Transparent electromagnetic wave shield

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Reexamination Certificate

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C428S300700, C428S399000, C428S400000, C428S401000, C428S930000, C428S923000, C428S195100

Reexamination Certificate

active

06210787

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to surface covering for the screens of display devices, especially plasma displays (hereinafter abbreviated as PDP) which need to be guarded against leakage of electromagnetic waves, and for other transparent structures which are required to be capable of being seen through, for example, windows of a room where medical instruments are installed.
With rapid progress of electronics and consequential prevalence of computers and other electronic devices in recent years, concern is growing over disturbance caused by electromagnetic waves which would generate erroneous operation of electronic devices. One means for preventing such electromagnetic wave disturbance is active shielding capable of confining the unnecessary electromagnetic waves at the source of generation, which can be realized, for instance, by designing the housing of the electronic device to be electroconductive. Various materials such as metal foil, punched metal foil, metal mesh, metal fiber, plated organic or inorganic fiber, etc., have been used or tried for preventing leakage of electromagnetic waves, but transparency is an absolute requirement for the displays such as PDP and see-through windows, and any of said materials was unsuited for use from the aspect of light permeability.
Further, since oxidation proceeds on the metal surface with the lapse of time, even metal mesh which, among said materials, is considered to be best suited for meeting the transparency requirement, has the problem that high frequency contact tends to break at the lattice points, making it difficult to maintain a stable electromagnetic wave shielding effect for a long time. It has also been conceived to use a composite oxide of indium oxide and tin oxide (hereinafter referred to as ITO) which is proof against oxidative degradation and widely used as electrode for liquid crystal displays, but it is reported that this composite oxide is not so effective in preventing leakage of electromagnetic waves, and its application has been limited to uses relating to destaticization means. It has been attempted to elevate conductivity of this material to the same level (1 &OHgr;/□ or less) as metal, but actually the highest conductivity that could be obtained with this material was 4 &OHgr;/□ even when a film thereof was formed on a glass substrate under heating, and it has been technically impossible to deposit ITO on a plastic film.
There also exists weight problem. Use of glass substrates which have a large size, such as 40 to 50 inches or greater in diagonal—which is the size expected to become most popular and to be applied to PDP—and accordingly are heavy in weight, posed the problem from the aspect of installability, too. On the other hand, in case of using a plastic substrate for weight reduction, from the point of heat resistance it becomes impossible to apply substrate heating, which is the most important means for enhancing transparency and conductivity, which makes it unable to realize low resistance. Further, when it is tried to reduce resistance by increasing film thickness, problem would arise on liability to exfoliation or cracking by buildup of internal stress in the film, due to the difference in linear expansion coefficient between the ITO film and plastic substrate. Thus, 20 to 40&OHgr; was the limit that could be achieved in the attempts for forming an ITO film with low resistance of the same level as metal, and it was hardly possible to attain the object.
OBJECT OF THE INVENTION
An object of the present invention is to provide inexpensively an electromagnetic wave shielding transparent film having high transparency as well as excellent electromagnetic wave shielding effect, which is best suited for application to displays, especially plasma displays, and windows of a medical instrument room.
SUMMARY OF THE INVENTION
In the first embodiment of the present invention, there is provided a transparent electromagnetic wave shield comprising a transparent polymer film and a linear-patterned conductive layer formed on at least one side of said polymer film, wherein the line intervals in the linear pattern are random between 20 &mgr;m and 1 mm.
In a preferred mode of practice, the linear pattern of the conductive layer is of a lattice form consisting of the straight lines arranged both longitudinally and laterally, or a form made by longitudinal and lateral arrangement of the curves defined by the Sin function, Tan function, exponential function, logarithmic function or inversely proportional function expressed by each of the following formulae (1) to (6), or a form consisting of a combined arrangement of these straight lines and curves.
y=A·
sin (&agr;
x+&phgr;
)  (1)
y=B
·Tan (&bgr;
x+&psgr;)
  (2)
(A, B, &agr;, &bgr;, &phgr;, &psgr;: arbitrary constants)
y=C·
exp (
&ggr;x+
&rgr;)  (3)
y=D·
ln (&dgr;
x
+&xgr;)  (4)
(C, D, &ggr;, &dgr;, &rgr;, &xgr;: arbitrary constants)
y=E/x
  (5)
(E: arbitrary constant)
In a more preferred mode of practice, the ratio of the line width P (&mgr;m) of the linear pattern to the thickness D (&mgr;m) of the conductive layer (P/D ratio) falls within the range of 1 to 540, preferably 2 to 240.
The second embodiment of the present invention is a transparent electromagnetic wave shield comprising a transparent polymer film and, formed on at least one side thereof, an adhesive layer optionally, a transparent metal oxide film and a thin metal layer successively in this order, wherein the thin metal layer alone is selectively etched to form a linear pattern, and the line intervals in the linear pattern are random between 20 &mgr;m and 1 mm. Preferably, the thin metal layer is composed of copper.
The third embodiment of the present invention is a transparent electromagnetic wave shield comprising a transparent polymer film and, laminated successively on at least one side thereof, an adhesive layer containing a near infrared screening material and a colorant for making color compensation, and a conductive layer, said conductive layer being worked into a linear pattern, wherein the line intervals in said linear pattern are random between 20 &mgr;m and 1 mm.
The fourth embodiment of the present invention provides a transparent electromagnetic wave shield comprising a transparent polymer film and, laminated successively on at least one side thereof, an adhesive layer
1
and a conductive layer, said conductive layer being worked into a linear pattern so that the line intervals in the pattern become random between 20 &mgr;m and 1 mm, the thus worked laminated film being further bonded to a transparent polymer reinforcement by an adhesive layer
2
, wherein a near infrared screening material and a colorant for making color compensation for said infrared screening material are contained in at least one of said adhesive layer
1
and adhesive layer
2
, and there is further provided at least one ultraviolet screening layer for preventing deterioration of the near infrared screening material.
In the transparent electromagnetic wave shield according to the third or fourth embodiment, preferably at least one layer of water vapor barrier is further provided.
The fifth embodiment of the present invention is a transparent electromagnetic wave shield comprising a transparent polymer film and, successively laminated on at least one side thereof, an adhesive layer
1
and a conductive layer, said conductive layer being worked into a linear pattern where the line intervals are random between 20 &mgr;m and 1 mm, the thus worked laminated film being further bonded to a transparent polymer reinforcement by an adhesive layer
2
, wherein a near infrared screening material and a colorant for making color compensation for said infrared screening material are contained separately in the adhesive layer
1
and the adhesive layer
2
, respectively, or contained in the adhesive layer
2
alone.
In the transparent electromagnetic wave shields according to the first to fi

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