Melt processible fluororesin composition and injection molded article formed from same
Provided is a melt processible fluororesin composition for injection molding of articles that has melt flow that facilitates injection molding, that can enhance strength of a fluororesin weld line area in an injection molded article, and that achieves excellent release from a mold. The fluororesin composition includes two or more types of melt processible fluororesins having different melt flow rates; one of the melt processible fluororesins being a high melt flow rate melt processible fluororesin having a melt flow rate of 35 g/10 min or greater, and another being a low melt flow rate melt processible fluororesin having a melt flow rate of 10 g/10 min or greater but less than 35 g/10 min; and wherein the ratio of the melt flow rate (MFRa) of the high MFR melt processible fluororesin to the melt flow rate (MFRb) of the low MFR melt processible fluororesin (MFRa/MFRb) is from 1 to 10.
1. A melt processible fluororesin composition comprising:
a mixture of two or more types of melt processible fluororesins having melt flow rates that are different from each other, and from 0.01 to 1 wt. % of a high molecular weight polytetrafluoroethylene based on the total weight of melt processible fluororesins and polytetrafluoroethylene;
one of the two or more types of melt processible fluororesins being a high melt flow rate melt processible fluororesin having a melt flow rate of 35 g/10 min or greater, and another being a low melt flow rate melt processible fluororesin having a melt flow rate of 10 g/10 min or greater but less than 35 g/10 min, and wherein
the ratio of the melt flow rate (MFRa) of the high melt flow rate melt processible fluororesin to the melt flow rate (MFRb) of the low melt flow rate melt processible fluororesin (MFRa/MFRb) is greater than 1 but less than or equal to 10, and wherein
the high melt flow rate melt processible fluororesin and the low melt flow rate melt processible fluororesin are tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymers (PFA).
2. The melt processible fluororesin composition according to claim 1 , wherein said melt processible fluororesin composition has a melt flow rate of from 10 to 100 g/10 min.
3. The melt processible fluororesin composition according to claim 1 , wherein the content of the high melt flow rate melt processible fluororesin is from 5 to 95 wt. % of the total amount of the melt processible fluororesins.
4. The melt processible fluororesin composition according to claim 1 , wherein the content of perfluoro(alkyl vinyl ether) in the high melt flow rate tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer is from 1.5 to 5.0 mol %, and the content of perfluoro(alkyl vinyl ether) in the low melt flow rate tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer is from 1.0 to 4.0 mol %.
5. The melt processible fluororesin composition according to claim 1 , wherein at least one of said high melt flow rate melt processible fluororesin and said low melt flow rate melt processible fluororesin are fluorinated so as to reduce the number of fluororesin chain unstable endgroups and replace such endgroups with —CF 3 endgroups.
6. The melt processible fluororesin composition according to claim 1 , wherein,
i) said composition is fabricated in accordance with ASTM D-2116 into a micro dumbbell-shaped test piece, by injection-molding said melt processible fluororesin composition at an injection pressure and holding pressure of 50 MPa to form a molded sheet having a weld line and a thickness of 1.9±0.5 mm, and cutting from said molded sheet said micro dumbbell-shaped test piece including said weld line,
ii) said micro dumbbell-shaped test piece is subjected to a tensile fatigue test performed under conditions: distance between supports of 22 mm, tensile test speed of 200 mm/min, 23° C., sinusoidal wave, and stress ratio of 0.1, to generate tensile fatigue test results,
iii) said tensile fatigue test results are plotted in a plot of stress at break in MPa on the Y axis versus cycle number in logarithmic scale on the X axis, and
iv) the equation Y=a*In(X)+b is fitted to said tensile fatigue test results by the least squares method,
wherein when X is at least 1,000, a Y value of greater than 14.5 MPa and a value of the slope (a) of greater than −0.15 are obtained.
7. An injection molded article formed by subjecting the melt processible fluororesin composition described in claim 1 to injection molding.
8. The injection molded article of claim 7 , wherein said article contains at least one weld line.
9. The melt processible fluororesin composition according to claim 1 , wherein the tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymers consist essentially of tetrafluoroethylene and perfluoro(alkyl vinyl ether).
10. The melt processible fluororesin composition according to claim 1 , wherein the tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymers consist of tetrafluoroethylene and perfluoro(alkyl vinyl ether).
11. The melt processible fluororesin composition according to claim 1 , wherein the low melt flow rate melt processible fluororesin has a melt flow rate of 12 g/10 min or greater but less than 32 g/10 min.
12. The melt processible fluororesin composition according to claim 1 , wherein the melt processible fluororesin composition is injection-molded with a weld line.