CA2036868A1 - Non-moire shielded window - Google Patents
Non-moire shielded windowInfo
- Publication number
- CA2036868A1 CA2036868A1 CA 2036868 CA2036868A CA2036868A1 CA 2036868 A1 CA2036868 A1 CA 2036868A1 CA 2036868 CA2036868 CA 2036868 CA 2036868 A CA2036868 A CA 2036868A CA 2036868 A1 CA2036868 A1 CA 2036868A1
- Authority
- CA
- Canada
- Prior art keywords
- pattern
- elements
- substrate
- conductive
- group
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/86—Vessels; Containers; Vacuum locks
- H01J29/867—Means associated with the outside of the vessel for shielding, e.g. magnetic shields
Landscapes
- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
- Transforming Electric Information Into Light Information (AREA)
- Optical Elements Other Than Lenses (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An EMI/RFI shielded substrate, preferably a window or CRT screen is disclosed. The conductive pattern is formed of a series of randomly distributed vertices interconnected with linear and/or curvilinear elements. The pattern is formed by moving the vertices of a normal rectangular grid from their established x,y coordinates to new x',y' coordinates which are a small distance from the x,y coordinates at an angle, .alpha. , which is from 0° to 360°. Preferably, the vertices are displaced by an increment that is 50% or less of the distance between the vertices of the x,y coordinate pattern.
An EMI/RFI shielded substrate, preferably a window or CRT screen is disclosed. The conductive pattern is formed of a series of randomly distributed vertices interconnected with linear and/or curvilinear elements. The pattern is formed by moving the vertices of a normal rectangular grid from their established x,y coordinates to new x',y' coordinates which are a small distance from the x,y coordinates at an angle, .alpha. , which is from 0° to 360°. Preferably, the vertices are displaced by an increment that is 50% or less of the distance between the vertices of the x,y coordinate pattern.
Description
2~3~
¦ NoW-MOIRE~ ~HIELDED WI~DOW
This invention relates to a shielded window~ more particularly, it relates to an EMI/RFI shielded window that prevents the generation of moire' patterns.
BACKGROUND OF THE INVENTIOM
A normal cathode ray tube (CRT) such as may be used in a computer terminal is composed of a transparent screen with a phosphor layer Eormed on its inner surface. The phosphor layer is stimulated by one or more electron beams so that the layer emits light energy. This light energy is the visual representation viewed by an observer of the screen. I
The screen and tube are typically not shielded against the radiation of EMI/RFI energy generated within the CRT. The ingress and egress of EMI~RFI energy must be controlled for health and security reasons. For e~ample, recent studies have suggested that the EMI/RFI energy emanating from CRT devices may affect the health of its users. Additionally, it is known that EMI/RFI emissions from CRT devices can affect the operation of adjacent unshielded devices and may also be detected and read by highly sensitive detectors One approach to eliminating the movement of EMI/RFI
energy through the CRT screen has been to use a transparent shield which contains an electrically conductive mesh or grid. Mounting such mesh is dificult and time consuming as the mesh tends to distort or tear easily. The shielded structure suffers from reduced visual opacity in that the mesh '~3~
interferes with one's viewing of the screen. More importantly, the use of the conductive mesh causes the formation of moire' patterns which interfere with the viewing of the screen.
Moire' patterns are caused by the overlaying of two patterns which are similar in spatial frequency and distribution. In CRT devices, they are caused by the overlaying of two similar grid patterns. The first grid ;s the wire mesh used in the EMI~RFI shielding device. The second grid is formed by the C~T scan linPs and pixel delineation. The frequency and distribution of the second grid is variable as each CRT screen has different spatial distributions. The problem is more severe when using a high resolution screen, as the spatial definition of the pi~els is closer to that of the wire screen, thus generating denser moire interference lines.
One method for avoiding the generation of moire' patterns is to eliminate the wire mesh, while maintaining the EMI/RFI shielding. Various coated shields or screens have been offered and while the shields do reduce or elimina~e the moire' patterns, they also have major disadvantages. The main problem with such coatings is that the visual opacity of the CRT screen is significantly reduced (generally up to 50% less than on an unshielded screen). This requires the operator to increase the screen's luminescence to a higher level which reduces the useful life of the screen. Additionally, the coatings are generally less conductive than the wire mesh and therefore do not provide the same effective level o EMI~RFI
shielding.
Another method for avoiding the generation of moire' patterns is the use of a randomly oriented, non linear conductive pattern such as one formed from a large number of interconnected circles or ovals which are distributed in such a manner so as to prevent the generation of moire' patterns.
While providing excellent shielding and moire' prevention, the manuacture of such a pattern is difficult and costly to reproduce.
The present invention overcomes the difficulties encountered with the present devices. The shield of the present invention provides escellent EMI/RFI shielding and ~isual opacity without generating moire' patterns.
SUMMARY AND OBJE~TS OF THE INVENTION
The present invention is a randomly oriented conductive pattern useful as an EMI/RFI shield on CRT screens and similar devices. The random, pattern provides excellent EMI/RFI shielding capabilities without generating moire' patterns.
It is an object of the present invention to provide a transparent E~I/RFI shield with good visual opacity and which does not cause the generation of a moire' pattern.
Another object of the present invention is to provide an EMI/RFI shield comprising a substrate which is transparent or translucent and a shielding means formed of a randomly oriented linear pattern.
A further object of the present invention is to provide a method of forming an EMI/RFI shield 40r CRT devices that does not generate moire' patterns comprising the steps of 203~ o generating a randomly oriented, linear pattern, creating a photomask of such pattern, imaging the pattern onto a resist formed on a transparent substrate, developing the resist, etching away a selected portion of the resist and~or substrate so as to form the pattern on the substrate, plating the resultant pattern to render it conductive and applying a conductive termination layer along the edges of the substrate so that the shield is electrically continuous with the CRT
device.
Additionally, an object of the present invention is to form a conductive pattern by distorting a straight grid pattern such that all vertices are displaced by some small increment at a random angle, and applying the pattern to a surface to be rendered conductive.
These and other objects of the present invention will be made clear from the specifications, drawings and appended claims.
DESCRIPTION OF THE DRAWINGS
Figure 1 shows a planar view of a normal, grid-like pattern.
Figure 2 shows a planar view of a pattern according to the present invention.
Figure 3 shows a cross-sectional view o a preferred embodiment of the present invention.
Figure 4 shows a cross-sectional view of a further embodiment of the present invention.
DETA I LED DE SCR I PT I ON OF THE I NVENT I ON
The present invention relates to a highly conductive, randomly oriented, pattern formed on a transparent or translucent substrate for use in EMI~RFI shielding applications.
%033i~6~
In shielded windows that use a mesh or a conductive grid, such as is shown in Figure 1, the grid is formed of a series of vertical and horizontal elements of equal length which intersect at a series of vertices. A verte~ ~vertices~ ¦
is herein ~efined as a point at which adjoining linear elements intersect and terminate. In the formation o Figure 1, the angle formed between intersecting and joining vertical elements (la, lb) and horizontal elements (2a, 2b) is 90 at the vertes 3. Li~ewise, the angle formed between adjoining intersecting vertical elements la and lb is 180 as it is for adjoining, intersecting horizontal elements 2a and 2b.
Each verte~ has a definitive position on the substrate. This portion is normally defined in reference to a horizontal (x) and a vertical (y) coordinate. Thus each verte~ will have its own unique ~,y coordinate.
Figure 2 shows a preferred embodiment of a conductiYe pattern formed according to the present invention. As can be seen, the vertical elements (lla,llb) as well as the horizontal elements, (12a,12b~ and the vertices ~13) are randomly distributed about the pattern and randomly oriented to each other. Further, as shown in Figure 2 the length of each element is not necessarily equal to that of the other elements, preferably ad~oininq elements are not of equal length.
The pattern of Figure 2 is formed by taking the arranged vertices of Figure 1 and moving each verte~ from a normal ~,y coordinate by some small increment at a random angle,o~ . Preferably, the increment is less than 50% the length of an element in the regular grid of Figure 1. More preferably, it is from 10 to 50% of the distance between the 203~i~68 vertices of the regular pattern of Figure l. Moreover, it is preferred that the increment be from 20 to about 90~ of the distance ~etween vertices in the regular grid of Figure l.
The angle, ~ , can be any angle from 0 to 369.
As can be appreciated from Figure 2, the conductive pattern is formed o a series of vertical elements and horizontal elements interconnected by a series of vertices such that a substantial number of the adjoining vertical elements and horizontal elements meet at an angle that is less than or greater than but not equal to 90. Correspondingly, the intersection of two adjoining vertical elements, or two adjoining horizontal elements, is less than or greater than but not equal to 180. This array is generated throughout the entire conductive pattern.
Other similar patterns may also be gsnerated using the same basic principles mentioned above, namely that the vertices are distorted by a small increment and a random angle, O~ , from that which it would normally occupy in a purely horizontally and vertically aligned grid pattern.
While the above patterns have been d~scribed with reference to a four sided ~square or rectangular~ grid reference, it is clear that other such patterns can be formed from triangular or other polygonal grid patterns to form randomly angled linear patt~rns that do not generate moire patterns.
Moreover, one can use curvilinear elements of various curvatures instead of linear elements. The curvilinear elements may all have the same curvature or preferably may be of different curvatures. One may also form the pattern from a combination of linear and curvilinear elements.
203~86~
A device according to the preferred embodiment of the invention is shown in Figure 3 and comprises one or more layers o a transparent or translucent substrate 30. The substrate 30 may be formed from such materials as glass, and various rigid plastics, either thermoplastic or thermoset including but not limited to polyacrylates and polycarbonates. At least one surface of the substrate 30 contains a conductive pattern 31 formed of randomly oriented, interconnected electrically conductive elements 32. In this preferred example, the elements 32 are shown as being linear.
The elements 32 are shown as being in contact with each of their adjoininq horizontal and vertical vertices so that electrica1 continuity is maintained throughout the pattern 31. While each element 32 is in contact with its neighboring elements, the elements are preferably arranged so that they do not present a linear component that is greater in length than the length of one element.
The size of the elements 32 depends in large part upon the shielding and visual opacity charactaristics desired. The smaller the elements, the greater the shielding characteristics and the lesser the visual opacity and vice versa. Pr~ferahly the selected elements 32 should be of size such that they do not severely detract from either characteristic.
Two dimensions are relevant in discussing the size of the elements 32; the length of the elements and the annular width o the elements.
With linear elements, the length can be the same as that generally used to form a linear grid such as that of the mesh of the prior art such as from about .002 inches to about 0.10 inches. In general, the linear elements range from about four elements per inch to about one hundred elements per inch, preferably about 50 to 100 elements per inch.
203u8~
The annular width is herein d~fined as the distance from one outer edge of the element to the corresponding outer edge of the element. If a variation in annular width occurs, either due to the manufacturing process or due to a desired purpose, the annular width shall be an average of the distances taken from various points across the diameter of the element. The annular width of an element should be fairly consistent throughout. The annular width of the elements ranqes from about .0002 inches to about .005 inches, preferably about .001-.002 inches.
Preferably, the elements 32 of a pattern will vary over a range of lenyths due to the distortion of the vertices. Moreover, the arrangement o elements in the pattern may be selective such that the length of elements in one portion of the substrate are different from those in another area. For e~ample, if one wishes to have less visual opacity around the edge of the conductive substrate, one may use element~ 32 along the edge of the substrate that have a smaller average length and/or greater width than the elements on the inner portion of the substrate. Also, one may use elements of different average lengths and/or widths to ensure that there is complete and adequate conductivity throughout the pattern.
Preferably, the conductive pattern 31 is terminated along its outside edges with a conductive strip, commonly called a bus bar 33.
The bus bar 33 may be a conductive layer formed on or in the surface of the substrate. The bus bar 33 can be formed in a manner identical to the formation of the pattern e~cept preferably it is void free. However, if desired, one could 203~
use elements 32 that are smaller in diameter and/or thicker in annular width along the edges of the pattern 31 to form the bus bar 33.
A~ditionally, the bus bar 33 can be formed of a separate conductive layer sintered or bonded to the edge areas of the substrate 30. For e~ample, the bus bar 33 can be a conductive ink or epo~y, a conductive metal plating, a metal strip, a conductive, sinterable frit such as silver coated glass, or more preferably, a conductive metal tape, such as CHO-FOIL~, available from Chomerics, Inc.
The bus bar 33 is designed in such a manner that it establishes and maintains electrical continuity between the substrate 30 and the frame, cabinet or closure to which it is attached. The bus bar 33 may do so directly, ilÇ~ its surface meets and mates with a conductive surface of the frame, cabinet or closure to which the substrate is attached.
Preferably, the bus bar is connected to a conductive lead such as a grounding strap, a metal frame, or a conductive gaæket that establishes contact with the surface to which the substrate is mounted. By using the intermediate connection between the bus bar of the substrate and surface, one avoids the problems of establishing a perfect fit between the surfaces as would be re~uired by a direct connection between the surface and the substrate.
Figure 4 shows another preferred embodiment of the present invention.
The surface 41 of the substrate 40 containing the pattern 42 may also be covered by a protective coating 43, such as a conformal coating to prevent oxidation and damage to the conductive pattern during handling. Such coatings are well known and generally are formed of a sprayable plastic 21~3~
materlal, such as polyurethane. The coating can also be a film, ~uch as MYLAR~ films or KAPTON~ films, which may be bonded to the substrate surface.
The surface 41 of the substrate 40 containing the pattern 42 may also be covered by a transparent conductive coating 43, such as indium tin o~ide. This coating may he applied by vacuum deposition, sputtering, or spray pyrolysis.
The addition of this conductive coating will increase the effective shielding of the assembled window.
If ~esired, the substrate can be joined with another suhstrate to form a laminate of two or more layers. In this embodiment, the surface of the substrate containing the conductive pattern faces the inner surface of the other substrate. Such lamînations and processes for forming them are well ~nown and generally consist of a bonding layer between the substrates to hold the two substrates together.
Typically, a polyvinyl butyral material is used as the bonding aqent~ although other similar adhesive material such as polyurethanes can be used. Alternatively, the two substrates can b~ melt bonded together, although one must take care not to injure the conductive pattern in doing so.
A preferred method of forming the pattern on the conductive window of this invention is by a photolithography or an electroforming method.
In the preferred process, a desired pattern is first created. The pattern can be drawn by hand or preferably by a computer qenerated program. A preferred simple means for creating the randomly oriented pattern of the present invention is to use a computerized print program which will lay out a series of elements of the desired length and width in an arrangement so that the vertices of the elements are .
2036~6~
randomly oriented from their normal x and y coordinate by a small increment and angle, ~ . A photomask is made of the pattern and imaged onto a resist coated substrate. The resist coated substrate is esposed to actinic radiation and developed. The developed image is then plated to form a conductive pattern.
A suitable computer program used to generate the pattern follows the following logic: The ~,y coordinates for a series of equally spaced vertices are generated and stored.
Preferably, the ~,y coordinates are equidistant from each other i.e. a square like grid pattern. Each coordinate is then moved by a small increment in either the ~ or y or both the x and y coordinate and at a random angle, ~ , wherein o~ ¦
can b~ any angle between 0 to 360. The small incremental distance may be uniform i.e, a percentage of the distance between the established adjoining ~,y coordinates or it may be random, varying over a preselected range, i,e. equal to or less than a certain percentage of the distance between the established adjoining s,y coordinates. A new series of ~',y' I
coordinates are then plotted. Elements are then formed to interconnect the vertices, e.q. using the elements to interconnect the ~' to x~ and y~ to y' coordinates of adjoining vertices. The output of the computer program is the x'/y~ coordinates and element lengths which are used to drive a computer ~lotter or photomask generator. The generated photomask may be either a positive or a negative photomask.
One preferred embodiment is to use a resist coated metal layer substrate to form the desired pattern. The substrate has a metal layer bonded or plated onto its desired surface. The metal la~er is coated with a resist layer. The resist is e~posed to a negative photomask and developed and 2~3~j8~
the unwanted portion of the metal layer is etched away to leave a conductive metal pattern on the surface of the substrate. As discussed above, in relation to the resist covered substrate, add;tion~l conductive layer~ may be placed upon the conductiv~ pattern, preferably by a plating process.
Suitable substrates include, but are not limited to glass and various transparent or translucent plastics. The metal layer may be formed of any conductive metal such as silver, gold, platinum, palladium~ nickel, copper, tin, zinc, aluminum, etc. It is preferred that the metal layer be formed of copper due to its cost, availability and ease of etchin~ and plating. The metal layer may be in the form of a metal foil or film which is embedded into or bonded onto the substrate surface. It may also be formed by vapor deposition, sputter coatinq or other deposition means which form a unîform metal layer on the substrate's surface. As stated above, the resultant pattern can be further plated or treated to render it more conduc~ive.
In another pr~ferred emhodiment, one c~n form the pattern on a re~ist coated substrate which will form the conductive window. This substrate may be formed of any transparent or translucent material typically used for such conductive windowsO E~amples of such materials include, but are not limited to, glass and various plastics such as polycarbonates and polyacrylates. In this embodiment, the resist is formed on the desired surface of the substrate. The resist is then esposed to the pattern formed on a positive photomask and developed. The substrate is then etched, preferably with an acid, tc create the desired pattern in the substrate surface. The etched pattern is then filled with a 2036~68 conductive material such as a conductive ink a conductive adhesive, preferably a conductive epo~y, a conductive frit, such a3 a conductive ceramic frit, or a conductive metal, such as copper, silver, nickel, gold, tin, zinc, aluminum or platinum. It is preferred to use a conductive adhesive, especially a silver filled epoxy. If desired, the conductive pattern may additionally be plated with conductive metals, such as, but not limited to silver, gold, platinum, nickel, tin, zinc, aluminum or copper to enhance its conductivity and reduce o~idat;on.
If one desires to form a free standing conductive rnaterial incorporatin~ the desired pattern, one can form a resist on a suitable mandrel, generally havinq a metal surace, e~pose and wash the resist, and etch the desired pattern into the mandrel's surface. A plating is then formed on the mandrel's surface such a~; by an electrodeposition bath. The plated material is then removed from the mandrel and applied like any other conductive mesh known in prior art to the tranæparent substrate.
The shielding capability of the present invention is equal to that of shielded devices usi~g a mesh like grid. For example, a conductive substrat~ formed according to this invention, having linear elements of an average length of 0.010 inches and an average annulus width of 0.0013 inches has a shielding capability comparable to that of a wire mesh shielding device having 100 openings per inch and a mesh diameter of 0.0015 inches (a shielding capability of 65 dBs at 100 megahertz).
If desired, the substrate containing the conductive pattern may be curved, either before or after formation of the conductive pattern. Typically the curvature is ormed after ~ 2~3~8 ~
the formation of the conductive pattern by placing the substrate in an ov~n and allowing the substrate to soten and flow or slump to the correct curvature. If necessary, a mold or means for applying pressure to the substrate surface may be used to ensure the formation of the correct curvature.
The present invention may be used in a computer terminal as an EMI/RFI shield. It also has applications in the area of EMI/RFI shielded windows, such as in high security buildings and vehicles. It may also be used in applications that require a conductive or heated window such as a rear window defogger in an automo~ile. It is believed that in this application the conductive pattern is less distractive to the operator than the grid like formation that is currently in use.
Additionally, when the conductive pattern is formed as a freestanding material, it can be a replacement for knitted or braided conductive mesh used in forming conductive gaskets.
While the present invention has been described with reference to its preferred embodiments, other embodiments can achievP the same result. variations and modifications of the present invention will be obvious to those skilled in the art and ît is intended to cover in the appended claims all such modifications and equivalents as fall within the true spirit and scope of this invention.
¦ NoW-MOIRE~ ~HIELDED WI~DOW
This invention relates to a shielded window~ more particularly, it relates to an EMI/RFI shielded window that prevents the generation of moire' patterns.
BACKGROUND OF THE INVENTIOM
A normal cathode ray tube (CRT) such as may be used in a computer terminal is composed of a transparent screen with a phosphor layer Eormed on its inner surface. The phosphor layer is stimulated by one or more electron beams so that the layer emits light energy. This light energy is the visual representation viewed by an observer of the screen. I
The screen and tube are typically not shielded against the radiation of EMI/RFI energy generated within the CRT. The ingress and egress of EMI~RFI energy must be controlled for health and security reasons. For e~ample, recent studies have suggested that the EMI/RFI energy emanating from CRT devices may affect the health of its users. Additionally, it is known that EMI/RFI emissions from CRT devices can affect the operation of adjacent unshielded devices and may also be detected and read by highly sensitive detectors One approach to eliminating the movement of EMI/RFI
energy through the CRT screen has been to use a transparent shield which contains an electrically conductive mesh or grid. Mounting such mesh is dificult and time consuming as the mesh tends to distort or tear easily. The shielded structure suffers from reduced visual opacity in that the mesh '~3~
interferes with one's viewing of the screen. More importantly, the use of the conductive mesh causes the formation of moire' patterns which interfere with the viewing of the screen.
Moire' patterns are caused by the overlaying of two patterns which are similar in spatial frequency and distribution. In CRT devices, they are caused by the overlaying of two similar grid patterns. The first grid ;s the wire mesh used in the EMI~RFI shielding device. The second grid is formed by the C~T scan linPs and pixel delineation. The frequency and distribution of the second grid is variable as each CRT screen has different spatial distributions. The problem is more severe when using a high resolution screen, as the spatial definition of the pi~els is closer to that of the wire screen, thus generating denser moire interference lines.
One method for avoiding the generation of moire' patterns is to eliminate the wire mesh, while maintaining the EMI/RFI shielding. Various coated shields or screens have been offered and while the shields do reduce or elimina~e the moire' patterns, they also have major disadvantages. The main problem with such coatings is that the visual opacity of the CRT screen is significantly reduced (generally up to 50% less than on an unshielded screen). This requires the operator to increase the screen's luminescence to a higher level which reduces the useful life of the screen. Additionally, the coatings are generally less conductive than the wire mesh and therefore do not provide the same effective level o EMI~RFI
shielding.
Another method for avoiding the generation of moire' patterns is the use of a randomly oriented, non linear conductive pattern such as one formed from a large number of interconnected circles or ovals which are distributed in such a manner so as to prevent the generation of moire' patterns.
While providing excellent shielding and moire' prevention, the manuacture of such a pattern is difficult and costly to reproduce.
The present invention overcomes the difficulties encountered with the present devices. The shield of the present invention provides escellent EMI/RFI shielding and ~isual opacity without generating moire' patterns.
SUMMARY AND OBJE~TS OF THE INVENTION
The present invention is a randomly oriented conductive pattern useful as an EMI/RFI shield on CRT screens and similar devices. The random, pattern provides excellent EMI/RFI shielding capabilities without generating moire' patterns.
It is an object of the present invention to provide a transparent E~I/RFI shield with good visual opacity and which does not cause the generation of a moire' pattern.
Another object of the present invention is to provide an EMI/RFI shield comprising a substrate which is transparent or translucent and a shielding means formed of a randomly oriented linear pattern.
A further object of the present invention is to provide a method of forming an EMI/RFI shield 40r CRT devices that does not generate moire' patterns comprising the steps of 203~ o generating a randomly oriented, linear pattern, creating a photomask of such pattern, imaging the pattern onto a resist formed on a transparent substrate, developing the resist, etching away a selected portion of the resist and~or substrate so as to form the pattern on the substrate, plating the resultant pattern to render it conductive and applying a conductive termination layer along the edges of the substrate so that the shield is electrically continuous with the CRT
device.
Additionally, an object of the present invention is to form a conductive pattern by distorting a straight grid pattern such that all vertices are displaced by some small increment at a random angle, and applying the pattern to a surface to be rendered conductive.
These and other objects of the present invention will be made clear from the specifications, drawings and appended claims.
DESCRIPTION OF THE DRAWINGS
Figure 1 shows a planar view of a normal, grid-like pattern.
Figure 2 shows a planar view of a pattern according to the present invention.
Figure 3 shows a cross-sectional view o a preferred embodiment of the present invention.
Figure 4 shows a cross-sectional view of a further embodiment of the present invention.
DETA I LED DE SCR I PT I ON OF THE I NVENT I ON
The present invention relates to a highly conductive, randomly oriented, pattern formed on a transparent or translucent substrate for use in EMI~RFI shielding applications.
%033i~6~
In shielded windows that use a mesh or a conductive grid, such as is shown in Figure 1, the grid is formed of a series of vertical and horizontal elements of equal length which intersect at a series of vertices. A verte~ ~vertices~ ¦
is herein ~efined as a point at which adjoining linear elements intersect and terminate. In the formation o Figure 1, the angle formed between intersecting and joining vertical elements (la, lb) and horizontal elements (2a, 2b) is 90 at the vertes 3. Li~ewise, the angle formed between adjoining intersecting vertical elements la and lb is 180 as it is for adjoining, intersecting horizontal elements 2a and 2b.
Each verte~ has a definitive position on the substrate. This portion is normally defined in reference to a horizontal (x) and a vertical (y) coordinate. Thus each verte~ will have its own unique ~,y coordinate.
Figure 2 shows a preferred embodiment of a conductiYe pattern formed according to the present invention. As can be seen, the vertical elements (lla,llb) as well as the horizontal elements, (12a,12b~ and the vertices ~13) are randomly distributed about the pattern and randomly oriented to each other. Further, as shown in Figure 2 the length of each element is not necessarily equal to that of the other elements, preferably ad~oininq elements are not of equal length.
The pattern of Figure 2 is formed by taking the arranged vertices of Figure 1 and moving each verte~ from a normal ~,y coordinate by some small increment at a random angle,o~ . Preferably, the increment is less than 50% the length of an element in the regular grid of Figure 1. More preferably, it is from 10 to 50% of the distance between the 203~i~68 vertices of the regular pattern of Figure l. Moreover, it is preferred that the increment be from 20 to about 90~ of the distance ~etween vertices in the regular grid of Figure l.
The angle, ~ , can be any angle from 0 to 369.
As can be appreciated from Figure 2, the conductive pattern is formed o a series of vertical elements and horizontal elements interconnected by a series of vertices such that a substantial number of the adjoining vertical elements and horizontal elements meet at an angle that is less than or greater than but not equal to 90. Correspondingly, the intersection of two adjoining vertical elements, or two adjoining horizontal elements, is less than or greater than but not equal to 180. This array is generated throughout the entire conductive pattern.
Other similar patterns may also be gsnerated using the same basic principles mentioned above, namely that the vertices are distorted by a small increment and a random angle, O~ , from that which it would normally occupy in a purely horizontally and vertically aligned grid pattern.
While the above patterns have been d~scribed with reference to a four sided ~square or rectangular~ grid reference, it is clear that other such patterns can be formed from triangular or other polygonal grid patterns to form randomly angled linear patt~rns that do not generate moire patterns.
Moreover, one can use curvilinear elements of various curvatures instead of linear elements. The curvilinear elements may all have the same curvature or preferably may be of different curvatures. One may also form the pattern from a combination of linear and curvilinear elements.
203~86~
A device according to the preferred embodiment of the invention is shown in Figure 3 and comprises one or more layers o a transparent or translucent substrate 30. The substrate 30 may be formed from such materials as glass, and various rigid plastics, either thermoplastic or thermoset including but not limited to polyacrylates and polycarbonates. At least one surface of the substrate 30 contains a conductive pattern 31 formed of randomly oriented, interconnected electrically conductive elements 32. In this preferred example, the elements 32 are shown as being linear.
The elements 32 are shown as being in contact with each of their adjoininq horizontal and vertical vertices so that electrica1 continuity is maintained throughout the pattern 31. While each element 32 is in contact with its neighboring elements, the elements are preferably arranged so that they do not present a linear component that is greater in length than the length of one element.
The size of the elements 32 depends in large part upon the shielding and visual opacity charactaristics desired. The smaller the elements, the greater the shielding characteristics and the lesser the visual opacity and vice versa. Pr~ferahly the selected elements 32 should be of size such that they do not severely detract from either characteristic.
Two dimensions are relevant in discussing the size of the elements 32; the length of the elements and the annular width o the elements.
With linear elements, the length can be the same as that generally used to form a linear grid such as that of the mesh of the prior art such as from about .002 inches to about 0.10 inches. In general, the linear elements range from about four elements per inch to about one hundred elements per inch, preferably about 50 to 100 elements per inch.
203u8~
The annular width is herein d~fined as the distance from one outer edge of the element to the corresponding outer edge of the element. If a variation in annular width occurs, either due to the manufacturing process or due to a desired purpose, the annular width shall be an average of the distances taken from various points across the diameter of the element. The annular width of an element should be fairly consistent throughout. The annular width of the elements ranqes from about .0002 inches to about .005 inches, preferably about .001-.002 inches.
Preferably, the elements 32 of a pattern will vary over a range of lenyths due to the distortion of the vertices. Moreover, the arrangement o elements in the pattern may be selective such that the length of elements in one portion of the substrate are different from those in another area. For e~ample, if one wishes to have less visual opacity around the edge of the conductive substrate, one may use element~ 32 along the edge of the substrate that have a smaller average length and/or greater width than the elements on the inner portion of the substrate. Also, one may use elements of different average lengths and/or widths to ensure that there is complete and adequate conductivity throughout the pattern.
Preferably, the conductive pattern 31 is terminated along its outside edges with a conductive strip, commonly called a bus bar 33.
The bus bar 33 may be a conductive layer formed on or in the surface of the substrate. The bus bar 33 can be formed in a manner identical to the formation of the pattern e~cept preferably it is void free. However, if desired, one could 203~
use elements 32 that are smaller in diameter and/or thicker in annular width along the edges of the pattern 31 to form the bus bar 33.
A~ditionally, the bus bar 33 can be formed of a separate conductive layer sintered or bonded to the edge areas of the substrate 30. For e~ample, the bus bar 33 can be a conductive ink or epo~y, a conductive metal plating, a metal strip, a conductive, sinterable frit such as silver coated glass, or more preferably, a conductive metal tape, such as CHO-FOIL~, available from Chomerics, Inc.
The bus bar 33 is designed in such a manner that it establishes and maintains electrical continuity between the substrate 30 and the frame, cabinet or closure to which it is attached. The bus bar 33 may do so directly, ilÇ~ its surface meets and mates with a conductive surface of the frame, cabinet or closure to which the substrate is attached.
Preferably, the bus bar is connected to a conductive lead such as a grounding strap, a metal frame, or a conductive gaæket that establishes contact with the surface to which the substrate is mounted. By using the intermediate connection between the bus bar of the substrate and surface, one avoids the problems of establishing a perfect fit between the surfaces as would be re~uired by a direct connection between the surface and the substrate.
Figure 4 shows another preferred embodiment of the present invention.
The surface 41 of the substrate 40 containing the pattern 42 may also be covered by a protective coating 43, such as a conformal coating to prevent oxidation and damage to the conductive pattern during handling. Such coatings are well known and generally are formed of a sprayable plastic 21~3~
materlal, such as polyurethane. The coating can also be a film, ~uch as MYLAR~ films or KAPTON~ films, which may be bonded to the substrate surface.
The surface 41 of the substrate 40 containing the pattern 42 may also be covered by a transparent conductive coating 43, such as indium tin o~ide. This coating may he applied by vacuum deposition, sputtering, or spray pyrolysis.
The addition of this conductive coating will increase the effective shielding of the assembled window.
If ~esired, the substrate can be joined with another suhstrate to form a laminate of two or more layers. In this embodiment, the surface of the substrate containing the conductive pattern faces the inner surface of the other substrate. Such lamînations and processes for forming them are well ~nown and generally consist of a bonding layer between the substrates to hold the two substrates together.
Typically, a polyvinyl butyral material is used as the bonding aqent~ although other similar adhesive material such as polyurethanes can be used. Alternatively, the two substrates can b~ melt bonded together, although one must take care not to injure the conductive pattern in doing so.
A preferred method of forming the pattern on the conductive window of this invention is by a photolithography or an electroforming method.
In the preferred process, a desired pattern is first created. The pattern can be drawn by hand or preferably by a computer qenerated program. A preferred simple means for creating the randomly oriented pattern of the present invention is to use a computerized print program which will lay out a series of elements of the desired length and width in an arrangement so that the vertices of the elements are .
2036~6~
randomly oriented from their normal x and y coordinate by a small increment and angle, ~ . A photomask is made of the pattern and imaged onto a resist coated substrate. The resist coated substrate is esposed to actinic radiation and developed. The developed image is then plated to form a conductive pattern.
A suitable computer program used to generate the pattern follows the following logic: The ~,y coordinates for a series of equally spaced vertices are generated and stored.
Preferably, the ~,y coordinates are equidistant from each other i.e. a square like grid pattern. Each coordinate is then moved by a small increment in either the ~ or y or both the x and y coordinate and at a random angle, ~ , wherein o~ ¦
can b~ any angle between 0 to 360. The small incremental distance may be uniform i.e, a percentage of the distance between the established adjoining ~,y coordinates or it may be random, varying over a preselected range, i,e. equal to or less than a certain percentage of the distance between the established adjoining s,y coordinates. A new series of ~',y' I
coordinates are then plotted. Elements are then formed to interconnect the vertices, e.q. using the elements to interconnect the ~' to x~ and y~ to y' coordinates of adjoining vertices. The output of the computer program is the x'/y~ coordinates and element lengths which are used to drive a computer ~lotter or photomask generator. The generated photomask may be either a positive or a negative photomask.
One preferred embodiment is to use a resist coated metal layer substrate to form the desired pattern. The substrate has a metal layer bonded or plated onto its desired surface. The metal la~er is coated with a resist layer. The resist is e~posed to a negative photomask and developed and 2~3~j8~
the unwanted portion of the metal layer is etched away to leave a conductive metal pattern on the surface of the substrate. As discussed above, in relation to the resist covered substrate, add;tion~l conductive layer~ may be placed upon the conductiv~ pattern, preferably by a plating process.
Suitable substrates include, but are not limited to glass and various transparent or translucent plastics. The metal layer may be formed of any conductive metal such as silver, gold, platinum, palladium~ nickel, copper, tin, zinc, aluminum, etc. It is preferred that the metal layer be formed of copper due to its cost, availability and ease of etchin~ and plating. The metal layer may be in the form of a metal foil or film which is embedded into or bonded onto the substrate surface. It may also be formed by vapor deposition, sputter coatinq or other deposition means which form a unîform metal layer on the substrate's surface. As stated above, the resultant pattern can be further plated or treated to render it more conduc~ive.
In another pr~ferred emhodiment, one c~n form the pattern on a re~ist coated substrate which will form the conductive window. This substrate may be formed of any transparent or translucent material typically used for such conductive windowsO E~amples of such materials include, but are not limited to, glass and various plastics such as polycarbonates and polyacrylates. In this embodiment, the resist is formed on the desired surface of the substrate. The resist is then esposed to the pattern formed on a positive photomask and developed. The substrate is then etched, preferably with an acid, tc create the desired pattern in the substrate surface. The etched pattern is then filled with a 2036~68 conductive material such as a conductive ink a conductive adhesive, preferably a conductive epo~y, a conductive frit, such a3 a conductive ceramic frit, or a conductive metal, such as copper, silver, nickel, gold, tin, zinc, aluminum or platinum. It is preferred to use a conductive adhesive, especially a silver filled epoxy. If desired, the conductive pattern may additionally be plated with conductive metals, such as, but not limited to silver, gold, platinum, nickel, tin, zinc, aluminum or copper to enhance its conductivity and reduce o~idat;on.
If one desires to form a free standing conductive rnaterial incorporatin~ the desired pattern, one can form a resist on a suitable mandrel, generally havinq a metal surace, e~pose and wash the resist, and etch the desired pattern into the mandrel's surface. A plating is then formed on the mandrel's surface such a~; by an electrodeposition bath. The plated material is then removed from the mandrel and applied like any other conductive mesh known in prior art to the tranæparent substrate.
The shielding capability of the present invention is equal to that of shielded devices usi~g a mesh like grid. For example, a conductive substrat~ formed according to this invention, having linear elements of an average length of 0.010 inches and an average annulus width of 0.0013 inches has a shielding capability comparable to that of a wire mesh shielding device having 100 openings per inch and a mesh diameter of 0.0015 inches (a shielding capability of 65 dBs at 100 megahertz).
If desired, the substrate containing the conductive pattern may be curved, either before or after formation of the conductive pattern. Typically the curvature is ormed after ~ 2~3~8 ~
the formation of the conductive pattern by placing the substrate in an ov~n and allowing the substrate to soten and flow or slump to the correct curvature. If necessary, a mold or means for applying pressure to the substrate surface may be used to ensure the formation of the correct curvature.
The present invention may be used in a computer terminal as an EMI/RFI shield. It also has applications in the area of EMI/RFI shielded windows, such as in high security buildings and vehicles. It may also be used in applications that require a conductive or heated window such as a rear window defogger in an automo~ile. It is believed that in this application the conductive pattern is less distractive to the operator than the grid like formation that is currently in use.
Additionally, when the conductive pattern is formed as a freestanding material, it can be a replacement for knitted or braided conductive mesh used in forming conductive gaskets.
While the present invention has been described with reference to its preferred embodiments, other embodiments can achievP the same result. variations and modifications of the present invention will be obvious to those skilled in the art and ît is intended to cover in the appended claims all such modifications and equivalents as fall within the true spirit and scope of this invention.
Claims (32)
1. An EMI/RFI shielded article comprising a transparent or translucent substrate and a randomly oriented, conductive pattern on at least one surface of the substrate, the pattern being formed of a series of interconnected elements which meet to form a grid-like pattern wherein a substantial number of adjoining elements meet an angle which is less than or greater than, but not equal to 90°.
2. The transparent article of Claim 1 wherein the electrically conductive pattern is selected from the group consisting of conductive metals and conductively filled adhesives, inks and frits.
3. The transparent article of Claim 1 wherein the transparent substrate is selected from the group consisting of glass and rigid transparent plastics.
4. The transparent article of Claim 1 wherein the elements are of a shape selected from the group consisting of linear or curvilinear elements.
5. The transparent article of Claim 1 further comprising a bus bar formed along at least one outer edge of the pattern, the bus bar being electrically conductive and in intimate contact with at least one edge of the pattern.
6. The transparent article of Claim 1 wherein the elements are linear in shape of a length from about .002 inches to about .10 inches and an annular width of about .0002 inches to about .005 inches.
7. An EMI/RFI shielded device comprising a transparent or translucent substrate and a randomly oriented, pattern formed on a surface of the substrate, wherein the pattern is comprised of a series of interconnected, linear elements wherein the vertices of such elements are randomly 1.
located in both the vertical and horizontal coordinates relative to a normal grid like pattern having elements of equal length.
located in both the vertical and horizontal coordinates relative to a normal grid like pattern having elements of equal length.
8. The EMI/RFI shielded device of Claim 7 wherein the substrate is selected from the group consisting of glass and rigid plastics; and the elements are of a form selected from the group consisting of linear elements, curvilinear elements and mixtures thereof.
9. The EMI/RFI shielded device of Claim 8 wherein the rigid plastics for the substrate are selected from the group consisting of polyvinyl butyrals, polyurethane, polyacrylates, and polycarbonates.
10. The EMI/RFI shielded device of Claim 7 wherein the pattern is etched into the surface of the substrate.
11. The EMI/RFI shielded device of Claim 7 wherein the pattern is formed of an electrically conductive material selected from the group consisting of electrically conductive metals, electrically conductive inks, electrically conductive adhesives, electrically conductive fillers and electrically conductive frits.
12. The EMI/RFI shielded device of Claim 7 further comprising a second substrate bonded to the surface of the first substrate upon which the pattern is formed so as to form a laminate.
13. The laminated shielded window comprising a first substrate, an electrically conductive, randomly oriented, pattern formed on a surface of the first substrate, the pattern being comprised of a series of interconnected elements a substantial number of which meet at an angle which is less than or greater than but not equal to 90° so as to form a grid-like array, a bonding layer applied to the surface of the first substrate having the conductive pattern and a second substrate attached to a surface of the bonding layer formed on a surface opposite the surface attached to the first substrate.
14. The window of Claim 13 wherein the first and second substrates are selected from the group consisting of glass and rigid plastics; the bonding layer is selected from the group consisting of transparent plastic adhesives; the elements are of a shape selected from the group consisting of linear elements, curvilinear elements and mixtures thereof.
15. The window of Claim 13 wherein the elements are linear in shape and, having a length of from about .002 inches to about .10 inches and an annular width of from about .0002 inches to about .005 inches.
16. The window of Claim 13 wherein the pattern is formed of a conductive material selected from the group consisting of conductive metals, conductive inks, conductive adhesives and conductive frits.
17. The window of Claim 13 wherein the bonding layer is selected from the group consisting of polyvinyl butyrals, polyurethanes, epoxies and mixtures thereof.
18. The window of Claim 13 further comprising a bus bar formed along at least one edge of the pattern and containing an electrical lead for establishing electrical conductivity between the pattern and a surface to which the window is mounted.
19. A method for forming a moire'-free EMI/RFI
shield comprising the steps of:
a) generating a negative photomask pattern having a series of randomly oriented, interconnected, elements; said elements being interconnected in such a manner that a substantial portion of adjoining vertical and horizontal elements form an angle that is less than or greater than but not equal to 90°
adjoining horizontal elements and adjoining vertical elements form an angle that is less than or greater than but not equal to 180°;
b) coating a substrate with a conductive metal;
c) coating the metal with a photoresist;
d) exposing the photoresist to the negative photomask;
e) developing the exposed photoresist;
f) etching the exposed metal to the substrate;
g) removing the photoresist;
h) plating a conductive metal on the exposed metal pattern; and i) placing the plated substrate within a frame for mounting to an electronic device.
shield comprising the steps of:
a) generating a negative photomask pattern having a series of randomly oriented, interconnected, elements; said elements being interconnected in such a manner that a substantial portion of adjoining vertical and horizontal elements form an angle that is less than or greater than but not equal to 90°
adjoining horizontal elements and adjoining vertical elements form an angle that is less than or greater than but not equal to 180°;
b) coating a substrate with a conductive metal;
c) coating the metal with a photoresist;
d) exposing the photoresist to the negative photomask;
e) developing the exposed photoresist;
f) etching the exposed metal to the substrate;
g) removing the photoresist;
h) plating a conductive metal on the exposed metal pattern; and i) placing the plated substrate within a frame for mounting to an electronic device.
20. The method of Claim 19 wherein the elements are selected from the group consisting of linear elements, curvilinear elements and mixtures thereof .
21. The method of Claim 19 wherein the substrate is a metal-clad glass or plastic.
22. The method of Claim 19 wherein the electrically conductive material is selected from the group consisting of noble metals, non noble metals, conductive adhesives, conductive inks, and conductive frits.
23. The method of Claim 19 further comprising a step of coating the plated pattern of (h) with a protective layer.
24. The method of Claim 23 wherein the protective layer is selected from the group consisting of conductive metal platings, conductive metal films, conductive metal coatings, polymeric coatings, polymeric films, an additional substrate layer and combinations thereof.
25. The method of Claim 24 wherein the protective layer is a conductive metal coating of indium tin oxide.
26. The method of Claim 25 wherein the protective layer is an additional substrate layer.
27. A method for forming a moire'-free EMI/RFI
shield comprising the steps of:
a) generating a positive photomask pattern having a series of randomly oriented, interconnected, elements; said elements being interconnected in such a manner that a substantial portion of adjoining vertical and horizontal elements form an angle that is less than or greater than but not equal to 90° adjoining horizontal elements and adjoining vertical elements form an angle that is less than or greater than but not equal to 180°;
b) coating a substrate with a photoresist;
c) exposing the photoresist to the positive photomask;
d) developing the exposed photoresist;
e) etching the exposed substrate;
f) removing the photoresist;
g) filling the etched pattern in the substrate with an electrically conductive material; and h) placing the plated substrate within a frame for mounting to an electronic device.
shield comprising the steps of:
a) generating a positive photomask pattern having a series of randomly oriented, interconnected, elements; said elements being interconnected in such a manner that a substantial portion of adjoining vertical and horizontal elements form an angle that is less than or greater than but not equal to 90° adjoining horizontal elements and adjoining vertical elements form an angle that is less than or greater than but not equal to 180°;
b) coating a substrate with a photoresist;
c) exposing the photoresist to the positive photomask;
d) developing the exposed photoresist;
e) etching the exposed substrate;
f) removing the photoresist;
g) filling the etched pattern in the substrate with an electrically conductive material; and h) placing the plated substrate within a frame for mounting to an electronic device.
28. The method of Claim 27 wherein the small increment is from 10 to about 50% of the distance between the vertices in the evenly spaced pattern.
29. The method of Claim 28 wherein the small increment is from 20 to about 40% of the distance between the vertices in the evenly spaced pattern.
30. An EMI/RFI shielded device comprising a substrate having a surface upon which a conductive pattern is formed, the pattern is comprised a series of randomly oriented vertical and horizontal elements interconnected at a plurality of vertices, the vertices being displaced from a normal vertical/horizontal (x,y) position by a random angle, .alpha. , and a small incremental distance so as to be a new vertical/
horizontal (x',y') position.
horizontal (x',y') position.
31. The shielded device of Claim 30 wherein the random angle, .alpha. , is from 0 to 360° and the incremental distance is less 50% of the distance between normally spaced vertices.
32. The shielded device of Claim 30 wherein the incremental distance is from about 20 to about 40% of the distance between normally spaced vertices.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US48891190A | 1990-03-06 | 1990-03-06 | |
| US488,911 | 1990-03-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2036868A1 true CA2036868A1 (en) | 1991-09-07 |
Family
ID=23941630
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2036868 Abandoned CA2036868A1 (en) | 1990-03-06 | 1991-02-21 | Non-moire shielded window |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0446038A3 (en) |
| JP (1) | JPH04217397A (en) |
| CA (1) | CA2036868A1 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3185048B2 (en) * | 1996-10-04 | 2001-07-09 | モレックス インコーポレーテッド | Flat flexible cable |
| EP0883156B9 (en) * | 1997-06-03 | 2005-09-21 | Hitachi Chemical Co., Ltd. | Electromagnetically shielding bonding film |
| US6086979A (en) * | 1997-11-11 | 2000-07-11 | Hitachi Chemical Company, Ltd. | Electromagnetically shielding bonding film, and shielding assembly and display device using such film |
| MY123910A (en) * | 1998-08-10 | 2006-06-30 | Sumitomo Bakelite Co | Transparent electromagnetic wave shield |
| WO2008140007A1 (en) * | 2007-05-09 | 2008-11-20 | Toray Industries, Inc. | Conductive board, electromagnetic shielding board for plasma display and method for manufacturing conductive board |
| KR101285512B1 (en) * | 2010-10-22 | 2013-07-17 | 주식회사 엘지화학 | Display device compring conductive pattern |
| TWI623776B (en) | 2012-12-17 | 2018-05-11 | Ｌｇ伊諾特股份有限公司 | Method of designing and optical substrate |
| JP6503728B2 (en) * | 2013-12-26 | 2019-04-24 | 大日本印刷株式会社 | Display device |
| JP6477079B2 (en) * | 2015-03-18 | 2019-03-06 | 大日本印刷株式会社 | Touch panel sensor, touch panel device, and display device |
| JP2016212517A (en) * | 2015-04-30 | 2016-12-15 | 凸版印刷株式会社 | Conductive film, touch panel, and display device |
| KR102541112B1 (en) | 2016-04-05 | 2023-06-09 | 미래나노텍(주) | Touch sensor comprising atypical sensor pattern |
| CN109360251A (en) * | 2018-09-06 | 2019-02-19 | 秦皇岛波盾电子有限公司 | A kind of non-angular Transparent shielding random grid pattern generation method |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1272812A (en) * | 1960-11-02 | 1961-09-29 | Method for enhancing images such as images obtained on a television screen and frames conforming to those used in the foregoing method or similar method | |
| JPS61253751A (en) * | 1985-05-02 | 1986-11-11 | Mitsubishi Plastics Ind Ltd | Electromagnetic wave shielding filter |
| NO872943L (en) * | 1986-07-21 | 1988-01-22 | Mitsui Toatsu Chemicals | Cathode ray tube screen filter. |
| IL86113A (en) * | 1987-04-28 | 1992-02-16 | Ppg Industries Inc | Electroforming of electromagnetic pulse shielding elements |
-
1991
- 1991-02-21 CA CA 2036868 patent/CA2036868A1/en not_active Abandoned
- 1991-03-05 JP JP6246491A patent/JPH04217397A/en active Pending
- 1991-03-06 EP EP19910301879 patent/EP0446038A3/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP0446038A3 (en) | 1992-01-08 |
| EP0446038A2 (en) | 1991-09-11 |
| JPH04217397A (en) | 1992-08-07 |
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