Tokyo Shibaura Electric Co. Ltd. v. Zenith Radio Corporation

548 F.2d 88, 193 U.S.P.Q. (BNA) 73
Court of Appeals for the Third Circuit·Decided January 7, 1977·No. 76-1237·Published·Cited by 28 cases

Opinion

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 *90 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

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.

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Tokyo Shibaura Electric Co. Ltd. v. Zenith Radio Corporation, 548 F.2d 88, 193 U.S.P.Q. (BNA) 73 (3d Cir. 1977).

548 F.2d 88 (Tokyo Shibaura Electric Co. Ltd. v. Zenith Radio Corporation) — published by Counsel Stack Legal Research, free access to 12M+ legal documents.

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