Cathode-ray tube with multi-layer resin coating on faceplate providing implosion protection

An implosion protected cathode ray tube which comprises a glass envelope having a faceplate; and a layered protective structure deposited over and positioned frontwardly of the faceplate. The layered protective structure includes a first resin-coated layer held in contact with the faceplate, a hard coated layer for protecting the first resin-coated layer and a second resin-coated layer formed between the first resin-coated layer and the hard coated layer. The first resin-coated layer has a hardness which corresponds to 1H or lower of hardness of drafting pencil lead, and an elongation at breakage within the range of 65 to 85%. The first resin-coated layer also has a break strength of 3.5 kilograms per square millimeter or greater. The hard coated layer has a hardness which corresponds to 5H or higher of hardness of drafting pencil lead, and an elongation of 3% or smaller at breakage. The second resin-coated layer has a hardness generally intermediate between the hardness of the first resin-coated layer and that of the hard coated layer and also an elongation at breakage generally intermediate between the elongation of the first resin-coated layer at breakage and that of the hard coated layer at breakage.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to cathode ray tubes and, more 
particularly, to implosion protected cathode ray tubes. 
2. Description of the Prior Art 
A cathode ray tube comprises a glass envelope having an electron gun and a 
phosphor screen positioned inside and at opposite ends of the glass 
envelope. In the case of the cathode ray tube used in a television 
receiver set, the glass envelope is typically of a shape having a 
generally cylindrical neck portion closed at one end thereof by a stem and 
accommodating therein the electron gun, a generally funnel-shaped portion 
flared outwardly from the other end of the neck portion with its opening 
closed by a faceplate on the inside of which the phosphor screen is 
deposited. 
As a matter of design, the glass envelope, also known as the vacuum 
enclosure, is highly evacuated to a substantial vacuum and is susceptible 
to implosion when exposed to severe conditions, for example, abrupt change 
in temperature or violent handling. The implosion is known as a phenomenon 
in which the glass envelope collapses inwardly in the presence of a great 
difference in pressure inside and outside the glass envelope. 
The implosion of the glass envelope of the cathode ray tube is accompanied 
by outward scattering of fragments of glass used to form the glass 
envelope. The scattering of glass fragments outwardly of the television 
receiver set is hazardous to television viewers who will be eventually 
injured when seated close to the television reciever set. 
To minimize the hazardous conditions, numerous attempts have hitherto been 
suggested to provide an implosion protected cathode ray tube, that is, a 
cathode ray tube designed to have a minimized possibility of outward 
scattering of glass fragments even when imploded, such as disclosed in, 
for example, the Japanese Examined Patent Publication (Koho) No. 51-18311 
published in 1976; the Japanese Laid-open Patent Publications (Kokais) No. 
54-128265 published Oct. 4, 1979, and corresponding to U.S. patent 
application Ser. No. 890,612 filed Mar. 20, 1978, now U.S. Pat. No. 
4,204,231 ; No. 60-47352 published in 1985; and No. 61-124039 published 
June 11, 1986, and the Japanese Laid-open Utility Model Publications No. 
59-71559 published in 1984; No. 59-71560 published in 1984; and No. 
59-76065. All of the prior art publications except for the Japanese 
Examined Patent Publication No. 51-18311 disclose the use of a protective 
panel fitted to the faceplate of the cathode ray tube in a respective 
method. 
Of these prior art publications, the Japanese Examined Patent Publication 
No. 51-18311 discloses the use of a reinforcement band of steel 
encompassed exteriorly around the perimeter of the faceplate of the 
cathode ray tube. The technique disclosed in this prior art publication is 
merely to physically reinforce the cathode ray tube, rather than to 
provide an implosion protected cathode ray tube, and therefore, the 
cathode ray tube according to this prior art publication still has a 
problem in that, once the cathode ray tube is imploded, fragments of glass 
may scatter outwardly of the television receiver set. 
The reinforcement of the cathode ray tube by the use of the steel 
reinforcement band may be satisfactory where the cathode ray tube is of a 
small size. However, when it comes to the cathode ray tube of about 30 
inches or more in screen size, the pressure difference inside and outside 
the glass envelope is very high and, for example, it is generally 
recognized that the cathode ray tube of 37 inch screen size is loaded 13 
tons due to the high pressure difference. Therefore, the mere use of the 
steel reinforcement steel band is not an effective measure to the large 
size cathode ray tube. 
The Japanese Laid-open Patent Publication 54-128265 discloses a cathode ray 
tube wherein a protective panel made of glass material is secured to the 
faceplate of the glass envelope and spaced therefrom a predetermined 
distance, for example, 1.6 to 6.4 mm. The space represented by the 
predetermined distance between the faceplate and the protective panel is 
filled with thermosetting resin such as polyester resin, polyurethane 
resin or epoxy resin which, when cured, serves as a bonding agent. To 
define the space between the faceplate and the protective panel and also 
to temporarily secure the protective panel to the faceplate during the 
filling of the thermsetting resin in fluid state into the space between 
the faceplate and the protective panel, a double sided adhesive tape of 
generally rectangualr frame structure complemental in shape to the shape 
of either the faceplate or the protective panel is interposed between the 
faceplate and the protective panel. 
FIG. 4 of the accompanying drawings illustrates another well known version 
of the cathode ray tube. The glass envelope is identified by 1 and has the 
faceplate 2 to which a protective panel 7 made of glass material is 
secured through the intervention of a deposit of bonding material 8, for 
example, polyurethane resin. The faceplate 2 makes use of a reinforcement 
band of steel encompassed exteriorly therearound. 
While all of the methods disclosed in the prior art publications except for 
the first-mentioned publication and including the method disclosed in FIG. 
4 of the accompanying drawings are generally satisfactory in that the 
fragments of glass forming the glass envelope will not scatter outwardly 
of the television receiver set even when the cathode ray tube implodes. 
However, the use of the protective panel frontwardly of the faceplate has 
some problems which will now be discussed. 
The protective glass panel generally used has a thickness within the range 
of 3 to 5 mm and therefore has a substantial weight which in turn results 
in increase of the overall weight of the cathode ray tube. In addition, it 
is not easy to manufacture the protective glass panel having a surface 
curvature complemental to that of the faceplate and if not impossible, the 
protective glass panel requires a high manufacturing cost which eventually 
results in increase of the manufacturing cost of the cathode ray tube. 
Where the protective glass panel having a surface curvature less 
complemental to that of the faceplate is used and secured to the faceplate 
with the use of the deposit of bonding material, not only is a substantial 
amount of bonding material required to secure the protective panel to the 
faceplate of the cathode ray tube, but also the bond deposit would have a 
varying thickness between the faceplate and the protective glass panel 
such that lens-like portions would be formed somewhere in the screen of 
the cathode ray tube enough to distort corresponding portions of the image 
being reproduced on the screen. 
Moreover, since the protective glass panel is rigid and is not deformable, 
the protective glass panel which has once been bonded to the faceplate in 
the wrong way and which therefore requires a re-mounting can hardly be 
removed from the faceplate in readiness for the re-mounting. 
These problems might have been satisfactorily removed according to the 
Japanese Laid-open Patent Publication No. 61-124039. This prior art 
publication discloses a cathode ray tube wherein a portion of the glass 
envelope except for the neck portion is encompassed by a protective 
covering of heat-shrinkable sheet material together with the reinforcement 
band encircling exteriorly of the faceplate. However, even the technique 
disclosed in this prior art publication has a problem in that there is a 
possibility that, upon the heat shrinkage of the protective sheet, the 
resultant protective covering may have wrinkles and/or blisters formed 
therein. Therefore, the use of the heat-shrinkable sheet for the formation 
of the protective covering appears not to have a favorable productivity. 
SUMMARY OF THE INVENTION 
Therefore, the present invention has been devised with a view to 
substantially eliminating the above described problems and disadvantages 
inherent in the prior art cathode ray tubes and has for its essential 
object to provide an improved cathode ray tube of implosion protected type 
which is relatively light-weight and substantially free from the 
possibility of the televised image being distorted. 
Another important object of the present invention is to provide an improved 
cathode ray tube of the type referred to above, which is easy to 
manufacture and can be manufactured at a relatively high productivity 
without substantially increasing the manufacturing cost of the cathode ray 
tube. 
To this end, the present invention provides an implosion protected cathode 
ray tube which comprises a glass envelope having a faceplate. The 
faceplate of the glass envelope is exteriorly applied with a first 
resin-coated layer, a hard coated layer for protecting the first 
resin-coated layer and a second resin-coated layer formed between the 
first resin-coated layer and the hard coated layer. All of the first 
resin-coated layer, the hard coated layer and the second resin-coated 
layer are transparent or substantially transparent by nature or when 
cured, or alternatively, one or all of the first resin-coated layer, the 
second resin-coated layer and the hard coated layer may be colored if 
desired for the purpose of adjusting the light transmissivity of the 
faceplate of the cathode ray tube. 
In accordance with the present invention, the first resin-coated layer has 
a hardness corresponding to 1H or lower of hardness of a drafting pencil 
lead and an elongation at breakage within the range of 65 to 85%. This 
first resin-coated layer also has a break strength of 3.5 kilograms per 
square millimeter or greater. 
The hard coated layer has a hardness corresponding to at 5H or higher of 
hardness of the drafting pencil lead and an elongation of 3% or smaller at 
breakage. The second resin-coated layer has a hardness generally 
intermediate between the hardness of the first resin-coated layer and that 
of the hard coated layer and also an elongation at breakage generally 
intermediate between the elongation of the first resin-coated layer at 
breakage and that of the hard coated layer at breakage. 
Specifically, a measure of how much a drafting pencil lead resists abrasion 
by the fibers of the paper being marked on represents the degree of 
hardness of the drafting pencil lead which is expressed by HB, F, H and 2H 
to 10H. Hence, the hardness of each of the first resin-coated layer, the 
hard coated layer and the second resin-coated layer hereinabove and 
hereinafter referred to for the purpose of the present invention is 
expressed in terms of the hardness of the drafting pencil lead. By way of 
example, when reference is made to the first resin-coated layer having a 
hardness corresponding to 1H of hardness of the drafting pencil lead, it 
should be understood as meaning that the first resin-coated layer has a 
hardness enough to resist abrasion by the drafting pencil lead of 1H 
hardness with no mark left on the first resin-coated layer. Similarly, the 
hard coated layer having a hardness corresponding to 5H of the drafting 
pencil lead is enough to resist abrasion by the drafting pencil lead of 5H 
hardness with no mark left on the hard coated layer. 
Preferably, the first resin-coated layer is made of polyurethane acrylate 
of a type containing a relatively great quantity of urethane resin. Also, 
preferably, the second resin-coated layer can exhibit an elongation at 
breakage within the range of 0.5 to 15% and is made of polyurethane 
acrylate of a type containing a relatively large quantity of acrylic 
resin. The hard coated layer can be made of, for example, acrylic resin of 
ultraviolet-curable type. 
Preferably, the first and second resin-coated layers have respective 
thicknesses within the range of 20 to 200 micrometers and within the range 
of 20 to 70 micrometers. 
Yet preferably, at least one of the first and second resin-coated layer is 
made of an ultraviolet-curable synthetic resin, that is, the synthetic 
resin of a kind which can be cured when exposed to ultraviolet rays of 
light. 
According to the present invention, instead of the use of the protective 
glass panel such as in the prior art cathode ray tubes, the layered 
structure of the resin coatings is employed which is light in weight. This 
layered structure, that is, each of the first resin-coated layer, the hard 
coated layer and the second resin-coated layer, can be formed by the use 
of a spraying technique or any other suitable painting technique and can, 
therefore, have a uniform thickness over the entire surface thereof which 
is essential to ensure a high-quality image reproduction without any 
distortion. 
Also, since the faceplate of the glass envelope of the cathode ray tube is 
completely covered by the layered structure of synthetic resin, the 
faceplate can be advantageously reinforced and, if an external violent 
impact which would be strong enough to break the protective glass panel or 
the faceplate itself is applied to the faceplate of the cathode ray tube 
embodying the present invention, resultant fragments of glass used to form 
the faceplate may not scatter outwards and may be retained by the layered 
structure due to a high bonding ability exhibited by the layered 
structure. 
In any event, since the first resin-coated layer has a relatively high 
break strength and also a high elongation at breakage, it has a minimized 
possibility of being broken or burst upon the application of an external 
impact, making it possible to avoid abrupt ingress of the atmospheric 
pressure into the glass envelope which would result in the implosion of 
the cathode ray tube. This in turn brings about such an advantage that the 
possibility of the cathode ray tube being imploded can be minimized. 
It is, however, pointed out that, when the hard coated layer is formed over 
and in contact with the first resin-coated layer having the high 
elongation at breakage, the resultant hard coated layer may have crackings 
formed therein as a result of change in temperature. For this reason and 
in order to substantially eliminate the formation of crackings in the hard 
coated layer, the present invention makes use of the second resin-coated 
layer having a less elongation at breakage and an appropriate hardness. 
The provision of the second resin-coated layer according to the present 
invention can render it to withstand change in temperature ranging from 
-10.degree. C. to 150.degree. C. 
BRIEF DESCRIPTION OF THE DRAWINGS 
In any event, the present invention will become more clearly understood 
from the following description of a preferred embodiment thereof, when 
taken in conjunction with the accompanying drawings. However, the 
embodiment and the drawings are given only for the purpose of illustration 
and explanation, and are not to be taken as limiting the scope of the 
present invention in any way whatsoever, which scope is to be determined 
solely by the appended claims. In the drawings, like reference numerals 
denote like parts in the several views, and: 
FIG. 1 is a schematic side view of an implosion protected cathode ray tube 
embodying the present invention; 
FIGS. 2 and 3 are schematic side views of the implosion protected cathode 
ray tube, showing different steps of a process of forming a layered 
structure on the faceplate; and 
FIG. 4 is a view similar to FIG. 1 showing the prior art implosion 
protected cathode ray tube.

DETAILED DESCRIPTION OF THE EMBODIMENT 
Before the description of the present invention proceeds, it should be 
noted that like parts are designated by like reference numerals throughout 
the several views of the accompanying drawings. 
Referring to FIG. 1, the cathode ray tube of, for example, 37 inches in 
screen size comprises the highly evacuated glass envelope 1 having the 
faceplate 2 as hereinbefore described in connection with the prior art 
cathode ray tube shown in FIG. 4. In accordance with the present 
invention, the faceplate 2 has a layered protective structure deposited 
over the entire surface thereof. This layered protective structure 
includes a first resin-coated layer 3 held in tight contact with the 
surface of the faceplate 2, a second resin-coated layer 4 deposited on the 
first resin-coated layer 3 so as to overlay the first resin-coated layer 
3, and a hard coated layer 5 deposited on the second resin-coated layer 4 
so as to overlay the second resin-coated layer 4. 
The first resin-coated layer 3 is capable of exhibiting an elongation of 65 
to 85% at breakage and has a break strength of a value equal to or greater 
than 3.5 kilograms per square millimeter and also a hardness of a value 
equal to or lower (softer) than the 1H hardness of a drafting pencil lead. 
The hard coated layer 5 is capable of exhibiting an elongation at breakage 
of a value equal to or smaller than 3% and has a hardness of a value equal 
to or higher (harder) than the 5H hardness of the drafting pencil lead. 
The second resin-coated layer 4 has an elongation at breakage which is 
generally intermediate between that of the first resin-coated layer 3 and 
that of the hard coated layer 5, and also a hardness which is also 
generally intermediate between that of the first resin-coated layer 3 and 
that of the hard coated layer 5. 
The first resin-coated layer 3 is made of polyurethane acrylate containing 
a relatively large quantity of urethane resin, such as the one sold under 
a trade identification of "GRANDIC.FC-0612" manufactured by Dainippon Ink 
Kogyo K. K. of Japan, and has a thickness of about 100 micrometers. 
The second resin-coated layer 4 is made of polyurethane acrylate containing 
a relatively large quantity of acrylic resin, such as the one sold under a 
trade identification of "GRANDIC.FC-0608" manufactured by Dainippon Ink 
Kogyo K. K. of Japan, and has a thickness of about 30 micrometers. 
It is to be noted that, other than polyurethane acrylate, any one of 
acrylic resin, urethane resin and silicone resin may be employed as a 
coating material for both of the first and second resin-coated layers 3 
and 4. However, the use of the polyurethane acrylate for both of the first 
and second resin-coated layers 3 and 4 is recommended because it has 
excellent properties in respect of the physical characteristic, the 
smoothness, the light transmissivity, the handling property, the 
workability and the cost. 
The hard coated layer 5 is made of acrylic resin of ultraviolet-curable 
type, that is, of a type which can be cured when exposed to ultraviolet 
rays of light, such as the one sold under a trade identification of 
"GRANDIC.FC0605" manufactured by Dainippon Ink Kogyo K. K. of Japan, and 
has a thickness of about 5 micrometers. 
The layered protective structure deposited on the faceplate 2 of the glass 
envelopes of the cathode ray tube according to the present invention is 
formed in the manner which will now be described with particular reference 
to FIGS. 2 and 3. 
As shown in FIG. 2, a coating material for the first resin-coated layer 3 
is first sprayed onto the faceplate 2 under a pressure of 3.5 kilogram per 
square centimeter with the use of a spraying technique 9, and is then 
dried by radiating ultraviolet rays of light for 30 seconds with the use 
of a high pressure mercury lamp 10 of 80 W/cm rated output to cure, i.e., 
harden, the first resin-coated layer 3, which lamp 10 is positioned at a 
location spaced about 15 cm from the faceplate 2. Subsequent to the curing 
of the first resin-coated layer 3, a coating material for the second 
resin-coated layer 4 is similarly sprayed under a pressure of 3.0 kilogram 
per square centimeter so as to cover the first resin-coated layer 3, 
followed by the radiation of ultraviolet rays of light for 30 seconds with 
the use of a similar mercury lamp of 80 W/cm rated output to complete the 
second resin-coated layer 4. 
After the complete formation of the second resin-coated layer 4, a coating 
material for the hard coated layer 5 is sprayed under a pressure of 1.0 to 
2.0 kilogram per square centimeter and is then exposed to ultraviolet rays 
of light to cure the hard coated layer 5, thereby completing the layered 
protective structure. 
Thereafter, a steel reinforcement band is encompassed around the faceplate 
2 in a well known manner to complete the implosion protected cathode ray 
tube. 
While the preferred embodiment of the present invention has been described 
with the ultraviolet-curable coating matrial used for each of the first 
resin-coated layer 3, the second resin-coated layer 4 and the hard coated 
layer 5, a thermosetting resin may be employed in place of the 
ultraviolet-curable coating material. 
The sum of the thicknesses of the respective first and second resin-coated 
layers 3 and 4 has been shown to be 130 micrometers, however, the sum of 
the thicknesses thereof may not be always limited to such value and may be 
within the range of 50 to 300 micrometers. Particularly, 70 to 150 
micrometers in total thickness of the first and second resin-coated layers 
3 and 4 is preferred in view of the transparency, the surface smoothness, 
the productivity and the implosion protective effect. Therefore, in the 
practice of the present invention, the first resin-coated layer 3 may have 
a thickness within the range of 20 to 200 micrometers and the second 
resin-coated layer 4 may have a thickness within the range of 20 to 70 
micrometers. 
With respect to the thickness of the hard coated layer 5 which has been 
shown to be about 5 micrometers in the foregoing embodiment, it may not be 
always limited to such value, but may be within the range of 5 to 30 
micrometers, a particular value of which has to be chosen in consideration 
of the selected thickness of each of the first and second resin-coated 
layers 3 and 4. If the thickness of the hard coated layer 5 is smaller 
than the smallest limit of 5 micrometers, a satisfactory implosion 
protective effect cannot be obtained, but if it is greater than the 
greatest limit of 30 micrometers, the hard coated layer 5 will become 
susceptible to cracking. 
The first resin-coated layer 3 has been described as having an elongation 
at breakage within the range of 65 to 85%. If the elongation of the first 
resin-coated layer 3 at breakage is smaller than 65%, the layered 
structure will not exhibit a satisfactory shock absorbing effect and will 
not bring about a satisfactory effect of minimizing the outward scattering 
of glass fragments in the event that the cathode ray tube is imploded. On 
the other hand, if the elongation of the first resin-coated layer at 
breakage is greater than 85%, the hard coated layer 5 overlaying the first 
resin-coated layer 3 with the intervention of the second resin-coated 
layer 4 will not give a satisfactory hardness and may be caused to be 
susceptible to cracking. 
The hardness of the first resin-coated layer 3 is closely related with the 
elongation thereof at breakage. If the hardness of the first resin-coated 
layer 3 is greater than 1H hardness of the drawing pencil lead, the 
elongation of the first resin-coated layer 3 at breakage within the range 
of 65 to 85% will become difficult to attain. 
On the other hand, the break strength of the first resin-coated layer 3 is 
preferred to be 3.5 kilograms per square millimeter or greater for the 
purpose of the satisfactory implosion protective effect. 
The hard coated layer 5 is preferred to have a hardness equal to or higher 
than the 5H hardness of the drafting pencil lead for the purpose of 
minimizing the formation of scratches on the outer surface thereof and 
also the surface contamination. 
As hereinbefore described, the elongation at breakage of the hard coated 
layer is preferred to be equal to or smaller than 3%. If it is greater 
than 3%, the hardness of the hard coated layer 5 which is equal to or 
higher than 5H hardness of the drafting pencil lead will become difficult 
to attain. It is, however, to be noted that the hard coated layer 5 is not 
provided for absorbing shocks which would be generated upon the implosion 
of the cathode ray tube, and therefore, the break strength of the hard 
coated layer 5 can be chosen of any suitable value provided that it can 
satisfy the required elongation at breakage. 
The second resin-coated layer 4 interposed between the first resin-coated 
layer 3 and the hard coated layer 5 has been described as having an 
elongation at breakage which is generally intermediate between that of the 
first resin-coated layer 3 and that of the hard coated layer 5, and a 
hardness which is also generally intermediate between that of the first 
resin-coated layer 3 and that of the hard coated layer 5. Specifically, in 
order to minimize the possibility of cracking of the second resin-coated 
layer 4 and, also, to protect the hard coated layer 5 from cracking, the 
second resin-coated layer 4 is preferred to have an elongation at breakage 
within the range of 0.5 to 15%. The break strength of the second 
resin-coated layer 4 can be chosen of any suitable value because of a 
similar reason as discussed in connection with the hard coated layer 5 
above. 
From the foregoing full description of the preferred embodiment of the 
present invention, it has now become clear that, since any one of the 
first resin-coated layer, the second resin-coated layer and the hard 
coated layer can be formed by the use of any known spraying technique or a 
similar painting technique, and since inexpensive synthetic resin is 
employed as a coating material for any one of the first and second 
resin-coated layers and the hard coated layer, the present invention is 
effective to provide the improved implosion protected cathode ray tube 
that is light in weight, substantially free from distortion of the 
televised image, easy to manufacture and, yet, capable of exhibiting a 
maximized implosion protective effect. 
Although the present invention has fully been described in connection with 
the preferred embodiment thereof with reference to the accompanying 
drawings used only for the purpose of illustration, those skilled in the 
art will readily conceive numerous changes and modifications within the 
framework of obviousness upon the reading of the specification herein 
presented of the present invention. Accordingly, such changes and 
modifications are, unless they depart from the spirit and scope of the 
present invention as delivered from the claims annexed hereto, to be 
construed as included therein.