US 3516724 A
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United States Patent C U.S. Cl. 350-96 8 Claims ABSTRACT 0F THE DISCLOSURE A plurality of light-transmitting rods are embedded in an opaque block with one end of each rod aligned in a common display plane, whereby selective illumination of said ends by passage of light through the rods from lamps positioned at the opposite ends thereof may be utilized to form characters which may be perceived and read. The surface of the display plane is covered with a colored layer to change the color of the characters and thereby increase the readability thereof. The light-transmitting rods are made of a polycarbonate resin and the remaining parts of epoxy resins to form an integral overall assembly.
This invention relates to a colored readout assembly for display of illuminated characters and, more specifically, to the fabrication of such an assembly as an integral structure which can withstand wide extremes of temperature and pressure in service.
Readout assemblies of the nature described above are often used in service conditions which involve wide extremes of temperature and pressure as, for example, in the instrument panels of aircraft. Military jet aircrafts, in particular, repeatedly undergo large differentials in temperature and pressure in routinely ascending to and descending from very high altitudes. Government specifications require that readout assemblies withstand such extremes without splitting, cracking or exploding and the problem of meeting such specifications is further made difficult by the frequent requirement for a colored layer or filter over the illuminated characters. Such layers or filters are necessary because at night the lamp currents must be lowered to provide proper contrast and avoid glare. and this causes changes in the spectral quality of the light which must be compensated by the filter. It has proven to be a formidable problem to manufacture readout assemblies that are capable of satisfying all of these requirements. In particular, small air bubbles often become trapped between the surface of display plane and the colored layer, and these bubbles in effect explode under the rigorous service conditions to cause splitting, cracking or other loss of structural integrity, which makes the assembly unacceptable.
The present invention overcomes these problems and is based upon the discovery that the use of certain synthetic resins for the components of an integral readout assembly will result in a final structure which is capable of withstanding the rigorous service conditions described above without objectionable structural deterioration. More particularly, it has been found that thermoplastic polycarbonate resins and opaque and colored thermosetting epoxy resins, each of defined molecular structure, constitute uniquely-suited materials for fabrication of durable readout assemblies which may be relied upon to maintain structural integrity. The uniqueness is found in the fact that while each of these materials performs a necessary physical function in the overall assembly, i.e. the polycarbonate rods passing light and forming the characters at the ends thereof, the opaque epoxy resin maintaining the alignment of the rods and blocking light, and the colored epoxy resin giving color compensation to the il- 3,516,724 Patented June 23, 1970 luminated characters. the materials also have the unexpected capability to bond with each other so intimately and so tenaciously that the final assembly becomes an integral whole of unprecedented strength and durability. Such qualities make the readout assembly of the invention eminently suited for service under the most rigorous conditions.
As noted above, it is necessary to use a polycarbonate resin to form the light-transmitting rods of the readout assembly of the invention. Such resins comprise linear aromatic polyesters of carbonic acid and are defined by the following formula:
wherein X is carbon in which case R1 and R2 are hydrogen, alkyl, aryl or cycloalkyl and the same or different, or X is oxygen in which case R1 and R2 are absent, or X is sulfur in which case R1 and R2 are oxygen, and n is a number from about 75 to about 350 which represents the number of repeating units in the linear molecules of the resin. Specific polycarbonate resins embraced by the foregoing formula and useful in the practice of the invention include bis(p-hydroxyphenyl) methane wherein X is a carbon and R1 and R2 are hydrogen; 1,1-bis(p-hydroxyphenyl)ethane wherein X is carbon, R1 is hydrogen and 'R2 is methyl; 1,1 bis(p hydroxyphenyl) l phenylethane wherein X is carbon. R1 is methyl and R2 is phenyl;
1,1 bis(p hydroxyphenyl)cyclohexane wherein X is carbon and R1 and R2 are methylene links in a cyclohexyl ring; bis(p-hydroxyphenyl)ether wherein X is oxygen and R1 and R2 are absent; and bis(p-hydroxyphenyl) sulfone wherein X is sulfur and R1 and R2 are oxygen. The best results have been achieved with polycarbonate resins of the above formula, wherein X is carbon and R1 and R2 are lower alkyls of one to four carbon atoms. A specific example is 2,2 bis(hydroxyphenyl)propane wherein X is carbon and R1 and R2 are methyl, this resin being available commercially under the trade name Lexan. Such lower alkyl species of polycarbonate resins are preferred as the material from which the light-transmitting rods are made for the readout assembly of the invention.
The polycarbonate light-transmitting rods are assembled, in aligned positions as previously described, in a solid block of opaque epoxy resin. This epoxy resin is a polymeric material prepared in conventional manner by reacting epichlorohydrin with bisphenol-A in the presence of sodium hydroxide. For the purpose of this invention. the epoxy resin should have an epoxide equivalent within the range from about 175 to about 200 and a molecular weight from about 450 to about 750. As is known, the epoxide equivalent is the weight in grams of resin which contains one gram-equivalent of epoxide and thus a measure of the concentration of epoxy groups in the resin. These resins may be cured in conventional manner with polyfunctional reagents such as amines, anhydrides, acids, phenolic and amino resins, and sulfides, and thereby are converted into hard, infusible, crosslinked polymers.
In order to form the block of opaque epoxy resin with the polycarbonate rods embedded therein, the rods are first placed in a suitable mold cavity in the desired aligned position. Then, the epoxy resin is mixed with the curing agent and, if not already opaque, with an opacifying filler such as powdered carbon or any other inert light-impervious powdered solid to form a curable composition which is poured into the remaining free space of the mold cavity and allowed to cure. The outer surfaces of the polycarbonate rods are first coated with a reflective coating such as silver or other bright metal to increase the light transmittance of the rods when incorporated in the final assembly. A clear compatible material with lower refractive index may also be used as a coating material.
The above-described assembly is removed from Athe mold after completion of cure and an integral colored layer or filter is next formed over the common display plane thereof in which the character display ends of the polycarbonate rods are aligned. The material used for this colored layer is again an epoxy resin having the same structme as previously defined above with the exception that the resin is transparent or translucent so that the illuminated characters of the polycarbonate rods may be seen through the layer. A dye of any desired color, blue, red, green, etc. is admixed with the curable epoxy resin composition. One method of forming the colored layer on the display side of the readout assembly includes the use of a resilient mold which is just large enough to accept the assembly and form a retaining barrier around the viewing surface. The assembly is pushed into this mold and the filter material is poured over its upper surface. After curing, the assembly is removed and the top surface of the filter layer is ground off by an abrasive wheel, leaving about .020 inch on the display plane. It has been found that a thin film of the liquid filter material runs down the sides of the display assembly between the block and the inner mold surface. This film is not objectional and may serve as an additional anchoring means to hold the filter layer in place.
As previously noted, the final integral structure can withstand extremes of temperature and pressure in service without separation of its components or other objectionable deterioration. The reasons for this are not clearly understood but it will be noted that the molecular structures of the materials used have a strong similarity. That is to say, the repeating units of the epoxy resins, viz glycidyl ethers of bisphenol-A, and the repeating units of the polycarbonate resin, viz bisphenol-A or like esters of carbonio acid, have a marked structural resemblance and it is believed that this fact at least partially accounts for the remarkable ainity which maintains the several components of the readout assemblies of the invention firmly united in adverse environments.
Further details of the invention will be readily understood by reference to the accompanying drawings of which:
FIG. 1 is a perspective view of one of the light-transmitting rods used in the readout assembly,
FIG. 2 is a perspective view of a plurality of rods embedded in an opaque epoxy resin block with a central portion of the block removed for better illustration of details,
FIG. 3 is a perspective view showing how a colored layer is fused over the surface of the common display plane of three of the opaque blocks, and
FIG. 4 is a cross-sectional view taken along line IV IV of FIG. 3.
Referring totFIG. l, a light-transmitting rod is there illustrated having one cylindrical end portion 11 and another attened end portion 12. The rod is made of a polycarbonate resin such as 2,2-bis(phydroxyphenyl)propane.
Referring to FIG. 2, sever. light-transmitting rods are aligned in position so that the flattened ends 12 thereof are in a common display plane and are embedded in an opaque epoxy resin block 13 of which the surface 14 is flush with the common display plane. The surfaces of the polycarbonate rods extending through the block 13 are coated with a layer of silver metal 10A so that, when the opposite ends 11 of the rods are exposed to light, the light transmission through the rods 10 to the flattened ends 12 is increased. The block 13 is formed from a polymer of epichlorohydrin and bisphenol-A having an epoxy equivalent from about 175 to about 200 and a molecular weight from about 450 to about 750. As will be evident, selective illumination of the flattened ends 12 of the rods 10 will allow display of characters comprising any integer from Oto 9.
Referring to FIG. 3, an integral array of three of the blocks 13 is there illustrated which may be used to display any three integer number. A resilient cavity mold 15 is provided having a cavity 16 which is just large enough to receive a block 13 which is pushed into the cavity. The cavity is deep enough so that a retaining wall remains around the display surface after the block 13 has been pushed to the bottom.
A colored curable epoxy resin 14 having the molecular structure of the opaque resin is next poured over the display surface. After a curing period, the block 13 and the attached filter film is removed from the mold and placed on a grinder where the top surface of the filter film is ground off. It has been found that a resultant film of about .020 of an inch gives good results. The finished colored readout assembly is shown in FIG. 4.
The invention has now been described in terms of its general principles and a specific embodiment thereof. The specific arrangement of seven rods shown in the drawings is only one possible arrangement and obviously a larger or smaller number of rods may be aligned in other positions to form illuminated characters other than integers. Also, the attened ends 12 of the rods may be of various other shapes for displaying illuminated characters formed from spots of light such as discs, triangles, ovals, rectangles, etc.
Accordingly, it will be understood that it is intended to cover all changes and modifications of the preferred embodiments of theinvention, herein chosen for the purpose of illustration, which do not constitute departures from the spirit and scope of the invention.
What is claimed is:
1. A readout assembly comprising a plurality of light transmitting rods made of a polycarbonate resin, said rods being embedded in an opaque epoxy resin body comprising a polymer of epichlorohydrin and bisphenol-A having an epoxide equivalent from about to about 200 and a molecular weight from about 450 to about 750, one of the ends of said rods being aligned for display of illuminated characters and the opposite ends of said rods being exposable to light for formation of said characters by passage of said light through said rods, and a colored layer of light-transmitting material being integrally bonded with the opaque epoxy resin body and the said ends of the rods that are aligned for display, said light-transmitting material comprising a coloring agent and an epoxy resin having an epoxide equivalent and molecular weight within the values specied for said opaque epoxy resin.
2. A readout assembly as in claim 1 wherein the character display ends of said rods are flattened.
3. A readout assembly as in claim 1 wherein the surfaces of said rods embedded in said opaque epoxy resin body are coated with a reiiective metal coating.
4. A readout assembly as in claim 1 wherein the surfaces of said rods embedded in said opaque epoxy resin body are coated with a layer of transparent material having a refractive index lower than the refractive index of the rods.
5. A readout assembly as in claim 1 wherein said opaque epoxy resin body is in the form of a block and the character display ends of said rods are aligned in a lc)c1)mmon plane which is Hush with a surface of said ock.
6. A readout assembly as in claim 5 wherein said surface of said block is covered by said colored layer of epoxy resin.
7. A readout assembly as in claim 6 adjoined with at least one other such assembly for display of a multiplicity of said illuminated characters.
8. A readout assembly comprising a light transmitting rod made of a polycarbonate resin, said rod being ernbedded in an opaque epoxy resin body comprising a polymer of epichlorohydrin and bisphenol-A having an epoxide equivalent from about 175 to about 200 and a molecular weight from about 450 to about 750, one end of said rod being positioned for display and the opposite end of said rod being exposable to light for passage of said light through said rod and a colored layer of light transmitting material being integrally bonded with the opaque epoxy resin body and the end of the rod that is positioned for display, said light transmitting material comprising a coloring agent and an epoxy resin having an epoxide equivalent and molecular weight within the values specified for said opaque epoxy resin.
References Cited UNITED STATES PATENTS Freeman et al.
DAVID H. RUBIN, Primary Examiner U.S. Cl. X.R.