NA
`
`United States Patent p19)
`Melbyetal.
`
`(11]
`
`[45]
`
`US005254388A
`Patent Number:
`
`Date of Patent:
`
`5,254,388
`Oct. 19, 1993
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`
`Appl. No.:
`
`820,611
`
`[22]
`
`[86]
`
`PCT Filed:
`
`PCT No.:
`
`Dec. 20, 1991
`
`PCT/US91/09724
`
`§ 371 Date:
`§ 102(e) Date:
`
`Dec. 20, 1991
`Dec. 20, 1991
`
`[63]
`
`{51}
`[52]
`
`(58)
`
`Related U.S. Application Data
`Continuation-in-part of Ser. No. 632,123, Dec. 21,
`1990, abandoned:
`
`Int. C15 occescssesesseeseeesieeseessseasgensaveneees B32B 3/00
`WS. C1. ceecccscssscestsesssctsesseesteees 428/120; 428/163;
`428/167; 428/168; 428/170; 428/212; 428/218;
`430/12; 430/23
`Field of Search. ............... 428/120, 163, 167, 168,
`428/170, 212, 218; 430/12, 23
`
`LIGHT CONTROL FILM WITH REDUCED
`GHOST IMAGES
`
`[56]
`
`Inventors: Sanford Cobb Jr., Saint Mary’s Po,
`Minn.; Leo A. Meyer; Jeffrey J.
`Melby; Scott G, Theirl, all of St.
`Paul, Minn.
`Minnesota Mining and
`Manufacturing Company, St. Paul,
`Minn.
`
`Assignee:
`
`References Cited
`U.S. PATENT DOCUMENTS
`4/1973
`ONSEN .....sssesscconssensevevsereesseeanssee -161/6
`4/1972
`12/1972
`2/1974
`11/1975
`11/1975
`8/1982
`8/1988
`
`Re. 27,617
`3,653,138
`3,707,416
`3,791,722
`3,919,559
`3,922,440
`4,342,821
`4,764,410
`4,766,023
`4,788,094 11/1988
`4,815,821
`3/1989 Nonogaki et al. 0... 350/164
`
`8/1988
`
`FOREIGN PATENT DOCUMENTS
`
`0275205 7/1988 European Pat. Off...
`Primary Examiner—Patrick J. Ryan
`Assistant Examiner—Abraham Bahta
`Attorney, Agent, or Firm—Gary L. Griswold; Walter N.
`Kirn; Stephen W. Buckingham
`[57]
`ABSTRACT
`A louvered plastic film has louvers including central
`regions with a relatively high coefficients of extinction
`and outer regions with relatively low coefficients of
`extinction. Such a film provides a dramatic reduction in
`ghost images.
`
`30 Claims, 2 Drawing Sheets
`
`
`
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`i
`eat
`aeow
`
`APPLE 1008
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`1
`
`APPLE 1008
`
`

`

`U.S. Patent
`
`Oct. 19, 1993
`
`Sheet 1 of 2
`
`5,254,388
`
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`U.S. Patent
`
`Oct. 19, 1993
`
`Sheet 2 of 2
`
`5,254,388
`
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`

`1
`
`3,254,388
`
`LIGHT CONTROL FILM WITH REDUCED GHOST
`IMAGES
`
`This is a continuation-in part of application, No.
`07/632,123 filed Dec. 21, 1990, now abandoned.
`
`BACKGROUND OF THE INVENTION
`U.S. Pat. No. Re. 27,617 (Olsen) teaches a process of
`making a louveredlight control film by skiving a billet
`of altercating layers of plastic having relatively lower
`and relatively higher optical densities. Upon skiving the
`billet, the pigmented layers serve as louver elements,
`which,as illustrated in the patent, may extend orthogo-
`nally to the resulting louvered plastic film. U.S. Pat. No.
`3,707,416 (Stevens) teaches a process wherebythe lou-
`ver elements may be canted with respect to the surface
`of the louvered plastic film to provide a film which
`transmits light in a direction other than perpendicular to
`the surface of the film. U.S. Pat. No. 3,919,559 (Stevens)
`teaches a process for attaining a gradual changein the
`angle of cant of successive louver elements.
`Amongthe uses for such louvered plastic films are
`lenses and goggles as shown in U.S. Pat. No. 3,791,722
`(Ahiberget al.), to be worn wherehigh levels of illumi-
`nation or glare are encountered. The film may also be
`used for transparent. covering for a backlighted instru-
`ment panel, such as the instrument panel of an automo-
`bile, to minimize reflections from the windshield. A
`louvered plastic film may also be used to give a black
`and white photographic negative the appearance of a
`positive made from the negative as taught in U.S. Pat.
`No. 3,653,138 (Cooper).
`U.S. Pat. No. 3,922,440 (Wegwerthet al.) points out
`that because louvered plastic films to are thin sheet
`materials: (1) they are not by themselves capable of
`structurally withstanding extreme stresses and (2) they
`are subject to distortion from physical stress and tem-
`peratures” (col. 1, lines 19-22). Furthermore, the skiv-
`ing by which the louvered plastic films are produced
`results in irregular surfaces which seriously limits the
`optical quality of the film. Typically such filmsare, for
`practical purposes, translucent rather than transparent.
`Accordingly, as in Example 1 of that patent, the lou-
`vered plastic film usually is laminated under pressure
`between two clear plastic films of a material such as
`cellulose acetate butyrate, the material usually used in
`making louvered plastic films. Typically, the louvered
`plastic film is skived from the billet. to a thickness: be-
`tween.0.1 and 0.4 mm andeachof the outerplastic films
`has a thickness of between 0.1 and 0.3 mm. Theratio of
`the thickness of the skived film to the width of the clear
`regions will control the permitted view angle, with a
`greater ratio providing a narrower angle. Wegwerth’s
`process of laminating louvered plastic films between
`twoclear films requires an expensive press whichis also
`expensive to operate. This is in part from the need to
`distribute heat uniformly and in part from the need. to
`apply pressure with precision. Because the resulting
`laminates cannot be larger than the platensof the press
`in. which they are laminated, the press must be suffi-
`ciently large to produce the required size thus increas-
`ing the expense of the press.
`U.S. Pat. Nos. 4,764,410 (Grzywinski) and 4,766,023
`(Lu) teach alterative to the Wegwerth method. These
`alternative methods include the steps of (1) coating the
`skived louvered plastic film with a solventless monomer
`composition which polymerizes to an adhesive state or
`
`5
`
`10
`
`20
`
`40
`
`45
`
`50
`
`55
`
`60
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`2
`a hard state, respectively, upon exposure to radiation,
`(2) overlaying the monomer composition with a plastic
`film, and (3) exposing the coating to radiation to poly-
`merize the composition. After polymerization the plas-
`tic liner which was placed over the monomer composi-
`tion may be left in place to serve as protection for the
`louvered plastic film, or may be removed, leaving the
`polymerized composition exposed.
`Such films are used for various purposes..One com-
`mon use is to prevent light from automobile control
`panels from reaching the windshield and causing dis-
`tracting and dangerousreflections at night. Another use
`is to cover the screen of a CRT or other display to
`prevent persons other than the operator from reading
`data displayed thereon.
`.
`.
`A problem that is commonto all of the louvered films
`described above, arises from the difference betwéen the
`clear and dark layers. Typically the clear and dark
`layers are formed of the same material. A preferred
`material is cellulose acetate butyrate (CAB), although
`other materials may be used. The louvers are, however,
`rendered dark by the inclusion of very fine particles of
`another material. A preferred material is carbon black.
`If carbon black is used these particles have an average
`diameter of less than 0.1 xm. Thus they are much
`smaller than the wavelength ofthe light.
`In spite of the small size of these particles, and, in fact,
`in part because of that size, the presence ofthe particles
`causes the index of refraction of the composite to be
`different from that of the plastic alone. Since the index
`of refraction of the clear and dark layers are different,
`light is reflected at the interface between the two. The
`effect of this reflection is the creation of “ghost” im-
`ages. The percentage of the incident light that is re-
`flected increases with increasing angle of incidence and
`increasing difference of index of refraction. For these
`purposesthe angle of incidenceis the angle between the
`ray of light and a normal to the interface between the
`clear and dark layers. As a result the ghost images of a
`typical film are most noticeable at angles between 5°
`and 25° from the axis of the louvers. Such ghost images
`are aesthetically displeasing, at best. Furthermore,if the
`film is to be used to cover a CRT screen or other dis-
`play, the ghost images can cause misinterpretation of
`data and significantly contribute to operator fatigue.
`One approachto elimination of the ghosting problem
`is to provide a matte finish on the interface between the
`clear and dark layers. This tends to eliminate distinct
`ghost images, but does not reduce the total amount of
`light reflected. Thus the ghost image is replaced by a
`blurred, butclearly visible, glow. In addition the cre-
`ation of such a matte surface is very difficult in the
`currently preferred coextrusion processes wherein the
`clear and dark layers are extruded together in a single
`process.
`An alternative approach is to reduce the amount of
`carbon black incorporated into the layers forming the
`louvers. In this case, the difference in index of refraction
`between the clear and dark layers is less than in the
`previously described film and thus reflections are re-
`duced. However,if the louvers remain the same width
`as those with higher optical density, they will no longer
`meet opacity requirements. Thus, such films may not be
`used as privacy screens. Alternatively the louvers may
`be made wider to meet opacity requirements. This,
`however, will reduce the on-axis transmission through
`the louvered film to unacceptably low levels and/or
`make the louvers individually visible.
`
`4
`
`

`

`3
`
`SUMMARYOF THE INVENTION
`
`According to the invention, a louvered plastic film
`has a plurality of clear regions separated by louvers.
`Each louver has a central region with a relatively high
`coefficient of extinction and outer regions, adjacent said
`clear regions, having relatively low coefficients of ex-
`tinction.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic cross section of a louvered
`plastic film according to the invention;
`FIG.2 is an enlarged drawing of a portion of the
`louveredplastic film of FIG. 1; and
`FIG.3 is a schematic cross section of a privacy screen
`for a cathode ray using a louvered plastic film of the
`invention.
`
`DETAILED DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`5,254,388
`4
`difference in index of refraction between it and layer 12.
`Therefore verylittle of the light is reflected by layer 24.
`Mostof the light will enter layer 16 and be refracted. As
`the light traverses layer 16, some will be absorbed.
`Some, however, will strike layer 20 on surface 26. Some
`of light beam 22 will enter layer 20 where, due to the
`relatively high concentration of carbon black,it will be
`absorbed. Some oflight beam 22 will be reflected at
`surface 26 due to the large difference in index of refrac-
`tion between layer 16 and layer 20.
`The advantageofthe inventionlies in the fact that the
`effective optical density of a medium is directly propor-
`tional to the distance that the light must travel through
`that medium andthefact that reflection at an interface
`between two materials with different indices of refrac-
`tion increases with increasing angle of incidence.Thus,
`the light that is most likely to be reflected at the inter-
`face between layers 16 and 20 is the light that enters
`layer 16 at a grazing angle. Such light must travel a long
`distance through layer 16 both before and after reflec-
`tion from surface 26ifit is to reemerge through surface
`24. Therefore, the majority of light entering layer 16
`will be absorbed even though layer 16 has only a com-
`paratively light loading of carbon black.
`To fully appreciate a film of the present invention,it
`should be compared with a prior art louvered film. In a
`typical prior art film, clear layers 0.0953 mm thick are
`separated by louvers with a thickness of 0.0114 mm.
`The clear regions and the louvers both are made pri-
`marily of CAB butthe louvers further include 5 percent
`carbon black by weight. A simple calculation will show
`that the clear regions make up about 89 percent of such
`a film. In a preferred embodimentof the invention clear
`regions, such as clear region 12, are 0.0876 mm thick.
`Thelightly loaded regions, such as layers 16 and 18,are
`0.00445 mm thick, while the dark regions, such as layer
`20, are 0.010 mm thick. Lightly loaded regions 16 and
`18 include 0.75 percent carbon black by weight while
`heavily loaded region 20 includes 5 percent carbon
`black by weight. In such a film the clear regions make
`up about86 percent ofthe film. Thus, such a film manu-
`factured according to the invention will produce a dra-
`matically reduced ghost image while covering a back-lit
`display, yet will provide only very slightly reduced
`on-axis transmission as comparedto a film of the prior
`art. Ghost images could be further reduced by including
`additional intermediate layers between layers 16 and 20.
`For any given application the preferred construction
`will be determined by the acceptable amount of ghost-
`ing, the minimum acceptable on-axis transmission and
`acceptable difficulty of construction.
`Although a wide variety of film parameters are possi-
`ble within the scope of the invention, values within
`certain ranges are preferable in general, the lightly
`loaded outer portions of the louvers should be in the
`range of 0.12 to 1.0 percent carbon black by weight and
`the heavily loaded inner portion should be in the range
`of 1.5 to 10 percent carbon black by weight. For use
`with-video displays the film should be between 0.08 and
`0.6 mm thick. The clear regions should be between 0.05
`and 0.25 mm wide, the outer regions of the louvers
`should be 0.0025 and 0.01 mm wide and the central
`regionsof the louvers should be between 0.005 and 0.02
`mm wide. In somesituations more distant objects are to
`be viewed through a film. One such application is the
`use Of a film as a sunscreen in the rear window of an
`automobile. In such situations thicker films with wider
`
`20
`
`25
`
`30
`
`45
`
`Thepresent invention overcomesthe problemsofthe
`prior art by using louvers having an outer portion with
`a relatively low optical density and an inner portion
`having a relatively high optical density. Alternatively
`stated, the outer portions havea relatively lower coeffi-
`cient of extinction and the inner region hasa relatively
`higher coefficient of extinction. For these purposes the
`transmission through a medium is given by the formula
`
`T=10774
`
`whereT is the decimal fraction of light that is transmit-
`ted, x is the coefficient of extinction and d is the optical
`path length through the medium. In CAB with carbon
`black incorporated in the percentages contemplated in
`the invention, the coefficient of extinction is approxi-
`mately equal to 4750C whereC is the decimal fraction
`of carbon blackin the film and the coefficient of extinc-
`tion is expressed in inverse millimeters. In this case, d in
`the equation above would be expressed in millimeters.
`A desirable film would have louvers in which each
`louver varied continuously from clear at its edges to
`very dark at its center. Creation of such graded optical
`density films would be very difficult, however. There-
`fore, a preferred embodiment uses a multilayer louver
`construction.
`FIG. 1 illustrates a louvered film 10 according to the
`present invention. It should be noted that FIG. 1 is an
`edge view ofthe film and that in normal use it would be
`viewed from an angle perpendicular to that of the Fig-
`~ ure. Louvered film 10 has cover sheets 11 provided for
`clarification and includes alternating clear layers, such
`as layer 12 and louvers, such as louver 14. Louver 14, in
`turn, includes outer layers 16 and 18 and inner layer 20.
`Louver 14 will be described as containing carbon black,
`although other darkening agents could be used. Inner
`layer 20 includes a comparatively high concentration of
`carbon black in order to provide louver 14 with the
`required opacity. Outer layers 16 and 18 have carbon
`black, but in a lower concentration than that of layer 20.
`Thus, while they have a lowercoefficient of extinction
`than layer 20, they also have an index of refraction that
`is closer to that of clear layer 12.
`The operation of the louvers may be moreclearly
`understood by reference to FIG. 2. FIG. 2 is an ex-
`panded view of a portion of clear layer 12 and louver
`14. A light ray 22 enters transparent layer 12. It then
`strikes layer 16 at surface 24. Because layer 16 has only
`a low concentration of carbonblack,there is not a large
`
`5
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`

`

`3,254,388
`
`15
`
`20
`
`30
`
`5
`6
`clear areas and louvers may be used andareoften pref-
`will work well as the neutral density conductive coat
`erable. Therefore, more generally stated,
`the films
`and the antireflective coat are available from Viratec
`should be between 0.08 and 1.5 mm thick, with clear
`Thin Films Inc. under the trade names NDAR and
`regions having widths in the range of 0.05 to 1.0 mm.
`CDAR,respectively. An alternative neutral density
`The louvers should have outer regions between 0.0025
`conductive coating is available from the same source
`and 0.015 mm wide and central regions 0.005 and 0.03
`under the trade name TDAR.
`mm wide.
`To use the structure of FIG. 3 as a privacyfilter, a
`One embodimentthatis not optimized for any partic-
`section the size of the screen of the CRT on which the
`ular application, but is useful in a wide variety of appli-
`filter is to be placed is prepared. Thefilter is then placed
`cations is made of CAB and has louvers having dark
`in front of the CRT screen. In operation, antireflection
`heavily loaded central regions that include 3 percent by
`coating 36 prevents glare resulting from reflection of
`weight carbon black and are 0.01 mm wide. Thelightly
`ambient room light from the front of the privacyfilter.
`loaded outer layers are 0.2 percent carbon black and are
`Glass layers 30and 32 provide stability as well as pro-
`0.0075 mm wide. The clear regions are 0.09 mm wide.
`viding a surface on whicha hard antireflective coat may
`Thefilm thickness is preferably in the range of 0.15 mm
`be provided. Antireflection coat 38 prevents reflection
`to.0.5 mm. Thicker films will allow a lower range of
`of ambientlight entering the system from the back sur-
`viewing angles through the film. A preferred form of
`face of the privacy filter. This is particularly important
`carbonblackis available from Cabot Corporation under
`because such light will pass through the louvered film a
`the name XC72.
`second time but displaced slightly from where it passed
`A film according to the invention could be manufac-
`throughthefirst time. As a result, the reflections of the
`tured in a variety of ways. The most straight forward
`louvers will not be precisely aligned with the actual
`would be to manufacture layers 12, 16, 18 and 20 sepa-
`louvers creating very distracting moiré patterns. By
`rately, stack them intoabillet, repeating layers in the
`providing an efficient antireflective coating 38, such
`proper order and skive them as taught bythepriorart.
`moiré patterns are avoided.
`Extremely thin layers, especially layers such as 16,18
`The remaining layer is conductive layer 34. It pro-
`and 20, are difficult to handle, however. In a preferred
`vides several functions. If it is at the lower end of the
`method of manufacture the layers are co-extruded. In
`order to do so the extruder must havethree feeds and at
`thickness range specified above, approximately 300
`angstroms, it will have a resistivity of approximately
`least four outputs. Preferably the extruder would have
`five outputs. The extruder would then extrude a sheet
`5000 ohmsper square. Witha resistivity in that range,it
`that would run from the center of layer 12 to the center
`will prevent static electric build up on the privacy
`of the next transparent layer. It would include, there-
`screen, thus helping to reduce the amount of dust col-
`fore, half of two transparent layers as well as the two
`lecting thereon. If the thicknessis closer to the thicker
`lightly loaded layers and one heavily loaded layer. Such
`range mentioned above, 600 angstroms, it will have a
`sheets could then be stacked into a billet, heat-pressed
`resistivity on the order of 500 ohmsper square and will,
`and skived as taught by theart.
`in addition to preventstatic build up, provide the termi-
`The present invention is particularly suited for use in
`nal operator with shielding against electric fields. In
`privacy screens for CRT’s. As explained previously, the
`addition, as mentioned above, layer 34 acts as a neutral
`reduction of ghost images in such screenssignificantly
`density layer. A neutral density layer is one that absorbs
`reduces operator fatigue. A privacy screen utilizing the
`a portionofthe light traveling therethrough. Since the
`louvered film of the invention is shown in FIG. 3. The
`ambientlight travels through the privacyfilter, strikes
`privacy screen of the FIG. 3 includesclarifying cover
`the CRT screen and is reflected, and travels back
`sheets 11, clear regions 12, lightly loaded dark regions
`through the privacy filter must travel through the neu-
`16 and 18, and heavily loaded dark regions 20. Prefera-
`tral density filter twice, it will be attenuated twice.
`bly coversheets 11 are polyurethanefilms, clear regions
`Thus, if the neutral density filter has a density of 50
`12 are CAB, and dark regions 16, 18, and 20 are CAB
`percent, only 25 percent of the glare that would arise
`with carbon black. In addition, glass layers 30 and 32
`from the CRT screen itself will be present. Since the
`are provided exterior to clarifying cover sheets 11. Ina
`light emitted by the CRT travels through the neutral
`preferred method of manufacture, cover sheets 11 are
`density filter only once,it is attenuated only by 50 per-
`placed on a louvered film and glass layers 30 and 32 are
`cent. Thus, although reducing the effective output of
`placed thereon. Theentire structure is then autoclaved _
`the CRT,the neutral density filter increases the ratio of
`underpressure causingall five layers to heat laminate to
`the CRT brightness to that of the glare.
`one another. In practice, layers 34, 36, and 38, discussed
`Oneother factor that must be considered is the dot
`below, would typically be applied to glass layers 30 and
`pitch of the CRT. If the width of clear regions 12 as
`32 prior to lamination.
`well as the widths of the louvers are not carefully se-
`A layer of an electrically conductive or semiconduc-
`lected, moiré patterns will be visible to the user. One
`tive material is applied to one surface. A variety of
`solution to this is to carefully adjust the width of these
`materials may be used, but in a preferred embodiment
`regions for use with a particular CRT. A problem with
`layer 34 is a layer of indium tin oxide or a metal nitride
`this is that CRT’s currently available on the market
`that may be either sputtered or vacuum deposited onto
`have a wide variety of dot pitches and the available
`giass layer 30. Preferably layer 34 has a thickness in the
`pitches are changing rapidly as screen resolutions are
`range of 300 to 600 angstroms. Preferably layer 34 is
`being improved. An alternative solution is to make a
`also a neutral density layer, although a separate neutral
`density layer could be provided or omitted altogether.
`single set of louver spacings, but to rotate the louvered
`film slightly so that the louvers run 10 to 14 degrees
`Finally, antireflection layers 36 and 38 are provided. A
`detailed discussion of the theory and structure ofantire-
`from the vertical. Since the louvers are no longer run-
`flection coatings is provided by H. A. McCloudin Thin
`ning parallel to the rows of phosphors, the problem of
`Film optical Fibers, Second Edition, 1986. Films that
`moiré patterns is greatly reduced.
`
`60
`
`35
`
`40
`
`45
`
`55
`
`65
`
`6
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`

`

`7
`
`EXAMPLE
`
`5,254,388
`
`8
`9. The louvered plastic film of claim 8 wherein said
`clear regions have widths in the range 0.05 mm to 1.0
`mm.
`
`-_0
`
`In orderto test the invention, a sample film was man-
`ufactured. This sample had louvers including a reduced
`concentration layer on oneside only. Thus, the strength 5
`of the ghost image on the side without a reduced con-
`centration layer represented those ofthe prior art while
`the ghost image on the side with the reduced concentra-
`tion layer represented that of a film of the invention.
`Specifically, the film included a louvered film that was
`0.375 mm thick. Cover sheets with a thickness of 0.25
`mm were press laminated to each major surface for
`clarification. The clear layers were 0.175 mm wide and
`each louver consisted of a 0.007 mm layer that include
`0.6 percent carbon black by weight and a 0.011 mm
`layer that included 5 percent carbon black by weight.
`A light box with a 25 mm aperture was set up in a
`darkened room. The sample film was positioned 1.2 m
`from the light box. A Spectra Prichard photometer was
`set to have a 6 minute aperture and positioned on the
`opposite of the film from the light box. The film was
`positioned on an adjustable slide so that it could be
`moved perpendicular to the line connecting the light
`box and the photometer. Theslide was mounted so that
`the film could be rotated about an axis parallel to the
`louvers. The image brightness was measured at a vari-
`ety of angles to the normalto the film on both the side
`where the 5 percent layer was exposed and the side
`where the 0.6 percent layer was exposed. The measure-
`ment was made in Foot Lamberts. Theresults of these
`measurements are summarized in the table below.
`
`10. The louvered plastic film of claim 8 wherein said
`outer regions of said louvers have widths in the range
`0.0025 mm to 0.015 mm.
`11. The louvered plastic film of claim 8 wherein said
`central regions of said louvers have widths in the range
`0.005 mm to 0.03 mm.
`12. The louvered plastic film of claim 8 wherein said
`louvers are of a clear material with a light absorbing
`material incorporated therein.
`13. The louvered plastic film of claim 12 wherein
`both said clear regions and said louvers are of cellulose
`acetate butyrate.
`14. The louvered plastic film of claim 13 wherein said
`light absorbing material is carbon black.
`15. The louveredplastic film of claim 14 wherein said
`clear regions have widths in the range 0.05 mm to 1.0
`mm,said outer regions of said louvers have widths in
`the range 0.0025 mm to 0.015 mm andsaid central re-
`gions of said louvers have widths in the range 0.005 mm
`to 0.03 mm.
`16. The louveredplastic film of claim 15 wherein said
`outer regions of said louvers are in the range 0.12 to 1.0
`percent by weight carbon black andsaid central regions
`of said louvers are in the range 1.5 to 10.0 percent by
`weight carbon black.
`17. The louveredplastic film of claim 15 wherein said
`film has a thickness in the range 0.08 mm to 0.6 mm,said
`clear regions have widths in the range 0.05 mm to 0.25
`mm,said outer regions of said louvers have widths in
`the range 0.0025 mm to 0.01 mm and said central re-
`gions of said louvers have widths in the range 0.005 mm
`to 0.02 mm.
`18. The louveredplastic film of claim 17 wherein said
`outer regions ofsaid louvers are in the range 0.12 to 1.0
`percent by weight carbon black andsaid central regions
`of said louvers are in the range 1.5 to 10.0 percent by
`weight carbon black.
`19. A louveredplastic film according to claim 1 fur-
`Weclaim:
`ther comprising an antireflection coating.
`1. A louvered plastic film comprising a plurality of
`20. A louvered plastic film according to claim 1
`clear regions separated by louvers wherein each of said 45
`wherein said film has first and second major surfaces
`louvers has a central region havingafirst coefficient of
`and said first major surface has a layer of glass adhered
`extinction and an outer region adjacentsaid clear region
`thereto.
`having a secondcoefficient of extinction, said first coef-
`21. A louvered plastic film according to claim 20
`ficient of extinction being at least 1.5 times said second
`wherein said glass has an antireflection coating.
`coefficient of extinction.
`22. A louvered plastic film according to claim 20
`2. The louvered plastic film of claim 1 wherein said
`wherein said. second major surface has a layer of glass
`louvers are of a clear material with a light absorbing
`adhered thereto.
`material incorporated therein.
`23. A louvered plastic film according to claim 22
`3. The louvered plastic film of claim 2 wherein said
`wherein said layer of glass adhered to said second major
`light absorbing material is carbon black.
`surface has a neutral density coating.
`4. The louvered plastic film of claim 2 wherein both
`24. A louvered plastic film according to claim 22
`said clear regions and said louvers are of cellulose ace-
`wherein said layer of glass adhered to said second major
`tate butyrate.
`surface has an electrically conductive coating.
`5. The louvered plastic film of claim 4 wherein said
`25~A louvered plastic film according to claim 24
`light absorbing material is carbon black.
`wherein said electrically conductive coating has an
`6. The louvered plastic film of claim 5 wherein said
`electrical resistivity ofless than 5000 Ohmsper square.
`outer regions of said louvers are in the range 0.12 to 1.0
`26. A louvered plastic film according to claim 25
`percent by weight carbon black.
`wherein said electrically conductive coating has an
`7. The louvered plastic film of claim 4 wherein said
`electrical resistivity of less than 500 Ohmsper square.
`central regions of said louvers are in the range 1.5 to 65
`27. A louvered plastic film according to claim 24
`10.0 percent by weight carbon black.
`wherein said electrically conductive coating also serves
`8. The louvered plastic film of claim 1 wherein said
`film has a thickness in the range 0.08 mm to 1.5 mm.
`as a neutral density coating.
`
`Nn5
`
`w0
`
`Ghost Image Brightness
`Incident Angle
`(Foot Lamberts)
`of Light
`5% Side
`0.6% Side
`(Degrees)
`2.7
`0.34
`§
`17
`0.10
`10
`0.87
`0.05
`15
`20
`0.43
`0.04
`
`25
`0.26
`0.03
`
`35
`
`40
`
`50
`
`55
`
`7
`
`

`

`5,254,388
`
`9
`28. A louvered plastic film according to claim 24
`wherein ‘said electrically conductive coating has an
`antireflection coating.
`29. A louvered plastic film according to claim 28
`wherein said layer of glass adhered to said first major
`surface has an antireflection coating.
`,
`30. A privacy screen for use with a cathode ray tube
`
`10
`display said screen comprising louvered plastic film
`having a plurality of clear regions separated by louvers
`wherein eachof said louvers has a central region having
`a relatively high coefficient of extinction and outer
`regions adjacent said clear regions having relatively
`low coefficients of extinction.
`*
`*
`*
`*
`*
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`8
`
`