GB1579746A

GB1579746A - Colour picture tube

Info

Publication number: GB1579746A
Application number: GB973377A
Authority: GB
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1976-03-08
Filing date: 1977-03-08
Publication date: 1980-11-26
Also published as: JPS5721232B2; DE2710089B2; DE2710089A1; JPS52107768A; DE2710089C3

Description

(54) COLOR PICTURE TUBE (71) We, TOKYO SHIBAURA ELECTRIC COMPANY LIMITED, a Japanese corporation, of 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a color picture tube.

Conventionally, in order to increase the contrast of a picture of a color television receiver upon incidence thereinto of a bright ambient light, red, blue and green colored pigments each of which absorbs ambient light having color components other than its own color are provided in red, blue and green phosphor regions of a color television tube, respectively, The respective pigment so acts as to absorb those components of an ambient light which have colors other than that of a light emitted from the corresponding phosphor region.

Therefore, the reflection of such an ambient light is decreased to raise the contrast of a picture of the color television receiver.

Such pigment, for example, as shown in Figure 1, is usually disposed between the inner surface of a glass panel 2 and red, green and blue phosphor regions 4, 6 and 8 in such a manner as to correspond to these regions 4, 6 and 8 in the form of pigment regions 10, 12 and 14. This technique is disclosed in U.S.

Patent No. 3,114,065. Used as such pigment is material consisting of PVA, ADC and filter material, or of frit glass and filter material.

Alternatively, such pigment, for example, as shown in Figure 2, is mixed into red, green and blue phosphor regions 4, 6 and 8 in colorto-color correspondence relationship, namely, in a manner that, for example, a blue pigment is fixed into a blue phosphor region 8. The technique is given in U.S. Patent No. 3,114,065.

In the former case, the pigment is not mixed into the phosphor region, and attenuation of the energy of electron beams due to the action of the pigment does not occur. Accordingly, the whole of such energy acts to excite the phosphor region. Further, the pigment is provided, as a region, between the inner surface of the glass plate and the phosphor region, so that an ambient light thorough the glass plate is absorbed in the pigment region to be prevented from entering the phosphor region. Thus is raised the contrast of a picture of the color television receiver. However, each pigment region has to be formed on the position on the glass plate where a corresponding phosphor region is to be formed. As a result, the process for manufacturing the color picture tube becomes complicated.

In the latter case, the pigment particles are distributed within the phosphor region, and the attenuation of the electron beam energy due to the action of the pigment particles is increased.

Further, where it is desired to accomplish the same extent of contrast enhancement as in said former case, a larger amount of pigment must be mixed as compared with that used in said former case. However where such a larger amount of pigment has been mixed, the brightness of the phosphor region is largely decreased relatively to the contrast enhancement.

Under the above-mentioned circumstances, the inventors of this application have endeavoured to realize a color picture tube which is capable of markedly increasing the contrast without causing so much a decrease in the brightness and yet easy to manufacture. And attention has been directed toward the following two points: One is that both in respect of luminous sensitivity and in respect of the amount of energy absorbed a blue pigment has the greatest capability of absorbing an ambient light. The other is that at the present stage of technique an electron gun corresponding to a blue phosphor region has the greatest margin for introduction of cathode current and the phosphor region has the greatest margin for the brightness.

The brightness of the screen of a colour television is evaluated in terms of the brightness of a standard white. The ratio among the cathode currents allowed to flow in the electron grins coriesponding to the red, green and blue phosplror regions in order to obtain a standard white having a colour temperature of 9300"K + 27 M.P.C.D. (Minimum Percept- ible Colour I)ifference) is 14 :15 10.

As seen from this, cathode current flowing through the electron gun corresponding to the blue phosphor region is less than the currents flowing through the electron guns corresponding to tire red and green phosphor regions.

Therefore, the electron gun corresponding to the blue phosphor region has more margin for introduction of current than those corresponding to the other red and green phosphor regions Electron beams supplied to tire respective phosphor regions have magnitudes proportional to currents flowing through tire corresponding electron grins. The blue phosphor region which receives the smallest amount of electron beam energy presents the smallest luminescence. and in conseqllence preserves much margin for the brightness.

An object of the invention is to provide a colour picture tube which is easy to manufactore and is largely increased in contrast with the decrease in brightness mininiized.

According to the present invention there is provided a colour picture tube including red green and blue phosphor regions adhered to an inner surface of a glass plate and electron guns for red, green and blue, wherein at least one of said red and blue phosphor regions but not the green phosphor region has mixed therein a pig merit having a colour substantially identical to that of the light cirrit led from said at least one phosphor region, permitting the transmission theietlirough of a light coiiiponcnt having the colour of the pigment, and capable of absorbing substantially all light components other than said light compollent, and the or each pigment is added to that one or the respective one of the blue and red phosphor regions so that a pigment conccntration gradient is formed in the phosphor region from its electron gun side to its glass plate side with the pigment con centration increased continuously from its electron gun side to its glass plate side.

Preferably, said blue phosphor region has a blue pigment mixed thereinto to an extent of 5 to 30 weight 'X, based thereon.

An embodiment of this invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a phosphor region screen of a prior art colour picture tube; Figure 2 shows a phosphor region screen of another prior art colour picture tube; Figure 3 shows a phosphor region screen of a colour picture tube according to the invention; Figure 4 shows the distribution pattern of a pigment in a blue phosphor region of the screen shown in Figure 3; Figure 5 shows the concentration gradient of the pigment in the blue phosphor region of the screen shown in Figure 3; Figure 6 is a curve diagram showing the relative luminous sensitivity relative to wave length; Figure 7 is a curve diagram showing relative energy characteristic curves of various ambient lights;; Figure 8 is a curve diagram showing reductions in reflection and brightness relative to tire proportion of pigment mixed; Figure 9 shows the incidence of electron beams and an ambient light into the colour picture tube according to the invention; and Figure 10A to 101-I show the process steps of manufacturing the color picture tube according to tire invention.

As shown in Figure 3, on the inner surface of a glass plate 20 are provided dot-shaped or stripe-shaped phosphor regions 22, 24 and 26 emitting red, green and blue light components, respectively. The red, green and blue phosphor regions 22, 24 and 26 are formed of Y2 O, S: Eu, ZnS: Cu, Awl, and ZnS Ag, C1, respectively. Between adjacent two of the phosphor regions 22, 24 and 26 is provided a lightabsorbing black material 28. Within the blue phosphor region 26 exists in a state mixed thereinto a blue pigment such as cobalt aluminate which permits transmission therethrough of a blue light component and is capable of absorb ing light components other than the blue light component.The distribution of the blue pigment (shown as black-colored dots in Figure 4) within the blue phosphor region 26, as shown in Figrire 4, is such that the particles of large size are distributed on the glass panel 20 side while the particles of smali size on an electron gun (not shown but provided leftwardly of the illustration). Accordingly, the concentration distribution of the blue pigment, as shown in Figure 5, becomes higher from the electron gun toward the galss plate 20. Preferably, the mixing amount of the blue pigment falls within the range of 5 to 30 weight F based on the account of the blue phosphor region. The effect of imposing a predetermined limitation upon such concentration distribution and mixing amount of the blue pigment will be apparent from a description as later made.

The reason why the blue pigment has been mixed into the blue phosphor region 26 will be explained as follows.

First, as previously mentioned, at the present stage of technique, an electron gun corresponding to a blue phosphor region has the greatest margin for introduction of cathode current and the phosphor region has the greatest margin for the brightness.

The brightness of the screen of a color television is evaluated in terms of the brightness of a standard white. The ratio among the cathode currents allowed to flow in the electron guns corresponding to the red, green and blue phosphor regions in order to obtain a standard white having a color temperature of 9300 K + 27 M.P.C.D. is 14:15 10.

As seen from this , cathode current flowing through the electron gun corresponding to the blue phosphor region is less than the currents flowing through the electron guns corresponding to the red and green phosphor regions.

Therefore, the electron gun corresponding to the blue phosphor region has more margin for introduction of current than those corresponding to the other red and green phosphor regions.

Electron beams supplied to the respective phosphor regions have magnitudes proportional to currents flowing through the corresponding electron guns, The blue phosphor region which receives the smallest amount of electron beam energy presents the smallest luminescence, and in consequence preserves much margin for the brightness. Accordingly, the brightness of the blue phosphor region can be enhanced by increasing a cathode current therefor by the extent corresponding to a reduction in the brightness due to the mixing of the blue pigment.

Secondly, luminous sensitivity of the human eye varies depending upon the colour or wave length of light components even when the light components have the same energy. From both viewpoints of the luminous sensitivity and the amount of light energy absorbed, the blue pigment has the greatest capability of absorbing an ambient light.

In Figure 6, a relative luminous sensitivity curve is shown which has been cited from a literatures of R.E. Bedford and G.W. Wyszeck; Luminosity functions for various field sizes and levels of refinal illuminance, J. Opt. Sef.

Amer, 48 (1958).

As apparent from Figure 6, the relative luminous sensitivity curve has its peak at a wave length (green light component) of around 550 (n m). However, the left and right halves of this relative luminous sensitivity curve are not symmetrical about the peak.

On the left side i.e., the blue region side, of the illustration the relative luminous sensitivity value, as seen, is smaller than that on the right side, i.e., the red region side, of the illustration.

Usually, a light component having a greater value of log V À is seen, to the human eyes, to have a greater brightness. According to the illustration, therefore, the green light component is seen to have the greatest brightness, the red light component to have the second great brightness, and the blue light component to have the smallest brightness. The main wave lengths X of light components emitted from the blue and red phosphors are 450 (nm) and 630 (nm), respectively. When now determining the relative luminous sensitivities V X corresponding to the main wave lengths, they are 500 and 3160, respectively.Thus, the red light component having a main wave length of 630 (nm) seems to human eyes to be six times as bright as blue light component having a main wave length of 450 (nm) even when the amounts of the red and blue light components as measured in terms of energy are the same.

Where an ambient light has impinged on the red and blue phosphor regions mixed, respectively, with red and blue pigment regions having similar light-transmitting performances, the red and blue pigment regions permit the transmission therethrough of the red and blue components respectively of the ambient light, and absorb the other light components. The transmitted light components have substantially the same account of energy. Since, however, the luminous sensitivity of the human eyes varies depending upon the color of the lights, the red light component is seen to have the greater brightness and the blue light component to have the smaller brightness.

Namely, when consideration is given from the viewpoint of luminous sensitivity, the blue pigment has the most excellent ambient light absorbing capability.

When the spectrum of an ambient light is taken into consideration, the predominance of the blue pigment is more clearly understood. In Figure 7, there are shown the spectrum curves of the daylight (A), the light of an ordinary incandescent lamp (B) and the light of an ordinary flourescent lamp (C), as the ambient lights which can exist when viewing a color television receiver. In Figure 7, the wave length is plotted on the abscissa and the relative amount of light energy on the ordinate.In any one of the ambient lights A, B and C, the amount of the energy of the blue light component (having a main wave length À of 450 nm), as seen, is smaller than the amount of the energy of the red light component having a main wave length of 630 nm and green light component (having a main wave length of 550 nm). The red pigment region permits the transmission therethrough of that red light component of the ambient light which has a large amount of energy relative to that of the blue component and absorbs the blue light component having a relatively small amount of energy. In contrast, the blue pigment layer conversely absorbs the red and green light components having a relatively large amount of energy and permits the transmission therethrough of the blue light component having a relatively small amount of energy.Accordingly, in view of both luminosity and man's luminous sensitivity, it is the most effective to mix blue pigment with the phosphor region. Some good result can be expected if red pigment is mixed with the red phosphor region. Thus, if blue and red pigments are added to the blue and red phosphor regions, respectively, better result can be obtained.

Next, description is made of the limitation of the amount of blue pigment to 5 to 30 weight % based on the amount of the blue phosphor. In Figure 8, on the abscissa is plotted the weight % of the mixing amount of the blue pigment as measured on the basis of the amount of the blue phosphor, while on the ordinate are plotted the reductions in the brightness and reflection of the screen. As seen, as the mixing amount of the blue pigment increases, both the brightness and the reflection decrease. Unpreferable from standpoint of viewing the colour television receiver are a decrease of 14% or more in the brightness and a reduction of 15% or less in the reflection. That is to say, when the brightness decreases by 14' or more, the screen becomes very dark to look very badly.

When reflection decreases by 15% or less, the ambient light reflection becomes intense also to look very badly. For the above-mentioned reasons, the mixing account of the blue pigment is desirably to 5 to 30 weight % based on the account of phosphor.

It will be assumed that electron beams 30, as shown in Figure 9, have been radiated from an electron gun (not shown) to the red, green and blue phosphor regions 22, 24 and 26. Then, the phosphor regions 22, 24 and 26 are excited to emit light of respective colors. Thus, a picture is formed on the glass plate 20. Let's now assume, under such a field condition, that an ambient light 32 such as daylight, incandescent light or fluorescent-lamp light has impinged on the glass plate 20. Then, the abmient light 32 are brought to the phosphor regions 22, 24 and 26 and the black material 28 through the glass plate 20. The ambient light having impinged on the red and green phosphor regions 22 and 24 are reflected and brought back to the exterior through the glass plate 20.On the other hand, the ambient lights having impinged onto the black material 28 are all absorbed thereinto. With regards to the ambient light having impinged on the blue phosphor regions 26, almost all of the blue light components thereof are transmitted through the blue pigment and almost all of components other than the blue light component are absorbed into the blue pigment.

As previously mentioned, the distribution of the blue pigment particles in the blue phosphor region 26, as shown in Figure 4, is such that the particles of small size are distributed on the electron-gun side while the particles of large size on the glass-plate 20 side.

Therefore, the electron beams 30 from the electron gun are initially transmitted through the low-concentration pigment region in the blue phosphor region 26. The energy of the electron beams 30, therefore, is for the most part not lost and so the most part thereof acts to excite the blue phosphor region 26.

On the other hand, the ambient light 32 incident through the glass plate 20 is initially transmitted through the high-concentration pigment region in the blue phosphor region 26. Red and green light components of the ambient light 32 are almost absorbed into the region 26, only the blue light components being transmitted through the region 26. As previously stated, the blue phosphor region 26 has a margin for increasing the brightness. Therefore, the brightness can be increased by increasing a cathode current therefor by the extent corresponding to a decrease in the energy of electron beams due to the action of the blue pigment. Accordingly, the invention can provide a color picture tube which is easy to manufacture and is largely increased in contrast without substantially causing a decrease in the brightness of the red, green and blue phosphor regions.

The blue phosphor region 26 having such a pgiment particle size distribution as shown in Figure 4 is manufactured as follows.

First, a pigment wherein the particles of the size smaller than 3Clm account for 60 to 80 weight % of the whole particles is mixed, in a given ratio, with a pigment wherein the particles of the size 4 to 6pm account for, 60 to 80 weight % of the whole particles. The mixture is added into a blue phosphor slurry and a photo sensitive material, for example, PVA (polyvinyl alcohol) is simultaneously added thereinto. Then, the resultant slurry is stirred.

Next, the resultant slurry is poured onto the inner surface of a glass plate, and is stretched over the entire surface of the glass plate by rotating it, namely by a so-called rotation-coating method. The stretched slurry is subject to rotation at a low speed for a specified time period. During this slow rotation the large-sized pigment particles in the stretched slurry go on being precipitated toward the inner surface of the glass plate and the small-sized ones thereof remain to stay in the area of the stretched slurry which is on the gun side. After a specified time period has passed which is necessary for the precipitation of the large-sized pigment particles, the glass plate is allowed to make a high-speed rotation, and solution and pigment particles floating on the surface side of the stretched slurry are removed by utilizing the centrifugal force.Thus is formed a thin phosphor region having a uniform thickness. In regards to the slurry viscosity, the slurry is preferable which, where measurement is made by &num;4 Ford Cup Measurement Method, requires 30 to 35 seconds to drop from the aperture of a specified diameter. Since the precipitation of the pigment particles varies depending also upon the particle size of the blue phosphor, the slurry viscosity is required to be determined with that taken into consideration. The blue phosphor region thus formed is sufficiently dried. Thereafter, this region is subject to light exposure through a shadow mask by using a light source radiating ultarviolet rays such as a mercury lamp. In the next developing process, first, a dilute ammonia water is sprayed onto the the phosphor region for a specified time period, thereby to decompose the photosensitive material PVA on the layer surface only and also to cause a dissolving and floating of the pigment particles in the vicinity of the region surface. Then, hot water is sprayed onto the region thereby to wash off the pigment particles in the vicinity of the region surface. In this dissolving of the pigment particles inside the region by excessively spraying the dilute ammonia water thereto. By carrying out the abovementioned series of manufacturing steps, there can be obtained the blue phosphor region 26 having such a particle size distribution as shown in Figure 4.

Hereinafter, explanation will be made of the process steps for forming a colour picture tube having such phosphor regions as shown in Figure 3.

First, to explain the method of preparing a dispersion of pigment, a blue pigment of cobalt aluminate is introduced into a distilled water and a surface active agent is added to the resultant solution. Thereafter, the aqueous solution thus obtained is subject to milling to dissolve the blue pigment to cause it to be dispersed thereinto. Subsequently, polyvinyl alcohol is introduced into the resultant aqueous solution dispersed with the blue pigment to prevent the pigment from coagulating. Thus is obtained a dispersion of pigment. The particle size distribution of the pigment particles in the above resultant aqueous solution can be adjusted by varying the milling time length or the pigment concentration in the aqueous solution. The pigment dispersion added to the blue phosphor region may be a mixture of two pigment dispersions having different particle size distributions.For example, it is composed of pigment dispersion wherein the particles of the size smaller than 3pm account for 60 to 80 weight % of the whole amount of pigment and pigment dispersion wherein the particles of the size 3 to 6pm account for 60 to 80 weight % of the whole amount of pigment. These two pigment dispersions are mixed with each other in a given ratio and stirred. Thereafter, the stirred pigment dispersion is added into a blue phosphor slurry to an extent of 5 to 30 weight % thereof, thus to prepare a blue phosphor slurry containing the pigment. In addition, a red and green phosphor slurry are prepared.

Under the above-prepared condition, the black material 50, as shown in Figure l0A, is formed on the inner surface of the glass panel 20 by a conventional method. Then, ultravioletrays from an ultraviolet-rays emitting source (not shown) are radiated onto the black material region 50 through a shadow mask (not shown), thereby to form the latent images 52 as shown Figure 10B. Thereafter, the black material region 50 is washed off by hot water to remove those portions of the region which have been subjected to no light exposure. Thus is obtained a black material region 50 having such a predetermined pattern as shown in Figure 10C.Subsequently, the blue phosphor slurry is applied onto the inner surface of the glass panel 20, thereby to form, as shown in Figure 10D, a thin blue phosphor region 54 having a uniform thickness by the use of the rotation-coating method as previously men- tioned. Subsequently, ultraviolet-rays from an ultraviolet-rays emitting source are radiated onto the region 54 through a shadow mask, thereby to form the latent images 56 as shown in Figure 10E. Subsequently, the photosensitive material adhered to the region surface is dissolved with a dilute ammonia water, thereby to cause a dissolving and floating of the pigment particles in the vicinity of the region surface. Thereafter, the region surface is washed off by hot water to remove those portions of the region which have been subjected to no light exposure.Thus is obtain ed a blue phosphor region 56 having such a predetermined pattern as shown in Figure 10F.

The use of a dilute ammonia water in place of hot water would provide a higher dissolving capability. Next, in the similar manner as mentioned above, a green phosphor region 58 without pigment is formed, as shown in Figure lOG. Similarly, a red phosphor region 60 without pigment is formed as shown in Figure lOH.

Note that upon the formation of the red and green phosphor regions 58 and 60 it is not necessary to dissolve the region surface with a dilute ammonia water. By carrying out the foregoing process steps a phosphor region screen having such a construction as shown in Figure 3 is obtained.

The above-mentioned embodiment referred to the colour picture tube having its glass plate provided with the ambient light absorbing black-material, but this invention can of course be applied also to a colour picture tube provided with no ambient light absorbing blackmaterial.

Further, in the above-mentioned embodiment pigment is mixed into the blue phosphor region only. However, pigment may be mixed into the red phosphor region only, or may alternatively be mixed into the blue and red phosphor region only.

Further, the above-mentioned embodiments were described on the basis of the existing condition wherein the colour temperature of a white colour is set at 9300"K + 27M, P, CD; and the red, green and blue phosphor regions are formed of Y2 02 S:Eu, ZnS:Cu, AQ, and ZnS:Ag, CQ, respectively.

But the phosphor region having pigment mixed thereinto can appropriately be selected, and simultaneously the mixing amount of the pigment can also be increased, according to the colour temperature set on the luminosity of the phosphor region used.

Attention is directed to the disclosure (including the claims) of our copending Application No. 9732/77 (Serial No. 1 579 745) which is directed to a colour picture display tube.

Claim 1 of Application No. 9732/77 (Serial Nol. 1 579 745) reads as follows: A colour picture display tube which comprises a glass panel and a plurality of groups consisting of green, blue and red phosphor regions on the inner surface of said glass panel, wherein black, liglrt-absorbing, particles are mixed only with said blue and/or said red phosphor regions, and at a concentration whose gradient progressively rises from tlrat side of said phosphor regions on which electron beams impinge to the inner surface of the glass panel WIlAT WE CLAIM IS: 1.A colour picture tribe including red green and blue phosphor regions adhered to an inner surface of a glass plate and electron guns for red, green aird blue, wherein at least one of said red and blue pllosphor regions but not the green phosphor region has mixed therein a pig ment having a colour substantially identical to tlrat of tile ligllt emitted from said at least one phosphor region permitting the transmission therethrough of a light component having tile colour of the pigment. arid capable of absorb ing substantially all light components oiler than said light component, and the or each pig ment is added to that one or the respective one of the blue and red phosphor regions so that a pigment concentration gradient is fornied in the phosphor region from its electron gun side to its glass plate side with the pigment concentration increased continuously from its electron gun side to its glass plate side.

2. A colour picture tube according to claim 1 wherein said blue phosphor region has a blue pigment mixed thereinto to an extent of 5 to 30 weight 'S based thereon.

3. A colour picture tube according to claim 1 or claim 2, wherein said red phosphor regions has a red pigment mixed. tllerein.

4. A colrrrrr picture tube according to claim 1 and substantially as llereinbefore described with reference to the acconipanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

wherein black, liglrt-absorbing, particles are mixed only with said blue and/or said red phosphor regions, and at a concentration whose gradient progressively rises from tlrat side of said phosphor regions on which electron beams impinge to the inner surface of the glass panel WIlAT WE CLAIM IS: 1.A colour picture tribe including red green and blue phosphor regions adhered to an inner surface of a glass plate and electron guns for red, green aird blue, wherein at least one of said red and blue pllosphor regions but not the green phosphor region has mixed therein a pig ment having a colour substantially identical to tlrat of tile ligllt emitted from said at least one phosphor region permitting the transmission therethrough of a light component having tile colour of the pigment. arid capable of absorb ing substantially all light components oiler than said light component, and the or each pig ment is added to that one or the respective one of the blue and red phosphor regions so that a pigment concentration gradient is fornied in the phosphor region from its electron gun side to its glass plate side with the pigment concentration increased continuously from its electron gun side to its glass plate side.
2. A colour picture tube according to claim 1 wherein said blue phosphor region has a blue pigment mixed thereinto to an extent of 5 to 30 weight 'S based thereon.
3. A colour picture tube according to claim 1 or claim 2, wherein said red phosphor regions has a red pigment mixed. tllerein.
4. A colrrrrr picture tube according to claim 1 and substantially as llereinbefore described with reference to the acconipanying drawings.