Obviousness

Under 35 U.S.C. § 103, an invention is considered obvious if the differences between the claimed invention and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art (POSITA). This analysis will focus on combinations of prior art references explicitly mentioned or described as generally known in the "Background of the Invention" section of US Patent 7851394.

The core of Claim 1 of US7851394 involves an alkali-free boroalumino silicate glass with specific compositional ranges for SiO2, Al2O3, B2O3, MgO (1.0-3.0 mole percent), CaO, SrO, and BaO, a critical Σ[RO]/[Al2O3] ratio between 1.00 and 1.25, the presence of at least 0.01 mole percent SnO2 for fining, and a density less than or equal to 2.41 grams/cm3. The invention aims to provide a glass suitable for flat panel display devices, particularly AMLCDs, that can be manufactured by downdraw processes (like the fusion process) with low gaseous inclusion levels, without relying on hazardous arsenic or antimony fining agents.

Prior Art References (from "Background of the Invention" section):

1. U.S. Pat. No. 3,338,696 (Dockerty) and U.S. Pat. No. 3,682,609 (Dockerty): These patents describe the fusion downdraw process for producing glass sheets, highlighting its ability to yield substrates without costly post-forming operations like polishing. The fusion process requires glasses with relatively high liquidus viscosities, preferably greater than 100,000 poises.
2. U.S. Pat. No. 5,374,595 (Dumbaugh et al.) and U.S. Pat. No. 6,319,867 (Chacon et al.): These references disclose glasses with strain points exceeding 650° C., which provide acceptable thermal stability for active plates based on a-Si and super low temperature p-Si thin film transistors (TFTs).
3. U.S. Pat. No. 5,785,726 (Dorfeld et al.), U.S. Pat. No. 6,128,924 (Bange et al.), U.S. Pat. No. 5,824,127 (Bange et al.), and co-pending patent application Ser. No. 11/116,669: These references disclose processes aimed at manufacturing arsenic-free glasses, reflecting a continuous effort in the art to reduce or eliminate hazardous arsenic levels due to environmental and health concerns. The background also notes that antimony, while used as a replacement for arsenic, also has environmental and health issues and is a less effective fining agent.
4. General knowledge in the art (as stated in the patent's background): The patent explicitly states that tin oxide (SnO2) has been a component of AMLCD glasses for many years, often introduced through tin oxide electrodes during Joule melting (e.g., Corning Incorporated Code 7059, 1737, and EAGLE 2000 glasses). It is noted that SnO2 has no known hazardous properties, making it a desirable fining agent, although it is considered "less effective" compared to arsenic or antimony.
5. General desired properties for AMLCD substrates (as stated in the patent's background): The industry desired glass compositions with a low density (preferably less than or equal to 2.45 grams/cm3, and more preferably less than or equal to 2.41 grams/cm3), a linear coefficient of thermal expansion (CTE) in the range of 28-34 × 10−7 /° C. (0-300° C.), and consistently low gaseous inclusion levels (less than or equal to 0.05 inclusions/cm3 for sheets having a volume of at least 500 cm3).

Obviousness Analysis under 35 U.S.C. § 103:

A person having ordinary skill in the art (POSITA) in 2005 (the priority date of US7851394) would be motivated to combine the teachings of these prior art references to develop an improved glass for AMLCD applications.

Combination of References and Motivation:

A POSITA would be driven by the following motivations to combine the elements present in the prior art:

• Environmental and Safety Imperative: The clear and continuous effort in the art to produce arsenic-free and antimony-free glasses would strongly motivate a POSITA to seek non-hazardous alternatives for fining. Given that SnO2 was already known as a component in AMLCD glasses and had no known hazardous properties, it would be an obvious choice to explore as a primary fining agent, despite its acknowledged "less effective" nature compared to arsenic or antimony.
• Manufacturing and Performance Demands for AMLCDs: To produce large, high-quality AMLCD substrates efficiently, the fusion downdraw process, as taught by the Dockerty patents, was a preferred manufacturing method. This process, however, imposes specific requirements on glass properties, notably a high liquidus viscosity. Concurrently, AMLCDs demand glasses with specific performance attributes: high thermal stability (strain point greater than 650° C., as taught by Dumbaugh et al. and Chacon et al.), chemical durability, and dimensional stability (a CTE in the range of 28-34 × 10−7 /° C.). Furthermore, the increasing size of display panels created a need for glasses with lower density (preferably ≤ 2.41 grams/cm3) to address weight and sag issues.
• Routine Optimization to Balance Conflicting Requirements: Faced with the challenge of incorporating a "less effective" fining agent (SnO2) into a glass composition that also meets stringent physical property and manufacturing process requirements (fusion process compatibility, high strain point, low density, desired CTE, alkali-free nature), a POSITA would engage in routine experimentation and optimization of known boroalumino silicate glass compositions. Glass chemists are accustomed to adjusting the concentrations of various oxides, including network formers (SiO2, Al2O3, B2O3) and modifiers (alkaline earth oxides like MgO, CaO, SrO, BaO), to balance multiple desired properties. The specific compositional ranges of Claim 1, including the MgO content of 1.0-3.0 mole percent and the Σ[RO]/[Al2O3] ratio of 1.00-1.25, while not explicitly taught in the background as the solution, would fall within the scope of predictable variations and optimizations a POSITA would undertake to simultaneously achieve: (1) effective non-hazardous fining with SnO2, (2) compatibility with the fusion process (high liquidus viscosity), and (3) the desired physical and chemical properties (e.g., low density, high strain point, suitable CTE) for AMLCD substrates.

Therefore, the combination of: (1) the Dockerty patents teaching the fusion process and its constraints, (2) the Dumbaugh/Chacon patents teaching high strain point glasses, (3) the Dorfeld/Bange patents teaching the motivation for arsenic-free glasses, (4) the general knowledge in the art of SnO2 as a non-hazardous fining agent in AMLCD glasses, and (5) the well-known industry desires for specific glass properties (low density, CTE, low inclusions), would render the claimed invention obvious to a POSITA seeking to develop an improved, environmentally friendly, and high-performance AMLCD glass. The specific compositional ranges would be arrived at through routine experimentation and optimization in light of these known requirements and desired outcomes.