Shadow mask having vertical pitch about 8/(2n-1) times horizontal pitch

A color picture tube, wherein a set of three electron beams emitted from respective three electron-emitting members of an electron gun, or from respective three electron guns, is projected onto a screen, and sets of each three luminous strips on this screen are selectively energized to emit luminous color lights, characterized in that the numeral ratios between said luminous strips by pieces and said slots of the shadow mask, respectively, are about 1:1 vertically and about 3:1 horizontally, and also that every strip as well as its set is complete insulated from adjacent strips and their sets by a light-absorbent film filling all the gaps inbetween. With such construction, a color picture tube having excellent brightness and contrast characteristic, being free from disturbing vertical strips, has been obtained.

BACKGROUND OF THE INVENTION 
This invention relates to an improvement of a color picture tube, wherein a 
set of three electron beams for emitting red, green and blue lights, 
respectively, is emitted from a three-beam type electron gun, and passing 
through a vertically oblong slot of a shadow mask, is led to a black 
matrix-type screen standing behind the shadow mask so as to energize 
selectively any of three color-luminous strips which form a set of each 
three colors on said screen to correspond to said set of three electron 
color-beams and to produce desired color-lights. 
Apertures of the shadow mask of the color picture tube of this type 
characterizing the vertically slotted mask as described above are formed 
in vertically oblong slots. Consequently, as compared with the 
ordinary-type color picture tubes employing masks having ordinary round 
apertures, it is already known that this type of tube can select larger 
ratio of apertures for the mask. Accordingly not only does it reduce 
electricity wastefully consumed by a portion of the electrons striking the 
mask and failing to pass through it, but also it is able to produce 
brighter pictures on the screen. Besides, it has the advantage of being 
almost free from color derangement in the vertical direction even in case 
of thermal expansion of the shadow mask. 
However, in the known construction of this type of color picture tube, its 
screen has the form of massed vertical stripes of red, green and blue 
luminous strips alternately arranged to emit lights of the respective 
colors when energized. And furthermore, the light-absorbing film placed in 
the gaps between the luminous strips for the purpose of improving the 
contrast serves only to form vertical stripes on the screen. Therefore, it 
entails the shortcoming of deteriorating pictures coming out on the screen 
by distinct vertical stripes. Besides, the area covered by the 
light-absorbing film on the screen is not sufficient, and accordingly the 
improving effect on the contrast is not satisfactory either.

DETAILED DISCLOSURE OF THE PRESENT INVENTION 
The present invention has been made in view of the foregoing points, of 
which explanation will be made in detail hereunder in conjunction with 
embodying examples shown in the drawing. 
Shown in FIG. 1, an electron gun 1 is of a known "In-Line Gun Assembly" 
(Refer to U.S. Pat. No. 3,553,523 of Jan. 5, 1971) type having three 
electron-emitting members 2, 3 & 4 for emitting blue, red and green 
lights, respectively, which members are aligned with small spaces 
inbetween on a plane in horizontally deflecting directions. Electron beams 
5, 6 & 7 for emitting blue, red and green luminous color-lights, 
respectively, from the electron gun 1 receive a deflection effect from a 
deflection means (not illustrated) and reach a screen 9 through a shadow 
mask 8 formed with a mildly convex surface. 
As shown in FIG. 2, the shadow mask 8 has numerous vertically oblong 
rectangular slots 10, 10, . . . arranged in multiple rows vertically and 
horizontally. The electron beams flattened by passing through these 
rectangular slots of the shadow mask produce each three vertically oblong 
rectangular spots per slot on a screen 9. 
The size of slots 10, 10 . . . of the shadow mask 8 and the dimensions of 
gaps between each other vary depending on the size of the face plate of 
the tube. To take for instance a color picture tube having an 18-inch face 
plate (i.e. of the size with diagonal line of about 45 cm) designed in 
horizontal of 490 slots 10, 10 . . . , the relevant size and dimensions at 
the middle part of the tube are as follows: 
Width (horizontal dimension) "a" of slot: 0.195 mm 
Horizontal arrangement pitch "b" of slots: 0.7 mm 
Vertical arrangement pitch "c" of slots: 0.9 mm 
Bridge width "d": 0.13 mm 
The number of slots 10, 10 . . . in the horizontal arrangement is to be 
selected depending on the size of face plate of the tube, but it must be 
at least 300. The pitch "c" in the vertical arrangement of the slots is to 
be selected on the basis of 8/(2n-1) times the scanning-line pitch (where 
n is an integer), such as about 8 times, about 8/3 times, about 8/5 times 
or about 8/7 times the pitch. This mode of selection is advantageous in 
moderating the occurrence of adverse moire. The number of slots in the 
vertical arrangement is to be no less than 100. On the other hand, the 
bridge width "d" must be selected by considering the brightness of 
pictures, the mechanical strength of shadow mask, the occurrence of 
adverse moire, etc., but it should be selected to be no more than 30%, 
preferably to be no more than 20%., of the vertical length of a slot. 
Furthermore, it is desirable for the slots to be arranged in a 
horizontally zigzag fashion, though in vertically straight rows, as shown 
in the drawing, in consideration of said adverse moire and mechanical 
strength of the shadow mask. 
On the screen 9 which is a coated formation on the inner face of the face 
plate 11 of the tube, a large number of sets of phosphor strips (each set 
consisting of three vertically oblong strips 12, 13 & 14, aligned 
horizontally, to emit green, red and blue fluorescences, respectively) are 
orderly arranged both vertically and horizontally as shown in FIG. 3. And 
each luminous strip is completely surrounded by a light-absorbent film 15 
which fills up entire gaps between strips as well as their sets. The three 
strips 12, 13 and 14 in each set are arranged with small gaps inbetween in 
the order, from left to right, of green, red and blue fluorescent 
phosphors, respectively, and this set arrangement is repeated in the same 
order in the vertical and horizontal rows of sets all over the face plate 
11. Therefore, all strips on the left, middle and right rows of the entire 
strip sets emit respectively the same colored fluorescences. The three 
strips horizontally arranged in each set constitute a set of picture 
elements and jointly correspond to one of the slots 10 of the shadow mask. 
8. 
The light-absorbent film 15, as is well known, is made of graphite powder 
or the like and binding agent by applying the selective exposure method 
with the shadow mask 8 as a light-shielding mask. The light-absorbent film 
15 is first coated on the inner surface of the face plate to form a film 
with apertures in vertical and horizontal rows, before forming the 
luminous trips. Therefore, the shape and positions of the sets of luminous 
strips under formation are defined by the apertures of the light absorbent 
film. Thus after completion of the tube, the light-absorbent film absorbs 
a part of undesirable outside light incident through the face plate and 
prevents deterioration of the contrast due to reflection from the film 
face. 
The luminous strips 12, 13 and 14 are shaped rectangular about similar to 
each slot 10. Their vertical gap "e" corresponding to the bridge width "d" 
of the slots is to be set between 0.03 mm and 0.30 mm, preferably between 
0.05 mm and 0.20 mm. A part of light-absorbent film covering this vertical 
gap between adjacent strips constitutes a horizontal bridge. Therefore, 
the light-absorbent film 15 forms a net pattern with numerous apertures in 
vertical and horizontal rows and covers a major part of the whole area of 
the screen At the same time, the bridges on the face plate divide the 
vertical stripes of luminous material into short strips by crossing 
horizontal rows thereof and acting as non-luminant multi-dividing belts. 
As a result, vertical stripes of the luminous strips and those of the 
light-absorbent film become almost obscure. 
Now, examples of various dimensions concerning the luminous strips on the 
screen in correspondence to those already stated concerning the slots on 
the shadow mask, are given as follows: 
Width "f" of luminous strip: 0.19 mm 
Horizontal arrangement pitch "g" of strip set: 0.74 mm 
Vertical arrangement pitch "h" of strips: 0.95 mm 
FIG. 4 is an enlarged view exemplifying the relative dimensions between an 
area A showing the enclosure section of rectangular electron beams and the 
luminous strips B on the face of screen 9. Here, section A of rectangular 
electron beams is enlarged by 5% to 20% widthwise and lengthwise over the 
dimensions of slots 10, due to dispersion in relative distances between 
the shadow mask 8 and the screen 9. Against this, the width of luminous 
strips B is designed at a smaller value than the width of section A of the 
electron beams, and the width "j", which is the width of the horizontal 
guardband, is designed to be 0.01 mm to 0.04 mm in the middle part of 
screen and to be 0.03 mm to 0.08 mm in the peripheral part of the screen. 
On the other hand, the length of luminous strips B is designed at a value 
equal to or slightly shorter than the length of section A of the electron 
beams, which value corresponds to about 0.9 to 1.2 times the length of the 
slots. Symbol "k" indicates the vertical gap of the electron beams on the 
screen. 
FIG. 5 shows changes of the brightness of screen and the contrast value 
against e/h value in the picture tube of the aforementioned embodying 
example, wherein D indicates the e/h value when the vertical gap "e" of 
the luminous strips becomes equal with the vertical gap "k" of the 
electron beams on the screen, and E indicates the e/h value when the 
length of luminous strips almost becomes equal with the length of mask 
slots. 
As is clear from the said chart, the most suitable e/h value from the 
aspects of both screen brightness and contrast lies in a region defined by 
the lines D and E. However, this value varies somewhat depending on the 
size of tubes, etc. Taking such into consideration, it has been proved by 
experiments that the optimum e/h value lies between 0.05 and 0.35, more 
desirably between 0.08 and 0.25. 
As described above, according to the color picture tube of this invention, 
the multi-dividing belts of light-absorbent film are provided between each 
vertical arrangement of the sets of luminous strips to form horizontal 
zigzag stripes of non-luminant film. In other words, the total number of 
luminous strips in the horizontal arrangement is made about three times 
the corresponding number of slots on the shadow mask, and at the same 
time, the vertical number of the luminous strips is made about the same as 
that of the slots of shadow mask. In addition, all gaps between each and 
every luminous strip are filled up with the light-absorbent film. As a 
result, the color picture tube of this invention produces little 
undesirable stripes and can produce clear pictures on the screen. 
Further improved effect can be obtained by selecting the vertical gap "e" 
of the luminous strips at a higher value than the vertical gap "k" of the 
electron beams (namely: e.gtoreq.k) on the screen, and also by selecting 
the e/h value between 0.05 and 0.35 as mentioned before. On the other 
hand, the forms of slots and luminous strips need not necessarily be 
rectangular, but can, of course, be of other shapes so long as they are 
vertically slender.