Convergence device for electron beams in color picture tube

A convergence device for electron beams in a color picture tube includes a pair of four-pole magnet rings, a pair of six-pole magnet rings and a pair of two-pole magnet rings, the absolute value of the temperature coefficient of magnetization of which is equal to or less than 0.05%/.degree. C. measured in a temperature range of 0.degree. C. to 120.degree. C.

BACKGROUND OF THE INVENTION 
The present invention relates to a static convergence device for in-line 
electron beams emitted from three guns located at a bottom in a color 
picture tube. 
A static convergence assembly (STC) for use with an in-line color cathode 
ray tube (Color-CRT) has an effect to make electron beams emitted from 
guns located at a bottom of a tube, strike coincident regions of a viewing 
screen. 
A STC comprises a pair of juxtaposed four-pole magnet rings and a pair of 
justaposed six-pole magnet rings which are rotatably mounted about axially 
spaced regions of the tube neck. The described ring magnet structures may 
advantageously be used in combination with a pair of juxtaposed two-pole 
magnet rings called purity rings, each magnetized across a diameter of a 
ring for effecting movement of all three beams in the same direction, for 
accomlishing both purity and convergence adjustments. These prior art 
devices are described in U.S. Pat. No. 3,725,831, British Patent 
Specification No. 1,429,292 and Japan Patent Publication No. 55-30659. 
Previously, four-pole magnet rings and six-pole magnet rings in a STC were 
composed of a mixture of Ba-ferrite magnetic material and resin material 
which was called a Ba-ferrite type of plastic magnet. 
However, the above-mentioned STC had drawbacks in that the magnet rings 
caused an undesirable discrepancy of beams on a viewing screen after a 
temperature change in a STC even after focusing three beams to a point on 
the viewing screen by adjustments to the STC. The undesirable discrepancy 
of beams after a temperature change in a STC occurred by reason of the 
magnetization of the magnet rings comprised of Ba-ferrite type plastic 
magnet material in the STC which were reduced or enhanced too much by a 
temperature change of the STC, because the Ba-ferrite type plastic magnet 
material had rather big temperature coefficient of magnetization as 
-0.2%/.degree.C. 
The temperature coefficient (.alpha.) of magnetization as used in the 
specification and drawings of the present invention is defined by a 
formula: 
##EQU1## 
where .PHI.b is the magnetic flux (Maxwell) of the permanent magnet at a 
temperature of Tb.degree.C. and .PHI.a is the magnetic flux (Maxwell) of 
the permanent magnet at a temperature of Ta.degree.C. 
Recently such an undesirable beam discrepancy on a viewing screen which is 
caused by a rather big temperature coefficient of magnetization of magnet 
rings in a STC becomes more and more serious in current state of the art 
high-performance color picture tubes. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to remove the drawbacks of 
the prior art and to provide a convergence device where changes of 
magnetic flux in ring magnets in the convergence device according to a 
temperature change is small, so a discrepancy of beams on a viewing screen 
caused by the temperature change is satisfactorily suppressed. 
This invention is directed to a convergence device comprising a pair of 
juxtaposed four-pole magnet rings and a pair of juxtaposed six-pole magnet 
rings which are rotatably mounted about axially spaced regions of a tube 
neck, wherein at least the four-pole magnet rings are composed of 
permanent magnet material provided with an absolute value of temperature 
coefficient of magnetization equal to or less than 0.05%/.degree.C.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention will be further understood from the following detailed 
description and the drawings. 
Referring first to FIG. 1 which is a somewhat simplified side view of an 
in-line, tri-beam shadow-mask color cathode ray tube (CRT), the tube 
comprises a viewing screen 1, a funnel region 2, a neck 3, a deflection 
yoke 4, and a static convergence 5 assembly (STC). FIG. 2 is an enlarged 
side view of the STC portion of the tube shown in FIG. 1, wherein 6a and 
6b illustrate a pair of four-pole magnet rings, 7a and 7b illustrate a 
pair of six-pole magnet rings, 8a and 8b illustrate a pair of two-pole 
magnet rings called purity rings, each of which is provided with a 
projection 13 for easy rotation during adjustments. The spacer 9 between 
the paired four-pole magnet rings 6a, 6b and the paired six-pole magnet 
rings 7a, 7b and the spacer 9 between the paired six-pole magnet rings 7a, 
7b and the purity rings 8a, 8b serves to prevent a simultaneous rotation 
of these paired rings. 
All the ring magnets and the spacers can be fixed by a press of the stop 
ring 10 toward the ring part 11 after adjustments of electron beams. A 
metallic clamp 12 is used to fix the STC on the neck of the CRT. 
FIGS. 3a, 3b and 3c are diagrammatic showings illustrating various 
directions of beam position shifts obtainable with a pair of four-pole 
magnet ring elements, a pair of six-pole magnet ring elements and a pair 
of two-pole ring elements, respectively. The shift directions of a blue 
beam (B), a green beam (G) and a red beam (R) are shown by the arrows in 
the figures. As shown in FIG. 3a the side beams (B and R) can be shifted 
variously to the opposite directions by magnetic fields produced by the 
paired magnetic rings according to rotational positions of a pair of 
four-pole magnet ring elements. Beams B and R can be directed to the 
central beam (G) by a rotational adjustment of the paired magnet rings. It 
is preferable that the central beam (G) would not be caused to shift by 
the magnetic field adjustment for the other beams (B and R). Suppression 
of the temperature change of magnetization of the four-pole magnet rings 
is most effective for preventing an undesirable discrepancy of beams 
caused by a temperature change of a STC, because the magnetic field 
created by the four-pole magnet rings acts on the electron beams. In FIG. 
3b the shift directions of the beams in a pair of six-pole magnet ring 
elements are shown. The two outside beams (B and R) move in substantially 
the same direction by the effect of the magnetic field created by the two 
magnet rings 7a and 7b. Preferably the central beam would not be affected 
by a rotational adjustment of the paired magnet rings. The shift 
directions of the electron beams in the purity magnet rings are shown in 
FIG. 3c. The three beams move in substantially the same direction 
according to the relative position of the two magnet rings. The color 
purity can be adjusted by these beam movements. As explained above, the 
relative positions of the paired magnet rings determine the shift 
direction and the shift amount of the electron beams. Although the 
following explanations concern the paired four-pole magnet rings, similar 
explanations can also be applied to the paired six-pole magnet rings and 
paired two-pole magnet rings. FIGS. 4a-4d illustrate the effect of the 
relative locations of the two magnet rings 6a and 6b on movement of the 
electron beams in the paired four-pole magnet rings. FIG. 4a illustrates 
how the two magnet rings aid each other to provide a maximum amount of 
movement in the opposite direction of the two outside beams (B and R). In 
this situation, the field direction at the beam (B) is vertically downward 
while the field direction at the beam (R) is vertically upward; the 
resultant beam position shifts are lateral and to the right at the beam 
(B) and lateral and to the left at the beam (R). The diagrammatic showing 
of FIG. 4b illustrates the nature of the beam position shifts that result 
from the fields of the four-pole ring pair 6a and 6b for a particular 
orientation wherein ring 6a is positioned with its north poles directly 
above and below the axial beam (G) location; ring 6b is similarly 
positioned (whereby the fields of the two rings are similarly directed, 
and are fully aiding). 
With the indicated orientation, the field at the beam (B) is laterally 
directed with a polarity producing a downward shift of the blue beam. The 
field at the red beam location is also laterally directed but with 
opposite polarity, producing an upward shift of the red beam. 
FIG. 4c illustrates the two magnet rings 6a and 6b angularly disposed 
relative to each other such that their respective magnetic poles are 
superimposed. This results in an effective cancellation of the magnetic 
field of each such that there is no movement imparted to the electron 
beams. 
FIG. 4d illustrates the magnetic poles of ring magnets 6a and 6b disposed 
about 45.degree. C. from each other. This results in opposite diagonally 
directed beam position shifts (downward and to the right for the blue 
beam, and upward and to the left for the red beam). The shift amount of 
the beams is smaller than the one in the configuration in FIG. 4a or FIG. 
4b because some of the magnetic field for each ring magnet is cancelled by 
the field of the other. 
This invention is directed to a static convergence device for use with a 
Color-CRT having the effect of causing beams emitted from three electron 
guns to be arrayed in-line at the bottom of the tube, wherein each of the 
paired four-pole magnet rings, used in combination with a pair of six-pole 
magnet rings, and preferably with a pair of two-pole magnet rings 
comprises permanent magnets made of metallic magnetic material inserted or 
fixed at the pole positions of a ring which is non-magnetic or magnetic, 
or a permanent magnet which is a mixture of metallic magnetic material and 
a bonding agent as a polymeric material, wherein the permanent magnets are 
provided with absolute temperature coefficients (.alpha.) of magnetization 
equal to 0.05%/.degree.C. or less than 0.05%/.degree.C. measured in a 
temperature range of 0.degree. C. to 120.degree. C., in order to prevent 
an undesirable discrepancy of beams caused by temperature change in a STC. 
In the present invention, the magnets in the paired six-pole magnet rings 
or the magnets in the paired two-pole magnet rings also can be composed of 
a magnet having a low temperature coefficient. The utilization of the 
magnets having a low .vertline..alpha..vertline. value in the paired 
six-pole magnet rings and also in the paired two-pole magnet rings in 
combination with the paired four-pole magnet rings having a low 
.vertline..alpha..vertline. value are preferable to prevent a discrepancy 
of beams caused by a temperature change in the STC. 
The magnets used in this invention have an absolute temperature coefficient 
equal to or less than 0.05%/.degree.C. The reasons for the temperature 
coefficient range of magnetization of the magnets to be used for the 
paired ring magnets are the following. The original Ba-ferrite type of 
plastic magnet material is provided with a temperature coefficient of 
magnetization of about -0.2%/.degree.C. which causes about 16% of magnetic 
flux reduction by a temperature rise (.DELTA.T) of 80.degree. C. 
In the case of a STC comprising paired four-pole magnet rings, paired 
six-pole magnet rings and paired two-pole magnet rings, all of which are 
made of Ba-ferrite type of plastic magnet material to enable a shift of 
side beams by 4 mm, a 0.64 mm in the position discrepancy of the side 
beams after a temperature change of 80.degree. C. would occur. This 
discrepancy magnitude is too great in current state of the art 
high-performance color picture tubes. In the same CRT, the discrepancy 
magnitude of side beams caused by the same temperature change would be 
reduced to a value of less than 0.16 mm by the use of ring magnets having 
an absolute temperature coefficient of magnetization equal to or less than 
0.05%/.degree.C. in the four-pole magnet rings. 
Examples of preferable metallic materials having a temperature coefficient 
of magnetization less than that of Ba-ferrite type of plastic magnet 
material are Cunife, Vicalloy, Alnico or Fe-Cr-Co. As Cunife has a rather 
high temperature coefficient of about 0.09%/.degree.C. and Vicalloy 
comprises about 50 weight % of Co which is expensive and not economical, 
Alnico or Fe-Cr-Co, having a temperature coefficient of magnetization of 
about 0.01 to 0.03%/.degree.C., is preferred to be used as a magnet 
material for the magnet rings according to the present invention. 
As is known to persons skilled in the technical area, the temperature 
coefficient of magnetization of a Fe-Cr-Co magnet greatly depends on its 
magnet shape. 
The temperature coefficient (.alpha.) of magnetization of a Fe-Cr-Co magnet 
is negative when measured at a point of infinite permeance coefficient, 
for example at the point of Br, but the absolute value of the negative 
temperature coefficient becomes smaller as the permeance coefficient of 
the magnet becomes smaller. 
As stated above, a Fe-Cr-Co magnet is a characteristic in that its 
temperature coefficient of magnetization reverses at a critical point of a 
permeance coefficient (Pc) even if the magnet is composed of the same 
composition provided with the same hysteresis characteristic. 
Because of the above stated reasons, it is possible to obtain an extremely 
low temperature coefficient of a Fe-Cr-Co magnet if the proper shape of 
the magnet is chosen. The preferable shapes of Fe-Cr-Co magnets are those 
with a diameter of 1.5 to 4.0 mm.phi. and a thickness of 2.0 to 6.0 mm 
because a Fe-Cr-Co magnet having a diameter of less than 1.5 mm.phi. or a 
thickness of less than 2.0 mm cannot be provided with a sufficient 
magnetic flux to be used in the magnet ring of a STC and it is difficult 
to obtain such a shape of Fe-Cr-Co magnet provided with an absolute 
temperature coefficient value of less than 0.05%/.degree.C. which is a 
necessary characteristic to magnet rings in a STC. 
To the contrary, a STC would become too big to be used in combination with 
other devices in a practical CRT if an outer diameter of magnets 
incorporated in the STC exceeds 4.0 mm.phi. or the thickness of the STC 
exceeds 6.0 mm. Because of the above stated reasons, it is necessary for 
the magnets used in a ring of a diameter of 1.5 to 4.0 mm.phi. and a 
thickness of 2.0 to 6.0 mm. Preferably, the ratio of the magnet thickness 
to the outer diameter of the magnet should be 1.4 to 2.7. 
Although the above explained embodiments of the invention concern 
cylindrical shaped magnets, rectangular shaped magnets also can be used in 
the ring magnets incorporated in a STC according to the invention if the 
magnets have a cross section of 1.7 mm.sup.2 to 12.6 mm.sup.2. The 
preferable absolute temperature coefficient value is equal to or less than 
0.01%/.degree.C. and, more preferably equal to or less than 
0.005%/.degree.C. The advantages of using ring magnets for a STC having an 
absolute temperature coefficient value of equal to or less than 
0.01%/.degree.C. and more preferably 0.005%/.degree.C. are stated below. 
As already explained, a magnet comprised of a Ba-ferrite type of plastic 
generally has a temperature coefficient of about -0.2%/.degree.C., which 
causes a magnetic flux reduction of about 16% compared with the original 
magnetic flux, for a temperature change (.DELTA.T) of 80.degree. C. 
The amount of reduction of magnetic flux in ring magnets in a STC 
theoretically causes about 0.64 mm of beam discrepancy in each case so 
that the needed correction amount for side beams by a STC is 4 mm. A CRT 
provided with such a degree of beam discrepancy is undesirable. 
On the other hand, a STC incorporated with ring magnets having a 
temperature coefficient of equal to or less than 0.01%/.degree.C. will 
result in high performance in a CRT because the beams discrepancy would be 
suppressed to a negligibly small value range which is less than 0.016 mm. 
It is also possible to use a mixture of metallic magnet material and resin 
material for the ring magnets, provided that the metallic magnet material 
is Alnico magnet material, Fe-Cr-Co magnet material, or a mixture thereof, 
preferably having an absolute temperature coefficient value of 0.01 to 
0.03%/.degree.C. 
These magnets can be produced by the following methods, for example. 
First compound pellets are made from a hot blend of the magnet material and 
resin. 
Before mixing with resin the magnet particles can be surface treated with a 
known coupling agent. 
The surface treatment for magnetic particles can be performed by the 
preceeding steps followed by spraying the coupling agent on the magnetic 
particles during stirring, mixing the particles thereafter, and drying. In 
this case, the resin can contain lubricant material and/or plastic agent. 
The compound obtained according to the above described process would be 
ejected into a cavity surrounded by metal dies as a hot melt and taken out 
of the cavity after the ejection and then cooling. The obtained magnet 
body can be a four-pole magnet ring after magnetization without a further 
processing, but it is also possible to finish the magnet body at the 
outside wall thereof. 
Although there is no limitation of the weight ratio of magnetic material to 
resin material from the standpoint of the temperature coefficient of 
magnetization, it is general practice to select the ratio of magnetic 
material to resin material of 50:50 to 95:5, preferably 80:20 to 90:10. 
These ratios are preferable because a mixture containing too much magnetic 
material could not be formed into a magnet body and, to the contrary, the 
mixture containing too few magnetic materials could not be provided with 
sufficient magnetic properties. The preferable magnetic characteristics of 
a ring magnet according to the invention are the following: 
Br (Residual Magnetic Flux) 2,900-3,000G, 
Hc (Coersive Force) 700-800 Oe, 
(BH).sub.MAX (Maximum Energy Product) 0.6-0.8 MGOe. 
The following polymer materials can be used as a bonding material for the 
permanent mgnetic powder: Thermoplastic resins such as Polyamide resin, 
Polyethylene, Polypropylene, Ethylene copolymer, ABS Resin, AS Resin, 
Polycarbonate, Polyethylene terephthalate, Polybutylene terephthalate; 
Thermosetting resins cuh as Phenolic plastic, alkyd resin; or other resins 
such as Styrene-butadiene rubber, Nitrile rubber, Ethylene-propylene 
rubber, Piparon, Acrylic rubber. The mentioned resins can be used by 
themselves or mixed with other resins as the bonding material. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following are the preferred embodiments of the present invention but 
other embodiments according to the present invention are also possible. 
EXAMPLE 1 
A four-pole magnet ring was constructed by insertion of four Fe-Cr-Co 
magnets, each of which has a shape of a diameter of 2.0 mm.phi. and a 
thickness of 5.0 mm and magnetic characteristics of Br=8200G, Hc=4800e and 
.alpha.=+0.004%/.degree.C., into a plastic ring having an outer diameter 
of 46 mm.phi., an inner diameter of 34 mm.phi. and a thickness of 2.7 mm, 
as shown in FIG. 5. 
The magnetization directions of the magnets are also shown in the figure. 
The six-pole magnet rings and the two-pole magnet rings, having an outer 
diameter of 46 mm.phi., an inner diameter of 34 mm.phi. and a thickness of 
1.4 mm, were made from a mixture comprising a Ba-ferrite material and 
plastic material (Hitachi KPM-3, .alpha.=-0.194%/.degree.C.) and then by 
injection mold casting. 
Each of these magnets was provided with a projection for easy rotation 
handling which is necessary for adjustments in a STC where electron beams 
emitted from the guns in a CRT were focused. 
The STC comprising these magnets was incorporated into a CRT to measure the 
degree of shift of the beams by the magnetic field in the STC. 
In this measurement we used a CRT where the distance between the side beams 
(Blue beam and Red beam) was 4.2 mm measured at the viewing screen in the 
absence of the STC. The maximum beam shift of 5.9 mm was obtained by a 
relative rotation of the four-pole magnet rings incorporated with the 
Fe-Cr-Co magnets which is sufficiently effective to shift the beams by the 
STC. The discrepancy of the beams caused by temperature variation was only 
0.1 mm after a temperature rise of 80.degree. C. 
EXAMPLE 2 
Each of the four-pole magnet rings was constructed by fixing four Alnico 
magnets, each of which has a diameter of 2.0 mm.phi., a thickness of 5.0 
mm, Br=7400G, Hc=530 Oe and, .alpha.=-0.016%/.degree.C., at the pole 
positions of a plastic ring having the same shape as shown in Example 1. 
Similar measurements were performed using a CRT having the four-pole 
magnet rings according to this example, together with the six-pole magnet 
rings and two-pole magnet rings as used in Example 1. 
The maximum shift of the side beams by the STC was 5.7 mm and we could 
focus the three beams to a point on a viewing screen. 
The degree of discrepancy of the side beams caused by a temperature rise of 
80.degree. C. was 0.2 mm. 
EXAMPLE 3 
An Alnico magnet (Hitachi YCM-4D having magnetic properties of Br=6, 150G, 
Hc=1,130 Oe and (BH).sub.MAX =2.5MGOe) was mechanically pulverized to form 
magnet particles of less than 100 mesh and the particles were heat-treated 
at a temperature of 400.degree. C. for 30 minutes in an Ar-gas atmosphere. 
In succession, the 5 kg weight magnet particles were sprayed with 75 g 
weight of Silane coupling agent (Shinetsu Chemical KBM-603), during ten 
minutes of mixing in a Henshell-Mixer. The surface treatment for the 
magnet material was accomplished by drying the coated particles at a 
temperature of 100.degree. C. for 60 minutes. A compound was obtained by a 
kneader mixing of 4.4 kg weight of the magnetic alloy particles and 308 g 
of Nylon 12 (Ube-Kosan, P-3014U) pellets. 
The obtained compound was heated at a temperature of 295.degree. C. and 
then injected into a cavity formed in dies having an outer diameter of 46 
mm.phi., an inner diameter of 34 mm.phi. and a thickness of 1.7 mm. The 
injection mold casting was performed in dies heated to a temperature of 
80.degree. C., under an injection pressure of 800 kg/cm.sup.2. 
After the injection mold casting the obtained magnets were magnetized 
according to the directions shown in FIG. 6. 
The composite magnets had magnetic characteristics of Br=3,050G, Hc=760 Oe, 
(BH).sub.MAX =0.7 MGOe and a temperature coefficient of 
.alpha.=-0.020%/.degree.C. 
The six-pole magnet rings and the two-pole magnet rings were made from a 
mixture of Ba-ferrite material and a resin material (Hitachi KPM-3). 
These latter magnet rings each had an outer diameter of 46 mm.phi., an 
inner diameter of 34 mm.phi. and a thickness of 1.4 mm. Each magnet was 
magnetized as usual to have six poles or two poles and then paired. 
Each magnet was provided with a projection 13 for easy relative rotation as 
shown in FIG. 5. 
The measurements of the degree of shift of the beams emitted from the gun 
in a CRT were conducted using a CRT incorporated with the STC comprising 
these magnets produced according to the above described process. 
The reference CRT which was used to test the STC as constructed above was 
the same as one used in Example 1. 
The following experimental results were obtained. The maximum shift amount 
of the electron beams was 5.85 mm at various locations in the four-pole 
magnet rings. The embodied complex magnets comprising Alnico particles 
were sufficiently effective to shift the beams incorporated in the STC. 
The temperature rise in a STC of 80.degree. C. caused about 0.15 mm of 
color discrepancy in the side beams which is negligibly small for a 
practical CRT. 
EXAMPLE 4 
In this example four-pole magnet rings, six-pole magnet rings and also 
two-pole magnet rings were produced by insertion of Alnico magnets 
(Br=7400G, Hc=530 Oe), having an outer diameter of 2.0 mm.phi., and a 
thickness of 5.0 mm, into a plastic ring by a similar method as for the 
four-pole magnet rings as described in Example 1. The measurements were 
performed using the CRT incorporated with these magnet rings, which was 
the same as used in Example 1. 
The experimental results showed that the maximum shift amount of the side 
beams was 5.70 mm and the three beams were focused to a point on a viewing 
screen. The color discrepancy of the side beams was 0.15 mm after a 
temperature rise of 80.degree. C. 
EXAMPLE 5 
Magnet particles were obtained by a heat treatment of 400.degree. 
C..times.30 minutes in Ar-gas atmosphere of Alnico particles of less than 
100 mesh which were produced by mechanical pulverization of Alnico block 
(Hitachi YCM-4D, having Br=6,150G, Hc=1130 Oe and (BH).sub.MAX =2.5MGOe). 
The 5 kg weight of magnet particles were sprayed with 75 g of Silane 
coupling agent (Shinetsu Chemical KBM-603) during their stirring in a 
Henshell-Mixer and they were again mixed for ten minutes after the spray, 
then dried at 100.degree. C. for 60 minutes to finish the surface 
treatment. 
A compound was produced by a kneader mixing of 4.4 kg of the surface 
treated magnet particles and 308 g of Nylon 12 (Ubekosan, P-3014U) 
pellets. 
The hot compound, at a temperature of 295.degree. C., was used to form 
magnet rings in a cavity, having an outer diameter of 46 mm.phi., an inner 
diameter of 34 mm.phi. and a thickness of 1.7 mm, whose shape can be 
understood by FIG. 6, by injection mold casting at an injection pressure 
of 800 kg/cm.sup.2 in the cavity formed by heat controlled dies. 
The magnets produced by the above stated method were magnetized to have 
four poles, each neighboring pole forming an angle of 90 degrees as shown 
by FIG. 5. 
Six-pole ring magnets and two-pole ring magnets as shown in FIGS. 6b and 6c 
were also produced by a similar injection process as the one to produce 
the mentioned four-pole ring magnets. These magnetized magnet rings were 
provided with magnetic characteristics of Br=3,050G, Hc=760 Oe, and 
(BH).sub.MAX =0.70MGOe. 
These magnets were installed with their projection for easy rotation during 
adjustments to the STC, as shown in FIG. 6. 
The shift amounts of the side beams by a STC comprising these magnet rings 
were measured after they were incorporated in the STC of the CRT. The CRT 
provided with the magnet rings produced in this example was the same as 
used in Example 1. 
The maximum shift amount 5.80 mm of the side beams was obtained by the 
relative location of the magnets in the paired four-pole magnet rings. It 
was confirmed that the paired magnet rings comprising Alnico magnet 
particles and the resin material fulfilled their functions in the STC at 
room temperature. 
The measured discrepancy of the side beams caused by a temperature rise of 
80.degree. C. was 0.10 mm. 
EXAMPLE 6 
Four-pole magnets, six-pole magnets and two-pole magnets were produced by 
insertion of Fe-Cr-Co magnets each having an outer diameter of 2.5 mm.phi. 
and a length of 4.0 mm, at the pole positions of each plastic ring having 
the same shape as shown in Example 1. The CRT incorporated with the STC 
comprising these magnets produced was used to measure the beam shift 
amounts. 
As the maximum shift amount of the side beams was 5.05 mm by the STC 
comprising these plastic rings incorporated with pole magnets of Fe-Cr-Co 
having a mean magnetic flux 59.4 Mx, the target of the magnetic flux to be 
provided to the Fe-Cr-Co magnets was 60.0 Mx. 
EXAMPLE 7 
Various shapes of pole magnets of Fe-Cr-Co magnet material were produced. 
The Fe-Cr-Co magnets had characteristics of Br=8,200-8,350G and Hc=440-465 
Oe. The results of the measurements are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Total 
Diameter 
Length 
Temp. Coefficient 
Evalua- 
Magnetic Flux 
Evalua- 
Evalua- 
No. 
(mm.phi.) 
(mm) 
(%/.degree.C.) 
tion (Mx) tion tion 
__________________________________________________________________________ 
1 1.0 2.0 -0.001 .circle. 
21.8 
2 " 5.0 +0.024 45.4 
3 1.5 2.0 -0.007 30.6 
4 " 3.0 -0.001 .circle. 
46.3 
5 1.5 4.0 +0.005 .circle. 
65.3 .circle. 
.circleincircle. 
6 " 5.0 +0.013 78.7 .circle. 
7 2.0 3.0 -0.005 .circle. 
60.4 .circle. 
.circleincircle. 
8 " 4.0 -0.001 .circle. 
89.0 .circle. 
.circleincircle. 
9 2.0 5.0 +0.004 .circle. 
111.6 .circle. 
.circleincircle. 
10 " 6.0 +0.009 123.6 .circle. 
11 2.5 3.0 -0.008 72.6 .circle. 
12 " 4.0 -0.004 .circle. 
102.9 .circle. 
.circleincircle. 
13 " 5.0 -0.001 .circle. 
133.7 .circle. 
.circleincircle. 
14 " 6.0 -0.003 .circle. 
159.6 .circle. 
.circleincircle. 
15 3.0 3.0 -0.011 86.6 .circle. 
16 " 4.0 -0.007 118.3 .circle. 
17 3.0 5.0 -0.003 .circle. 
161.7 .circle. 
.circleincircle. 
18 3.5 3.0 -0.013 95.2 .circle. 
19 " 5.0 -0.005 .circle. 
174.9 .circle. 
.circleincircle. 
20 4.0 3.0 -0.014 102.5 .circle. 
21 " 5.0 -0.008 182.8 .circle. 
22 4.0 6.0 -0.005 .circle. 
241.4 .circle. 
.circleincircle. 
23 4.5 3.0 -0.016 111.2 .circle. 
24 " 5.0 -0.009 202.7 .circle. 
__________________________________________________________________________ 
The temperature coefficients of magnetization were measured by a vibrating 
type magnetometer in a temperature variation range of 0.degree. C. to 
120.degree. C. The data in Table 1 are mean reversible temperature 
coefficients. The .circle. evaluation symbol signifies each shape having 
a temperature coefficient the absolute value of which is equal to or less 
than 0.005%/.degree.C. 
The magnetic fluxes were measured on the magnets after a sufficient 
magnetization. Shapes having magnetic fluxes of equal to or more than 60.0 
Mx were designated evaluation with symbols according to the experimental 
results. 
The .circleincircle. symbols in the total evaluation column signify 
excellent magnets having both a magnetic flux of equal to or more than 
60.0 Mx and a temperature coefficient of equal to or less than 
0.005%/.degree.C. 
EXAMPLE 8 
Magnet rings were produced by insertion of Fe-Cr-Co magnets having a 
sufficient magnetic flux and a small temperature coefficient, into a 
plastic ring having a shape with an outer diameter of 48 mm.phi., an inner 
diameter of 34 mm.phi. and a thickness of 4.2 mm. 
The locations of the inserted magnets in the four-pole magnet are shown in 
FIG. 5a. The locations of the inserted magnets in the six-pole magnet and 
the two-pole magnet are shown in FIGS. 5b and 5c, respectively. 
The measurement of the CRT incorporated with the produced magnet rings were 
performed by a similar method as in Example 1. 
The maximum shift amount of the side beams ranged from 5.05 mm by a STC 
incorporated with No. 2 sample to 16.70 mm by a STC incorporated with No. 
10 sample, and in each case it was possible to focus the three beams at a 
specific point by adjustments of four-pole magnet rings and six-pole 
magnet rings. 
The maximum color discrepancy of beams caused by a temperature rise of the 
STCs was at most 0.05 mm which is sufficiently small for an actual picture 
tube. 
These experimental results are shown in Table 2. 
TABLE 2 
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Color Dis- 
Diameter Length Max. beam shift 
crepancy 
No. (mm) .phi. 
(mm) (mm) (mm) 
______________________________________ 
1 1.5 4.0 5.45 .ltoreq.0.05 
2 2.0 3.0 5.05 " 
3 " 4.0 7.55 " 
4 2.0 5.0 9.60 " 
5 2.5 4.0 8.90 " 
6 " 5.0 11.40 " 
7 2.5 6.0 13.35 " 
8 3.0 5.0 13.40 " 
9 3.5 5.0 14.20 " 
10 4.0 6.0 16.70 " 
______________________________________ 
COMISON EXAMPLE 
We produced two-pole magnets, four-pole magnets and six-pole magnets using 
bonded magnets (Hitachi KPM-3), a mixture of Ba-ferrite material and 
plastic material. 
They had the same shape, namely an outer diameter of 46 mm.phi., an inner 
diameter of 34 mm.phi., and a thickness of 1.4 mm. The magnetizations for 
them were performed as each neighboring pole forms an equal angle in each 
magnet ring. The maximum shift amount of the side beams was 5.30 mm but 
the color discrepancy caused by a temperature rise in the STC incorporated 
in the Ba-ferrite type of bond magnets, was 0.65 mm after a temperature 
rise of 80.degree. C. 
As explained above, a color CRT where the color discrepancy of beams is 
small can be achieved according to the present invention, because the STC 
incorporated in the CRT comprises a magnet ring which is plastic ring 
having pole magnets where metallic magnets are inserted at the pole 
positions, or a plastic magnet where magnet particles are bonded with an 
agent such as a resin, wherein the magnet material has an absolute value 
of the temperature coefficient of magnetization of 0.05%/.degree.C. or 
less.