US3672893A

US3672893A - Process of manufacturing screens for shadow-mask tubes

Info

Publication number: US3672893A
Application number: US60433A
Authority: US
Inventors: Ronald C Robinder; William A Rowe; James W Schwartz
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1970-08-03
Filing date: 1970-08-03
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27

Abstract

THE SCREEN IS COVERED WITH A WATER-SOLUBLE COATING MATERIAL COMPRISING A NEGATIVE PHOTOSENSITIVE RESIST AND AN INHIBITOR TO RENDER THE RESIST UNRESPONSIVE TO ULTRAVIOLET LIGHT. AN ADDITIVE, SUCH AS DYE THAT MAY BE BLEACHED OR ACTIVATED BY EXPOSURE TO A VISIBLE LIGHT WAVELENGTH, IS ALSO INCLUDED IN THE COATING TO COUNTERACT THE EFFECT OF THE INHIBITOR WHEN ACTIVATED BY EXPOSURE. THE SCREEN, COATED WITH THIS MATERIAL, IS FIRST EXPOSED TO THE VISIBLE RADIATION FROM ONE COLOR POSITION AND THROUGH A SHADOW MASK HAVING APERTURES LARGER THAN THE PHOSPHOR DOTS OF THE SCREEN. THE SCREEN IS THEN EXPOSED TO ULTRAVIOLET, AGAIN THROUGH THE SHADOW MASK BUT FROM A SECOND COLOR POSITION AND RESULTS IN ELEMENTAL AREAS OF THE COATING MATERIAL, WHERE THE TWO EXPOSURE PATTERNS OVERLAP, BEING RENDERED INSOLUBLE. THE COATING PATTERN IS DEVELOPED BY WASHING THE SCREEN WITH WATER.

D R A W I N G

Description

June 27, 1972 R. c. ROBINDER ET AL PROCESS OF MANUFACTURING SCREENS FOR SHADOW-MASK TUBES Filed Aug. 5, 1970 Inventors Ronald C. Robinder William A.Rowe 7 Jame s W. Schwartz ByC/"mA/%%h Anv.

United States Patent Office 3,672,893 Patented June 27, 1972 Filed Aug. 3, 1970, Ser. No. 60,433

rm. c1. G03c 1/00, 5/00 US. Cl. 9636.1 15 Claims ABSTRACT OF THE DISCLOSURE The screen is covered with a water-soluble coating material comprising a negative photosensitive resist and an inhibitor to render the resist unresponsive to ultraviolet light. An additive, such as a dye that may be bleached or activated by exposure to a visible light wavelength, is also included in the coating to counteract the elfect of the inhibitor when activated by exposure. The screen, coated with this material, is first exposed to the visible radiation from one color position and through a shadow mask having apertures larger than the phosphor dots of the screen. The screen is then exposed to ultraviolet, again through the shadow mask but from a second color position and results in elemental areas of the coating material, where the two exposure patterns overlap, being rendered insoluble. The coating pattern is developed by washing the screen with water.

BACKGROUND OF THE INVENTION The present invention concerns the processing of screens for shadow-mask color-picture tubes, characterized by the fact that the elemental phosphor deposits are smaller in size than the apertures of the shadow-mask or color-selection electrode. The most common versions of such tubes are the so-called black-surround and postdeflection-acceleration or focus tubes.

A black-surround color tube of the shadow-mask variety differs from conventional shadow-mask tubes in that the deposits of different phosphors on the screen are individually surrounded by a material having lightabsorbing properties, such as graphite, from whence the name black-surround derives. The current commercial version of this tube features a mosaic screen constituted of a multiplicity of dot triads arranged in a regular pattern over the image area. Each such triad comprises a dot of green, a dot of blue and a dot of red phosphor and the dot size is smaller than usual so that the phosphor dots of a given triad are physically separated from one another in the image area rather than being in tangential contact. Since the phosphor dots are spaced from one another those parts of the screen which intervene the dots are available to receive a deposit of a light-absorbing material which usually is applied before the phosphors. A curved shadow mask is positioned in close parallel relationship to the screen and serves to accomplish color selection in the usual way. Preferably, the holes of the shadow mask are larger in size than the phosphor dots of the screen to provide a tolerance band for improved purity of the white color field of the tube. A black-surround tube of this type is described and claimed in Pat. 3,146,368, issued Aug. 25, 1964 in the name of Joseph P. Fiore et al. and assigned to the assignee of the present invention.

In the post-deflection-focus tube there is a similar ar rangement of phosphor dots and shadow-mask apertures, similar in that the apertures of the mask are larger than the phosphor dots. Both these tubes present problems of fabrication and they lend themselves to much the same mask-screen processing but for convenience the remainder of this disclosure will address itself principally to the black-surrounded tube which currently is a commercial device, whereas the post-deflection-focus tube is not.

A number of screening proposals have been made and described for processing the black-surround screen. It has been suggested, for example, that the shadow mask be formed with apertures of a desired final size but provided with a filler of one kind or another which temporarily reduces the apertures in size to that which is required for photographic screening in which the mask is employed to locate and dimension the phosphor deposits. After screening is completed, the filler is removed, leaving the mask with apertures desirably larger than the phosphor deposits. This is an elegant process conceptually but difliculties are experienced in attempting to utilize it in mass production. Among other things, there are severe problems in obtaining uniformity of the phosphor dots.

Another approach which has found commercial success is referred to as reeetch. In this process the shadow mask as initially formed has apertures dimensioned as required for screening. The mask is used in photographic printing of the screen in the customary way and when that is finished, the mask is subjected to further etching or to what has become known as a re-etch step. In reetching, the apertures of the mask are enlarged to achieve a final size which exceeds the diameter of the phosphor dots by a desired amount. Very considerable success has been achieved in utilizing the re-etch process in the mass production of black-surround screens. The process has one inherent limitation, however, and that is that if the tube is damaged in processing after the mask has been re-etched, that mask is lost and cannot be reutilized in processing a tube simply because its apertures will have become too large to be useful in screening. Some loss is frequently encountered in the post-screening fabrication steps of a color-picture tube, for example, in aluminizing or in sealing the faceplate section to the remainder of the envelope and therefore some undesirable mask losses ensue. If the black-surround screen can be successfully fabricated without re-etch or without resort to other expedients for changing the size of the mask apertures in tube manufacture, and this is possible with the process of the present invention, economies of manufacture are possible.

Accordingly, it is an object of the invention to provide an improved process for the manufacture of cathoderay tube screens of the shadow-mask variety characterized by the fact that the apertures of the mask are larger than the elemental phosphor deposits.

It is another and particular object of the invention to improve the processing of a black-surround screen for a shadow-mask type of color-picture tube.

SUMMARY OF THE INVENTION The process 'of the invention is directed to applying a coating to selected elemental areas of the image screen of a color-picture tube and includes the following steps:

The image screen is first covered with a coating material that normally has a particular solubility in a given solvent and further has the property that two successive exposures to energy reverse its solubility in the solvent. The coated screen is subjected to a first exposure for a first exposure interval with energy which does not materially afiect the solubility of the coating material in the solvent. Thereafter, the material is subjected to a second exposure for a second exposure interval with energy which, without the conjoint effect of the first exposure, likewise has no material effect on the solubility of the coating material in the solvent. The energy distribution patterns in the first and second exposure intervals are related to one another to subject only those preselected portions of the coating material that cover the aforesaid selected elemental areas of the image screen to both the first and second exposures and the intensity of the energy and the duration of the exposure intervals are effective to reverse the solubility of the doubly exposed preselected portions ments as there is flexibility both as to the nature of the energy employed for the exposures and to the specifics of the coating material. The scope or latitude of processing available is more readily understandable if a particular solubility characteristic is assumed for the coating material. For that purpose, the discussion will proceed on the understanding that the material is normally soluble in a .given solvent, preferably water, and is rendered insoluble as a result of the multiple exposures. Of course, it is recognized that material having the reverse characteristic, being normally insoluble but becoming soluble in response to the exposure, may likewise be utilized.

A variety of forms of energy have the ability to modify the solubility of such material; for example, the application of electrons by means of a scanning beam, heat, ion

bombardment, and electromagnetic radiation in both the visible and invisible portions of the spectrum suggest themselves and indeed many have been disclosed in the prior art in connection with screening color-picture tubes where a sensitized photoresist is the coating material that is subjected to the exposure. And so with the process of the present invention, a photoresist is a convenient material to be used in coating a black-surround or similar pattern on selected elemental areas of an image screen.

In one particular embodiment of the invention, the

screen is covered with a photoresist coating material that has been rendered unresponsive to actinic energy by the presence of an inhibitor in the coating. The coating composition has the further property that the inhibitor ingredient may be countered or nullified by exposure to visible light. Accordingly, when the coated screen is exposed tovisible light in the first exposure interval, the photoresist component of the exposed portions of the coating is conditioned to respond to actinic energy in the second and succeeding exposure interval. By exposing the coating material through the shadow mask and by appropriately positioning the enery sources relative to one another in the two exposures, the desired coating pattern may be obtained since the change in solubility of the coating material is confined only to those portions of the coating that have been subjected to both of the exposures, that is, the coating portions when the two exposure patterns overlap. Any area of the screen which is subjected to a single exposure, in either the first or second exposure interval, is

not rendered insoluble and, accordingly, makes no contribution to the desired pattern in the final development step when the screen is treated with the solvent of the coating material.

Another specific embodiment of the invention permits the processing to be accomplished with a single type of energy employed in both exposure intervals. For example,

and as described more particularly hereafter, the coating materlal may comprise a resist which has not been sensitized and may also comprise a suitable sensitizer which 13- Initially isolated from the resist ingredient by means of a barrier. By utilization of a barrier that is rendered permeable to the sensitizer upon exposure to actinic energy, the first exposure may release the sensitizer to coact with the resist so that a second exposure, conducted after a suflicient time delay to permit sensitizing of the photoresist, forms a latent image of the. desired coating pattern to be developed by rinsing the screen with a solvent for the coating material.

These various processes of the invention are useful in the preparation of a screen for a black-surround tube and for a post-deflection-focus tube as well. Where black surround is desired, the pattern developed in accordance with the invention includes another ingredient that is inorganic and is capable of absorbing light so that the screen in its final form exhibits black surround. For a post-deflectionacceleration tube, however, which is not to feature black surround, the coating pattern is developed of an organic material, such as polyvinyl alcohol, to serve the very desirable purpose of defining the screen areas into which the phosphors are to be deposited and this feature it shares with the black-surround process. They differ though in that the coating pattern, being volatilizable, is completely removed during bakeout of the post-deflection-acceleration tube if it is not to feature black surround.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 represents a portion of the mask-screen structure that may be employed in a black-surround or a postdefiection-focus tube; and

FIGS. 2-7, inclusive, are exposure patterns utilized in explaining various screen processing embodiments of the subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Color tubes may have circular or rectangular envelope configurations at the faceplate or screen section which includes the image area. In this area there is a repeating sequence of phosphor deposits of the thre primary colors since commercial television is currently practiced as an additive type of system. The phosphor may be deposited in a variety of forms such as stripes, hexagons, circular dots or the like. The specifics of the envelope as to size and configuration and the particulars of the phosphor dots are of no special concern but for convenience it will be assumed that the tube in process is rectangular having a mosaic screen defined by a multiplicity of dot triads.

In FIG. 1, there is illustrated a fragment of a color tube screen 9 with phosphor deposits represented by circles and the legends G, B and R symbolically designate those deposits which are formed of green, blue and red phosphors, respectively. It will be observed that the phosphor dots are not in tangential contact. This is because they are smaller than usual and therefore are separated from one another, providing elemental areas of the screen around each such dot and it is to these selected elemental areas of the image screen that a coating is to be applied in accordance with certain applications of the process of the invention, whether that coating include a light-absorbing material or not.

Superposed over and in close spaced relation to the screen is a shadow mask 10, only a portion of which is shown in FIG. 1. It is a relatively thin metallic sheet havmg a field of apertures 11 which corresponds in shape as well as dimensionally to the field of dot triads of the screen. Both of these components are approximate sphericalsections and they are aligned so that each mask aperture has a precise location in respect of an associated dot trlad to the end that three electron beams issuing from a gun cluster (not shown) reach the screen through the mask apertures and approach at such angles that each beam excites only the color phosphor to which it has been assigned. In these matters, the role of the screen and mask in obtaining color selection are entirely conventional and need not be considered further. Attention will he give, instead, to process embodiments of the present invention by which a coating may be applied to those elemental areas of screen 9 which surround each part of the screen that is assigned to receive a phosphor deposit, achieving this selected coating without the need to change the size of apertures 11 of the mask at any time even though these apertures are larger in diameter than the phosphor dot deposits.

In broad definition, the invention process features covering the entire screen with a material which has a particular solubility in a solvent but has the property that two successive exposures to energy are able to reverse its solubility. Assume, for convenience, that the material is normally soluble but can be rendered insoluble. Sometimes the process is conducted simply to convert the coating material from being soluble to only partial solubility or a condition of tackiness but, preferably, the process is controlled to achieve substantial insolubility. The first exposure has no material effect on solubility and may be likened to arming the material so that it may respond to and be activated by a second exposure. The conjoint effect of both exposures causes the material to become insoluble. Viewed in that light, it is clear that only those portions of the coating subjected to both exposures become insoluble so that control of the energy distribution patterns of both exposures facilitates achieving the desired coating pattern for the screen.

The first process application will be described with particular reference to FIGS. 2-4. In the first step the image screen of the picture tube is covered with material that is normally soluble in water but has the property that two successive exposures to energy, undertaken in a particular order or sequence, are required to reverse its solubility, rendering it insoluble in water. In general, photosensitive colloids such as polyvinyl alcohol (PVA), fish glue, albumen and gelatins are suitable for use as the principal ingredient of the coating material although it is convenient to restrict this discussion to the use of PVA. It is well known that PVA, sensitized with ammonium dichromate, is a photosensitive resist normally soluble in water but rendered insoluble upon exposure to actinic radiation such as the light output of a mercury arc lamp which is predominantly ultraviolet. In order to achieve an operation akin to arming followed by activation as suggested above, there is included in the coating material as a second ingredient or constituent an inhibitor the function of which is to cause the PVA to be unresponsive to ultraviolet. Additionally, the inhibiting effect must abate in response to exposure of the coating to energy which in elfect arms the PVA coating for actviation by ultraviolet. Of course, it is also required that the energy employed to counteract or annul the effect of the inhibitor must not of itself cause the PVA constituent to become insoluble. Moreover, the energy used to activate the PVA once it has been armed must not have any appreciable nullifying eifect on the inhibitor.

There is considerable choice as to the inhibitor employed. For example, the inhibitors fall into two general categories i.e. chemical ones which affect the dichromate ions or shift the pH of the coating solution to drastically slow down the reaction to ultraviolet and optical ones which absorb ultraviolet. Examples of the first type include hydroxylated amino compounds, such as triethanolamine, diethanolamine, and 2(2-amino'ethylamino) ethanol. Other chemical classes that may be potential inhibitors include anthraquinones, nitrophenol and urea derivatives. Certain dyes are suitable for the second type such as color index yellow 23 which is available commercially as Amacid Yellow T extra from Koppers Chemical; also Phenamine Brilliant Blue, 6B, concentrated, distributed by General Analine Film. Moreover, the difierence in characteristics of the inhibitor dictate the conditions to be established in the first exposure interval to counteract the inhibitor and arm the coating for activation. By way of illustration, the inhibitor may have such properties that exposure to a particular type of energy may destroy its effect. For example, the inhibitor may be a dye that may be bleached by exposure to a particular wavelength of light. Alternatively, an additive to the coating material may be activated by exposure to energy to chemically change or attack the inhibitor and destroy its eifect. The process embodiment presently under consideration will proceed on the basis that such an additive is included in the coating material.

More particularly it will be assumed that the inhibitor of the coating material is triethanolamine (TEA) and that the additive for counteracting it is the dye rhodamine B. A suitable formula for the coating composition is as follows:

A sensitized PVA solution in water, 4 percent weight by volume and with a PVA to dichromate ratio of 5-1 is prepared and to 40 cc. of that solution is added 1-2 cc. of a 10 percent solution of TEA in water. The next ingredient is 24 cc. of a one percent solution of rhodamine B in water. This material is coated over the inner surface of the faceplate of the tube in process which, of course, serves as the image area or screen and it is then dried, preferably using air rather than heat. When dried, the coating material is essentially insensitive to actinic energy, such as ultraviolet, due to the presence of the inhibitor TEA. The faceplate of the tube in process with its screen area bearing the dried coating and with its shadow mask in position is introduced into an exposure chamber or lighthouse of essentially conventional construction and is subjected to a first exposure for a first exposure interval with energy, selected such that by itself it does not materially affect the solubility of the PVA ingredient in water. Since the first exposure step is simply to counteract the influence of the inhibitor, it is accomplished for the specific coating composition under consideration by exposure to yellow light. If this takes place in the customary lighthouse employing a mercury arc lamp as a light source, a yellow filter such as that designated Corning 3-69 is interposed in the exposure light path. In practice a light intensity of 3500 foot Lamberts and an exposure time of 20 minutes has been used in this first exposure step. This step does annul the inhibitor but does not materially efiect the solubility of the coating in water.

Having armed the coating composition with the first exposure, it is then subjected to a second exposure through the shadow mask and for a second exposure interval with energy, again selected such that without the conjoint effect of the first exposure, it has not material influence on the solubility of the coating material in water. In the specific process embodiment under discussion the second exposure is with ultraviolet light of an intensity of 4,000 foot Lamberts for a period of 8-11 seconds. Those portions of the coating where the inhibitor is still eifective do not respond to the exposure to ultraviolet and the second exposure has no meaningful effect on the solubility of such coating portions. Of course, it is essential to achieve some insolubilization of the coating material in order to develop the desired coating pattern over those selected elemental areas of the screen that intervene the screen areas assigned to receive phosphor deposits. It is for this reason that the energy distribution patterns of the first and second exposure intervals are related to one another to subject to both the first and second exposures only those preselected portions of the coating that cover the elemental areas of the image screen desired to be permanently coated. The exposure patterns may be related as required simply by adjusting the relative positions of the light sources in the two exposure steps. Their conjoint effect is to cause the doubly exposed coating portions to become insoluble and thereby establish a latent image of the desired coating pattern so that washing of the screen with water develops the pattern established by the successive and cooperative effect of the two exposures.

Both exposures may be made with the light output of a mercury arc lamp, the first through a filter as described and the second with no filter in the path between the mercury lamp and the faceplate in process. If both exposures are to be made in one lighthouse, it is necessary to selectively insert and remove the filter from the light path and it is further necessary to be able to shift the light source between two positions chosen to provide the desired overlap of energy distribution patterns in the two exposure intervals. Alternatively, one lighthouse may be permanently arranged to satisfy the requirements of the first exposure and another lighthouse arranged to meet the requirements of the second exposure. In such a case, the faceplate is exposed in the first lighthouse and then transferred to the second for the next exposure.

In FIG. 2, the circles designated B crosshatched with lines having a positive slope denote the energy distribution pattern of the first exposure, that is, the exposure through the shadow mask with yellow light. Because of the selectivity imposed by the apertures of the shadow mask, the exposure is confined to portions of the coating that cover the areas of the screen assigned to receive deposits of blue phosphor and extends beyond the phosphor receiving portions to the contiguous parts of the screen which surround the blue phosphor assigned portions but only into the interspaces of the phosphor dots. That is to say, the exposure covers only screen areas assigned to blue phosphor and the surrounding elemental areas which extend to but do not impinge upon the neighboring screen areas that are assigned to receive deposits of other phosphors. This is readily accomplished by positioning the light source of the lighthouse to simulate the electron gun of the tube in process assigned to excite the blue phosphor dots. The shadow mask as used in the exposure steps has apertures of the size desired for final utilization for color selection in the tube. As explained above, the apertures exceed by a known amount the size of the phosphor dots and that is why the exposed portions of the coating equal in size the phosphor dot area and the surrounding contiguous elemental screen areas constituting the separation of each phosphor dot from its neighbors. The second exposure step of the process, again through the apertures of the mask, has a distribution pattern represented in FIG. 2 by the areas designated R crosshatched with lines having a negative slope. The difference in slope is adopted simply as a convenience in showing that B portions of the coating on the screen are subject to the first exposure with yellow light, whereas the R portions of the coating are subject to the second exposure with ultraviolet light. The distribution pattern of the second exposure is likened to the first in that it exposes coating portions which cover areas of the screen assigned to receive phosphor and the adjacent inter-dot spacing area. But in this case, as designated by the legend R, the second exposure centers about portions of the screen assigned to receive red phosphor. To that end, the light source of the lighthouse is positioned to simulate the red electron gun of the tube. Neither exposure taken by itself has any significant effect on the solubility of the PVA. The first exposure, by activating the dye ingredient of the coating, suppresses the effect of the inhibitor of that coating. This conditions all of the B designated portions of the screen coating to respond to ultraviolet. The second exposure with ultarivolet centers on the red phosphor assigned portions of the screen and for the most part is ineffective because of the influence of the inhibitor. Where the distribution or exposure patterns overlap, however, conditions are established necessary for causing the PVA to become insoluble. This occurs in the six segmented areas where the opposing slope crosshatchings intersect. It is only in these areas where the coating has first been exposed to the yellow light for conditioning for activation and then to ultraviolet which renders the PVA insoluble. Consequently, the first two process steps illustrated in FIG. 2 achieve six segments of the desired coating pattern.

FIG. 3 shows the conditions resulting from the first two process steps, indicating in solid shading those preselected portions of the coating that have become insoluble in water. The third process step is one in which the coating of the screen is exposed a second time to ultraviolet, again through the mask but now with the light source of the lighthouse positioned so that the energy distribution pattern is centered on the areas of the screen assigned to green, that is, in its third position the light source simulates the green electron gun. As a consequence, those segments of the distribution patterns represented by B and G which overlap are areas where the PVA has become insoluble simply because the necessary double exposure has occurred in those areas in the proper 'order. The conditions existing at the completion of the third exposure step are represented by the solid patterns of FIG. 4. Clearly they include only the B/R overlap areas and the B/G overlap areas. To complete a circle of insoluble coating material around the center of the screen section designated G, two additional process steps are required. It is necessary to subject the screen to an-' other exposure of yellow light through the mask but this time centered about either the R or the G portions of the screen coating. As shown, the second exposure to yellow light is centered on the coating portions R covering screen areas assigned to red phosphor. The fifth and final exposure step is again an exposure with ultraviolet through the mask and with the distribution portion centered on the coating portions G covering screen areas assigned to green phosphor. This completes the exposure steps and causes the R/'G overlap segments of the last two exposure steps to complete a ring of insoluble coating around the cusp shaped core or central member G. If the screen is now washed with Water, the entire coating is removed except for a pattern of rings where the coating has become insoluble. Each such ring is concentric with an elemental area of the screen that is assigned to receive a deposit of phosphor and each ring is confined to the spaces that intervene neighboring deposits of phosphor. Every part of the screen intended to receive a deposit of phosphor is similarly circumscribed by a ring of in solubilized PVA.

Simplification from a five to a four step process can be achieved by utilizing the process steps giving rise to the exposure conditions of FIGS. 2 and 5. As described above, the exposure represented in FIG. 2 causes the coating portions subject to the overlap of the B/ R distribution patterns to become insoluble. This is accomplished with the first two exposure steps and the third exposure is again through the mask and with yellow light but with the source now positioned to have the distribution pattern centered on those portions of the coating that cover the areas of the screen assigned to receive red phosphor, as indicated by the crosshatching with a positive slope in the R areas of FIG. 5. Observe that in this simplified procedure exposure steps 2 and 3 are easily taken in a single lighthouse and merely require the interposition of a suitable filter in the light path at step 3; the position of the light source need not be changed. In the fourth exposure step, ultraviolet light is projected through the mask onto the screen with the light source positioned to have the distribution pattern centered on coating portions covering the screen areas assigned to green. This, too, is represented in (FIG. 5 and causes the coating Where the B/G and R/ G patterns overlap to become insoluble. In this fashion, a ring of insoluble PVA is completed around the center of the pattern which is the cusp-shaped area designated G.

In the described illustrative embodiments of the invention, activation of the dye constituent of the coating material by exposure to visible light has been found to initiate a chemical change which has the effect of cancelling the inhibiting influence of the inhibitor constituent. The mechanism involved is not clearly understood but the results have been confirmed in practice. In place of the additive rhodamine B, it is expected that methyl violet B, concentrated, may be employed.

A similar coating process again employs a coating layer of a photoresist composition but one which does not transmit ultraviolet of long wavelengths. For example, a sensitized PVA layer may have an overcoat of material which is not transmissive of long wavelength ultraviolet light or the coating composition may be an admixture of these two ingredients. It is convenient in this process to coat the panel with a layer of PVA and superpose thereover a dye such as Amacid Yellow T extra which may be bleached by exposure to short wavelength ultraviolet and, until bleached, is not transmissive of longer wavelength ultraviolet. This layer must not bleach in response to long wavelength ultraviolet and the PVA must not respond and become insoluble in response to short wavelength ultraviolet. When the screen is coated with a material having these properties, short wavelength ultraviolet is employed in the first exposure interval for arming purposes and longer wavelength ultraviolet is utilized in the succeeding, second exposure interval to insolubilize the PVA. Either the five or four step procedures described above may be utilized in developing a pattern of insoluble PVA in those portions of the coating which cover elemental screen areas surrounding and intervening the screen areas assigned to receive phosphor deposits. Neither exposure taken alone forms any part of the desired coating pattern because the single exposure does not render the PVA insoluble.

Still another process may be predicated on the fact that the response of sensitized photoresists, such as dichromated PVA, to actinic energy is a function of the intensity of the energy and the duration of the exposure interval and a certain critical or minimal exposure is necessary to cause the resist to become insoluble in water. In principle, therefore, the resist may be underexposed by ultraviolet in the first exposure interval and further exposed to ultraviolet in the second interval to exceed the critical minimum exposure in overlapping areas of the distribution patterns. There is some likelihood, however, of nonuniformity in the coating pattern from such a process which is avoided in the earlier described process embodiments, particularly those where one type of energy performs one process step such as arming and another performs a difierent step such as activation.

In any event, consideration will be given to an embodiment which does not utilize an inhibitor. The coating material may again be 4 percent dichromated PVA with a 5-1 ratio and the coating may be developed by utilization of either the four or five step process described above. The first exposure is with ultraviolet derived from a mercury arc lamp with an intensity of 4,000 foot Lamberts for an exposure interval of seconds. While PVA does respond to this exposure, the exposure interval is less than the critical time for the intensity of energy employed to obtain insolubilization of the PVA. The second exposure, with an energy distribution pattern overlapping that of the first as described above, is from the same light source but through a green gelatin filter. The intensity is 1500 foot Lamberts and a suitable exposure time is 1-20 seconds. Here again, those portions of the PVA coating that are subject to both exposures are rendered insoluble, whereas either exposure taken alone is not able to cause exposed portions of the coating to become insoluble.

The last described process may be modified by the addition of a dye, such as 2 cc. of one percent rose bengal to cc. of the starting PVA solution. This process is essentially the same as the last described one and achieves the result by utilizing a first exposure to ultraviolet to initiate the chemical reaction of the photosensitive material and utilizing the second exposure to visible light to continue the reaction as required to achieve a condition of insolu- 10 bility in overlap areas of the exposure patterns. In the last modification the dye absorbs the visible light, converting it to chemical energy to enhance the action and improve the coating pattern.

Still another variant of the inventive process utilizes the same energy, that is to say, the same in type and wavelength, in both exposures and completes forming the desired coating pattern with only three exposure steps through the shadow mask to determine the energy distribution pattern. This modification features a coating material requiring two exposures for development but with the second exposure effective only if performed after a predetermined time delay subsequent to the first exposure. By way of illustration, the coating material may comprise PVA as one ingredient and a sensitizer as a second ingredient but, in effect, isolated from the PVA as applied to the screen area. If their isolation be by way of a barrier layer, then the first exposure shall make the barrier layer permeable to the sensitizer, admitting the sen sitizer to the PVA but requiring a certain interval of time to accomplish sensitizing of the PVA so that it may respond to the second exposure.

Resort may be had to the known technique of microencapsulation in which liquid dichromate is encapsulated in a polymeric enclosure such as Shipley AZ positive resist which reacts upon exposure to ultraviolet light and decomposes to release the dichromate to sensitize the PVA. Where this approach is taken, the coating material may be an admixture of PVA and the micro-encapsulated dichromate. The latter is a free flowing powder insoluble in water. Alternatively, the coating of the screen may comprise polyvinyl alcohol as a first layer over which is superposed a dichromate sensitizer which is chemically isolated from the PVA by an intervening barrier layer. For example, a positive resist may be employed as the barrier since this type of resist is normally water insoluble and is rendered soluble upon exposure to actinic energy as required selectively to admit the dichromate sensitizer to the PVA layer.

A process of this aype may be practiced with the energy distribution patterns of FIGS. 6 and 7. The first exposure is centered on the portions of the coating that cover areas of the screen assigned to receive green phosphor and this exposure which is with ultraviolet light is designated in FIG. 6 by solid crosshatching. Its effect is to release the sensitizer and permit its migration into the PVA to render the PVA photosensitive. After a suificient time interval, of the order of 30 minutes, a second exposure is made, also with ultraviolet but with the energy pattern centered on either areas assigned to receive blue or red phosphor deposits. In FIG. 6 the broken crosshatching of positive slope indicates exposure to the same type of energy employed in the first exposure but delayed relative thereto and centered over the areas to receive blue phosphors. The overlap B/ G portions are rendered insoluble. In FIG. 7 the solid areas represent the portions of the desired coating pattern developed from the first two process steps depicted in FIG. 6. It will be observed that in FIG. 7 solid crosshatching is applied to the B pattern indicating that sufficient time has transpired that the B as well as the G designated areas of the screen are areas wherein the PVA has become sensitized. The third exposure, again with ultraviolet light, takes place with the pattern centered about the screen portions assigned to receive red phosphor as indicated by the broken crosshatch lines of FIG. 7. As a consequence, both the G/R and the B/ R overlapping portions of the patterns are rendered insoluble and the desired coating pattern is completed. Notice, for example, that the central portion G of the screen segment represented in FIG. 7 will have been completely surrounded by a circle of insoluble PVA.

Another approach, utilizing an encapsulated component in the coating material, features two different exposures to release the encapsulated ingredient. In such a case, the resist component of the coating material will not have been sensitized and either a sensitized or an immediate polymerizing agent, such as boric acid, may be encapsulated along with a photoactivated material, such as a diazo, and included as a component of the coating. With this kind of coating material, the coated surface is first exposed to actinic energy to which the diazo responds and decomposes, releasing nitrogen. The second exposure is with heat, for instance with infrared, to increase the temperature of the nitrogen gas sufficiently to cause expansion and release of the encapsulated sensitizer or polymerizing agent. In order to confine the reaction distinctly to the overlapping portions of the radiation patterns of the two exposures the heat exposure should be intense. Diazos that are selectively responsive to chosen ones of a wide variety of different wavelength radiations are well known, providing quite a range of wavelengths for use in this process. It is convenient to use a green or blue sensitive diazo to be decomposed by visible light of the appropriate wavelength and then heat by infrared. If an immediate polymerizing agent is employed, it must be recognized that its polymerizing agent is employed, it must be recognized that its polymerizing effect introduces a self limiting characteristic into the process which impedes diffusion of the polymerizing agent. This may be compensated or accommodated by incorporating porosity in the photoresist as, for instance, by having the resist of foamy consistency. Also, the capsules must be small and must be densely packed.

Photochromic glasses having absorption bands in green and blue are also suitable for practicing the invention. For example, the faceplate under process may be coated with a layer of sensitized polymeric compound and overcoated with a layer that absorbs ultraviolet. The final layer of the coating includes photochromic glass beads with green or blue absorption bands. Such glass beads are normally transparent so the first exposure of the coated surface is to ultraviolet which darkens the entirety of the final coating layer, rendering it opaque and developing the absorption bands. The intermediate ultraviolet absorption layer protects the sensitized polymeric first layer during this exposure step. Having rendered the photochromic glass layer opaque, selected portions thereof are now subjected to an infrared radiation which bleaches the exposed portions. Thereafter, the coated surface is exposed to green or blue light having a distribution pattern chosen so that only the areas of overlap of the infrared and green-blue radiations efl'ect solubilization of the polymeric compound of the first coating layer.

There is a choice available in screening color-picture tubes with respect to the order in which the phosphor deposits on the one hand and the surround material on the other are applied to the screen. The preference is to develop the surround coating pattern attainable with any of the processes described above before applying the different phosphors. The advantage is that the rings of coating which define the surround pattern developed on the screen delineate with precision the elemental areas of the screen upon which the phosphor materials are to be deposited. In short, this determines both the location and the dimension of the phosphor dots and since the ring components of the coating have themselves been precisely positioned on the screen by exposures through the shadow mask of the tube, the elemental screen areas available for phosphor dots are not only properly related to the position of the shadow mask but also are smaller in size than the apertures of that mask which is the desirable condition for both black-surround and post-deflection-acceleration tubes.

Further flexibility in processing the entire screen is available with respect to the manner in which the lightabsorbing material is included in the coating pattern developed around the screen areasassigned to receive phosphor. By way of illustration, graphite or other pigment may be included as an ingredient of the coating material applied to the screen in developing the surround-coating pattern.

Alternatively, the surround-coating pattern may be developed of PVA applied over a layer of light-absorbing material or such material may be deposited on the surface of the coating after it has been developed into the desired surround pattern. Finally, instead of utilizing graphite or a similar pigment, one may follow the teachings of Pat. 3,365,292, issued Jan. 23, 1968 to Fiore et al. which features including an inorganic material in the surround coating which has the property that in bakeout of the screen at which time the screen is raised to a high temperature, the material converts and becomes light absorptive. Manganese carbonate and manganese oxalate are suitable; each decomposes to black manganous dioxide when heated to the bakeout temperature.

Of course, if the black-surround feature is not to be employed, the coating pattern developed by utilization of the subject invention is of an organic material which bakes out in the final processing of the tube leaving on the screen simply dots of various color phosphors separated from one another and defining the desired phosphor triads, properly positioned in relation to the apertures of the shadow mask.

The invention has yet another attractive advantage in screening a black-surround tube in that it may be used beneficially in applying the phosphor deposits into those areas of the screen which are bare and are surrounded by the black-surround pattern developed in any of the process applications described hereinbefore. Generally, in screening a black-surround tube, the surround pattern is developed initially and then the phosphors are applied, as stated above. The phosphor deposits may be made in the conventional way which entails applying a photosensitive slurry over the entire screen area and exposing it through the apertures of the shadow mask. If the slurry includes green phosphor in powdered form, the exposure light is positioned to simulate the electron gun assigned to excite green phosphors. This insolubilizes those portions of the slurry which cover areas of the screen assigned to receive green phosphor and the remainder slurry coating may be removed by washing with water. Although this is a very acceptable process of phosphor deposition, it may entail more usage of phosphor material than necessary simply because the exposure may insolubilize portions of the slurry coating which cover screen areas assigned to receive phosphor as well as the surround pattern circumscribing those areas. In other words, when the illustrative image of the green phosphor deposits has been devoleped, it may cover the black surround as well as the screen areas assigned to green phosphor. In addition to requiring the application of a larger amount of phosphor than absolutely essential, this may have the disadvantage of an unwanted light contribution to the image produced on the screen if, for any reason, the black surround is not sufliciently opaque. These shortcomings may be avoided if the pattern of phosphor deposits is made by utilization of the present invention.

Again, considering the deposit of green phosphor, a process steps are identical with those described above slurry is first applied over the screen and over the blacksurround pattern that had previoiusly been developed. This slurry coating is then exposed in a lighthouse and through the shadow mask with the light source positioned to simulate the green electron gun. To this extent, the but insolubilization will not have been accomplished as yet simply because, in utilizing the present invention, successive exposures are necessary to achieve that end. The second exposure may be by means of a flooding beam of the appropriate type of energy directed to the outside surface of the faceplate panel, that is to say, the surface of the panel which does not bear the black surround and phosphor slurry coating. The flooding illumination of the second exposure establishes the necessary two exposures in the proper sequence only as to those areas of the faceplate assigned to receive the phosphor in process. The other areas of the faceplate intended to be covered with other color phosphors will not have received the first exposure and the slurry which overcoats the black-surround pattern will not have received the second exposure, assuming the black surround to be nontransmissive of the energy of the flooding illumination, as will normally be the case. In this fashion, the phosphor may be accurately deposited in the holes of the black-surround pattern whether those holes are circular, star-shaped, cusp-shaped or any other configuration that may be desired.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. The process of applying a coating to selected elemental areas of the faceplate of a color picture tube which includes the following steps:

covering said faceplate with a material that normally has a particular solubility in a given solvent and has the property that two successive exposures to energy reverse its solubility in said solvent;

subjecting said material to a first exposure pattern for a first exposure interval with energy without materially affecting its solubility in said solvent; thereafter subjecting said material to a second exposure pattern for a second exposure interval with energy which, without the conjoint effect of said first exposure, has no substantive elfect on the solubility of said material in said solvent, the exposure patterns in said first and second exposure intervals overlapping in those preselected portions of said material that cover said elemental areas of said faceplate and the intensity of the energy and duration of said exposure intervals being elfective to reverse the solubility of said preselected portions of said material in said solvent; and

thereafter treating said faceplate with said solvent to develop the image pattern established by said overlapping exposures of said material.

2. The process in accordance with claim 1 for applying a coating in elemental areas of the faceplate which surround individual ones of a multiplicity of faceplate portions interlaced with one another and assigned to receive different color phosphors in which:

the exposure pattern in said first interval exposes the portions of said faceplate assigned to receive one of said phosphors and also contiguous parts of said faceplate that surround said assigned portions but are to remain free of phosphor deposits,

in which the exposure pattern in said second interval exposes other portions of said faceplate that are assigned to receive another of said phosphors and also contiguous parts of said faceplate that surround said other assigned portions but likewise are to remain free of phosphor deposits,

and in which the interlace pattern of said faceplate portions is such that said contiguous parts of said faceplate are coextensive with said selected elemental areas of said faceplate.

3. The process in accordance with claim 2 in which said faceplate portions are of dot configuration interlaced to define dot triads on said faceplate that are individually aligned with apertures of a shadow mask having an aperture diameter that exceeds the diameter of said faceplate portions,

and in which said faceplate is exposed in said first and second intervals through said apertures of said mask to determine the exposure patterns in said first and second intervals.

4. The process in accordance with claim 3 in which said material is normally soluble in said solvent and, in response to the conjoint effect of both said first and said 14 second exposures, is rendered insoluble in said solvent.

5. The process in accordance with claim 3 in which said first and said second exposure steps are repeated a sufficient number of times from energy sources located relative to said mask to produce said coating pattern in the form of rings individually circumscribing one of said faceplate portions.

6. The process in accordance with claim 1 in which the energy used in said first exposure interval has no substantial efiect on the solubility of said material in said solvent but is eifective to activate said material to be responsive to another energy which has a characteristic differing from said first-mentioned energy and is capable of reversing the solubility of said material in said solvent after such activation,

and in which said other energy is used in said second exposure interval.

7. The process in accordance with claim 3 in which the energy used in said first exposure interval has no substantial effect on the solubility of said material in said solvent but is effective to activate said material to be responsive to another energy which has a characteristic differing from said first-mentioned energy and is capable of reversing the solubility of said material in said solvent after such activation,

in which said other energy is used in said second exposure interval,

in which said material is exposed a second time to said other energy before said developing step,

and in which the exposure pattern of said other energy during the second exposure thereto exposes portions of said faceplate that are assigned to receive a third one of said phosphors and also the contiguous parts of said faceplate that surround the portions thereof assigned to said third phosphor but are also to remain free of phosphor deposits.

8. The process in accordance with claim 3 in which the energy used in said first exposure interval has no substantial effect on the solubility of said material in said solvent but is effective to activate said material to be responsive to another energy which has a characteristic differing from said first-mentioned energy and is capable of reversing the solubility of said material in said solvent after such activation,

in which said other energy is used in said second exposure interval;

in which said material is exposed a second time to both said first and said other energies, in the recited order, before said developing step,

in which said second exposure to said first energy has an exposure pattern that exposes portions of said faceplate assigned to said other phosphor and also contiguous parts of said faceplate that surround faceplate portions assigned to said other phosphor and are to remain free of phosphor deposits,

and in which said second exposure to said other energy has an exposure pattern that exposes portions of said faceplate assigned to a third one of said phosphors and also contiguous parts of said faceplate that surround faceplate portions assigned to said third phosphor and are likewise to remain free of phosphor deposits.

9. The process in accordance with claim 6 in which said material has as one constituent a photosensitive resist that is normally responsive to said other energy and further has as a second constituent an inhibitor which suppresses the response of said resist to said other energy but which may be rendered ineffective by exposure to said first-mentioned energy.

10. The process in accordance with claim 9 in which said inhibitor constituent is a dye subject to being bleached and rendered ineffective by exposure to said first-mentioned energy.

11. The process in accordance with claim 9 in which said first-mentioned and said other energies are derived from a common polychromatic light source,

said material is exposed to said first-mentioned energy by directing light thereto from said source through a filter that is transmissive of light wavelengths to which said inhibitor responds,

and in which said material is exposed to said other energy by applying light wavelengths from said source to which said filter is not substantially transmissive.

12. The process in accordance with claim 9 in which said coating material includes an additive which is activated in response to exposure to said first-mentioned energy to destroy the inhibiting properties of said inhibitor.

13,. The process in accordance with claim 12 in which said inhibitor constituent is a hydroxylated amine,

and in which said additive is a dye capable of destroying said amine under the influence of said first-mentioned energy.

14. The process in accordance with claim 1 in which said material comprises an unsensitized photoresist as well as a sensitizer therefor but isolated therefrom by a barrier 16 which, upon exposure, is rendered permeable to said sensitizer,

said first exposure step renders said barrier permeable and admits said sensitizer to said photoresist, and said second exposure is delayed relative to said first exposure for a suflicient period to allow said sensitizer to permeate said barrier to sensitize said resist. 15. The process in accordance with claim 14 in which said barrier is responsive to actinic radiation;

and the same radiation is used in both exposure intervals.

References Cited UNITED STATES PATENTS 3,146,368 8/1964 Fiore et al. 96-36.l 3,563,742 2/ 1971 Philpot et al 96-351 3,005,708 10/ 1961 Hesse 96-36.1 3,569,761 3/1971 Lange 96-36.1

NORMAN G. TORCHIN, Primary Examiner 0 M. F. KELLEY, Assistant Examiner US. Cl. X.R.