Tokyo Shibaura Elec. Co., Ltd. v. Zenith Radio Corp.

• Decision Date: 07 January 1977
• Docket Number: No. 76-1237,76-1237
• Citation: 548 F.2d 88
• Parties: TOKYO SHIBAURA ELECTRIC CO. LTD., et al. v. ZENITH RADIO CORPORATION, Appellant.
• Court: U.S. Court of Appeals — Third Circuit

Page 88

548 F.2d 88

193 U.S.P.Q. 73

TOKYO SHIBAURA ELECTRIC CO. LTD., et al. v. ZENITH RADIO CORPORATION, Appellant.

No. 76-1237.

United States Court of Appeals Third Circuit.

Argued Oct. 8, 1976.

Decided Jan. 7, 1977.

Thomas S. Lodge, Wilmington, Del., Dugald S. McDougall, McDougall, Hersh & Scott, Chicago, Ill., for appellant.

James M. Tunnell, Jr., Morris, Nichols, Arsht & Tunnell, Wilmington, Del., Edward F. McKie, Jr., Dale H. Hoscheit, Schuyler, Birch, Swindler, McKie & Beckett, Washington, D.C., for appellee.

Before VAN DUSEN and ROSENN, Circuit Judges, and CAHN, ^* District Judge.

OPINION OF THE COURT

ROSENN, Circuit Judge.

The quest to improve the brightness and contrast of the color television picture tube forms the backdrop of this appeal. The appellees, a Japanese company and its United States subsidiaries (hereinafter referred to collectively as "Toshiba"), brought an action against Zenith Radio Corporation ("Zenith") seeking a declaration of the invalidity, non-infringement, and unenforceability of Zenith's United States Letters Patent No. 3,146,368 ("the '368 patent"). ¹ Zenith counterclaimed, alleging that Toshiba's Blackstripe picture tube infringed the '368 patent. The district court decided that Claims 1, 2, 3, 4, 5, 6, and 9 of the '368 patent were not invalid for lack of novelty or because of the manner in which they were obtained, and that, assuming the patent to be valid and enforceable, those claims were infringed by the Blackstripe tube. The court also determined, however, that the color picture tube concepts embodied in the '368 patent were obvious in view of the prior art, and that the patent was therefore invalid under 35 U.S.C. § 103 (1970). ² Tokyo Shibaura Electric Co. v. Zenith Radio Corp., 404 F.Supp. 547 (D. Del. 1975). The sole issue presented on appeal is whether Zenith's patent is invalid for obviousness. ³ After a thorough review of the record, we conclude that it is, and affirm the judgment of the district court.

I.

The facts of this case, including a comprehensive exposition of the state of color picture tube technology prior to the '368 patent, are recited with commendable clarity in the reported opinion of the district court. 404 F.Supp. at 550-58. We shall therefore sketch only the essential details.

In a conventional color tube produced commercially prior to the '368 patent, the inside surface of the viewing screen is coated with tangent triads of phosphor dots. Each triad is composed of phosphors chemical materials which, when bombarded by electron beams emanating from a cluster of three guns mounted in the neck of the tube, emit the colors of either red, green, or blue. Any visible color can be reproduced by bombarding the appropriate combination of these phosphors, and the brightness of the emitted colors can be regulated by varying the intensity of bombardment.

Accuracy of color reproduction requires that the electron beam bombard the proper phosphor at the proper time with the proper intensity. Every commercially available color television set today employs a "shadow mask" to enhance precision in color selection. The mask, a thin metal membrane positioned immediately behind and parallel to the screen, is perforated with a large number of small apertures; each aperture is located directly behind the center of a triad of tangent phosphor dots, one emitting red light, one blue, and one green. In a shadow mask tube, each of the three electron guns emits electrons intended to strike only the phosphors of a given color. ⁴ The guns, the mask, and the screen are so situated that the beams from the three guns converge at the mask, with each beam at a different angle. As a consequence, only so much of each beam as will strike the proper phosphor is able to penetrate the mask. The following cross-sectional view illustrates the design of a shadow mask tube: ⁵

NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE

Ideally, the landing areas of the electron beams would be exactly coincidental with the proper phosphor areas on the screen. Perfect registration of the electron beams, however, demands a precision of mask and screen alignment that is unattainable in a mass production context. In order to achieve accurate color reproduction, it is therefore necessary to incorporate a tolerance for fabrication and alignment errors into the design of the tube.

All tubes sold commercially prior to the '368 patent allowed for manufacturing errors by making the apertures in the shadow mask slightly smaller than the phosphor dots on the screen. The beam landing areas on the screen, in turn, were smaller than the phosphor dots that they were intended to strike. A "guardband" surrounding the beam landing area within the phosphor resulted, ensuring accurate color reproduction even if a beam wandered slightly because of misalignment of the mask and screen. This method of providing an allowance for manufacturing errors is known today as "positive tolerance."

The conventional shadow mask tube had several disadvantages. For example, the phosphors that were not being bombarded at any given moment reflected room light, reducing contrast. Because the phosphor dots lay tangent to one another, they virtually covered the screen and reflected a large amount of room light back at the television viewer. Contrast could be improved by constructing the viewing screen of gray, light-absorbing glass, but this had the side effect of reducing picture brightness.

The '368 patent solved some of the most obvious problems of the conventional shadow mask tube. Claim 1 of the patent describes a shadow mask tube in which the phosphor areas on the screen are "spaced from all adjacent such areas by intermediate light absorbing areas," and in which the mask itself is perforated by apertures that are larger than the phosphor dots. Such a tube provides better picture contrast than the conventional tube: Because less screen area is covered by phosphors, and because a significant portion of the screen is covered by black, light-absorbing material, much less room light is reflected back at the viewer. Moreover, the increased contrast permits the use of a clear glass viewing screen, which improves brightness.

To use the positive tolerance concept in the '368 tube would adversely affect brightness. The spaced phosphors in the '368 design are reduced in size to accommodate the surrounding light-absorbing material; if the electron beam landing areas were made even smaller than the phosphor dots to provide positive tolerance, the illuminable phosphor areas on the screen would be much less than in a conventional tube. The '368 patent, however, recognizes that the positive tolerance system of ensuring accurate color reproduction is not necessary when each phosphor dot is surrounded by black material. The patent teaches that that material provides a built-in guardband which protects against slightly wandering electron beams. With that guardband, the beam landing areas can be larger than the phosphor dots. In fact, even though the dots in a '368 tube are smaller than the dots in a conventional tube, the beam landing area made possible by the black guardband can be used to maintain the brightness level of a conventional tube. (If the size of the phosphor dot in a '368 tube is reduced to the size of the beam landing area in a conventional tube, the size of the landing area in the '368 tube can be increased to the size of the phosphor dot in a conventional tube. The illuminated areas of the phosphors in both tubes are then the same.) When the clear glass viewing screen disclosed by the '368 patent is used, brightness exceeds that of a conventional tube. The system of electron beam landing areas larger than the phosphor dots is known today as "negative tolerance." ⁶

The district court determined that the two most relevant prior art references were a patent issued to Frank J. Bingley in July, 1958, ⁷ and an article by Sam H. Kaplan ⁸ entitled "Theory of Parallax Barriers" published in the July, 1952 issue of the Journal of the Society of Motion Picture and Television Engineers. The Bingley patent is concerned primarily with index tubes rather than shadow mask tubes. In index tubes, the phosphors are deposited on the viewing screen in stripes. One electron gun sweeps the screen with a single beam that is unimpeded by a shadow mask; the beam bombards the phosphors of each color in turn. ⁹ The Bingley patent, however, also deals in part with shadow mask tubes. The patent discloses a shadow mask tube with spaced phosphor dots separated by black, light-absorbing material. Although Bingley says nothing about the relationship between beam landing areas and phosphor sizes in the context of a shadow mask tube, Bingley does say that in an index tube the scanning beam spot size may be larger than the width of the phosphor strip. Furthermore, Bingley discloses the use of a clear glass faceplate.

The Kaplan article teaches two alternative ways of avoiding overlap of electron beams onto the wrong phosphor dots in a shadow mask tube: either the size of the apertures in the shadow mask can be reduced, thereby reducing the size of the beam landing areas, or the size of the phosphor dots can be reduced, so that in the spaces where beam landing areas overlap the beams will not strike any phosphors. The first alternative results in the positive tolerance system employed in conventional shadow mask tubes. The second alternative results in a tube in which beam landing areas are larger than their corresponding spaced phosphor dots, ¹⁰ although it does not necessarily result in the negative tolerance tube of the '368 patent. ¹¹

The district court observed that the level of ordinary skill in the art of color television picture tube design was high, and determined that "a person having ordinary skill in the art" at the time the '368 patent was conceived, 35 U.S.C. § 103 (1970), would have been led inexorably from the...