Abstract:
This invention secures the breakdown voltage between stem pins or the like for high voltage service in a cathode ray tube. This insulator formed is of a clay-like silicone compound having a tip-throughhole and pin-throughholes or a stem base with the electric insulator mounted to the stem base: A inter-stem electric insulation device is structured by mounting either one of the electric insulator or the stem base with the electric insulator to the stem of a cathode ray tube and by pressing to fix together. This structure does not occur bubble generation caused by the electric insulator, and makes the handling easy, and furthermore, accomplish an automatic mounting of the electric insulator to a stem.

Description:
This application is a division of Ser. No. 08/305,283 filed Sep. 12, 1994, U.S. Pat. No. 5,990,610. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an electric insulator being capable of insulating between high voltage stem pins in a cathode ray tube used for electric equipment provided with high voltage electrodes, which electric equipment particularly includes color television picture tubes and monitors of image screens and computers, and for other electrodes being subjected to a high voltage, and relates to an electric insulation device using therefor, and further relates to a method of electrical insulation using the electric insulator. 
     2. Description of the Related Art 
     The cathode ray tube described above is a typical example of electric equipment provided with high voltage electrodes. The high voltage inter-stem pin electric insulator in a cathode ray tube of the prior art and the method for producing a cathode ray tube using the insulator are described below referring to FIG.  1  and FIG.  2 . 
     FIG. 1 illustrates the method of electric insulation between stem pins including a high voltage stem pin of the prior art. 
     FIG. 1A shows a stem base, and FIG. 1B shows a neck of the cathode ray tube. FIG. 2 illustrates the neck of the cathode ray tube structured in accordance with the method of electrical insulation illustrated in FIG.  1 . FIG. 2A gives a view of the neck, and FIG. 2B gives the cross sectional view along the A—A line in FIG.  2 A. 
     In FIG. 1B, the reference number  1  designates the neck of a cathode ray tube which is installed in a color television picture tube or a monitor for an image screen or computer. The neck accepts an electron gun being mounted on a stem  2 , which is not shown, by insertion therein, and the stem  2  is provided with more than one stud electrode, stem pins  3 A,  3 B,  3 C, etc. The glass periphery of the stem  2  and the glass edge periphery of the neck  1  are welded together to integrate them. The assembled cathode is evacuated through the tip  4  of the exhaust pipe formed at the center of the stem  2 , then the tip  4  is sealed. The stem pins  3 A,  3 B,  3 C, etc. are studded along a specified pin pitch circle. 
     In FIG. 1A, the reference number  10  designates a stem base. The stem base  10  consists of a bottom disc plate  11 , a tip acceptor  12  which is formed at the center of the bottom disc plate  11  and protects the tip  4 , an acceptor for high voltage stem pin  13  in a fan-shape to receive a high voltage stem pin  3 B and act also as a part of the side wall of the tip acceptor  12 , a skirt  14  which covers the edge periphery of the neck  1  formed at the periphery of the bottom plate  11  and which prevents sagging of the paste electric insulator  5 , and more than one throughhole,  15 A,  15 B,  15 C, etc. aligning to the stem pins  3 A,  3 B,  3 B, etc. formed at the periphery of the bottom plate  11 . 
     A common material for the stem base  10  is a resin such as polycarbonate which has excellent insulation properties. The dielectric breakdown voltage of polycarbonate resin is 30 KV/mm. 
     A conventional method to electrically insulate between the stem pins  3 A,  3 B,  3 C, etc. being studded onto the stem  2  on the neck  1  of the cathode ray tube is to evacuate the cathode ray tube, to seal the tip  4 , then, as illustrated in FIG. 1B, to insert the nozzle of a tube  6  filled with paste electric insulator  5  between the stem pins  3 A,  3 B,  3 C, etc. of the stem  2 , and to squeeze out a small amount of the electric insulator  5  from the tube  6  using fingers  7 . 
     The stem base  10  shown in FIG. 1A is placed on the applied electric insulator  5  in a manner that the tip acceptor  13   12  accepts the tip  4  and that the acceptor for high voltage stem pin B accepts the high voltage stem pin  3 B and that each of the throughholes  15 A,  15 B,  15 C, etc. accepts a corresponding stem pin  3 A,  3 B,  3 C, etc. under a slight compression. Then, the configuration becomes the one illustrated in FIG.  2 . The structure assures the electric insulation between the stem pins,  3 A,  3 B,  3 C, etc. 
     As realized in the present color television picture tubes and monitors for image screens and computers, the cathode ray tubes for this equipment are requested to have high brightness and high resolution. To cope with the ever increasing demand, a high voltage is applied not only to the anode of the cathode ray tube but also to the electrode of the electron gun in the cathode ray tube. In particular, a focus electrode is unavoidably applied with a high voltage for improving the focusing characteristic. 
     The outside diameter of the neck  1  receiving the electron gun has an upper limit from the standpoint of saving the deflection power of the electron gun. Consequently, the area of stem  2  is limited. Since such a limited area of the stem  2  receives the stem pins  3 A,  3 B,  3 C, etc., which receive various levels of voltage, the spacing of these stem pins  3 A,  3 B,  3 C, etc. becomes close. 
     For example, a color cathode ray tube for monitoring a graphic display made by SONY CORP. has the pin pitch circle diameter of 15.24 mm, and the number of studded pins is  14  with the pin spacing of 3.42 mm. 
     Among these stem pins,  3 A,  3 B,  3 C, etc., the stem pin  3 A, for example, is called the G 1  pin which is applied with a voltage of 0 to several volts, and the stem pin  3 B is the one for focus electrode which is applied with maximum 9800 volts, and the stem pin  3 C is the one to supply voltage to the convergence electrode and is applied with 0 to 2000 volts. 
     Accordingly, there exists a maximum difference of 9800 volts between the stem pin  3 A and the stem pin  3 B, and a maximum of 8750 volts between the stem pin  3 B and the stem pin  3 C. For a new cathode ray tube, or if the surface of the glass stem  2  is clean, the glass dielectric breakdown voltage (the lead along the stem glass surface) between the stem pins  3 A and  3 B and between the stem pins  3 B and  3 C is not problem. However, a temperature rise or deposition of dust or dirt caused by static charge degrades the dielectric breakdown voltage during operation, or an excess voltage over the dielectric breakdown voltage is often applied to the stem pins, so the dielectric breakdown voltage is not necessarily secured during operation. 
     To assure the necessary dielectric breakdown voltage, conventional technology uses a paste silicone resin of a room-temperature-curing type such as KE03490 made by Shin-Etsu Chemical Co. Ltd. and SE-9168 made by Toray Dow Corning Co., Ltd. That type of resin is hereinafter referred to simply as “RTV resin”. 
     The RTV resin has basic electric characteristics, but it lacks flowability because of its paste property. As illustrated in FIG. 1B, the RTV resin  5  is squeezed out from the tube  6  between the stem pins before mounting the stem base  10  to the stem  2 , then the stem base  10  is attached. Usually, the application of RTV resin  5  is manually carried out. 
     However, the RTV resin raises several problems in that it likely develops bubbles during application. A solvent existing in resin foams at a temperature range of from 80 to 120° C. under the heat generated during the aging stage for activating the cathode of the electron gun, Bubbles also occur during the insertion and withdrawal of connector of an instrument employed several times for inspection in the period between application of the RTV resin and the complete curing, (normally 7 days). Bubbles interfere with the perfect functioning of the electric characteristics of the resin and degrade the dielectric breakdown voltage and, in the worst case, discharge occurs between the stem pins causing damage to the cathode ray tube. 
     OBJECTS AND SUMMARY OF THE INVENION 
     The inventors solved these problems by providing the following inventions. 
     1. The first invention is an electric insulator for inter-electrode insulation such as inter-stem insulation between pins for high voltage service in a cathode ray tube, which electric insulator comprises: 
     (1) An electric insulator comprising a clay-like silicone compound being formed to secure electrical insulation between stem pins or the like for high voltage service in a cathode ray tube. 
     (2) An electric insulator of (1), wherein the silicone compound has a volume resistivity ranging from 1×10 12  to 1×10 15  Ω•cm and a dielectric breakdown strength ranging from 10 to 30 KV/mm. 
     (3) An electric insulator of (1), wherein the clay-like insulator has a degree of plasticity giving a deformation ranging from {fraction (4/10)} to {fraction (7/10)} under a compression of 19 Kg-f. 
     (4) An electric insulator of (3), wherein a thickness of the formed shape is in a range of from 0.8 to 2.0 mm. 
     (5) An electric insulator of (1) through (4), wherein more than one throughhole are formed corresponding to at least a spacing of electrodes of electric equipment and accepting those electrodes penetrating therethrough. 
     (6) An electric insulator of (1) through (5), wherein throughholes corresponding to more than one stem pin including a high voltage stem pin in a cathode ray tube and to a tip an exhaust pipe of the cathode ray tube are formed. 
     2. The second invention is a stem base having throughholes corresponding to more than one stem pin in a cathode ray tube and to a tip of exhaust pipe of an the cathode ray tube, wherein the electric insulator is attached to the stem base while aligning these throughholes with the throughholes of the electric insulator described in (6) of 1. 
     3. The third invention is an inter-stem pin electric insulation device in a cathode ray tube, which comprises: a stem of a cathode ray tube; and the electric insulator described in 1 being attached to the external surface of the stem in a manner being penetrated by more than one stem pin including a high voltage stem pin which is protruding from the external surface of the stem and by a tip of an exhaust pipe of the cathode ray tube; a stem base provided with throughholes, a tip acceptor, and an acceptor for a high voltage stem pin, being placed and fixed in a manner that the stem pins penetrate the throughholes and that the stem base covers the tip at the tip acceptor and that the high voltage stem pin is isolated in the acceptor for the high voltage stem pin. 
     4. The fourth invention is a method for producing a cathode ray tube, which comprises: attaching an electron gun provided with more than one stem pin including a high voltage stem pin and with a stem introducing an exhaust pipe to a neck of a funnel which structures a tube body; welding the periphery of the neck edge with the periphery of the stem; forming a tip and closing it after evacuating the tube body through the exhaust pipe; attaching a clay-like electric insulator consisting of silicone compound which was formed aligning each of the throughholes for receiving the stem pins and the tip of the exhaust pipe; fitting the integrated stem base by penetrating the stem pins and the tip therethrough, and mounting and fixing the stem base to the stem. 
     Accordingly, an electric insulator of this invention suppresses the generation of bubbles described above or further eliminates the bubble formation, completely prevents the leak along the surface which is also described above, secures the electric insulation between high voltage stem pins or the like in a cathode ray tube, and does not damage the cathode ray tube. 
     Since the electric insulator of this invention is a clay-like formed shape, the work for insulating high voltage stem pins or the like from each other in a cathode ray tube is performed at a significantly improved efficiency. 
     In addition, the use of a stem base being attached with the electric insulator of this invention enhances the efficiency of the work for insulating high voltage stem pins or the like from each other. 
     Furthermore, the use of a the stem base of this invention allows a mechanical mounting of an electric insulation device between high voltage stem pins or the like instead of conventional manual work. The mechanical mounting procedure leads to an automatic operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 comprised of FIGS. 1A-1B illustrates the method of electric insulation between stem pins including a high voltage stem pin of the related art. 
     FIG. 1A shows a stem base, and 
     FIG. 1B shows a neck of the cathode ray tube. 
     FIG. 2 comprised of FIGS. 2A-2B illustrates the neck of a cathode ray tube structured in accordance with the method of electrical insulation shown in FIG.  1 . 
     FIG. 2A gives a view of the neck, and 
     FIG. 2B gives the cross sectional view along A—A line in FIG.  2 A. 
     FIG. 3 comprised of FIGS. 3A-3B shows an electric insulator of the first embodiment in the present invention. 
     FIG. 3A gives a view of the electric insulator. 
     FIG. 3B shows the cross sectional view along A—A line of FIG.  3 A. 
     FIG. 4 comprised of FIGS. 4A,  4 B and  4 C illustrates the procedure for attaching the electric insulator of FIG. 3 of the second embodiment in the present invention onto the stem base. 
     FIG. 4A gives a view of the electric insulator of FIG.  3 . 
     FIG. 4B gives a view of the electric insulator viewing from the stem side. 
     FIG. 4C is a stem base attached with an electric insulator of this invention. 
     FIG. 5 comprised of FIGS. 5A,  5 B and  5 C illustrates the structure of an electric insulation device of the present invention. The neck of a cathode ray tube which uses the electric insulator for more than one stem pin including a high voltage stem pin, is shown using the electrical insulator shown in FIG. 1 or the stem base shown in FIG.  4 . 
     FIG. 5A gives a view of the device. 
     FIG. 5B shows the cross sectional view along A—A line in FIG.  5 A. 
     FIG. 5C shows a cross sectional view of the stem of neck structuring the cathode ray tube. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An electric insulator of this invention, an electric insulation device using the electric insulator, and a method for producing a cathode ray tube using the electric insulator are described below referring to FIG.  3  through FIG.  5 . 
     FIG. 3 shows an electric insulator of this invention. FIG. 3A gives a view of the electric insulator, and FIG. 3B shows the cross sectional view along A—A line of FIG.  3 A. 
     FIG. 4 illustrates the procedure for attaching the electric insulator of FIG. 3 onto the stem base. FIG. 4A gives a view of the electric insulator of FIG.  3 . FIG. 4B gives a view of the electric insulator viewing from the stem side. FIG. 4C is a stem base attached with an electric insulator of this invention. 
     FIG. 5 illustrates the structure of an electric insulation device of this invention of the neck of cathode ray tube in which electric insulation between several stem pins including a high voltage stem pin is effected using the electrical insulator shown in FIG. 3 or the stem base shown in FIG.  4 . FIG. 5A gives a view of the device. FIG. 5B shows the cross sectional view along A—A line in FIG.  5 A. FIG. 5C shows a cross sectional view of the stem of neck structuring the cathode ray tube. 
     The components common to those in the figures of the related art, such as the electric device of the high voltage inter-stem pin in a cathode ray tube, have the same reference numbers with each other. 
     The following is the description of an electric insulator of the first embodiment in the present invention. 
     Referring to FIG. 3, the electric insulator  20  of this invention is formed to a disc having a thickness described below. The disc has a throughhole  21  for receiving a tip  4  at the center, and has throughholes  22 A,  22 B,  22 C, etc. for receiving stem pins  3 A,  3 B,  3 C, etc. including the high voltage stem pin  3 B, at an each corresponding position. 
     Those throughholes may be formed at a time when the electric insulator  20  is punched from a large flat electric insulator using a forming die. The punching of the throughhole  21  for the tip is preferably carried out to have a cross slit  23  at the inner periphery of the throughhole  21 . The electric insulator  20  with that type of slit  23  makes the insertion of tip  4  into the throughhole  21  easy and assures close contact of the outer periphery of the tip  4  with the inner periphery of the throughhole  21 , which ensures the electric insulation. 
     The electric insulator  20  is a clay-like silicone compound. An example of that type of silicon compound uses “Putty-stock SMX-5999” made by Fuji Polymer Co. Ltd. as the basic component. By mixing a plasticizer to “Putty-stock SMX-5999”, an electric insulator  20  having an adequate degree of plasticity is obtained. 
     FIG. 3 shows an example of the electric insulator  20  having the tip-throughhole  21 , the pin-throughholes  22 A,  22 B,  22 C, etc., and the slit  23 . An electric insulator may otherwise simply be formed by punching a silicone compound to the outside diameter, and it is pressed to the tip  4  of the neck  1  and to the stem pins  3 A,  3 B,  3 C, etc. to open these throughholes using a compression force, and then mounting it to the stem  2 . Nevertheless, an electric insulator  20  which forms the throughholes shown in FIG. 3 in advance has an advantage that the tip  4  and the stem pins  3 A,  3 B,  3 C, etc. are easily mounted without defecting the shape of the insulator. 
     The inventors carried out further extensive study and invented the stem base  40  with electric insulator, which is the second invention shown in FIG.  4 C. 
     The stem base  40  with electric insulator is formed by attaching the electric insulator  20  shown in FIG. 4A (FIG. 3) to the stem base  30  to integrate them. The material of the stem base  30  may be a high insulation resin such as polycarbonate which is used in prior art. 
     As illustrated in FIG. 4B, the stem base  30  consists of: a tip-throughhole  32  which is opened at the center of the disc base plate  31  and which accepts the tip  4 ; pin-throughholes  33 A,  33 B,  33 C, etc. including for the high voltage stem pin  3 B, which are arranged along the peripheral pitch circle on the base plate  31  and which receive stem pins  3 A,  3 B,  3 C, etc. at each corresponding position; and the tip acceptor  34  and an acceptor for high voltage stem pin  35  locating on the side not facing the stem  2  of the base plate  31  to protect the tip  4  of the neck  1 . 
     The stem base  30  has no skirt  14  which is seen on the stem base  10  of prior art. The skirt  14  may be formed at need. However, this invention uses a clay-like electric insulator  20  and is not the type of paste electric insulator  5 , so there is not possibility of sagging of the insulator. Therefore, no skirt  14  is required in this invention. Moreover, elimination of the skirt  14  allows an easy production of the stem base  40  with the electric insulator, which stem base  40  is described below. 
     The following is the third embodiment of the present invention. The stem base  40  with electric insulator is formed by attaching the electric insulator  20  shown in FIG. 3 to the stem base  30  in advance while aligning each of the tip-throughhole  21 , pin-throughholes  22 A,  22 B,  22 C, etc. with the tip-throughhole  32 , pin-throughholes  33 A,  33 B,  33 C, etc. on the stem base  30 , respectively. In other words, the stem base  40  with electric insulation has an integrated structure of the electric insulator  20  and the stem base  30 . 
     When this type of stem base  40  with electric insulation is prepared in advance, the production line of cathode ray tubes at an assembly plant is shortened, and a special advantage is given in automatic mounting of the stem base  40  with electric insulation to the stem  2  as described before. Furthermore, even if the assembly is carried out manually, the workability should be significantly improved. 
     Accordingly, as illustrated in FIG. 5, the stem base  40  with electric insulation of this invention is attached to the evacuated neck  1  of a cathode ray tube under a compression force while aligning the tip-throughhole  32  with the tip-throughhole  21  on the mating electric insulator  20  and aligning each pin-throughholes  33 A,  33 B,  33 C, etc. with the pin-throughholes  22 A,  22 B,  22 C, etc. on the mating electric insulator  20 , and with the stem pins  3 A,  3 B,  3 C, etc., respectively, and while pressing down on the stem base  40  with electric insulation at the mating state to firmly contact the stem  2 . The compression force is described later. In this manner, the inter-stem insulation is performed using the electric insulation device shown in FIG.  5 A and FIG.  5 B. 
     Otherwise, the electric insulator  20  shown in FIG. 3 may be directly mounted on the stem pins,  3 A,  3 B,  3 C, etc. and the tip  4  of the stem  2 , and may further accept the stem base  30  as shown in FIG. 4B or the stem base  10  of prior art. However, if the stem base  40  with electric insulation of this invention shown in FIG. 2C is used, the mounting can be performed by a robot, which means that the production line of cathode ray tubes is automated. 
     Either electric insulator of this invention may be used to enhance the curing by the heat of cathode aging (80-120° C.) after mounting the electric insulator to the stem  2  at room temperature as described before. Since the electric insulator of this invention has a clay-like property, the amount of included solvent is quite small compared with the paste electric insulator of the prior art. As a result, the generation of bubbles in the curing stage due to the heat is minimized, and the required breakdown voltage is secured. 
     The following is experimental examples of the clay-like silicone compound electric insulator of this invention. 
     Experimental Example 1 
     The clay-like silicone compound used had the following properties. The experiments were conducted with various thickness, T, of the electric insulator  20  shown in FIG.  3 B. 
     1. Volume resistivity: 1×10 14  Ω•cm 
     2. Dielectric breakdown strength: 25 KV/mm 
     3. Diameter of pin-throughhole: 0.97 mm 
     4. Degree of plasticity (Note 1): ½ 
     5. Adhesive force (Note 2): 10 Kg•f 
     6. Thickness: 0.5, 0.8, 1.3, 1.8, 2.0, and 2.3 mm 
     The clay-like silicone compound having the above listed properties was formed in a forming die to prepare the electric insulator  20  having the diameter of 22 mm, the pin-throughhole spacing of 4 mm corresponding to the spacing of stem pins  3 A and  3 B and of stem pins  3 B and  3 C. The electric insulator  20  was mounted to the stem  2  to measure the dielectric breakdown voltage between stem pins. The result is summarized in Table 1. 
     The term “degree of plasticity” means that the rate of shrinking of the sample thickness determined by sandwiching the clay-like silicone compound of 10 mm square between glass plates and by applying a compression force of 10 Kg*f. 
     The term “adhesive force” means the adhesive force determined by sandwiching the sample between a glass plate and the stem base  30  shown in FIG.  4 B and by applying a compression force of 10 Kg•f. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Thickness of electric 
                 0.5 
                 0.8 
                 1.3 
                 1.8 
                 2.0 
                 2.3 
               
               
                 insulator (mm) 
               
               
                 Inter-pin dielectric 
                 10 
                 30 
                 38 
                 45 
                 37 
                 15 
               
               
                 breakdown voltage (KV) 
               
               
                   
               
               
                 The figures of dielectric breakdown voltage are the average of 20 samples.  
               
             
          
         
       
     
     The depth, D, of the recess  2 A on the stem  2  shown in FIG. 5C, which recess generated during the closing stage of the cathode ray tube, was normally in a range of from 0.3 to 0.5 mm. An electric insulator  20  having the thickness of 0.5 mm had a tendency of incapable of absorbing the recess  2 A and degraded the dielectric breakdown voltage. When the thickness of the electric insulator  20  exceeds 2.0 mm, the thickness was too large and a loose mount occurred. In both cases, a preferable thickness of the electric insulator  20  was in a range of from 0.8 to 2.0 mm. 
     Experimental Example 2 
     The clay-like silicone compound used had the following properties. The experiments were conducted with various degree of plasticity of the electric insulator  20  shown in FIG.  3 . 
     1. Volume resistivity: same as in Experimental example 1 
     2. Dielectric breakdown strength: same as in Experimental Example 1 
     3. Diameter of pin-throughhole: same as in Experimental Example 1 
     4. Degree of plasticity: {fraction (2/10)}, {fraction (4/10)}, {fraction (5/10)}, {fraction (6/10)}, {fraction (8/10)} 
     5. Adhesive force: same as in Experimental Example 1 
     6. Thickness: 1.8 mm 
     The clay-like silicone compound having the above listed properties was formed in a forming die to prepare the electric insulator  20  having the diameter of 22 mm, and the pin-throughhole spacing of 4 mm corresponding to the spacing of stem pins  3 A and  3 B and of stem pins  3 B and  3 C. The dielectric electric insulator  20  was mounted to the stem  2  to measure the breakdown voltage between stem pins. The result is summarized in Table 2. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                 Degree of plasticity of electric 
                 2/10 
                 4/10 
                 5/10 
                 7/10 
               
               
                 insulator 
               
               
                 Inter-pin dielectric breakdown 
                 12 
                 35 
                 45 
                 40 
               
               
                 voltage (KV) 
               
               
                   
               
             
          
         
       
     
     The experimental results showed a tendency that an electric insulation having a lower degree of plasticity (excess hardness) could not absorb the recess  2 A of the stem  2  as observed in Experimental example 1, and likely left bubbles in the insulator, and degraded the breakdown voltage. 
     As described above, the electric insulator of this invention induces no degradation of dielectric breakdown voltage between stem pins nor fracture caused by unwelcome phenomena such as the generation of bubbles or irregular application of resin which are the disadvantages of conventional RTV resin. Consequently, the electric insulator of this invention does not suffer a discharge between pins and fully utilizes the electric characteristics inherent to silicon compound. In addition, the electric insulator of this invention can form the pin-throughholes and tip-throughhole simultaneously by punching the form in a forming die, which allows the mass-production of electric insulators which are easy to mount on stems. 
     Furthermore, the stem base with the electric insulator of this invention is easily handled manually, as described before, and is mounted by a mechanical means, and allows an automatic mounting. Accordingly, this invention provides various effects as described above. 
     The detailed description given above used a cathode ray tube as an example. This invention, however, is not limited to the cathode ray tube, and naturally deals with the electric insulation between electrodes of electric equipment such as between electrodes of a high voltage transformer actuating under a high voltage.