US2032761A - Fluorescent coating method - Google Patents

Description

March 3, 1936 C. P. MARSDEN FLUORESCENT COATING METHOD Filed Nov. 21, 1933 INVENTOR BY /-M- ATTORNEY Patented Mar. 3, 1 936 UNITED STATES FLUORESCENT COATING METHOD Charles P. Marsden, Bloomfield, N. J., assignor to Hyg'rade Sylvania Corporation, Salem, Mass, a corporation of Massachusetts Application November 21, 1933," Serial No. 698,945

5 Claims. (Ci. 91-68) This invention relates to coating methods and with particularity to coating with fluorescent material.

An object of the invention is to provide a novel method of applying a fluorescent coating to glass or other similar support.

A further object is to provide a novel method of applying a fluorescent coating to a cathode ray tube or similar device.

A feature of the invention relates to a cathode ray tube or similar device having a fluorescent coating which has a maximum uniformity.

A further feature relates to the method of attaching the fluorescent coating to the glass or other similar body.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed description and appended claims.

While the invention finds its greatest practical advantages in the manufacture of so-called cathode ray tubes or Braun tubes, the inventive method is not limited to the manufacture of any particular kind of tube, but is capable of application in any situation where a uniform coating of fluorescent material is to be applied to a supporting member.

In certain types of apparatus, for example cathode ray tubes, Braun tubes, or the like, there is provided a screen which comprises a material that fluoresces or emits light when bombarded by cathode rays or the like. For example, in one known type of construction employed for this purpose, the tube is'provided with a constricted or neck portion at one end and an enlarged, substantially flat screen portion at the opposite end, the interior face of this screen portion being provided with this fluorescent coating. Suitable electrodes are provided within the tube for gen-- erating, accelerating and oscillating the beam of cathode rays which, upon striking the screen, causes the latter to fluoresce or otherwise emit light rays. Such tubes are customarily used as oscillographs for wave analysis, frequency analysis, etc. Tubes of this general type have also been employed for television or picture transmission purposes, in which case the beam or cathode my not only has its spacial position varied in synchronism with a transmitter, but also the intensity and/or velocity and/or width of the impinging beam are varied to correspondingly vary the intensity of the fluorescent effect from the screen. While, for oscillograph or similar uses it is important that the fluorescent coating be uniform, minor variations of thickness or uniformity of the grain in the coating do not seriously affect results. However, in television or similar uses it is absolutely necessary, if truly faithful images are to be reproduced, that the fluorescent coating be not only of the highest uniformity as to thickness, but it is also important that the individual grains constituting the coating be, as far as possible, of the same degree of fineness. It is further highly important in all types of cathode ray tubes that the fluorescent 10 coating be firmly united to the glass or other support, since it is required to be bombarded continuously by the cathode rays.

Various methods have heretofore been proposed for applying the fluorescent coating. For exam- 15 pie, the most common way is to mix the fluorescent coating with a suitable binder which is then sprayed over the surface to be coated. Needless to say, with ordinary spraying methods it is extremely dificult to secure a coating of uniform thickness. 'Ihis may be due to a variety of causes. For example, in spraying it is required that the material be sprayed onto the receiving surface at substantially right angles, with the result that if a non-uniform or large grain of materialattaches itself to the supporting surface, succeeding traverses of the spray aggravate and accentuate the thickness of the coating at this point. Added to this is the fact that ii the coating is not evenly united to the support over its entire surface, the force of the spray may dislodge one or more grains from the coating. Other methods such as painting or the like obviously are incapable of producing uniform coats because of the appreciable physical dimensions of the painting tool as compared with the fine grain constituting the coating.

It has been found that a thoroughly uniform fluorescent coating may be achieved in accordance with this invention without spray, painting 40 or similar processes.

In accordance with the invention the surface of the tube to be coated is first provided witha tenuous film of tacky or sticky material or a material which exhibits pronounced adhesive properties for the powdered fluorescent material. This fluorescent material is preferably employed in powdered form and preferably mixed with another powdered weighty material such as powdered zinc or the like. The powdered mixture is then poured or deposited in any familiar manner upon the same flim to which it adheres. The support is then rotated, oscillated and/or swirled so as to agitate the powdered mixture relative to the said fllm, thus distributing the fluorescent powdered material in an even deposit over the fllm. The excess of powdered material may then beremovedbypouringorsimiiarprocess, after which the supportmaybeheatedbakedorflred toaduilredheattoremovethefllmand/or binders, resulting in a flrm attachment of the fluorescent material onto the glass or other nipport.

while the foregoing description gives a general plan of the preferred procedure to be employed, a detailed description will now be given of the manner of practicing the invention in connection with a typical form of cathode ray tube.

Referringtothedrawing,themunerallindicates generally a glass or other tube having a constricted or neck portion 2 and a flared or enlarged portion 3. The portion 3 terminates in a substantially flat portion A which serves to carry the fluorescent material. In accordance with well-known practice in the art of cathode ray tube design, the tube l is provided with an emitting cathode represented schematically by the numeral 5, and an electrode or electrodes 6 for varying the intensity of the cathode ray beam.

A concentrating or focusing electrode 1 is usually provided to restrict the beam to a comparatively narrow width. A pair of vertical deflecting plates 8 and a pair of horizontal deflecting plates 9 (one shown).are provided for oscillating the cathode ray beam over any predetermined path. A suitable anode or anodes II are provided for accelerating the electrons from the cathode i. The manner of producing and oscillating the cathode ray beam. above described constitutes no feature of the present invention and any wellknown means may be provided for this purpose.

Prior to attaching the constricted or neck portion 2 to the flared portion i, the latter flared portion 3 has the interiorsuri'ace of the wall I provided with a tenuous fllm preferably of the nature of a plasticized lacquer indicated in the drawing by the numeral II. It is preferred to employ a binder consisting of, for example, a solution of nitro cellulose in a volatile solvent, e. g., ethyl carbonate, amyl acetate, etc. This binder solution is then plasticized preferably by mixing with it dibutyl phthalate, and in order to retard the drying, a small percentage, such as 1% of diethyl oxalate may be mixed with the binder. It is to be understood, of course, that the invention is not limited to this particular plasticizing agent. For example, any diamyl or diethyl phthalate or phthalates may be employed or, if desired, dicresyl phosphate my be employed. The invention also contemplates the use of lacquer fllms containing gums, if these lattergumsareburnt outintheflnalflring. As above stated, the plasticized fllm is preferably of a tenuous character or sufliciently thin so as to be substantially completely transparent, although it will be understood that any other known transparent fllm may be employed which, upon flring, is completely-removed or becomes transparent.

The fllm is preferably deposited by pouring or other similar operation. For example, if the portion 4 of the tube is five inches in diameter, approximately 2 cc. of the above material may be dropped on the interior face of the portion I and allowed to flow evenly over the surface. Any excessofthematerial overtherequiredamount may be drained of! in any suitable manner, with the result that there is produced a tenuom uniform fllm which is substantially free from bubbles, flowing marks. etc. Thisfllmisthen allowed todryoritsdriedtothepointwhereit eomesappreciabiytackyorstickmandtheelcess,

fluorescent material. Any well-known fluorescent material such as ordinarily employed in cathode ray tubes or the like my be employed. Preferably this material is intimately mixed with a weighty powdered zinc of about 30 mesh. The mixed powdered materials are then pom-ed into the bulb and the bulb is swirled, oscillated, and somewhat violently shaken so as to distribute the relatively flne fluorescent material in an even depositoverthestickyflhn Ii. Asaruultoftbis agitating process the heavy grains or particles of zinc or other weighty material cause the powdered fluorescent material to be distributed in a uniform layer over the fllm ll. One posible explanation for this is that the very flne particles of the fluorescent material are held by a sufiicient adhesive force to prevent their dislodgment by the moving or swirling weighty particles of zinc, whereas the non-uniform or enlarged grains of the fluorescent material are carried by the swirling or agitated weighty material, with the result that the fluorescent coat which flnally adherestothefllm ll consistsofsubstantiallylmiform and finely grained fluorescent material. The excess of the powdered materials may then be poured out .or otherwise removed from the tube. If, upon examination of the tube, it is discovered that there is an excess of fluorescent material forming a lump at any particular portion ofthefllm,thiscanberemovedbyaddingmore zinc orsimilarweightymaterial andcontinuing the swirling action until the lump or non-uniformity is removed. The material having thus been removed, the edges of the coating may be trimmedbyrotatingthebulbandwipingoii'the material with a cloth or rubber scraper.

'iheendlofthetubeisthensubiectedtoheat, preferablytoraiseittoadullredheatortoa temperature at which the binder and/or the plasticized fllm ii is removed. Preferably also, the heat is maintained for a suflicient length of timetotakethefluorescentmaterialontothe member I.

Aimbepreparedinaccordancewiththeabove coatinghasbeenfound to extremelyuniform graining and thickness of fluorescent material anditwili be obviouaofcourse, that variuaily increased until the fllm is entirely removed.

If desired, the above procedure may be repeated so as to provide ve coats of fluorescent material, each coating having a thick ness practically consisting of a single grain.

The portion {thus prepared may then be unitedorsealedtotheneckportioniandthe tubemaythenbesubiectedtotheo' evacuation and treatment customarily employed in the manui'actin'e of vacuum tube and electron tube devices in general.

lthasbeenfoimdthattheformingmethodzg renders it possible to vary the thickness of the fluorescent coating from an almost transparent dery fluorescent material containing fine and coarse grains to a cathode ray tube which comprises, flowing onto said support a smooth thin fllm of a plasticized lacquer binder solution, drying said film until the odor of the solvents is substantially entirely removed and said film becomes appreciably tacky, depositing said powdery material on said fllm, and swirling said support to cause the coarser grains of said material to distribute the finer grains of said material in a uniform layer on said film, removing any excess of said material, and heating the support to remove excess lacquer and to bake said powdery material on said support.

2. The method of providing a cathode ray tube with a uniform coating of powdery fluorescent material which comprises, flowing onto a wall of said tube a thin fllm of a plasticized binder solution, drying said solution to the point where it becomes appreciably tacky and the odor of the solvents is substantially entirely removed, mixing with the powdery fluorescent material another powdery material of greater weight than the fluorescent material, depositing said mixture on said flim, swirling and shaking said tube to distribute said fluorescent material in a substantially uniform layer, removing any excess of said mixture, and heating the wall of said tube to bake said powdery material thereon.

3. The method of applying a uniform coating of fluorescent material to a cathode ray tube which comprises, flowing onto a wall of said tube a thin film of a transparent plasticized lacquer, mixing with the powdery fluorescent material a quantity of powdery material which is heavier than the powdery fluorescent material, depositing said mixture on said film while said fllm is appreciably sticky, swirling and shaking said mixture until lighter grains are distributed in a uniform layer over said film, removing excess of said mixture, and heating the wall of the tube to bake the powdery material thereon.

4. The method of providing a cathode ray tube with a fluorescent coating which comprises, mixing a phthalate with a nitrocellulose binder, de-

positing said mixture in a thin film onto a wall.

of said tube, drying said fllm until the solvents are substantially entirely removed, mixing with Y the fluorescent material another weightier powdered material, swirling the tube to cause the weightier material to distribute the grains of the fluorescent material uniformly over said film, and subsequently heating said fllm to remove said binder.

5. The method according to claim 4 in which the fluorescent material is mixed with a powdered zinc of approximately mesh.

CHARLES P. uansmm.

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