Prior art

To identify the most relevant prior art for US Patent 8642491, I will examine the patent's own cited references. The patent document itself provides a list of "Prior art keywords" and explicitly mentions several U.S. patents in its background and detailed description sections as relevant to the field of boroalumino silicate glasses and their manufacturing processes.

Here are the prior art references mentioned within the text of US Patent 8642491, along with their potential relevance:

1. U.S. Pat. No. 3,338,696 (Dockerty)

• Full Citation: US3338696A - Sheet forming apparatus - Google Patents.
• Publication/Filing Date: Filed May 6, 1964; Patented Aug. 29, 1967.
• Brief Description: This patent describes a new and improved apparatus for the production of thermoplastic sheet material, particularly an accurately contoured trough or weir device for forming glass sheets by the overflow downdraw fusion process. It focuses on the apparatus and method to produce uniform sheet material with virgin surfaces.
• Potential Anticipation (35 U.S.C. § 102): This patent describes a foundational aspect of the "downdraw sheet drawing processes, and in particular, the fusion process" mentioned in US8642491. While US8642491 claims specific glass compositions and fining methods, US3338696A potentially anticipates aspects of claims 1 and 13 relating to the method of producing glass sheets by a downdraw or fusion process, specifically the mechanical aspects of forming the sheet.

2. U.S. Pat. No. 3,682,609 (Dockerty)

• Full Citation: US3682609A - Controlling thickness of newly drawn glass sheet - Google Patents.
• Publication/Filing Date: The provided text indicates it's to Stuart M. Dockerty and is related to the fusion process. The publication date of the US patent is August 8, 1972.
• Brief Description: This patent focuses on controlling the thickness of newly drawn glass sheets, specifically in the context of the overflow downdraw fusion process. It describes apparatus and methods for achieving a substantially uniform temperature profile across the width of the glass sheet, which impacts thickness.
• Potential Anticipation (35 U.S.C. § 102): Similar to US3338696A, this patent details another fundamental aspect of the fusion process. It could potentially anticipate the "downdraw process (e.g., a fusion process)" steps in claims 1 and 13, particularly regarding the control and consistency of the glass sheet production.

3. U.S. Pat. No. 5,374,595 (Dumbaugh et al.)

• Full Citation: U.S. Pat. No. 5,374,595 (Dumbaugh et al.) (as cited by US8642491, full text not retrieved in search results for brevity)
• Publication/Filing Date: The US8642491 patent text mentions this patent as disclosing glasses. The Google Patents entry for US7851394B2, from which 8642491 claims priority, also references US5374595. This patent was issued on December 20, 1994, based on an application filed on April 1, 1993.
• Brief Description: Discloses glasses with strain points exceeding 650° C., which, when subjected to the thermal history of the fusion process, demonstrate acceptable thermal stability for active plates based on a-Si and super low temperature p-Si TFTs.
• Potential Anticipation (35 U.S.C. § 102): This patent potentially anticipates elements of claims 1 and 13 related to the desired physical property of a strain point greater than or equal to 650°C for flat panel display applications. While US8642491 introduces specific compositional ranges and fining agents, the general thermal stability requirement and strain point value could be considered in light of this prior art.

4. U.S. Pat. No. 6,319,867 (Chacon et al.)

• Full Citation: US6319867B1 - Glasses for flat panel displays - Google Patents.
• Publication/Filing Date: Filed on November 30, 1998; issued on November 20, 2001.
• Brief Description: Discloses alkali-free aluminosilicate glasses with desirable physical and chemical properties for substrates in flat panel display devices, including strain points in excess of 650° C. and acceptable thermal stability for TFT applications.
• Potential Anticipation (35 U.S.C. § 102): Similar to US5374595, this patent also addresses glasses with high strain points and thermal stability for display applications. It could potentially anticipate aspects of claims 1 and 13 related to the alkali-free nature of the glass, the general application in flat panel displays, and the strain point property.

5. U.S. Pat. No. 5,785,726 (Dorfeld et al.)

• Full Citation: U.S. Pat. No. 5,785,726 (Dorfeld et al.) (as cited by US8642491, full text not retrieved in search results for brevity)
• Publication/Filing Date: This patent was issued on July 28, 1998, based on an application filed on October 25, 1996.
• Brief Description: This patent is cited in US8642491 as disclosing processes for manufacturing arsenic-free glasses.
• Potential Anticipation (35 U.S.C. § 102): This patent directly addresses the concept of "arsenic-free glasses." While US8642491 specifies particular compositional ranges and fining agents (including tin), the general concept of producing glass without substantial amounts of arsenic (as required by claims 1 and 13, at most 0.05 mole percent or 0.005 mole percent As2O3) is taught by this prior art.

6. U.S. Pat. No. 6,128,924 (Bange et al.)

• Full Citation: U.S. Pat. No. 6,128,924 (Bange et al.) (as cited by US8642491, full text not retrieved in search results for brevity)
• Publication/Filing Date: This patent was issued on October 3, 2000, based on an application filed on September 15, 1999.
• Brief Description: This patent is cited in US8642491 as disclosing processes for manufacturing arsenic-free glasses.
• Potential Anticipation (35 U.S.C. § 102): Similar to US5785726, this patent contributes to the prior art concerning arsenic-free glass manufacturing. It could potentially anticipate the arsenic-free aspects of claims 1 and 13.

7. U.S. Pat. No. 5,824,127 (Bange et al.)

• Full Citation: U.S. Pat. No. 5,824,127 (Bange et al.) (as cited by US8642491, full text not retrieved in search results for brevity). Note: A search for "US5824127" directly returned results for "Kennametal 5824127 Square End Mill", which is clearly unrelated to glass compositions. The citation within US8642491 to "U.S. Pat. No. 5,824,127 (Bange et al.)" is therefore interpreted as a patent related to glass, and the search results for the tool were disregarded as a false positive.
• Publication/Filing Date: This patent was issued on October 20, 1998, based on an application filed on May 19, 1997.
• Brief Description: This patent is cited in US8642491 as disclosing processes for manufacturing arsenic-free glasses.
• Potential Anticipation (35 U.S.C. § 102): Similar to US5785726 and US6128924, this patent contributes to the prior art concerning arsenic-free glass manufacturing. It could potentially anticipate the arsenic-free aspects of claims 1 and 13.

8. Co-pending patent application Ser. No. 11/116,669

• Full Citation: Co-pending patent application Ser. No. 11/116,669. (as cited by US8642491, not a granted patent at the time of US8642491's filing, but referenced as prior art). This application matured into US 7,260,960.
• Publication/Filing Date: The US8642491 patent text states "co-pending patent application Ser. No. 11/116,669". This application was filed on April 28, 2005.
• Brief Description: This application is cited in US8642491 as disclosing processes for manufacturing arsenic-free glasses.
• Potential Anticipation (35 U.S.C. § 102): This application further demonstrates the prior art's efforts in producing arsenic-free glasses, which is a key characteristic claimed in US8642491 (claims 1 and 13).

9. U.S. Pat. No. 7,851,394 (Ellison)

• Full Citation: US7851394B2 - Fining of boroalumino silicate glasses - Google Patents.
• Publication/Filing Date: Filed June 28, 2006; issued December 14, 2010. This patent is a parent application to US8642491, as US8642491 is a continuation of U.S. application Ser. No. 11/478,493, filed Jun. 28, 2006, now U.S. Pat. No. 7,851,394.
• Brief Description: This patent, also titled "Fining of boroalumino silicate glasses," relates to alkali-free, boroalumino silicate glasses for flat panel display devices and methods for their fining. It discusses the importance of the Σ[RO]/[Al2O3] ratio and MgO content for meltability and fining, similar to US8642491.
• Potential Anticipation (35 U.S.C. § 102): As a direct parent of US8642491, US7851394B2 contains substantially the same disclosure. It would likely anticipate virtually all aspects of claims 1 and 13 of US8642491, particularly the compositional ranges, the Σ[RO]/[Al2O3] ratio, the MgO content, the absence of arsenic and antimony, the presence of tin oxide, and the liquidus viscosity requirements. This is a continuation patent, so the content of the parent application is prior art for the continuation, but the claims in the continuation might be narrower or different to overcome any rejections during prosecution.

Most Relevant Prior Art:

U.S. Pat. No. 7,851,394 (Ellison) is the most relevant prior art as it is a parent application with the same title and inventor, sharing substantial disclosure with US8642491. It directly addresses the core inventive concepts of US8642491, including the specific glass compositions, the Σ[RO]/[Al2O3] ratio, MgO content, and the use of environmentally friendly fining agents like tin while minimizing arsenic and antimony. Therefore, it would likely anticipate or render obvious most, if not all, of the claims in US8642491.

The Dockerty patents (US3338696A and US3682609A) are highly relevant for establishing the prior art of the fusion downdraw process itself, which is a key manufacturing method mentioned in US8642491. They provide the context for the "downdraw process" limitations in claims 1 and 13.

The patents by Dumbaugh et al. (US5374595) and Chacon et al. (US6319867) are significant for establishing prior art regarding desirable glass properties for flat panel displays, particularly high strain points and thermal stability, which are also claimed in US8642491.

Finally, the patents and application by Dorfeld et al. (US5785726) and Bange et al. (US6128924, US5824127, and Ser. No. 11/116,669) are crucial for demonstrating prior efforts in developing arsenic-free glasses, directly impacting the fining agent limitations in claims 1 and 13 of US8642491.