US3472672A - Process for producing color television tubes - Google Patents

Description

Oct. 14, 1969 C.J. PRAZAK m, ETAL 3. 7 57 PROCESS FOR PRODUCING COLOR TELEVISION TUBES Filed Aug. 26. 1966 I INVENTORS." CHARLES J. PRAZAK 111 KAP MIN SEO ATT'YS United States Patent 3,472,672 PROCESS FOR PRODUCING COLOR TELEVISHON TUBES Charles J. Prazak 1H, Elmhurst, and Kap Min Seo, Chicago, Ill., assignors to National Video Corporation, Chicago, 11]., a corporation of Illinois Filed Aug. 26, 1966, Ser. No. 575,464 Int. Cl. C09k 1/02; B44d 1/44 US. Cl. 117-335 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for producing color television tubes, and, more particularly, to a procedure for uniquely forming the phosphor patterns or dots provided as a screen on the interior surface of the tube enlarged end.

A problem has existed in color television tube production stemming from the fact that the various rinses or washings tended to wash away portions of the important phosphor dots, necessitating careful control of the washing operation and notwithstanding the fact that equal care had been used in drying the sequentially applied dots.

Here, it will be appreciated that other material groupings or patterns than dots can be employed advantageously in the practice of the invention. The general procedure has involved depositing a layer of polyvinyl alcohol on the tube face. This film is capable of being insolubilized, i.e., printed, by exposure to actinic rays. The phosphors may be incorporated in the film at the time of deposition, may be sprayed on prior to exposure, or may be applied after exposure. The exposure is achieved by projecting light from a point source through a shadow mask which produces an arrangement of dots which eventually react for example to the green electron beam in the finished tube. The portions in between dots that have not been irradiated are removed by washing with demineralized water. The same procedure is followed for laying down a pattern of blue dots, and thereafter red dots. Subsequent washings, unless carefully controlled, tend to remove portions of previously deposited dots. Further, to prevent cross-contamination (phosphor of a subsequent color-contaminating previously deposited phosphor), the dots must be satisfactorily dried prior to a subsequent deposition.

This delicacy of operation is avoided by the instant invention, and the provision of a procedure which makes possible the substantial minimization of the sensitivity of the dots to washing, even without drying, constitutes an important object of the invention.

Another object of the invention is to provide a novel procedure for the formation of the screen within a television tube wherein a hardening agent is employed to fix the binder grouping (i.e., the polyvinyl alcoholtype dot) which substantially eliminates the feather-like periphery and which further can be employed to compact the material groupings.

Other objects and advantages of the invention may be seen in the details of construction and operation set down in this specification.

3,472,672 Patented Oct. 14, 1969 The invention is explained in conjunction with the accompanying drawing, in which- FIG. 1 is a fragmentary perspective sectional view of the interior surface of a color television tube;

FIG. 2 is a plan view of an enlarged dot, i.e., a phosphor-supporting element in the partially dried or dried condition having the form developed by prior art procedures;

FIG. 3 is a plan view of phosphor-supporting dot developed in the practice of the invention; and

FIG. 4 is a plan view of a phosphor-supporting dot developed by the practice of the preferred form of the invention.

In the illustration given and with particular reference to FIG. 1, the numeral 10 designates a portion of the face of a color television tube, being constructed of glass (usually stippled lead glass or borasilicate glass) and which is seen to have provided on its inner face a green phosphor dot 11, a blue phosphor dot 12, and a red phosphor dot 13. As indicated previously, the dots are laid down sequentially, and this procedure, along with the procedure of the invention, can be best understood by a consideration of the following example of the practice of the invention.

EXAMPLE For this example, a 23-inch rectangular color television tube denominated 23EGP22 according to the JEDEC specifications, was employed. Into the face plate of such a tube, a polyvinyl alcohol solution was introduced, followed by the conventional slurry, slosh-and-swirl technique performed by rotating the face plate. The polyvinyl alcohol solution consisted of parts of 3% polyvinyl alcohol in demineralized water, 10 parts of ethylene glycol, 5 parts of ammonium dichromate, and 5 parts of dioxane (the latter serving as a surfactant). Following the swirling technique, the majority of the polyvinyl alcohol solution is poured off and spun off, leaving less than about 10% of the solution adherent to the inner face of the face plate.

Following this, the adherent material is partially dried so as to achieve a tacky surface and this is advantageously performed by subjecting the face plate for a few minutes to infra-red radiation.

The now-tacky polyvinyl alcohol-type film is exposed to ultra-violet radiation through a shadow mask, utilizing a point source of actinic light positioned at the green source position. Thereafter, the film is coated with P22 green phosphor. The green phosphor dots are now developed by washing with a fine spray of dernineralized water.

Fixing of the now-achieved dots (it being appreciated that the washing removes the portions of the undeveloped film between dots) is achieved through using spray nozzles operating at 40 psi. and delivering 0.2 g.p.m. of a 3% boric anhydride solution in demineralized water. Following this, the fixed dots are rinsed.

The foregoing steps are repeated, from the deposition of the polyvinyl alcohol layer through the developing, fixing and rinsing, for the blue dots, and thereafter for the red dots. Following the deposition, developing, fixing and rinsing of the last layer of dots, i.e., the red dots 13, an additional water spray is directed against the face plate so as to provide a thin water film on the phosphor dots. This is followed by centrifuging after which an acrylic plastic spray lacquer (with toluene and ketones as solvents) sprayed on under the same conditions. The lacquer film is air-dried for a few minutes, and thereafter aluminized in a vacuum evaporator.

Without the use of the above-mentioned fixing step (utilizing boric anhydride), the dot configuration such as that generally designated 14 in FIG. 2 is achieved. It

will be seen that the perimeter of the dot as at 15 is distorted along with feather-like projections as at 16. These projections carry phosphor powder and project into adjacent dots to cause cross-contamination. Also the pattern of phosphor powder laid down on the dot 15 is somewhat porous, resulting in pore areas as at 17.

We have discovered that the invention can also be practiced using boric acid in place of boric anhydride. When boric acid is employed as the fixer, a dot configuration such as that seen in FIG. 3 and generally designated 18 is achieved. It will be seen that the perimeter is still somewhat irregular as at 19, and that the surface of the dot 18 is not completely covered with phosphor powder, leaving blank spaces as at 20. However, the dot is characterized by the substantial absence of the objectionable feather-like projections 16 seen in FIG. 2.

Optimally, boric anhydride is employed as the fixer, in which case the configuration generally designated 21 and seen in FIG. 4 is achieved, wherein the perimeter is substantially smooth as at 22 and the surface is characterized by the absence of the void or blank spaces as at 17 and 20 in FIGS. 2 and 3, respectively. This is achieved through an advantageous compaction of the dot, resulting from the use of boric anhydride as contrasted to boric acid. Ordinarily, the dots will have a diameter somewhat larger than 0.017", and we find that when boric anhydride is employed, the mean diameter of the dot 21 (see FIG. 4) is reduced to 0.017". At the same time, the use of either of the fixers, i.e., boric anhydride, or boric acid, does not wash away material so as to reduce the thickness of the dot which usually has a thickness of the order of 0.0015".

Experience with other agents used for fixing polyvinyl alcohol in other applications such as sodium carbonate, borax and phosphoric acid, does not result in the advantageous de-feathering and compaction referred to above. In fact, the use of such agents is disadvantageous, since they result in washing away a portion of the phosphor dots.

From the foregoing, the use of either boric acid or boric anhydride solutions reduces the amount of the feathery or flapping material (as viewed under a microscope when in the developed, unrinsed condition) and when boric anhydride is employed, appears to shrink the dot and give a denser construction. The showing of FIG. 2 occurs when the developed film is unfixed, the feather-like projections suddenly extending from the perimeter of the dot. Use of the boron-containing materials fix each dot so that additional washing will not reduce its size, the phosphor dot being sufficiently inert under these circumstances so as to receive the application of a second polyvinyl alcohol film without drying. We further find that the invention is advantageous in that in subsequent processing the green material, for example, does not wash oil and possibly contaminate the blue field, as it would if the same were not firmly fixed.

We find that variation of the various ingredients is possible while still achieving the advantages of the invention. For example, the concentration of the polyvinyl alcohol in demineralized water (the water being achieved through an ion exchange operation) may be varied in the range of 24%; the ethylene glycol concentration may be varied from to parts, by volume); the ammonium dichromate also varied from 5 to 10 parts; and the dioxane 2 to 5 parts, While also achieving the beneficial results of the invention. The concentration of the aqueous solution of boric anhydride may be varied from about 2 to about 4%.

If desired, the drying which previously has been referred to as advantageously eliminated, can still be utilized between successive dot applications, and further phosphor coating may be applied prior to exposure. Thus, there is considerable flexibility in the use of the procedure.

We claim:

1. In a process for producing color television tubes having discrete binder material groupings, said binder being adapted to support phosphor material, the step of defeathering said groupings after the phosphor material is placed on the binder by rinsing the same with a hardening agent for said binder material, said hardening agent being selected from the class consisting of boric acid and an aqueous solution of boric anhydride, the concentration of boric anhydride being of the order of 24%.

2. The process of claim 1 in which the said hardening agent is an aqueous solution of boric anhydride, the defeathering step being accompanied by compacting of the dots.

3. The process of claim 1 in which the hardening agent is an aqueous solution of boric anhydride, the concentration of boric anhydride being about 3%.

4. The process of claim 1 in which said binder material is a solution containing as essential ingredients polyvinyl alcohol, ethylene glycol, ammonium dichromate, and dioxane.

5. The process of claim 4 in which the said polyvinyl alcohol is present in about parts, the ethylene glycol is present in 5 to 10 parts, the ammonium dichromate in 5 to 10 parts and the dioxane in 2 to 5 parts.

6. In a process for producing color television tubes wherein layers of binder are arranged to support different phosphors, said layers having irradiated portions to define discrete groupings and wherein the remainder of said layers are water removed, the step of de-feathering the periphery of said groupings after the phosphors have been placed on the binder by rinsing the groupings with a material adapted to harden said binder without the need for drying between successive water removals, said rinsing material being selected from the class consisting of boric acid and aqueous solution of boric anhydride, the concentration of boric anhydride being of the order of 24%.

References Cited UNITED STATES PATENTS 2,828,216 3/1958 Delrieu l1733.5 XR 2,877,605 3/1959 Hoshowsky 11733.5 XR 3,036,913 5/1962 Burg 9636.1 XR 3,054,672 9/1962 Angelucci 1l733.5 XR 3,342,594 9/1967 Kaplan 96-361 ALFRED L. LEAVITT, Primary Examiner W. F. CYRON, Assistant Examiner US. Cl. X.R. 1l762.2

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