US3245316A

US3245316A - Light distributing panel

Info

Publication number: US3245316A
Application number: US39953A
Authority: US
Inventors: Nicholas S Janetos; Brown Alfred Winsor
Original assignee: Owens Corning Fiberglas Corp
Current assignee: Owens Corning
Priority date: 1960-06-30
Filing date: 1960-06-30
Publication date: 1966-04-12
Anticipated expiration: 1983-04-12

Description

April 12, 1966 3 .zes a lg Filed June 30, 1960 N. s. JANETOS ETAL LIGHT DISTRIBUTING PANEL 3 Sheets-Sheet 1 A TTO/PA/EYS April 1966 N. s. JANETOS ETAL 3,245,316

LIGHT DISTRIBUTING PANEL 3 Sheets-Sheet 2 Filed June 30. 1960 STRAND omzcnou (52) ZOFQMED ozdmPn INVENTORS lV/(HOLAS 5. JM/A'ms & y ALF/Pm MMSOA 5mm w [five/M A ro/ways April 12, 1966 N. s. JANETOS ETAL 3,245,316

LIGHT DISTRIBUTING PANEL I Filed June 30, 1960 3 Sheets-Shut 3 INVENTORS A TTOIPA/E ya United States Patent 3,245,316 LIGHT DISTRIBUTING PANEL Nicholas S. Janetos, Providence, and Alfred Winsor Brown, Woonsocket, R.I., assignors to Owens-Coming Flberglas Corporation, a corporation of Delaware Filed June 30, 1960, Ser. No. 39,953

11 Claims. (CI. 88-65) This invention relates to light distributing panels and more particularly to light-control panels incorporating fibers and flakes of light transmitting material.

Among the desirable properties sought of light distribution panels are the dispersal or scatter of light transmitted therethrough in order to spread more uniformly the light flux emitted from the usual concentrated light source such as fluorescent tubes or incandescentbnlbs behind the panel. This light. dispersion in turn promotes a hiding, or a blotting out of the outlines of the concentrated source of light transmitted through the panel. The dispersion and hiding property is highly desirable in that it raises the allowable limit of brightness of the source and permits manufacture of such sources without much need for concern in regard to their distribution properties.

Another highly desired property in such a panel is its ability to control distribution of light flux passing therethrough. In many lighting installations, it is desired that the flux distribution be limited to a relatively small area below the panel to permit most effective utilization of the light given off by the source. Correspondingly, the visibility of the light source at distances away from the zone immediately below the panel is desired to be minimized. Viewing this property in another way, it can be said that it is desired that the panel eflfect a cutoff of light transmitted at a high angle from the source. In other instances, the light is desired to be widely distributed depending on the circumstances of use and dimensions of the zone in which the lighting installation is made.

According to the present invention, the reflective and refractive properties of glass platelets or flakes have been adapted to provide these desired properties in a panel as well as a polarization of light which unexpectedly test results indicate improves the visual acuity of persons in work areas lighted by use of such panels. To provide the desired polarization according to the present invention involves making the flakes visible by a mismatch in the index of refraction between the flakes and the structural matrix in which they are incorporated or alternately by other means, such as by provision of a space or gap immediately adjacent one or both faces of the flakes within the matrix, such space being formed by separation of the matrix from the flakes in such region. Separation of one flake surface from the matrix has been found possible by heat treatment of a panel subsequent to combination of the elements forming the panel construction. A frosty appearance is imparted to the interior of the panel by such heat treatment, resulting from the flake surface separation from the matrix, which lends further to the source hiding property of the otherwise more transparent or translucent panel. The resulting light polarization provided by the stacked visible flakes in the light transmitting matrix, physiologically has been found to be much easier on the viewer in the areas where such light is distributed. Visual acuity is increased considerably, permitting the viewer to utilize his visual capabilities more fully with diminished interference from extraneous distractions.

In view of the foregoing, it is the principal object of the invention to provide a more economical and improved light transmitting panel having improved source hiding, more uniform, light distribution, and polarizing properties capable of adjustment with regard to each of these 3,245,316 Patented Apr. 12, 1966 factors according to predetermined requirements by way of incorporation of glass fibers and glass flakes in a transparent or translucent resinous matrix defining the panel construction.

The light distribution panel of the present invention is, in brief, a resinous panel incorporating glass fibers and glass flakes, the glass fibers being generally in the form of a mat incorporated in the panel for tensile and flexural strengths in addition to the light-scattering or light dispersing properties as well as to provide the source hiding properties desired. Flakelets are incorporated into the resinous panel in addition to the fibers to impart a degree of rigidity and to provide the desired polarizing and high angle cutoff properties.

A difliculty is presented in the manufacture of such panels when flakes are incorporated in the panel in addisubjected to the heat treatment to effect a separation of the surfaces of the flakes from the matrix, the heat treatment promoting the separation of the two dissimilar materials also acts to cause a blossoming or corresponding separation of the matrix from the glass fiber surfaces. According to the principles of the present invention, such blossoming is prevented by incorporating a coupling agent in the sizing material applied to the glass fibers during fiber formation, such coupling agent having an aflinity for the resin matrix of the panel. Correspondingly, the flakes are made without supply of material which will promote such alfinity for the resin. Thus, upon subsequent heat treatment to effect the separation desired adjacent the flake surfaces, the fiber surfaces will be more solidly coupled thereto, thereby resulting in selective separation of the glass of the flakes from the resin over that of the fibers.

The glass fibers are made of glass selectively mismatched to the index of refraction of the resinous matrix so that in addition to the function of reinforcing the panel construction for tensile and flexural strengths, the fibers will promote the optical features of the panel by improving the source hiding properties. In the latter respect, it

had been found that glass fibers when para'llelly oriented within a resin panel in immediate side-by-side relationship will efiectively hide the dimensional outlines of a light source of elongated form, such as a fluorescent light tube, especially when such flbers are oriented in a longitudinal direction parallel to the fluorescent tube itself. That is, a panel incorporating glass fibers oriented parallel to the direction of the fluorescent tube will scatter the light emitted from the concentrated source as viewed through the panel that the source is in a sense splashed out, thus resulting in a more uniformdistribution of light transmitted through the panel. When the panel is oriented with the fibers lined up at right angles to the orientation of the elongated tubular light source, however, the source is clearly visible as a concentrated line of light behind the panel. To promote an overall uniform scattering of the concentrated light source, therefore, randomly arranged short lengths of bundles of parallel gl-ass fibers are incorporated in the panel to eliminate such visibility of the source through the panel. In other words, lengths of strands of parallel glass fibers aligned in parallel relation will provide excellent source hiding results in one general direction but not in a direction at right angles thereto. Thus, the present .panel can be selective source hiding property by arranging a suflicient number of layers of strand of parallel fibers so that light passed through the panel .will be interrupted by more than one fiber-oriented parallel to the light source regardless of the direction in which the panel is aligned with respect to the light source. Mats of chopped lengths of lengths of glass strands have been found highly eflective in providing this non-selective light-scattering and sourcehiding efiect.

Thus, according to the present invention, the panel of translucent or transparent resin is provided with a layer of glass fibers, preferably of fibers in the form of mat of chopped glass strands, and glass flakes are disposed in an immediately adjacent zone within the panel matrix to provide the desired high angle cutoff and polarizing properties.

Features of the invention lie in the high strength and flexibility of such panels imparted by the inherently high strength and highly flexible glass fibers, as well as the added strength and complementary somewhat more rigid propertiesof stacked parallelly aligned glass flakes.

A still further feature of the invention lies in the panels being light in weight by reason of the strength imparted by the glass fibers and flakes, which strength, in addition to the panel flexibility, also makes the panels relatively non-destruct-ible.

Another feature lies in the adaptability of the panel to custom made designs for specific lighting'installations, as well as its ease of handling for ready installation.

Still other features of the invention lie in the relative indestructibility of the panel and its adaptability to being made of different colors.

A still further feature is the relatively high degree of fire safety of the panel by reason of the presence of glass fibers and glass flakes, which fire safety has not heretofore been attainable in resinous lighting panels.

The invention is herein described principally in relation to incorporation of glass fibers and glass flakes as the optical control elements. Other materials of transparent or translucent character beside glass, however, can also be used. For example, cellulose acetate, nylon, vinyl chloride, polyesters and many other transparent or translucent fibrous and film materials can be utilized for these optical properties.

Other objects and features characteristic of the invention are set forth with particularity in the appended claims. The invention, however, with regard to organization and manner of construction, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a partially broken away perspective view of a panel made according to the principles of the present invention;

FIGURE 2 is an enlarged view of a section of chopped strand mat of the type adapted to incorporation in the panel of FIGURE 1;

FIGURE 3 is an enlarged view of a single section of a chopped strand or bundle of glass fibers of the type incorporated in the mat of FIGURE 2;

FIGURE 4 is an illustration of a group of flakes of the type adapted to incorporation in the panel of FIG- URE 1;

FIGURE 5 is an enlarged view in cross-section of a portion of the panel illustrated in FIGURE 1 showing more clearly the arrangement of. the fibers and flakes of FIGURES 3 and 4;

FIGURE 6 is a diagrammatic illustration of a longitudinal light source emitting light flux for transmittal through a panel having individual transparent fibers aligned in parallel relationship thereto, demonstrating the manner in which light is redirected by parallel fibers to hide the source while yet allowing transmission of the light therethrough;

FIGURE 7 is an illustration of the underside of the panel having parallel fibers aligned thereon with a longitudinal tube disposed on the other side of the panel illustrating the relative hiding power of the panel with fibers so oriented;

FIGURE 8 is a somewhat diagrammatic illustration of a longitudinal light source disposed on one side of ner in which stacked flakes effect polarization of the light transmitted therethrough;

FIGURE 11 is a cross-sectional side elevational view of another embodiment of the present invention;

FIGURE 12 is a cross-sectional side elevational view of still another embodiment of the present invention; and FIGURE 13 is a schematic diagram of a continuous process for producing panels according to the principles .of the present invention.

Turning to the drawings in greater detail, FIGURE 1 shows a resinous panel 10 incorporating therein -a multiplicity of glass flakes 11 generally oriented in planes parallel to the major surfaces of the panel. The corner of the panel is broken away to show also the plurality of fibersincorporated therein as a layer or mat 15 of such fibers.

The flakes are disposed in levels of the panel below the layer 15 of glass fibers. The fibers although as presently considered are preferably discontinuous, can also be continuous in form, but in both forms are randomly oriented within planes substantially parallel to the major surfaces of the panel for purposes which are hereinafter described in greater detail. The number and distribution of fibers in the panel as arranged in a mat layer such as shown in FIGURE 2 having a concentration of fibers such that in any straight line path through the panel, fibers are present in suflicient number so that each point portion of the panel has a fiber aligned to optically intercept light transmitted in lines through such point.

Correspondingly, flakes are stacked substantially parallel to each other in layers extending over the full area. below the layer of fibers, such stack of flakes being suflicient in number also to optically intercept the light transmitted through the panel, as well as being stacked sufiiciently to effect partial polarization of angularly incident light transmitted through the panel from the side on which the layer of randomly oriented fibers are disposed.

FIGURES illustrates the form in which discontinuous fibers may be incorporated in the panel 10, such fibers being in the form of a bundle 14 of parallel discontinuous fibers 12. Such a form can be produced by attenuating continuous fibers into a continuous strand of parallel fibers and then chopping the strand into discontinuous lengths. Bundles of discontinuous fibers chopped from continuous strands to generally the same length whencombined will provide a chopped strand mat such as is illustrated in FIGURE 2 which mat is readily adaptable to reinforcement of resinous products such as the present panel. In commercial practice, the strands of fibers are produced of 102, 204 or 408 filaments each, and while relatively small, are particularly adapted to providing the multiplicity of intercepted rays of light transmitted therethrough.

The flake and resin composite portion of the panel can be combined with the fiber resin composite portion of the panel in either a continuous process as described hereinafter or in a batch type process, both of which involve introducing fibers in the form of a mat 15 on a layer comprising a mixture of the resin 17 and the flakes 11 whereupon the fibrous layer 15 can be coveredwith a carbonates and polystyrene. As an example of still another resin classification, an unsaturated polyester acrylic resin which is water white has been used with success.

' from the resin is not desired at the fibers.

This material comprised 20% acrylic resin dispersed in a polyester comprising maleic anhydride, diethylene glycol and ethylene. Color fastness of the resin in such panels is desired since under the conditions of utilization in conventional lighting systems ultra-violet light generally causes a color modification. The panel structure is also required to be fire-safe by having a minimum flame spread and heat distortion properties. These properties are promoted by the fibrous layer which imparts considerable strength to the panel since fibers such as glass fibers have tremendous tensile strengths and accordingly are capable of imparting an extremely high degree of tensile and flex strength to such reinforced panels. The increased mineral content lends greatly to'the desired color and heat stability. The fibers also impart increased tear, shear and burst strengths to the panels.

During the process of combining the flake-resin mixture in the panel structure, the flakes 11 are passed between coacting rolls disposed sufficiently close to each other to assure that a thin layer of the mixture is produced within which the flakes will become oriented generally parallel to the major surfaces of the panel. Such orientation of the flakes imparts additional strength to the composite as well as some rigidity over that which would be provided by the fibers incorporated therein. A sufficient number of the flakes are incorporated in the mixture so that individual rays of light passing through resin flake layers are interrupted several times'before full transmission through the panel.

FIGURE 4 illustrates the general appearance of flakes 11, while FIGURE 5 illustrates more clearly how such flakes 11 are stacked in layers 16 through a substantial portion of the thickness of the panel 10. After the composite of resin fibers and flakes has been fabricated, it has been found that subsequent subjection of the cooled construction to heat treatment, after the panel has been first cooled, results in actual separation of a large portion of the interfaces between the glass flake surfaces and the resin surfaces from each other. This shows up on the form of spaces or gaps 18 on one or both sides of a substantial portion of the area of the flakes. It is not fully understood why such separation occurs on reheating in such composite constructions, but it is believed that migration of gases from either the resin or the glass bodies becomes concentrated at the interfaces of the dissimilar materials upon heating of the construction, thereby forcing separations therebetween.

Such gaps adjacent the flakes in the panel of the present invention are illustrated more clearly in FIGURE 4. Regardless of the mechanism by which the gaps are produced, however, they impart a highly desirable optical property to the panel by making possible the polarization or partial polarization of light transmitted through the panel by principles of selective reflection. Additionally, the flake resin gaps impart a decorative appearance to the otherwise clear panel, which appearance corresponds closely to that of mother-of-pearl. Thiscondition assists the glass fibers in eflecting a circuitous transmittance of light through the panel for source-hiding effects.

Although the separation or gaps 18 are desired at the interfaces of the flakes and resin, such separation of glass This selective separation of the resin from the glass was not previously possible since the resin itself was made to include a resin glass coupling agent. According to the present invention, therefore, the fiber surfaces are bonded more positively to the resin. This is accomplished by supplying the glass fibers with a coupling agent incorporated in the sizing material applied to the fibers during their formation. This coupling agent is designed to interbond the resin and glass of the fibers more positively at their interfaces. The flakes on the other hand are produced by any of a number of means described in the already published art, but are produced for the present purposes without such a coupling agent. Thus the glass flakes will not be bonded to the resin as tightly as will the glass of the fibers, and upon reheating the glass fibers will retain their bonded condition with the resin, whereas the glassflake surfaces will separate from the resin over large areas of their faces.

Coupling agents applied to the glass fibers to establish the solid attachment for the resin include materials such as vinyl tri-ethoxy silane, vinyl dichloro silane, vinyl tris beta methoxy ethoxy silane. .The amount of coupling agent required to establish this solid attachment need only be in the order of 0.5% to 1.0% of the total sizing applied to the glass fibers. A sizing material compatible with the resins for a panel of the present type is water mixed with the following constituents:

FIGURES 6 to 10 illustrate somewhat schematically the basic physical principles employed in the present light panel showing the manner in which the panel functions to produce the light distributing and flux control results desired.

FIGURES 6 and 7 show the manner in which light emitted from a tube 50 and passing through a clear panel having incorporated therein transparent fibers 52 aligned in a direction generally parallel to the longitudinal dimension of the tube 50 is dispersed by reason of the circular dimensionof the fibers acting as a trap and reflecting mechanism which changes the direction of the rays of light to the extent that the lighting source in the form of tube 50 is obscured even though the light therefrom is transmitted through the panel 51. FIGURE 7 is an illustration of the general appearance of the panel being viewed directly in an attempt to see the light source. The fibers having an index of refraction at least slightly mis-- matched with respect to the index of refraction of the resin matrix forming the foundation of the panel cause such a degree of circuity of the rays which otherwise define the source, that the source is practically hidden from view while the light therefrom is visible in uniformly distributed fashion over the panel surface.

correspondingly, FIGURES 8 and 9 illustrate the appearance of a longitudinal light source 70 viewed through a panel 71 having fibers 72 aligned at right angles to the longitudinal source 70. Upon viewing the light source 70 through the panel, the source is not hidden but is at least generally visible as illustrated in FIGURE 8. Each fiber in the panel of FIGURES 8 and 9 offers a longitudinal path extended across the width of the panel through which the light source may be viewed through each transverse fiber from practically any direction on the side of the panel opposite the light source. In the arrangement of FIGURES 6 and 7, however, the fibers viewed from angular positions with respect to the normal fibers 52 which act as lens-like constructions in which the light is reflected and re-refiected to an extent such that it no longer moves in a straight line from the source through the panel. Thus, the source 50 cannot be viewed directly, yet light therefrom is passed through the panel by reason of the reflection and re-reflection effecting the dispersal desired.

These principles are utilized according to the present invention to obscure the light source behind the panel by providing a sufiicient number of filaments, or portions of filaments, in the direct path of rays passing through the 7 to the appearance represented by the illustration of the lighted panel in FIGURE 7.

Aside fromthese optical results, however, the fibers perform the highly important function in reinforcing and heat stabilizing the panel so that its-thickness may be reduced to a minimum without sacrificing strength. In this respect, the strength advantage provided may under a given set of circumstances be the principal reason for incorporating the fibers in the panel and the optical properties can be reduced or eliminated by selecting fibers of material having the same index of refraction of the resinous matrix of the panel.

FIGURE 10 illustrates diagrammatically the principles by which polarization of light is effected in the present instance by a pile of glass flakes incorporated in the panel. Each of the surfaces of the flakes acts as a reflecting surface for incident light. If a beam of ordinary light 93 is incident to, or close to, the polarizing angle on stacked layers of flakes 91, some of the lateral light vibrations are reflected at each flake surface and all passed therethrough are refracted. The result is that the reflected light 95 is plane-polarized in the same plane, and the refracted beam 96, having had more and more of its lateral right angular vibrations separated therefrom, is partially plane-polarized. The larger the number of surfaces, the more nearly plane-polarized is the transmitted beam 96.

Light directed normal to the stack of flakes 91 passes straight through the stack without changing direction and with only a minimum diminishment in intensity by reason of absorption of the light in the matter itself. Thus, when the light source is viewed through the stack of flakes, the points immediately below the source receive the greatest amount from the source, whereas at points distant from immediately below, where the viewing angle would be a high angle to the normal, the intensity of the source appears diminished and the light transmitted to the viewing point is more polarized in character, varying in degree of polarization depending on the number of flakes interposed between the source and the point from which the light is viewed.

According to this invention, the flakes may be made of material having an index of refraction substantially matched to that of the resin matrix within which they are incorporated. Such matching would normally make the flakes relatively invisible in the matrix, but the reflection of the light from the surfaces is still effected according to this invention by providing the space gaps adjacent the flake surfaces in the manner illustrated in FIGURE 5.

If, however, as shown in FIGURE 10, the index of refraction of the flakes is different, say in the order of 0.2

above or below that of the matrix, then each flake surface is visible through the matrix and acts as a reflective surface without the need for interfacial gaps. By providing the space gap adjacent the flake surfaces as shown in FIGURE 5, the flakes become visible as a frosty mass within the matrix. Although, as explained above, the exact mechanism by which the gaps or separation occur is not fully understood, the separate surfaces interposed in the path of the rays effect polarized reflection of some of the light directed toward the panel so that the remaining light transmitted through the panel is at least partially polarized.

The flakes can be incorporated in the panel matrix by mixing them with the resin while the resin is in a plastic condition prior to formation of the panel. In sequence, as shown in FIGURE 13, the mat of glass fibers 135 is deposited on a parchment paper carrier 137. The resin flake mixture 131 is deposited on the glass fiber mat'in such a manner that the flakes are oriented in generally parallel relation to each other and parallel to the major surfaces of the panel base. A cellophane finishing sheet 136 is thereupon deposited over the resin flake layer to provide a smooth light outlet side in the finished panel.

Although cellophane has proven successful for the present purpose, the smooth surface can also be imparted to the panel by other materials. A number of resinous films, such as polyester films, will also provide the desired result. The combination is then passed between compression rolls 138 for impregnation of the resin into the fibrous glass layer. A wiping roll 133 having spiral embossed ridges extending over its periphery and backed up by a roll 134 wipes across the cellophane surface to remove air pockets from the wet laminate by forcing them laterally to the exposed edges of the wet laminate. The carrier on which the mixture of resin and flakes is deposited is preferably a parchment type release paper. The diffusing property imparted to the panel surface by the parchment paper is imparted to the surface by the paper because of the rough surface character of the cellulose paper. Beside having the proper degree of rough texture, the paper is desirably free of foreign matter. Such a paper is one commercially available under the tradename Patapar, a parchment paper having separating or releasing characteristics when joined to a layer of resin. The parchment roughness imparted to the panel provides a frosted or fine crinkled character to the panel surface from which it is separated. Such frosted or crinkled surface assists in softly diffusing the light transmitted through the panel.

After combination of the fibers, flakes and resin between the parchment paper carrier and the cellophane finishing sheet, the assembly is passed through a curing oven 139 to effect a cure of the resin. The cellophane is laid over the exposed resin flake surface to impart a smoother surface to the light emission side of the panel. When the resin used for the panel matrix is a polyester, and the panel, by way of example, is .04" thick, a successful curing cycle is three minutes'at 325 F.

After formation of the panel, the cellophane and parchment paper overlayers are separated from the panel to takeup rolls 140 and 141 respectively. The panel thus is left with one smooth side and the opposite side, the side corresponding to the light source side of the panel, is somewhat frosted or crinkly to assist in diffusion of the light entering into the matrix. The panel is then cut to size such as by way of a band saw.

After the curing and cutting operations, the semifinished panel is cooled to room temperature and then subjected to another heat cycle for treatment to effect what is termed popping of the panel wherein the heating causes the flakes to separate from the resin in a manner similar to the manner in which corn is popped upon being subjected to heat. panel a reheat cycle which has proven successful is 3 to 4 minutes at 300 F. The resulting flake separations, or gaps, between the resin and flakes surfaces imparts a frostiness to the panel, or what more descriptively might be termed as a pearlescent appearance. The popping" of flakes causes the clear resin panel to become frosty regardless of whether the glass of the flakes therein is matched in index of refraction to that of the resin or not. Where the flakes are not subjected to the popping step, they must be made visible by other mechanisms in'order to obtain the polarizing effects desired. Such visibility can also be attained by a mismatching ofthe indices of refraction between the glass and resin. For mosteffective polarization of light transmitted through the panels, the resin and glass flakes should have a mismatch between their indices of refraction more than 0.2. Resins generally have an index of refraction between 1.35 and 1.75. It has been found that the greater the mismatch, the fewer are the layers of flake required to obtain a given degree of polarization. v

The mismatch can be such that the flakes have a lower index of refraction that the resin, or vice verse where the resin has a lower index of refraction than the flakes. For example, a thermosetting resin such as a polyester resin which has an index of refraction of 1.54, or a thermoplastic resin such as an acrylic resin which has an index of For a polyester resin matrix refraction of 1.49, can be combined with glass flakes having an index of refraction in the order of 1.75. Glass The flakes can have any of a wide range of area dimensions such for example as flakes which will be supported by a /4" mesh screen or down to a size in the order of that which will be supported by a 250 mesh screen. The thickness of the flakes can by way of example be any size in the range above 2 microns and might be thicker to the point where they might in some instances be considered as platelets in being stiffer than what might usually be considered flakes.

Although the flakes are described herein as having been incorporated in the panel by mixing them with the resin prior to combination with the layer of fibers, it is also possible to incorporate the flakes in the panel by first forming them into a paper-like web. Such web of flakes can be made without need for special binders by washing them in a slurry operation and by proper cycling in such washing operation so that the hydroxyl ions migrate to the surfaces of the flakes where they will act as a gel to interbind the flakes to a web. Such migration and binding is promoted by use of water as a washing agent with a slight amount of hydrochloric acidv added to accelerate the migratory displacement of the binding constituents of the flakes.

Flakes are preferably flat for the purposes as outlined above but in some instances flakes of an arcuate configuration prove desirable to modify the treatment of incidental light passing through the panel. Light passing through arcuately shaped flakes passes through the individual flakes at different angles with such variation in transmittance through the flakes that they can in some instances selectively modify the degree of polarization of light passingthrough the panels in which they are incorporated.

Although the fibers incorporated in the panel construction have already been described in reference to randomly oriented bundles of parallel discontinuous lengths, the mat can also be one incorporating bundles of parallel continuous glass fibers randomly arranged inthe mat. Another type of mat using randomly arranged discontinuous individual glass fibers can also be used. A mat of individual discontinuous glass fibers has the feature of having a fine texture as well as an adaptability to a wider range of randomness for a given number of fibers in comparison to an equal weight mat made up of bundles of parallel fibers.

The fibers when used as light diffusing elements, beside their function as reinforcing elements, need have a mis match in index of refraction of only .02 compared to the index of theresin matrix. Fibers having an index mismatch above .02, and by way of example, in the order of .05 and more compared to the resin, have also proven successful for such purpose. The length of these fibers can be any of wide range of lengths and for example can be fibers chopped to a length of /2" or more.

In operation, the panel functions to control light flux passed therethrough by first acting to diffuse the light entering the panel by way of the parchmentized or frosted surface imparted to the light source side thereof, whereupon the diffused or scattered light upon further passage through the panel is refracted to a degree dependent upon the index of refraction of the resin matrix. The refracted light is then passed through the randomly arranged fibers lying in the plane parallel to the parchmentized back or top surface of the panel, which fiber arrangement promotes further obscurement of the light source by reflection and re-reflection within the fibers through which they pass. Such reflection and re-'reflection occurs, however, only if the index of refraction of 10 the glass fibers differs from that of the matrix. Should the indices of refraction of these two materials be substantially identical, then light passes through the fibrous mat layer as if the fibers were not there. In such instances, fibers, as described above, act primarily as strength giving elements. The presence of such strength giving elements reduces the need for some of the glass flakes otherwise incorporated in the panel for such strength purposes.

As an example of an actual construction, when glass .fibers were used as reinforcement for a 45 mil panel as well as diffusers, a glass fiber mat weighing /1 ounce per square foot, amounting to 12% by weight of the panel was used while 12% of 2.5 micron flakes provided the high angle light cutoff desired. When flakes were used as the sole optical elements and the fibers were not visible in the matrix and acted primarily as reinforcing elements, 20% of glass flakes by weight of the panel in one experimental construction produced the desired results. The range of the panel thickness can be in the order of above 25 mils and at present, from the standpoint of efficiency, strength and lightness of weight, is preferably in the range of from 40 to 60 mils thick. The amount of glass incorporated in such panels can range between 10% and 70%.

Upon passage into the flake-resin zone of the panel, the light having an angle of incidence differing from is partially reflected by the flake surfaces disposed adjacent zones of matter of different index of refraction from the flakes. That is, if the flakes have an index of refraction close to that of the resin so that they are not visible therein, then a separation of the flake surfaces from the resin presents a gaseous zone adjacent the flake surfaces having a different index of refraction from the flakes. Thus, by either separation of the flakes from the resin, or by providing flakes of different index of refraction from the resin, visibility is imparted to the flakes within the panel corresponding to a condition which will provide reflective surfaces to effect polarization of light passing through the panel. If the flakes are to be'subjected to a popping step, and the fibers are to be retained as strength giving elements, the fibers are provided with a coupling agent which will assure their solid bonded relation to the resin matrix without blossoming into visible elements in the manner corresponding in appearance to the flakes, because such blossoming results from a separation of the fiber surfaces from the resin and is not conducive to imparting the strength of the fibers to the panel.

Alternately, when the flakes have a different index of refraction from the resin, the pop ing step is not necessary since the polarizing effects desired can be obtained from the flakes without such special treatment. Under such circumstances, the coupling agent can be incorporated in the resin itself prior to combination with the fibers or flakes. When this method of production of the panels is used, both the fibers and the flakes act as strength giving elements for the panel.

Panels can be produced having polarizing characteristics by incorporation of the flake elements only. In such cases, however, the number of flakes required to provide'a panel with a fair degree of strength is much greater than the number required when the fiber elements are incorporated in the panel for such strength purposes. In other words, by utilization of fibers in the panel for the strength giving property which they will provide, flakes can then be incorporated principally for their optical properties and can be introduced by a mass corresponding to an optimum quantity for the optical properties desired. Such optimum quantity will be a much smaller quantity than might otherwise be required to provide the strengths corresponding to. those imparted by glass fibers.

which the fibers provide, their optical properties can be utilized by providing a mismatch in their index of refraction in comparison to that of the matrix.

By incorporation of a pigment into the panel resin, the light dispersion properties could be further promoted with a relatively small amount of loss of light. For example, any pigment which can be finely ground and which is chemically stable, such as zinc oxide, calcium carbonate, and titanium dioxide, can be advantageously incorporated in the resin to improve the source hiding and light dispersion properties. Further by way of example, 0.22% of pigment by weight of the panel can be utilized to advantage as a diffusion aid with but 2% to 3% light absorption. Beside source hiding and dis- I persion, the pigment also provides color shading control which covers some resin nonuniformities that might appear. In this respect, the white pigment materials will impart whiteness to a resin panel to cover the gray frequently imparted by the incorporation of glass in the resin.

It has been found that other additives can also be advantageously incorporated in the panel. For example, when a polyester acrylic resin is used, 1 in 5 parts by weight of styrene added thereto will increase rigidity and: advantageously reduce the usual brittleness of the material.

FIGURE 11 illustrates another embodiment of the present invention wherein the panel construction is a resinous matrix having a sandwich arrangement of two

layers

107 and 109 of flakes on opposite sides of a layer 105 of randomly oriented bundles of glass fibers. The glass fibers 105 are provided with at least a slight mismatch in index of refraction compared to the matrix to make them effective as light dispersing elements and are provided with a coupling agent to bond them securely to the resinous matrix 101 while the flakes of

layers

107 and 109 are each free of such coupling material to allow formation by heat treatment of gaps 108 at the flake resin interfaces. In this embodiment, the light transmitted through the panel is first partially polarized by the upper layer of flakes 107 whereupon continued passage of the light through the panel results in a diffusion of partially polarized light. The diffused partially polarized light, however, is also partially columnized in that the high angle light is cut off by the first layer of the flakes. The layer of fibers 105, although effective to diffuse the light, does not diffuse sufficiently to restore it to full distribution in the cutoff zone. Thus, the resultant light transmitted between the first layer of flakes and the diffusing layer of fibers is cut down in its width of distribution. Further transmittance of the diffused light through the second layer of flakes 109 :re-polarizes in part the light emitted from the panel and acts again to effect a'cutoff of the remaining light tending to be emitted at a high angle to a direction normal to the panel. Where the fibers are provided with the same index of refraction as the matrix, however, the diffusing property provided by the fibers disappears but their presence is at least equally valuable as reinforcing strength giving elements in the sheet. Thus, this embodiment provides two steps of high angle cutoff of the light as effected with an intermediate step of diffusion for source hiding properties and/or reinforcement for the sheet.

FIGURE 12 illustrates'still another embodiment of the present invention wherein a layer of flakes having interfacial gaps 118 in a resinous matrix is disposed between two layers of glass fibers. A layer of glass 'fibers 115 is disposed above a layer 117 of stacked flakes while a second layer 125 of glass fibers having a lesser concentration of fibers than the upper layer is disposed under the layer of stacked glass flakes 117. The flakes and the fibers are included in the resinous matrix 111 with the bundles of fibrous in both layers being provided with a coupling agent to assure that a blossoming out or gapping at the interfacial surfaces of the fibers does not occur. In this arrangement, the light transmitted through the upper layer of glass fibers is first uniformly dispersed, whereupon the dispersed light is subsequently partially polarized by passage through the layer of visible flakes 117. As in the previous embodiments herein described, visibility can be imparted to the flakes for the polarization properties by providing space gaps adjacent portions of the flake surfaces in a reheat cycle or by providing the flakes with a mismatch in index of refraction compared to the resin. The, stacked flakes act to cut off the high angle light and thereby act to columnize the light transmitted through the panel. The light passing through the layers of flakes 117, however, must pass through the fibers before being emitted from the panel. The thinner, less concentrated layer of glass fibers 125 acts to effect a small amount of dispersal of the emitted light to promote further the source hiding properties and to widen slightly the field of distribution effected by the panel. The resultant light emitted from the panel is of a more dispersed nature for source hiding purposes while still being effective to columnize the emitted light by cutting off a major portion transmitted at a relatively high angle to normal.

This embodiment is particularly of value in that the spaced layers of glass fibers impart a much higher strength to the panel than a single layer and even more so because of the spaced relation between the layers of reinforcing elements which provide more of a I beam type strength which allows it to support a greater amount of its own weight and correspondingly allows the panel to be used in spanning greater distances between supports. In this respect, it will he understood that either one or both of the layers of fibers can be of fibers having an index of refraction matched to that of the resin so that they are used solely for reinforcement purposes rather than the otherwise concomitant purpose of their use as optical elements.

Still further variation of the concepts of this invention are possible by orienting the fiber bundles or continuous fibers in parallel relation in one direction across the panel dimension or multiple layers at right angles to each other. Fibers can also be parallelly oriented in diagonal relation to the panel dimensions.

In summary, the panel construction of this invention is of a character which has a range of variable factors mak-, ing possible custom made constructions for specific lighting installations. In each case, the polarization of light provides a high angle cutoff which may be likened to the effects obtainable with grated panels or to the provision of louvers in light fixtures. At the same time, the polarization of such light enhances the visual acuity of viewers in areas supplied with light from the panels. Still further, the panel can be made light in weight by reason of the high strength imparted by the fibers and flakes embodied therein, while in addition, the flexible character of the panel lends to it relative indestructibility. Light in addition to the random arrangement of fibers as a layer in the panel, while further obscurement is made possible by the flakes themselves. The resulting panel is highly efficient in distributing light from a concentrated source and distributes light to a high degree of uniformity such thatthe construction is adapted to performing a multiplicity of functions not available heretofore in combination in a single panel construction.

In view of the foregoing description, it will be understood that modifications and variations may be effected in the detail of the present invention without deviating from the scope and novel concepts thereof.

We claim: 1

1. A light distribution control sheet comprising a layer of resinous light transmitting material, said sheet embodying a multilayer zone of light transmitting flakes coextensive with the major surfaces of said sheet, and an adjacent zone of randomly distributed glass fibers embedded within said resinous material coextensive with said multilayer zone of flakes, the surfaces of said flakes being aligned predominantly parallel to the major surfaces of said sheet, at least a majority of said flakes having a gaseous space within the resin immediately adjacent at least one surface while the surfaces of said glass fibers are chemically coupled to said resin without spaces existing at the surfaces theerof.

2. A light distribution control sheet comprising a matrix of light transmitting resin, two spaced multilayer zones of light transmitting flakes, each zone being coex tensive with the major surfaces of said sheet, a layer of glass fibers embedded within said matrix interposed between said spaced zones of flakes, said fibers being provided with a coupling agent bonding them positively to the resinous matrix, said glass flakes being made visible in said resin matrix to provide multilayer polarization properties.

3. A light distribution control sheet according to claim 2 wherein the flakes in the spaced zones have an index of refraction at least 0.2 difference from the index of refraction of the resin matrix.

4. A light distribution control sheet acording to claim 2 in which the flakes in the spaced zones are visible by having gaps adjacent portions of the surfaces of the flakes in the respective zones.

5. A light distribution control sheet according to claim 2 in which the fibers have an index of refraction at least slightly mismatched to the index of refraction of the resin of the matrix.

6. A light distribution control sheet comprising a matrix of light transmitting resin, two parallelly spaced zones within said matrix comprising randomly and uniformly distributed glass fibers, one of said zones having a lesser concentration of fibers than the other, a multilayer zone of light transmitting flakes disposed between said pair of fibers containing zones, said flakes being made to be visible within said matrix to impart polarization properties to said sheet.

7. A light distribution controlsheet according to claim 6 wherein the flakes have an index of refraction at least 0.2 difference from the index of refraction of the resin matrix.

8. A light distribution control sheet according to claim 6 in which the flakes are visible by having gaps adjacent portions of the surface of the flakes.

9. A light distribution control sheet according to claim 6 in which the fibers of at least one of the Zones have an index of refraction at least slightly mismatched to the index of refraction of the resin of the matrix.

10. A light distribution control sheet comprising a layer of resinous light transmitting material, said sheet embodying a multilayer zone of light transmitting flakes coextensive with the major surfaces of said sheet, and an adjacent zone of randomly distributed glass fibers embedded within said resinous material coextensive with said multilayer zone of flakes, the surfaces of said flakes being aligned predominantly parallel to the major surfaces of said sheet, at least a majority of said flakes having a gaseous space within the resin immediately adjacent at least one surface while the surfaces of said glass fibers are positively interbonded with said resin assuring that no spaces exist at the surfaces thereof.

11. A light distribution control sheet comprising a matrix of light transmitting resin, two spaced multilayer zones of light transmitting flakes, each zone being coextensive with the major surfaces of said sheet, a layer of glass fibers embedded within said matrix interposed between said spaced zones of flakes, said fibers being positively interbonded with the resin of the resinous matrix assuring that no spaces exist at the surfaces thereof, said glass flakes being made visible in said resin matrix to provide multilayer polarization properties.

References Cited by the Examiner 1 UNITED STATES PATENTS JEWEL H. PEDERSEN, Primary Examiner.

EMIL G. ANDERSON, FREDERICK M. STRADER,

Examiners.

Kahn et al 88-65

Claims

1. A LIGHT DISTRIBUTION CONTROL SHEET COMPRISING A LAYER OF RESINOUS LIGHT TRANSMITTING MATERIAL, SAID SHEET EMBODYING A MULTILAYER ZONE OF LIGHT TRANSMITTING FLAKES COEXTENSIVE WITH THE MAJOR SURFACES OF SAID SHEET, AND AN ADJACENT ZONE OF RANDOMLY DISTRIBUTED GLASS FIBERS EMBEDDED WITHIN SAID RESINOUS MATERIAL COEXTENSIVE WITH SAID MULTILAYER ZONE OF FLAKES, THE SURFACES OF SAID FLAKES BEING ALIGNED PREDOMINANTLY PARALLEL TO THE MAJOR SURFACES OF SAID SHEET, AT LEAST A MAJORITY OF SAID FLAKES HAVING A GASEOUS SPACE WITHIN THE RESIN IMMEDIATELY ADJACENT AT LEAST ONE SURFACE WHILE THE SURFACES OF SAID GLASS FIBERS ARE CHEMICALLY COUPLED TO SAID RESIN WITHOUT SPACES EXISTING AT THE SURFACES THEREOF.