Patent Publication Number: US-6903502-B2

Title: Inner shield for color cathode ray tube

Description:
TECHNICAL FIELD 
   The present invention relates to an inner shield for color cathode ray tube. In particular, the present invention relates to an inner shield for color cathode ray tube, which effectively shields the effect of the external magnetic field on electron beams within the cathode ray tube and thus prevents the degradation of color purity. Resultantly, high quality images may be obtained. 
   BACKGROUND ART 
   Generally, in a color cathode ray tube, if any unwanted magnetic field from terrestrial magnetism or external circuits enters the passing zone of three electron beams of three primary colors, blue (B), green (G), and red (R), the three electron beams tend to break away from their original tracks due to the effect of the unwanted magnetic field. This is called miss-landing. The miss-landing causes the degradation of color purity in a color cathode ray tube. For this reason, color cathode ray tubes ordinarily contain an inner shield of a magnetic shielding material inside of the funnel where the three electron beams are easily affected by magnetic fields. 
   The inner shield has the basic structure of the hollow shape. However, such basic structure may not shield external magnetic fields sufficiently. Therefore, further developed inner shields with various shapes and structures have been introduced to shield external magnetic field more appropriately. 
   For example, Korea Patent Application No. 1997-029742 discloses an inner shield for color cathode ray tube. As illustrated in  FIG. 1 , the inner shield  10  comprises long side parts  15 , short side parts  17  and corner parts  19 , which form the large opening part  11  and the small opening part  13 . The long side parts  15  and the short side parts  17  are inclined towards the direction of the tube axis Z. At the small opening part  13 &#39;s side of the long side parts  15  and the short side parts  17 , the triangular extension members  151 ,  171  are connected respectively as one body. Also, at the small opening part  13 &#39;s side of the corner parts  19  between the long side parts  15  and the short side parts  17 , the extension members  191  are connected. In the long side parts  15  and short side parts  17 , the triangular notches  153  and  173  are formed respectively. The notches  193  are also formed in the corner parts  19 . Here, the extension members  151  and notches  153  are for concentrating magnetic flux at the long side parts  15 . Also, the extension members  171  and notches  173  are for concentrating magnetic flux at the short side parts  17 . Furthermore, the extension members  191  and notches  193  are for concentrating magnetic flux at corner parts  19 . 
   Japanese Patent Laid-Open No. Hei 5-159713 also introduces an inner shield. As illustrated in  FIG. 2   a ,  FIG. 2   b , and  FIG. 2   c , the inner shield  20  comprises long side parts  23  and short side parts  24 , which form the large opening part  21  and the small opening part  22 . On the small opening part  22 &#39;s side of the long side parts  23  and the short side parts  24 , recessed parts  29  and  30  are formed respectively. At the four diagonal points of the small opening part  22 , the recessed part  29  makes an angle θ v  with respect to the center axis  25  of the long side part  23 . The recessed part  30  also makes an angle θ v  with respect to the center axis  26  of the short side part  24 . The depth of the recessed parts  29  and  30  is H D -H V . 
   Additionally, Japanese Patent Laid-Open No. Hei 11-354040 also introduces an inner shield. As illustrated in  FIG. 3 , the inner shield  40  comprises long side parts  43  and short side parts  44  to form the large opening part  41  and the small opening part  42 . At the four diagonal points  45  of the small opening part  42 , the recessed parts  46  and  47  are formed on the long side parts  43  and the short side parts  44 , respectively. At the point  45 , the recessed part  46  makes an angle α with respect to the center axis  48  of the long side part  43 . The recessed part  47  makes an angle β with respect to the center axis  49  of the short side part  44  at the point  45 . The long side part  43  makes an angle δ from the bottom surface of the large opening part  41  and the short side part  44  makes an angle δ from bottom surface of the large opening part  41 . The diagonal axis  50  makes an angle ε to the surface of the large opening part  41 . The edge  51  of the diagonal axis  50  at the small opening part  42  side makes an angle ε′(≦ε) to the surface with the depth d 1  or d 2  at a right angle to the tube axis Z. The surface with the depth d 1 , d 2  at a right angle to the tube axis Z forms the angle δ′(≦δ) to the long side parts  43  and the short side parts  44 . 
   Notwithstanding the various shapes and structures of the conventional inner shields, the unwanted magnetic field from terrestrial magnetism or external circuits has not been sufficiently shielded from entering the electron beam passing zone of the color cathode ray tube and miss-landing has frequently occurred. Consequently, the color purity was degraded and it was difficult to obtain high quality images. 
   DISCLOSURE OF INVENTION 
   The purpose of the present invention is to provide an inner shield of a color cathode ray tube, which prevents miss-landing by effectively shielding unwanted electronic field generated from the terrestrial magnetism or external circuits and thus by reducing the path changes of electron beams. 
   Another purpose of the present invention is to provide an inner shield of a color cathode ray tube, which prevents the degradation of color purity and provides high quality images. 
   Another purpose of the present invention is to provide an inner shield of a color cathode ray tube, which improves the manufacture and processing efficiency, and the mass productivity. 
   In order to achieve the above mentioned purposes of the present invention, the inner shield of a color cathode ray tube according to the preferred implementation of the present invention comprises two long side parts facing each other and two short side parts facing each other, which form a small opening part at a electron gun&#39;s side and a large opening part at a panel&#39;s side. 
   The present invention, further comprises a plurality of first recessed parts recessed for a given depth at one or more slopes from each of diagonal points of said long side parts at a small opening part&#39;s side towards a large opening part&#39;s side of said long side parts; and a plurality of second recessed parts recessed for a given depth in a round shape in connection with said first recessed parts, wherein said slopes are corresponding to the ratio of a length of said first recessed parts in the direction of center axis of said long side parts to a length of said first recessed parts at the right angle to center axis of said long side parts. 
   Preferably, the absolute value of said slopes become smaller as said first recessed parts become far from said small opening part&#39;s side of said long side parts and close to said large opening part&#39;s side of said long side parts. 
   Preferably, each of said first recessed parts may be composed of a first inclined part with a first slope and a second inclined part with a second slope, an absolute value of said second slope is smaller than that of said first slope. Said first slope of said first inclined part has an infinite value. 
   Preferably, said second recessed parts may be in a U-shape. 
   Preferably, the present invention further comprises a plurality of third recessed parts recessed for a given depth at a third slope from each of diagonal points of said short side parts at said small opening part&#39;s side towards said large opening part&#39;s side of said short side parts, wherein said third slope is the ratio of a length of said third recessed part in the direction of center axis of said short side parts to a length of said third recessed part at the right angle to center axis of said short side parts; and a plurality of fourth recessed parts recessed at a fourth slope of 0 in connection with said third recessed parts, wherein said third and fourth slopes are ratios of a length of said third and fourth recessed parts in the direction of center axis of said short side parts to a length of said third and fourth recessed parts at the right angle to center axis of said short side parts. 
   Preferably, said third slope of said third recessed parts may be determined to be an infinite value. 
   Preferably, the present invention may comprise said third recessed parts recessed in a V-shape from each of diagonal points of said short side parts at said small opening part&#39;s side towards said short side part&#39;s large opening part&#39;s side. 
   Preferably, each of pointed parts of said third recessed parts at said large opening part&#39;s side has a given curvature. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a diagram illustrating an inner shield for color cathode ray tube according to the conventional technology. 
       FIG. 2   a  is a diagram illustrating another inner shield for color cathode ray tube according to the conventional technology. 
       FIG. 2   b  is a diagram illustrating a long side part of the inner shield illustrated in  FIG. 2   a.    
       FIG. 2   c  is a diagram illustrating a short side part of the inner shield illustrated in  FIG. 2   a.    
       FIG. 3   a  is a diagram illustrating still another inner shield for color cathode ray tube according to the conventional technology. 
       FIG. 3   b  is a diagram illustrating a long side part of the inner shield illustrated in  FIG. 3   a.    
       FIG. 3   c  is a diagram illustrating a short side part of the inner shield illustrated in  FIG. 3   a.    
       FIG. 4  is a diagram illustrating a color cathode ray tube in which the inner shield for color cathode ray tube according to the present invention is applied. 
       FIG. 5   a  is a diagram illustrating an inner shield for color cathode ray tube according to the first preferred embodiment of the present invention. 
       FIG. 5   b  is a diagram illustrating a long side part of the inner shield of  FIG. 5   a.    
       FIG. 5   c  is a diagram illustrating a short side part of the inner shield of  FIG. 5   a.    
       FIG. 6   a  is a diagram illustrating an inner shield for color cathode ray tube according to the second preferred embodiment of the present invention. 
       FIG. 6   b  is a diagram illustrating a long side part of the inner shield of  FIG. 6   a.    
       FIG. 6   c  is a diagram illustrating a short side part of the inner shield of  FIG. 6   a.    
       FIG. 7   a  is a diagram illustrating an inner shield for color cathode ray tube according to the third preferred embodiment of the present invention. 
       FIG. 7   b  is a diagram illustrating a long side part of the inner shield of  FIG. 7   a.    
       FIG. 7   c  is a diagram illustrating a short side part of the inner shield of  FIG. 7   a.    
       FIG. 8   a  is a diagram illustrating an inner shield for color cathode ray tube according to the fourth preferred embodiment of the present invention. 
       FIG. 8   b  is a diagram illustrating a long side part of the inner shield of  FIG. 8   a.    
       FIG. 8   c  is a diagram illustrating a short side part of the inner shield of  FIG. 8   a.    
       FIG. 9   a  is a diagram illustrating an inner shield for color cathode ray tube according to the fifth preferred embodiment of the present invention. 
       FIG. 9   b  is a diagram illustrating a long side part of the inner shield of  FIG. 9   a.    
       FIG. 9   c  is a diagram illustrating a short side part of the inner shield of  FIG. 9   a.    
       FIG. 10   a  is a diagram illustrating an inner shield for color cathode ray tube according to the sixth preferred embodiment of the present invention. 
       FIG. 10   b  is a diagram illustrating a long side part of the inner shield of  FIG. 10   a.    
       FIG. 10   c  is a diagram illustrating a short side part of the inner shield of  FIG. 10   a.    
       FIG. 11  is a table showing the landing changes in the case that the inner shield of the present invention and the conventional inner shield are turned to the northern direction. 
       FIG. 12  is a table showing the landing changes in the case that the inner shield of the present invention and the conventional inner shield are turned to the southern direction. 
       FIG. 13  is a table showing the landing changes in the case that the inner shield of the present invention and the conventional inner shield are turned to the western direction. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Reference will now be made in detail to the inner shield for color cathode ray tube according to the preferred embodiments of the present invention as illustrated in the accompanying drawings. 
     FIG. 4  is a diagram illustrating a color cathode ray tube in which the inner shield for color cathode ray tube according to the present invention is applied. 
   Referring to  FIG. 2 , the color cathode ray tube  60  has the panel  61  of the glass material and the funnel  62  of the glass material attached to the panel  61  as one body. On the inner surface of the panel  61  is provided the fluorescent screen  63  composed of fluorescent layers of the three colors, red, blue and green. Facing the fluorescent screen  63 , the shadow mask  64  is located inside of the panel  61 . The shadow mask  64  is composed of the mask main body  641  in which electron beam passing holes are formed and the frame  643  attached around the mask main body  641 . In the neck  621  of the funnel  62 , the electron gun  65  emitting three electron beams  65 R,  65 G,  65 B is located. The deflection yoke  66  is installed outside of the boundary between the neck  621  and the body part  623  of the funnel  62 . The inner shield  67 , which shields the electron beams  65 R,  65 G,  65 B emitted from the electron gun  65  from the unwanted magnetic field resulting from terrestrial magnetism or external circuits, is located inside of the funnel  62 . 
     FIG. 5   a  is a diagram illustrating an inner shield for color cathode ray tube according to the first preferred embodiment of the present invention.  FIG. 5   b  is a diagram illustrating a long side part of the inner shield of  FIG. 5   a .  FIG. 5   c  is a diagram illustrating a short side part of the inner shield of  FIG. 5   a.    
   Referring to  FIG. 5   a ,  FIG. 5   b , and  FIG. 5   c , the inner shield  670  according to the first preferred embodiment of the present invention is a hollow body comprising two long side parts  671  facing each other and two short side parts  672  facing each other. The large opening part  673  of the hollow body—the large opening part to face the shadow mask  64  shown in FIG.  4 —is created in the shape of a large rectangular form. The small opening part  674  of the hollow body—the small opening part to face the electron gun  65  shown in FIG.  4 —is created in the shape of a small rectangular form. The recessed parts  675  to concentrate magnetic flux on the long side parts  671  are created on the small opening part  674 &#39;s side of the long side parts  671  respectively. The recessed parts  676  to concentrate magnetic flux on the corner parts  677  between the long side parts  671  and the short side parts  672  are created on the small opening part  674 &#39;s side of the short side parts  672  respectively. 
   The recessed parts  675  of the long side parts  671  comprise the first recessed parts  675   a  and the second recessed parts  675   b . The first recessed part  675   a  may contain two inclined parts, the first inclined part  675   c  and the second inclined part  675   d  for example. The first inclined part  675   c  of the said first recessed part  675   a  is recessed for the first depth D 1  at the first slope from the four points  678  of the long side part  671  at the small opening part  674 &#39;s side towards the large opening part  673  of the relevant long side part  671 . The second inclined part  675   d  of the first recessed part  675   a  is recessed for the second depth D 2  at the second slope which is smaller than the first slope in connection with the first inclined part  675   c  of the first recessed part  675   a.    
   Here, the first and second slope is the absolute value of the ratio of the length of the first and second inclined part  675   c ,  675   d  from the relevant point  678  at the right angle to the long side part  671 &#39;s center axis  681  i.e., the horizontal component of the first and second inclined part to the length of the first and second inclined part  675   c ,  675   d  in the direction parallel to the long side part  671 &#39;s center axis  681  i.e., the vertical component of the first and second inclined part. The angles θ 1 , θ 2  are the angles with respect to the axis  683  at the points  678  and are greater than 0 degree and smaller than 90 degrees. θ 2  is greater than θ 1 . 
   The second recessed part  675   b  is recessed for the third depth D 3  towards the large opening part  673  of the long side part  671  in connection with the second inclined part  675   d  of the first recessed part  675   a  in a round shape for example, U-shape. The U-shaped second recessed part  675   b  is formed to concentrate more magnetic flux on the long side part  671  than on the short side part  672 . 
   The first recessed part  675   a  is illustrated to have two inclined parts  675   c  and  675   d  for the convenience of explanation. However, it is apparent that the first recessed part may actually have three or more inclined parts. 
   The recessed part  676  of the short side part  672  is composed of the third recessed part  676   a  and the fourth recessed part  676   b . The third recessed part  676   a  is recessed for the fourth depth D 4  at the third slope from the four points of the short side part  672  at the small opening part  674 &#39;s side towards the large opening part  673  of the relevant short side part  672 . The fourth recessed part  676   b  is recessed at the fourth slope of the value 0 in connection with the third recessed part  676   a.    
   Here, the third and fourth slope is the absolute value of the ratio of the length of the third and fourth recessed part  676   a ,  676   b  from the relevant points  678  at the right angle to the short side part  672 &#39;s center axis  691  i.e., the horizontal component of the third and fourth recessed part to the length of the third and fourth recessed part  676   a ,  676   b  in the direction  693  parallel to the long side part  672 &#39;s center axis  691  i.e., the vertical component of the third and fourth recessed part. The angle θ 4  is the angle with respect to the axis  693  at the points  678  and is greater than 0 degree and smaller than 90 degrees. 
   Here, it is preferable that the depth of the long side part  671 &#39;s recessed part  675  i.e., the sum of the first depth D 1 , the second depth D 2  and the third depth D 3  is in the range of 50 to 70% of the height of the long side part  671 . Also, it is preferable that the depth of the short side part  672 &#39;s recessed part  676 , the fourth depth D 4 , is in the range of 20 to 40% of the height of the short side part  672 . 
     FIG. 6   a  is a diagram illustrating an inner shield for color cathode ray tube according to the second preferred embodiment of the present invention.  FIG. 6   b  is a diagram illustrating a long side part of the inner shield of  FIG. 6   a .  FIG. 6   c  is a diagram illustrating a short side part of the inner shield of  FIG. 6   a . The same codes are assigned to the parts that are same as those in the first preferred embodiment of the present invention in their structures and functions. 
   Referring to  FIG. 6   a ,  FIG. 6   b  and  FIG. 6   c , the inner shield  770  according to the second preferred embodiment of the invention has the recessed part  685  modified from the long side part  671 &#39;s recessed part  675  of the first preferred embodiment of the present invention and has the same recessed part  676  of the short side part  672  as the first preferred embodiment. The recessed part  685  of the long side part  671  is composed of the first recessed part  685   a  and the second recessed part  685   b . The first recessed part  685   a  contains two inclined parts, the first inclined part  685   c  and the second inclined part  685   d  for example. The first inclined part  685   c  of the first recessed part  685   a  is recessed for the first depth D 1  at the first slope from the four points  678  of the long side part  671  at the small opening part  674 &#39;s side towards the large opening part  673  of the relevant long side part  671 . The second inclined part  685   d  of the first recessed part  685   a  is recessed for the second depth D 2  at the second slope which is smaller than the first slope in connection with the first inclined part  685   c  of the first recessed part  685   a.    
   Here, the first and second slope is the absolute value of the ratio of the length of the first and second inclined part  685   c ,  685   d  from the relevant point  678  at the right angle to the long side part  671 &#39;s center axis  681  i.e., the horizontal component of the first and second inclined part to the length of the first and second inclined part  685   c ,  685   d  in the direction parallel to the long side part  671 &#39;s center axis  681  i.e., the vertical component of the first and second inclined part. The first slope of the first inclined part  685  has the infinite value. The angle θ 2  is the angle with respect to the axis  683  at the points  678  and is greater than 0 degree and smaller than 90 degrees. The corresponding angle of the first inclined part  685   c  is 0 degree. 
   The second recessed part  685   b  is recessed for the third depth D 3  towards the large opening part  673  of the long side part  671  in connection with the second inclined part  685   d  of the first recessed part  685   a  in a round shape for example, U-shape. The U-shaped second recessed part  685   b  is formed to concentrate more magnetic flux on the long side part  671  than to the short side part  672 . 
   On the other hand, the short side part  672 &#39;s recessed part  676  is composed of the third recessed part  676   a  and the fourth recessed part  676   b . The third and fourth recessed parts  676   a ,  676   b  are structured in the same way as the third and fourth recessed parts of the first preferred embodiment of the present invention. Thus, the detailed explanation of the third and fourth recessed parts  676   a ,  676   b  is omitted in this part. 
     FIG. 7   a  is a diagram illustrating an inner shield for color cathode ray tube according to the third preferred embodiment of the present invention.  FIG. 7   b  is a diagram illustrating a long side part of the inner shield of  FIG. 7   a .  FIG. 7   c  is a diagram illustrating a short side part of the inner shield of  FIG. 7   a . The same codes are assigned to the parts that are same as those in the first preferred embodiment of the present invention in their structures and functions. 
   Referring to  FIG. 7   a ,  FIG. 7   b  and  FIG. 7   c , the inner shield  870  according to the third preferred embodiment of the present invention has the recessed part  695  modified from the long side part  671 &#39;s recessed part  675  of the first preferred embodiment of the present invention and has the same recessed part  676  of the short side part  672  as the first preferred embodiment of the present invention. The recessed part  695  of the long side part  671  is composed of the first recessed part  695   a  and the second recessed part  695   b . The first recessed part  695   a  contains only one inclined part—the first inclined part  695   c . The first inclined part  695   c  of the first recessed part  695   a  is recessed for the fifth depth D 5  at the first slope from the four points  678  of the long side part  671  at the small opening part  674 &#39;s side towards the large opening part  673  of the relevant long side part  671 . 
   Here, the first slope is the absolute value of the ratio of the length of the first inclined part  695   c  from the relevant point  678  at the right angle to the long side part  671 &#39;s center axis  681  i.e., the horizontal component of the first inclined part to the length of the first inclined part  695   c  in the direction  683  parallel to the said long side part  671 &#39;s center axis  681  i.e., the vertical component of the said first inclined part. The angle θ 5  is the angle with respect to the axis  683  at the points  678  and is greater than 0 degree and smaller than 90 degrees. 
   The second recessed part  695   b  is recessed for the third depth D 3  towards the large opening part  673  of the long side part  671  in connection with the first inclined part  695   c  of the first recessed part  695   a  in a round shape for example, U-shape. The U-shaped second recessed part  695   b  is formed to concentrate more magnetic flux on the long side part  671  than to the short side part  672 . Here, it is preferable that the depth of the long side part  671 &#39;s recessed part  695  i.e. the sum of the fifth depth D 5  and the third depth D 3  is in the range of 50 to 70% of the height of the long side part  671 . 
   On the other hand, the short side part  672 &#39;s recessed part  676  is composed of the third recessed part  676   a  and the fourth recessed part  676   b . The third and fourth recessed parts  676   a ,  676   b  are structured in the same way as the third and fourth recessed parts of the first preferred embodiment of the present invention. Thus, the detailed explanation of the third and fourth recessed parts  676   a ,  676   b  is omitted in this part. 
   As described above, the inner shields according to the first, second and third embodiment of the present invention comprise the first recessed part at the long side part&#39;s small opening part&#39;s side with one or more slopes and the second recessed part of the U-shape in connection with the first recessed part. As a result, the inner shield of the present invention may cause unwanted magnetic field arising from the terrestrial magnetism or external circuits to concentrate at the long side parts and corner parts rather than at the short side parts. Therefore, the unwanted magnetic field arising from the terrestrial magnetism or external circuits may sufficiently be shielded within the electron beams&#39; passing zone in the inner shield. 
     FIG. 8   a  is a diagram illustrating an inner shield for color cathode ray tube according to the fourth preferred embodiment of the present invention.  FIG. 8   b  is a diagram illustrating a long side part of the inner shield of  FIG. 8   a .  FIG. 8   c  is a diagram illustrating a short side part of the inner shield of  FIG. 5   a . The same codes are assigned to the parts that are same as those in the first preferred embodiment of the present invention in their structures and functions. 
   Referring to  FIG. 8   a ,  FIG. 8   b  and  FIG. 8   c , the inner shield  970  according to the fourth preferred embodiment of the present invention has the recessed part  686  modified from the short side part  672 &#39;s recessed part  676  of the first preferred embodiment of the present invention and has the same recessed part  675  of the long side part  671  as the first preferred embodiment of the present invention. The recessed part  686  of the short side part  672  is composed of the third recessed part  686   a  and the fourth recessed part  686   b . The third recessed part  686   a  is recessed for the sixth depth D 6  at the third slope from the four points  678  of the short side part  672  at the small opening part  674 &#39;s side towards the large opening part  673  of the relevant short side part  672 . The fourth recessed part  686   b  is recessed at the fourth slope 0 in connection with the third recessed part  686   a.    
   Here, the third and fourth slope is the absolute value of the ratio of the length of the third and fourth recessed part  686   a ,  686   b  from the relevant point  678  at the right angle to the short side part  672 &#39;s center axis  691  i.e., the horizontal component of the third and fourth inclined part to the length of the third and fourth inclined part  686   a ,  686   b  in the direction parallel to the short side part  672 &#39;s center axis  691  i.e., the vertical component of the third and fourth inclined part. The third slope of the third recessed part  686   a  has the infinite value. The angle of the third recessed part  686   a  is 0 degree in the figure. The angle of 0 degree is the angle with respect to the axis  693  at the points  678  of the short side parts  672 . Here, it is preferable that the depth of the short side part  672 &#39;s recessed part  686  i.e., the sixth depth D 6  is in the range of 20 to 40% of the height of the short side part  672 . 
   On the other hand, the recessed part  675  of the long side part  671  is composed of the first recessed part  675   a  including the first and second inclined parts  675   c ,  675   d  and the second recessed part  675   b . The first recessed part  675   a  and the second recessed part  675   b  are structured in the same way as the first and second recessed parts of the first preferred embodiment of the present invention. In order to avoid repetitious explanation, the detailed explanation of the recessed part  675  is omitted in this section. In the figure, only the recessed part  675  is illustrated for the convenience of the explanation. However, it is apparent that the recessed parts  685 ,  695  of the second and third preferred embodiment of the present invention may be adopted instead of the recessed part  675 . 
     FIG. 9   a  is a diagram illustrating an inner shield for color cathode ray tube according to the fifth preferred embodiment of the present invention.  FIG. 9   b  is a diagram illustrating a long side part of the inner shield of  FIG. 9   a .  FIG. 9   c  is a diagram illustrating a short side part of the inner shield of  FIG. 9   a . The same codes are assigned to the parts that are same as those in the first preferred embodiment of the present invention in their structures and functions. 
   Referring to  FIG. 9   a ,  FIG. 9   b  and  FIG. 9   c , the inner shield  980  according to the fifth preferred embodiment of the present invention has the third recessed part  696  modified from the short side part  672 &#39;s recessed part  676  of the first preferred embodiment of the present invention and has the same recessed part  675  of the long side part  671  as the first preferred embodiment of the present invention. The third recessed part  696  of the short side part  672  is recessed for the seventh depth D 7  at the third slope from the four points  678  of the short side part  672  at the small opening part  674 &#39;s side towards the large opening part  673  of the relevant short side part  672 , thus creating the V-shape. The third recessed part  696  at the large opening part  673 &#39;s side has a sharp point. Here, the V-shape third recessed part  696  is created in order to concentrate more magnetic flux at the corner parts  671  than at the short side parts  672 . 
   Here, the third slope is the absolute value of the ratio of the length of the third recessed part  696  from the relevant point  678  at the right angle to the short side part  672 &#39;s center axis  691  i.e., the horizontal component of the third inclined part to the length of the third recessed part  696  in the direction  693  parallel to the short side part  672 &#39;s center axis  691  i.e., the vertical element of the third inclined part. The angle θ 5  is the angle with respect to the axis  693  at the points  678 . Here, it is preferable that the depth of the short side part  672 &#39;s recessed part  696  i.e., the seventh depth D 7  is in the range of 20 to 40% of the height of the short side part  672 . 
   On the other hand, the recessed part  675  of the long side part  671  is composed of the first recessed part  675   a  including the first and second inclined parts  675   c ,  675   d  and the second recessed part  675   b . The first recessed part  675   a  and the second recessed part  675   b  are structured in the same way as the first and second recessed parts of the first preferred embodiment of the present invention. In order to avoid repetitious explanation, the detailed explanation of the recessed part  675  is omitted in this section. In the figure, only the recessed part  675  is illustrated for the convenience of the explanation. However, it is apparent that the recessed parts  685 ,  695  of the second and third preferred embodiment of the present invention may be adopted instead of the recessed part  675 . 
     FIG. 10   a  is a diagram illustrating an inner shield for color cathode ray tube according to the sixth preferred embodiment of the present invention.  FIG. 10   b  is a diagram illustrating a long side part of the inner shield of  FIG. 10   a .  FIG. 10   c  is a diagram illustrating a short side part of the inner shield of  FIG. 9   a . The same codes are assigned to the parts that are same as those in the fifth preferred embodiment of the present invention in their structures and functions. 
   Referring to  FIG. 10   a ,  FIG. 10   b  and  FIG. 10   c , the inner shield  990  according to the sixth preferred embodiment of the present invention has the third recessed part  706  modified from the short side part  672 &#39;s third recessed part  696  of the fifth preferred embodiment of the present invention and has the same recessed part  675  of the long side part  671  as the first preferred embodiment of the present invention. The third recessed part  706  of the short side part  672  is recessed for the eighth depth D 5  at the third slope from the four points  678  of the short side part  672  at the small opening part  674 &#39;s side towards the large opening part  673  of the relevant short side part  672 , thus creating the V-shape. 
   Here, the third slope is the absolute value of the ratio of the length of the third recessed part  706  at the right angle to the short side part  672 &#39;s center axis  691  i.e., the horizontal component of the third inclined part to the length of the third recessed part  706  in the direction parallel to the short side part  672 &#39;s center axis  691  i.e., the vertical component of the third inclined part. The angle θ 5  is the angle with respect to the axis  693  at the points  678 . Here, it is preferable that the depth of the short side part  672 &#39;s recessed part  706  i.e., the eighth depth D 8  is in the range of 20 to 40% of the height of the short side part  672 . 
   Although the principle that magnetic flux concentrates on the pointed or sharp angled part was applied in the third recessed part  706 , it is difficult to successfully form the pointed part  697  of the fifth preferred embodiment of the present invention at the time of manufacturing an inner shield. Furthermore, even if the pointed part is successfully formed, the pointed part may easily be bent or folded during the mass production. Thus, in order to improve the work efficiency, it is preferable to modify the pointed part  697  to become a rounded pointed part  707  with a certain curvature R. 
   On the other hand, the recessed part  675  of the long side part  671  is composed of the first recessed part  675   a  including the first and second inclined parts  675   c ,  675   d  and the second recessed part  675   b . The first recessed part  675   a  and the said second recessed part  675   b  are structured in the same way as the first and second recessed parts of the first preferred embodiment of the present invention. In order to avoid repetitious explanation, the detailed explanation of the recessed part  675  is omitted in this section. In the figure, only the recessed part  675  is illustrated for the convenience of the explanation. However, it is apparent that the recessed parts  685 ,  695  of the second and third preferred embodiment of the present invention may be adopted instead of the recessed part  675 . 
   As described above, the inner shields according to the fourth, fifth and sixth embodiment of the present invention contain the V-shape recess in the short side part at the small opening part&#39;s side. As a result, such inner shields may cause unwanted magnetic field arising from the terrestrial magnetism or external circuits to concentrate at the long side parts and corner parts rather than at the short side parts. Therefore, the unwanted magnetic field arising from the terrestrial magnetism or external circuits may sufficiently be shielded within the electron beams&#39; passing zone in the inner shield. 
   For the examination of the characteristics of the inner shield according to the present invention, among the various inner shields described above, the one with the long side part&#39;s recessed part having the U-shape second recessed part and the short side part&#39;s recessed part of the V-shape was selected. Then, a color cathode ray tube adopting the selected inner shield was manufactured and the changes in the landing of three electron beams red, blue and green were measured in the case that the said tube was turned to the southern, northern and western directions respectively. 
   In other words, in the case of the northern turn, red, blue and green electronic beams&#39; landing changes were measured horizontally H and vertically V at the top-left position TL, top-right position TR, top-center position TC, bottom-left position BL, bottom-right position BR, bottom-center position BC, middle-left position ML and middle-right position MR. Also, the landing changes of competitors&#39; inner shields A, B and C were measured in the same way. The results of the foregoing measurement are illustrated in FIG.  11 . 
   In the case of the southern turn, red, blue and green electron beams&#39; landing changes were measured horizontally H and vertically V at the top-left position TL, top-right position TR, top-center position TC, bottom-left position BL, bottom-right position BR, bottom-center position BC, middle-left position ML and middle-right position MR. Also, the landing changes of competitors&#39; inner shields A, B and C were measured in the same way. The results of the foregoing measurement are illustrated in FIG.  12 . 
   Furthermore, in the case of the western turn, red, blue and green electronic beams&#39; landing changes were measured horizontally H and vertically, V at the top-left position TL, top-right position TR, top-center position TC, bottom-left position BL, bottom-right position BR, bottom-center position BC, middle-left position ML and middle-right position MR. Also, the landing changes of competitors&#39; inner shields A, B and C were measured in the same way. The results of the foregoing measurement are illustrated in FIG.  13 . 
   As shown in  FIG. 11 ,  FIG. 12 , and  FIG. 13 , the inner shield I according to the present invention has the superior characteristics to the conventional competitors&#39; inner shields A, B and C. 
   Resultantly, in the inner shield according to the present invention, the unwanted magnetic field arising from the terrestrial magnetism or external circuits may be concentrated at the long side parts and corner parts rather than at the short side parts. Therefore, the unwanted magnetic field arising from the terrestrial magnetism or external circuits may sufficiently be shielded within the electron beams&#39; passing zone in the inner shield of the present invention. 
   Consequently, the present invention may prevent miss-landing by reducing the electron beams&#39; break-away from the normal tracks. Furthermore, the degradation of the color purity may be prevented and thus the high-quality images may be obtained. 
   INDUSTRIAL APPLICABILITY 
   As explained above, the inner shield for color cathode ray tube according to the present invention comprises a recessed part with one or more inclined parts and a U-shape recessed part at the small opening part&#39;s side of the long side part. Furthermore, at the small opening part&#39;s side of the short side part, a V-shape recessed part is formed. 
   As a result, more magnetic flux is concentrated at the long side parts and corner parts than at the short side parts. Thus, red, blue and green electron beams may sufficiently be shielded from the unwanted magnetic field arising from the terrestrial magnetism or external circuits. Accordingly, miss-landing is prevented and, furthermore, the color purity degradation is prevented and the high-quality images may be obtained. 
   The present invention is not limited to the attached drawings and detailed description of the present invention set forth above. Rather, it is apparent to the persons with ordinary knowledge in the relevant field that the present invention may be modified and changed in various manners within the extent not exceeding the essence of the present invention claimed in the following claims.