PTAB

IPR2018-01751

Sony Corp v. Fujifilm Corp

Log In
Key Events
Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Magnetic Recording Medium
  • Brief Description: The ’451 patent discloses a magnetic recording medium, such as data storage tape, comprising a magnetic layer of ferromagnetic powder dispersed in a binder. The invention purports to improve signal-to-noise ratio (SNR) by controlling specific structural parameters of this magnetic layer, namely its residual magnetization and the characteristics of magnetic particle clusters.

3. Grounds for Unpatentability

Ground 1: Obviousness over Ejiri, Hokkyo, and Chen - Claims 1-14 are obvious over Ejiri in view of Hokkyo and Chen.

  • Prior Art Relied Upon: Ejiri (Application # 2002/0015861), Hokkyo (a 1997 journal article on particulate recording medium noise), and Chen (a 1999 journal article on magnetic clusters).
  • Core Argument for this Ground: Petitioner argued that the challenged claims are unpatentable under 35 U.S.C. §103 because they merely recite the routine optimization of known properties for magnetic media. The primary reference, Ejiri, disclosed a magnetic medium with nearly all the claimed features. The secondary references, Hokkyo and Chen, provided the known principles and measurement techniques that would have guided a person of ordinary skill in the art (POSITA) to optimize Ejiri’s medium and arrive at the remaining claimed limitations, specifically the ratio of magnetic cluster sizes (Sdc/Sac). Petitioner contended this ratio is not an invention but a non-standard characterization of the well-understood goal of achieving good particle dispersion.
    • Prior Art Mapping: Petitioner asserted that Ejiri, whose inventor is the same as the ’451 patent’s, taught a magnetic recording medium suitable for high-density recording with an MR head, explicitly disclosing the layered structure, ferromagnetic powder composition, and methods for reducing particle "aggregation" to improve the carrier-to-noise ratio. Ejiri disclosed ranges for magnetic layer thickness, particle size, and volume packing density that anticipate or render obvious the limitations of dependent claims 2-3, 6, and 12-14. Further, Ejiri disclosed a range for residual magnetization (Φr) that significantly overlaps with the range in independent claim 1. Hokkyo taught the underlying theory for the claimed Sdc/Sac ratio by explaining that medium noise can be analyzed by comparing the DC-magnetized state (where noise is dominated by clusters) with the AC-erased state (where noise reflects fundamental particle properties). Chen taught using magnetic force microscopy (MFM) to measure magnetic cluster size and empirically confirmed that reducing cluster size improves SNR, providing a known methodology for the optimization process.
    • Motivation to Combine: A POSITA starting with Ejiri’s medium, which already sought to minimize particle aggregation for better performance, would combine the teachings of Hokkyo and Chen to further this goal. Hokkyo provided the theoretical framework to understand that minimizing clusters in both DC and AC states was critical, directly suggesting the analysis reflected in the Sdc/Sac ratio. Chen provided a known practical method (MFM) and data showing that minimizing cluster size was a proven path to higher SNR. A POSITA would therefore combine these teachings to systematically optimize the dispersion techniques in Ejiri, using the principles from Hokkyo and Chen to guide and verify the reduction of magnetic clusters, thereby arriving at the claimed Sdc/Sac ratio.
    • Expectation of Success: A POSITA would have had a high expectation of success because minimizing magnetic cluster size was a well-known "result-effective variable" in the art. The methods for achieving this, such as improving particle dispersion, were conventional and taught by Ejiri itself. Optimizing this known variable to achieve a predictable improvement in SNR was a matter of routine experimentation.

4. Key Claim Construction Positions

  • "residual magnetization Φr": Petitioner argued this term should be construed to mean the product of the magnetic material’s remanence (Mr) and the magnetic layer’s thickness (t), or Mr*t. This construction was asserted as necessary to reconcile the claimed units of milliamps (mA) with the standard physical properties of the magnetic material and was consistent with a prior agreement between the parties in related litigation.
  • "ratio (Sdc/Sac)...": Petitioner contended this phrase should be given its plain and ordinary meaning as understood from the specification: a ratio of the average area of magnetic clusters in a DC-magnetized condition (Sdc) to that in an AC-erased condition (Sac). Petitioner argued that while the ratio itself was not a standard term, the underlying concepts of magnetic clusters and their behavior in different magnetization states were well known, making the term’s meaning clear to a POSITA.

5. Key Technical Contentions (Beyond Claim Construction)

  • Sdc/Sac Ratio as a Known Concept: Petitioner’s central technical contention was that the claimed Sdc/Sac ratio does not represent an inventive concept but is merely a mathematical characterization of the long-standing industry goal of achieving ideal particle dispersion. A POSITA knew that minimizing magnetic clusters was essential for low-noise media. In an ideally dispersed medium, clusters would be minimized in any state, causing the Sdc and Sac values to converge and their ratio to approach 1. The claimed range of 0.8 to 2.0 was therefore not an unexpected discovery but an obvious target for a known optimization problem.
  • Criticality of Claimed Ranges: Petitioner argued that the patent owner failed to demonstrate the criticality of the claimed numerical ranges for either residual magnetization or the Sdc/Sac ratio. The specification’s data was alleged to be flawed, lacking controlled experiments and failing to show unexpected results across the full scope of the claimed ranges, thereby failing to overcome a prima facie case of obviousness.

6. Relief Requested

  • Petitioner requested the institution of an inter partes review and the cancellation of claims 1-14 of the ’451 patent as unpatentable.