Patent ID: 7387834

Claim:
A polytetrafluoroethylene fine powder having a standard specific gravity of 2.180 to 2.225, which is obtained by contacting polytetrafluoroethylene fine powder having a standard specific gravity of 2.180 to 2.225 with a fluorine radical source; wherein tanδ of a sample film prepared from said fluorinated polytetrafluoroethylene fine powder at 12 GHz, which is measured by the following method using a sample film prepared under the following conditions, is at most 2.0×10 −4 : (Conditions for preparing sample film) Said PTFE fine powder is compression molded into a cylinder; A film having a thickness of 0.5 mm which is cut out from said cylinder is baked by heating at 380° C. for 5 minutes in a convection electric furnace; Immediately thereafter, said film is taken out into air of room temperature (25° C.) and stood to cool to room temperature at 5 to 50° C./second, to prepare a sample film: (Measurement method of tanδ) Changes in resonance frequency and Q value of said prepared film are measured by a cavity resonator using a network analyzer and tanδ at 12 GHz is calculated from the following equation: tan ⁢ ⁢ δ = ( 1 / Qu ) × { 1 + ( W 2 / W 1 ) } - ( Pc / ω ⁢ ⁢ W 1 ) ɛ r = ( c π × L - F 0 ) 2 × { X 2 - Y 2 ⁡ ( L 2 ⁢ M ) 2 } + 1 X ⁢ ⁢ tan ⁢ ⁢ X = ( L / 2 ⁢ M ) ⁢ Y ⁢ ⁢ cos ⁢ ⁢ Y X = L 2 ⁢ ɛ r × k 0 2 - k r 2 Y = M ⁢ k 0 2 - k r 2 k 0 = ϖ c ϖ = 2 ⁢ π ⁢ ⁢ F 0 k r = 3.8317 D / 2 Q u = Q L 1 - 10 ( - Id / 20 ) Q L = F 0 F 1 - F 2 W 1 = 1 8 × ɛ r × ɛ 0 × L × π × ϖ 2 × μ 0 2 × J 1 2 × J 0 2 × ( 1 + sin ⁢ ⁢ X 2 ⁢ X ) W 2 = 1 4 × ɛ 0 × M × π × ( 1 - sin ⁢ ⁢ 2 ⁢ Y 2 ⁢ Y ) × ϖ 2 × μ 0 2 × J 1 2 × J 0 2 P C = P 1 + P 2 + P 3 P 1 = 1 2 × Rs × D 2 × L × π × ( 1 - sin ⁢ ⁢ X 2 ⁢ X ) × ( J 1 × 2 D ) 4 × J 0 2 P 2 = 1 2 × ( - cos ⁢ ⁢ X sin ⁢ ⁢ Y ) 2 × Rs × D 2 × M × π × ( 1 - sin ⁢ ⁢ 2 ⁢ Y 2 ⁢ Y ) × ( J 1 × 2 D ) 4 × J 0 2 P 3 = 1 2 × ( - cos ⁢ ⁢ X sin ⁢ ⁢ Y ) 2 × Rs × π × ( J 1 × J 0 × Y M ) 2 Symbols in the equations represent the following: D: diameter of cavity resonator (mm) M: length of cavity resonator (mm) L: length of sample (mm) c: light velocity (m/s) ID: amount of decay (dB) F 0 : resonance frequency (Hz) F 1 : upper frequency when the amount of decay from the resonance point is 3dB (Hz) F 2 : lower frequency when the amount of decay from the resonance point is 3dB (Hz) ε 0 : dielectric constant of vacuum (H/m) ε r : specific dielectric constant of sample μ 0 : magnetic permeability of vacuum (H/m) Rs: effective surface resistance considering surface roughness of conductor cavity (Ω) J 0 : −0.402759 J 1 : 3.83171, and wherein said standard specific gravity is measured pursuant to ASTM D4895-89 by water displacement of a molded article formed from the polytetrafluoroethylene fine powder.