for example, problems with respect to health and noises which influence other
equipment. For instance, it often happens .that false signals due to noises come into
a computer. It also happens that noises of a stereo are generated when both the stereo
and a television set are operating at the same time.
[0003] Many improvements have been carried out to dissolve the problems. One of the improvements
is a method of covering the equipment which generate electromagnetic waves, with electroconductive
material such as a metal. For example, a cloth capable of shielding electromagnetic
waves and an "Eyesaver" (the trade name of a commodity of Chori Kabushiki Kaisha,
a Japanese company) are known. The cloth is constructed by adhering carbon onto a
fiber with small diameter and then weaving the fiber to form a meshed structure, and
the cloth is applied on equipment which generate electromagnetic waves. "Eyesaver"
is constructed of glasses and metal wire positioned between the glasses.
[0004] However, since the above methods cause a partial intercepting of the ray from a display,
it becomes rather difficult for an operator of the equipment to look at the display
clearly.
[0005] A method forming an evaporation coating layer of electroconductive material on a
glass base plate is also known. Such a method is disclosed, for example, in Japanese
Patent Publication No. SHO 49-18447. However, when the method is applied to a plastic
base plate, the base plate is liable to soften or to melt, and is liable to be injured
at the surface. Therefore, the method can not be applied for manufacturing a light-transmissible
plastic plate.
[0006] Moreover, with respect to anti-reflection film technology, various forming methods
and various structures thereof are disclosed. Japanese Patent Publications No. SHO
59-48702, SHO 59-78301 and SHO 59-78304 disclose a method wherein a hard coating film
comprising a polyorganosilane or a hardened film comprising an epoxy resin is formed
on a plastic base plate and then an anti-reflection film comprising inorganic material
is coated on the above hard coating layer. Japanese Patent Publication No. SHO 56-113101
discloses a structure wherein an anti-reflection film comprising a plurality of oxide
compound layers is provided on a plastic base plate. The structure has high hardness
at the surface and a satisfactory anti-reflection function, but adhesion between the
base plate and the film, heat resistance, shock resistance, hot water resistance and
weather resistance thereof are not satisfactory. Japanese Patent Publications No.
SHO 45-6193, SHO 59-48702, SHO 59-78301 and SHO 59-78304 disclose other structures
including other anti-reflection films, but the adhesion between the base plate and
the anti-reflection film in these structures is also unsatisfactory, and the surfaces
of anti-reflection films are liable to be damaged. Moreover, the plates are liable
to be damaged by water or alcohol, and the structures have adhesion problems between
the base plate and the film after dipping the plate into hot water and also in severe
weather.
[0007] Although several conventional technologies have been described, all of these technologies
have a problem in connection with adhesion between a hard coating layer provided on
a base plate and a layer of anti-reflection film provided on the hard coating layer.
Therefore, the anti-reflection film tends to separate from the hard coating layer
over a long period of time.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a light-transmissible plate which
can shield electromagnetic waves wherein an electroconductive layer is coated on a
base plate, even if the base plate is constructed of a plastic material.
[0009] Another object of the present invention in one of its aspects is to provide a technology
wherein hardness at a surface of the light-transmissible plate can be increased.
[0010] A further object of the present invention is to provide a technology wherein the
light-transmissible plate can also have a function of anti-reflection.
[0011] Still another object of the present invention in another aspect thereof is to provide
a light-transmissible plate which includes an anti-reflection film having excellent
physical properties in various respects.
[0012] To accomplish the above objects, a light-transmissible plate according to the present
invention comprises :
(1) A light-transmissible plate shielding electromagnetic waves comprising a transparent
plastic base plate, a hard coating layer provided on a surface of the base plate,
the hard coating layer having scratch resistance, an electroconductive layer provided
on the surface of the hard coating layer, and a layer provided on the surface of the
electroconductive layer, said layer having a lower refractive index than the refractive
index of the electroconductive layer.
(2) A light-transmissible plate shielding electromagnetic waves comprising a transparent
plastic base plate, a hard coating layer provided on one surface of the base plate,
the hard coating layer having scratch resistance, an electroconductive layer provided
on the surface of the hard coating layer, a layer provided on the surface of the electroconductive
layer, said layer having a lower refractive index than the refractive index of the
electroconductive layer, and an anti-reflection film provided on another surface of
the base plate, the be anti-reflection film may / composed of a plurality of layers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will be better understood from the following detailed description
taken with accompanying drawings.
[0014] FIG. 1 is a sectional view of a light-transmissible plate having the function of
shielding electromagnetic waves and the function of resisting static charge according
to one embodiment of the present invention. Light-transmissible plate 100 is constituted
as follows. Hard coating layer 2 is provided on one surface of the transparent base
plate 1, and the hard coating layer 2 has scratch resistance. Electroconductive layer
3 is provided on a surface of the hard coating layer 2. Layer 4 is provided on a surface
of the electroconductive layer 3, and layer 4 has a lower refractive index than the
refractive index of the electroconductive layer 3. On another surface of base plate
1, hard coating layer 2' having scratch resistance is provided, and a anti-reflection
film 4' is provided on the hard coating layer 2'. Numeral 5 shows a portion of an
exposed surface of electroconductive layer 3. Light-transmissible plate 100 is disposed
so as to direct a surface having electroconductive layer 3 toward a surface generating
picture image, for example, a surface of a cathode-ray tube.
[0015] FIG. 2 is a plan view of the light-transmissible plate 100 in FIG. 1. Exposed surface
5 of electroconductive layer 3 may be formed either along the entire periphery of
the light-transmissible plate 100, or along only a part of the periphery. For shielding
electromagnetic waves and/or for eliminating static electricity, a metal frame (not
shown) is provided around the plate 100 so as to contact with electroconductive layer
3, or an earthing wire 6 is connected to the electroconductive layer 3. The earthing
wire 6 is connected desirably to a corner of electroconductive layer 3.
[0016] FIG. 3 - 7 show preferred embodiments according to the present invention in relation
to connecting an earthing wire. In FIG. 3, hole 9 is provided through the light-transmissible
plate 100, and an earthing wire 15 is connected thereto via metal fitting piece 6a.
In the connection, it is desirable to use a metal packing 7. Metal fitting piece 6a
is fixed by a fixing means, for example, set screw 10a and nut lOb (FIG.3), or a caulking
piece 8 (FIG. 4). Then the portion of the connection is covered by a plastic cover
11.' FIG. 5 shows an embodiment wherein metal fitting piece 6a is fixed nearly parallel
to light-transmissible plate 100 in plastic cover 11. FIG. 6 shows an embodiment wherein
helical insert 12 is fitted into hole 9 and earthing wire 15 is fixed by screw 13
via metal fitting piece 6a. In this case, providing a hole 11a on the cover 11 facilitates
removing the screw 13, and the structure is convenient for removing light-transmissible
plate 100 from equipment or cleaning the plate 100. FIG. 7 shows an embodiment wherein
earthing wire 15 is connected to the plate 100 via adjuster 14a and 14b.
[0017] FIG. 8 is a partial sectional view of a light-transmissible plate having an anti-reflection
film constituted by a plurality of layers according to a second embodiment of the
present invention. On one surface of transparent plastic base plate 1, hard coating
layer 2, electroconductive layer 3 and layer 4 having a lower refractive index than
the refractive index of electroconductive layer 3 are provided, and on another surface
of base plate 1, hard coating layer 2' having scratch resistance and anti-reflection
film 20 are provided. Anti-reflection film 20 is constructed of No. 1 layer 21, No.
2 layer 22, No. 3 layer 23 and No. 4 layer 24.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] First, the first embodiment of the present invention is described.
[0019] A hard coating layer having scratch resistance is provided on a surface of a transparent
plastic base plate. A plastic constituting the base plate may be any conventional
plastic. The transparent base plate means any plastic plate capable of transmitting
light. In the case that a light-transmissible plate is used for a display of a word
processor etc., it is desirable to apply a base plate set to the transmittance of
visible rays of 25 - 70% by its own color or dyeing. The fatigue of the eyes of an
operator is reduced by the above restriction. The hard coating layer having scratch
resistance means a coating layer having high hardness, for example, a layer including
polyorganosiloxane, silica or alumina, or a coating layer constructed of a hardening
paint, for example, an acrylic the paint. Although / surface of a plastic plate is
generally liable to be damaged, characteristics of the surface can be improved by
the hard coating layer, and at the same time, adhesion of a layer shielding electromagnetic
waves is raised by under-coating the hard coating layer. Most preferably, the hard
coating layer consists of a polyorganosiloxane which is produced by heat-condensing
after coating methyltrimethoxysilane and vinyltriethoxysilane or after coating hydrolysis
compound thereof. Desirable film thickness of the hard coating layer is in the range
of about 1 - 10 µm. The hard coating layer including the acrylic is constructed of,
for example, a compound crosslinked with an acrylic compound and an ester compound.
The acrylic compound is constructed of, for example, methacrylic acid and the ester
compound is constructed of, for example, an ester compound produced from an ester
and a polyfunctional glycol, for example, pentaerythritol or glycerin.
[0020] Next, an electroconductive layer is provided on a surface of the hard coating layer.
Any material having electroconductivity and capable of transmitting light can be used
for the electroconductive layer, but preferably the layer is constructed of a mixture
with indium oxide (In
20
3) and tin oxide (Sn0
2). The mixture is also called "ITO" hereinafter in this specification. "ITO" has high
electroconductivity, can shield electromagnetic waves effectively and can transmit
visible rays. A film thickness of the "ITO" layer may be any thickness as long as
the layer can satisfy the above functions. A desirable thickness is in the range of
100 - 3000Å (10-300nm) If a thickness of more than
300nm is utilized, cracking is liable to occur. The "
ITO" layer can be coated by sputtering. Other methods can be applied for forming the
"ITO" layer. For example, the "
ITO" layer is formed by evaporation coating using plasma due to high-frequency electric
discharge in an atmosphere of oxygen and in a temperature condition of less than 150°C,
with the assistance of an ion gun.
[0021] Next, a layer having a lower refractive index than the refractive index of the electroconductive
layer is provided on the surface of the electroconductive layer. Generally, since
an electroconductive layer includes metal, the refractive index of the layer is high.
For example, the refractive index of the "ITO" layer is about 2.0. As an amount of
reflection becomes larger due to the high refractive index, fatigue of the eyes of
the operator also becomes larger. Therefore, it is necessary to provide a layer having
a low refractive index on the surface of the electroconductive layer, thereby preventing
reflection to the light-transmissible plate. The layer having the low refractive index
may be any conventional low refractive layer, but desirably the layer is a layer including
inorganic silica. The layer including inorganic silica can be formed by sputtering
the silica or by vacuum evaporation coating of the silica. The film thickness of the
layer may be any thickness as long as the layer can appropriately prevent reflection.
[0022] In the first embodiment of the present invention, the hard coating layer, the electroconductive
layer and the layer having the low refractive index are provided on one surface of
the base plate, or on both surfaces of the base plate. In providing them on one surface;
it is preferable to provide at least the hard coating layer on another surface to
prevent damage of the another surface, and more preferably, the anti-reflection layer
is provided on a surface of the hard coating layer.
[0023] Next the second embodiment of the present invention is described.
[0024] In this embodiment, an anti-reflection film composed of a plurality of layers is
provided on a surface of the base plate, the surface being an opposite surface to
a surface on which the electroconductive layer is provided.
[0025] The anti-reflection film is provided on a surface of the hard coating layer which
is provided on one surface of the base plate. The film is constructed of No. 1 layer,
No. 2 layer, No. 3 layer and No. 4 layer. The No. 1 layer is provided on the surface
of the hard coating layer. The principal ingredient of the No. 1 layer is zirconium
oxide. The No. 2 layer is provided on the surface of the No. 1 layer, and the principal
ingredient of the No. 2 layer is silicon dioxide. The No. 1 layer becomes a binder
between the hard coating layer and the No. 2 layer, and the strength of both adhesions
between the hard coating layer and the No. 1 layer and between the No. 1 layer and
the No. 2 layer is increased. The No. 2 layer raises the strength of adhesion against
both the No. 1 layer and the No. 3 layer. At the same time, if the No. 1 layer and
the No. 2 layer are constructed as an equivalent film, the equivalent film can be
a film having a middle refractive index, compared with the No. 3 layer having a high
refractive index and the No. 4 layer having a low refractive index. The No. 3 layer
is provided on a surface of the No. 2 layer, and the principal ingredient of the No.
3 layer is titanium oxide. The No. 4 layer is provided on a surface of the No. 3 layer,
and the principal ingredient of the No. 4 layer is silicon dioxide. The equivalent
film (No. 1 layer and No. 2 layer) having the middle refractive index, the No. 3 layer
having the high index and the No. 4 layer having the low index, constitute the anti-reflection
film as a whole, with the film having the excellent function of preventing reflection.
[0026] The above anti-reflection film can be coated by vacuum evaporation or sputtering.
Vacuum evaporation is better than sputtering. The assistance of an ion beam may be
utilized for forming the film. Titanium oxide can be added into the No. 1 layer including
zirconium oxide as long as the effect of the present invention is not reduced. In
the same manner, Ta205 can be added to the No. 3 layer including titanium oxide.
[0027] The thickness of the anti-reflection film may be any thickness as long as the film
can prevent the reflection of visible rays. Preferable optical film thicknesses are
as follows when the design wave lengtha λ
0 is within 450 - 550 nm.
No. 1 layer; 0.05 - 0.15 λ0,
No. 2 layer; 0.05 - 0.15 λ0,
No. 3 layer; 0.36 - 0.49 λ0, and
No. 4 layer; 0.15 - 0.35 λ0.
Particularly, the thickness of No. 4 layer is desirably 0.25 λ
0.
[0028] The anti-reflection film constructed of a plurality of layers is provided on one
surface of the plastic base plate, or on both surfaces of the base plate. In providing
the film on one surface, it is desirable to provide the hard coating layer on another
surface to prevent i damage of the other surface. It is also provided that the anti-reflection
film may be positioned on one surface of the base plate, and that the hard coating
layer and indium oxide-tin oxide layer ("ITO" layer), or the layer including silicon
dioxide besides them are provided on another surface. In such a light-transmissible
plate, a layer having the function of preventing reflection is formed on one surface
and a layer having the function of shielding electromagnetic waves is formed on another
surface. In a structure in which the "ITO" layer is an outermost layer, the film thickness
of the "ITO" layer is preferably formed to a small size, for example, 100 - 500Å (10-50nm).
In a structure in which the layer including silicon dioxide is provided on the "ITO"
layer, the film thickness of the "ITO" layer is formed to a large size relatively.,
for example,
500 - 1000Å (50-100nm).
[0029] In the light-transmissible plate according to the present invention, an earthing
means may be connected thereto to eliminate static electricity. In the case that the
"ITO" layer is provided, an earthing wire may be connected to the "ITO" layer directly,
or continuity via a certain electroconductive piece between the "ITO" layer and the
earthing wire may be ensured. As another means, an outer frame constructed of metal
may be provided around the plate, and static electricity may be discharged via the
frame. Also in this case, the metal frame may preferably come into contact with the
"ITO" layer directly, or continuity via a certain electroconductive piece between
the metal frame and "ITO" layer may be maintained.
[0030] As described in the above, according to the first embodiment of the present invention,
providing the hard coating layer on the transparent plastic base plate can raise the
hardness of the light-transmissible plate, thereby providing characteristics of abrasion
resistance and wear resistance to the plate, even if the base plate consists of a
plastic having low hardness. Providing the electroconductive layer formed on the hard
coating layer and the layer having a low refractive index formed on the electroconductive
layer, can shield electromagnetic waves, and at the same time can prevent reflection.
[0031] According to the second embodiment of the present invention, since the anti-reflection
film having excellent static charge resistance is provided on the surface opposite
to the surface on which the electroconductive layer is provided, a light-transmissible
plate which shields electromagnetic waves can also eliminate static electricity and
prevent reflection. Moreover, since the anti-reflection film constructed of a plurality
of layers also has excellent strength of adhesion, durability, abrasion resistance,
wear resistance, shock resistance, chemical resistance, flexibility, heat resistance,
light resistance and weather resistance, excellent optical products can be obtained
as a whole.
[0032] A representative analysis of components of the electroconductive layer or the anti-reflection
film according to the present invention can be carried out by applying Auger electron
spectrophotometry. In this method, an electron beam is irradiated onto a surface of
a sample positioned in a high vacuum, and the Auger electron released from the surface
is measured by an analyzer with a partition of energy. Conditions of the measurement
are as follows.
analyzer; "JAMP-10S" produced by Nippon Denshi Kabushiki Kaisha (Japanese company)
degree of vacuum (when measuring an outermost surface); 1 x 10-7 Pa
degree of vacuum (when measuring in a direction of
depth) ; 6 x 10-6 Pa (argon atmosphere)
sampling; to fix a sample on a sample stand holding an edge of the sample down with
a copper plate
acceleration voltage ; 3.0 kV
current flowing through a sample ; 1 x 10-8 A
diameter of the electron beam ; 1 µm
slit used for the measurement ; No. 5
angle of inclination of a sample ; 40 - 70 degree
etching condition of Ar ion acceleration voltage 3.0 kV
current flowing through a sample 3 x 10-7 A
etching speed : 200A/min (20nm/min) (when SiO2)
[0033] The light-transmissible plate shielding electromagnetic waves according to the present
invention is effective, particularly when used as a filter for a television set or
a display. As other uses, it is possible to apply the plate as a lens, and it is also
possible to form it into various shapes, for example, a film, a block, etc.
EXAMPLES
[0034] The present invention will be more readily appreciate from the following detailed
description of the examples.
EXAMPLE 1
[0035] A polymethacrylate plate on the market is used as a transparent plastic base plate.
(The plate is "Acrylite" (trade mark) LN-084, produced by Mitsubishi Rayon Kabushiki
Kaisha, colored to gray, thickness; 2 mm.) A mixture of two compounds (one is obtained
by hydrolyzing vinyltriethoxysilane with glacial acetic acid, another is obtained
by hydrolyzing methyltriethoxysilane with glacial acetic acid) is used as a paint
for hard coating, as shown in example 1 of Japanese Patent Publication No. SHO 59-114501.
A paint for the present invention is made by adding sodium acetate, which is a hardener,
to the mixture and then by adding a surface lubricant including silicon to the mixture.
The paint is coated on a surface of the base plate with thickness of 2 µm, and it
is cured by heating. Thus a hard coating layer is formed.
[0036] Next, as an electroconductive layer, a mixture of In
20
3 and Sn0
2 is coated on the hard coating layer, and the mixture is coated with film thickness
of 700Å (70nm) by sputtering. The condition of the sputtering is at the same condition
as shown in example 7 - 9 of Japanese Patent Publication No. SHO 60-32053. That is,
the target utilized is indium-tin alloy, a magnetron -sputtering apparatus is used,
the atmosphere is a gas mixture of argon and oxygen (oxygen: 30 vol.%), and the vacuum
pressure of the atmosphere is 1 x 10-3 Torr.
[0037] Next, as a layer having low refractive index, a film constructed of silicon dioxide
is formed on the electroconductive layer. The film is formed by electron-beam method,
using vacuum evaporation coating apparatus (BMC-800T, produced by Shinku Kikai Kogyo
Kabushiki Kaisha). The film thickness is 940A (94nm).
[0038] On the other surface of the base plate, the same hard coating layer as the above
is provided. Then, a film of aluminium oxide and a film of silicon dioxide are formed
in order on the hard coating layer, thereby giving a function of hardening the surface
and preventing reflection to the plate.
[0039] The light-transmissible plate obtained as above has the following functions. Volume
of transmission of electromagnetic waves in the frequency of 10 GHz is reduced to
about 1/10 volume, compared with only a transparent plastic base plate. When the plate
is used as an optical filter for a word processor, it is excellent with respect to
preventing reflection, and fatigue of the eyes of the operator is effectively reduced.
Hardness of the surface is increased, thereby the plate is tough against abrasion.
EXAMPLE 2
[0040] A hard coating layer on the base plate is formed with the same manner as in example
1. Next, a film of o (lOnm) silicon dioxide with thickness of 100A/is formed as an
undercoating layer on the hard coating layer by sputtering. Then, on the undercoating
layer, "ITO" layer (film thickness; 1400Å (140nm) coated by sputtering and a film
of silicon dioxide coated by vacuum evaporation coating are formed in the same manner
as in example 1. On another surface of the base plate, a hard coating layer is formed
in the same manner as in example 1. Then, on the hard coating layer, layers of Y
20
3 (λ/4), TiO
2 (λ/2), SIO
2 (λ/4) are provided in order. λ is a design wave length.
[0041] The light-transmissible plate obtained as the above had the following functions.
The volume of transmission of electromagnetic waves in the frequency of 10 GHz is
reduced to about 1/22 volume, compared with only a transparent plastic base plate.
When the plate is used as an optical filter for a word processor, it is more effective
with respect to preventing reflection and preventing abrasion than example 1.
EXAMPLE 3
[0042] In the example, a polymethacrylate plate having a
; hard coating layer thereon, being on the market, is used as a base plate. (The plate
is "Acrylite" (trade mark) LN-084, produced by Mitsubishi Rayon Kabushiki Kaisha,
colored to gray, thickness; 2 mm.) Other layers, that is, the "ITO" layer and a layer
having a low refractive index is formed in the same manner as in example 1. The plate
in the example 3 is manufactured to an excellent plate as well as in example 1.
EXAMPLE 4
[0043] A polymethacrylate plate ("Acrylite" (trade mark) LN-084, colored to grey, thickness;
2 mm) is used as a base plate. As a paint for hard coating, a mixture of two compounds
(one is obtained by hydrolyzing vinyltriethoxysilane with glacial acetic acid, another
is obtained by hydrolyzing methyltriethoxysilane with glacial acetic acid) is used,
as shown in example 1 of Japanese Patent Publication No. SHO 59-114501. A paint for
the present invention was made by adding sodium acetate, which is a hardener, to the
mixture, and then by adding surface lubricant including silicon to the mixture.
[0044] The paint is coated on both surfaces of the base plate with a thickness of 2pm, and
then it is cured for 3 hours at 90°C. Thus hard coating layers are formed.
[0045] Next, the "ITO" layer is coated on the hard coating layer on one surface of the base
plate, and then the SiO
2 layer is provided on the "ITO" layer by vacuum evaporation coating. With respect
to another hard coating layer on another surface of the base plate, the surface is
set in a vacuum evaporation coating tank. After the tank is heated to 60°C and vacuumed
to 1 x 10
-5 Torr, the surface is cleaned with an Argon ion beam generated from the ion beam generating
device of the Kaofman type, under the acceleration voltage condition of 500 V. Then,
the following four layers are formed by electron-beam method, in order, from the surface
of the base plate.
(1) No. 1 layer; the principal ingredient of the layer is zirconium oxide, the optical
film thickness is about 42 nm, and the vacuum condition when forming the layer is
3 x 10-5 Torr.
(2) No. 2 layer; the principal ingredient of the layer is silicon dioxide, the optical
film thickness is about 42 nm, and the vacuum condition when forming the layer is
1 x 10-5 Torr.
(3) No. 3 layer; the principal ingredient of the layer is titanium oxide, the optical
film thickness is about 216 nm, and the vacuum condition when forming the layer is
4 x 10 5 Torr.
(4) No. 4 layer; the principal ingredient of the layer is silicon dioxide, the optical
film thickness is about 120 nm, and the vacuum condition when forming the layer is
1 x 10-5 Torr.
[0046] In the above paragraphs (1) - (4), a design wave length in accordance with the optical
film thicknesses is 480 nm.
[0047] The plate obtained in the above manner has a reflection interference color of royal
purple, and has an extremely excellent function of preventing reflection whereby the
surface reflection factor at 550 nm is about 0.2%. The plate also has an excellent
hardness at the surface. A sheet of polyester fiber, which is formed into a square
having a side of 2 cm and which is dropped into water, is positioned on the surface
of the plate, a load of 2 Kg is put on the sheet, and then the sheet is moved reciprocally
maintaining the above load condition, but there is no abrasion thereon.
[0048] An atmospheric exposure test is carried out by exposing the plate outdoors for one
month. The result is that there is no break away of the anti-reflection film and no
damage of the surface. When the plate is used as an optical filter for a word processor,
it is extremely excellent with respect to preventing reflection, and fatigue of eyes
of an operator is highly reduced. Durability of the plate is also excellent.
[0049] 'Moreover, the following measurement was carried out with respect to the property
of static charge resistance. An electrostatic voltmeter ("Statiron M", produced by
Shishido Seidenki Kabushiki Kaisha, Japanese company) is positioned spacedly 53 mm
from the front surface of a CRT. The CRT (NEC-KD551K) is connected to a personal computer
(PC-9801E, produced by Nihon Denki Kabushiki Kaisha). When the switch of the personal
computer is on, the electrostatic potential measured by "Statiron M" is more than
9 kV. Next, the plate according to the present invention is positioned between the
CRT and "Statiron M", at a position 30 mm from "Statiron M". The plate is grounded.
Then, the personal computer was on, but electrostatic potential measured by "Statiron
M" is maintained at 0. The effect of static resistance due to the plate was extremely
excellent.'
1. A light-transmissible plate for shielding electromagnetic waves characterized in
that,
a hard coating layer (2) is provided on a surface of a transparent plastic base plate
(1), said hard coating layer having scratch resistance;
an electroconductive layer (3) is provided on the surface of said hard coating layer
(2); and
a layer (4) is provided on the surface of said electroconductive layer (3), said layer
(4) having a lower refractive index than the refractive index of said electroconductive
layer (3).
2. A light-transmissible plate according to claim 1, wherein said electroconductive
layer (3) is a layer containing indium oxide and tin oxide.
3. A light-transmissible plate according to claim 2, wherein said layer containing
indium oxide and tin oxide is formed by sputtering.
4. A light-transmissible plate according to claim 2, wherein said layer containing
indium oxide and tin oxide is formed by evaporation coating, said evaporation coating
being performed using plasma due to high-frequency electric discharge, in an atmosphere
of oxygen and at a temperature of less than 150°C, with the assistance of an ion gun.
5. A light-transmissible plate according to any preceding claim, wherein the film
thickness of said electroconductive layer (3) is within the range of 10 to 300nm.
6. A light-transmissible plate according to any preceding claim, wherein said hard
coating layer (2) is a layer containing organopolysiloxane.
7. A light-transmissible plate according to any one of claims 1 to 5, wherein said
hard coating layer (2) is formed by coating with a hardening paint.
8. A light-transmissible plate according to any preceding claim, wherein said transparent
plastic base plate (1) is a coloured plate.
9. A light-transmissible plate according to any preceding claim, wherein said layer
(4) having said low refractive index is a layer constructed of inorganic silica.
10. A light-transmissible plate according to claim 9, wherein said layer constructed
of inorganic silica is formed by a vacuum evaporation coating.
11. A light-transmissible plate according to any preceding claim, wherein a ground
wire (6, 15) is connected to said electroconductive layer (3).
12. A light-transmissible plate according to any preceding claim, wherein an outer
frame is provided around said light-transmissible plate, said outer frame extending
along the edge of said light-transmissible plate and coming into contact with said
electroconductive layer.
13. A light-transmissible plate according to any one of claims 1 to 12, wherein a
further hard coating layer (2') is provided on the surface of the transparent plastic
base plate (1) opposite to the surface bearing the hard coating layer (2).
14. A light-transmissible plate comprising a transparent plastic base plate (1) both
sides of which bear layers according to any one of claims 1 to 12.
15. A light-transmissible plate according to any one of claims 1 to 13, having an
anti-reflection coating (4':21,22,23,24) on the side of the transparent plastic base
plate (1) opposite to the surface bearing the hard coating layer (2).
16. A light-transmissible plate according to claim 15, wherein the anti-reflection
coating consists of a plurality of layers (21-24).
17. A light-transmissible plate according to claim 16 wherein the anti-reflection
coating is applied to a hard coating layer (2') and consists of the following layers
-
a first layer (21) provided on a surface of said hard coating layer (2'), the principal
ingredient of said first layer (21) being zirconium oxide;
a second layer (22) provided on a surface of said first layer (21), the principal
ingredient of said second layer (22) being silicon dioxide;
a third layer (23) provided on a surface of said second layer (22), the principal
ingredient of said third layer (23) being titanium oxide; and
a fourth layer (24) provided on a surface of said third layer (23), the principal
ingredient of said fourth layer (24) being silicon dioxide.
18. A light-transmissible plate according to claim 16 or claim 17, wherein the optical
film thicknesses of said first to fourth layers (21, 22, 23, 24) are the following
thicknesses under a condition which a design wave length X
0 is within 450 - 550 nm;
First layer; 0.05 - 0.15 λ0,
Second layer; 0.05 - 0.15 λ0,
Third layer; 0.36 - 0.49 λ0, and
Fourth layer; 0.15 - 0.35 λ0.
19. A modification of the light-transmissible plate according to any one of claims
16 to 18, wherein the first and second layers are combined into a single layer.
20. A light-transmissible plate according to any one of claims 15 to 19, wherein the
layers of anti-reflection coating are films formed by evaporation coating.
21. A light-transmissible plate according to any . one of claims 15 to 19, wherein
the layers of anti-reflection coating applied to the hard coating layer (2') are films
formed by sputtering.
22. A light-transmissible plate according to any preceding claim, wherein said light-transmissible
plate is an optical filter for a cathode-ray tube.