JP3458601B2 - Tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer composition - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (hereinafter referred to as PFA) having excellent surface smoothness and stress crack resistance. The present invention relates to a PFA composition from which a molded article is obtained. 2. Description of the Related Art PFA is a polymer material which is excellent in heat resistance, chemical resistance, solvent resistance, etc., is thermoplastic and can be easily formed and processed. It is used in various applications such as parts of semiconductor manufacturing equipment such as tubes for fluid transfer requiring extremely high cleanliness, materials for coating the inner surface of containers, and wire covering materials. [0003] PFA is a crystalline resin. When cooled and solidified after melt molding, PFA is recrystallized to generate a large number of crystal nuclei in the melt, and crystals are formed in the same direction around the crystal nuclei. Although they grow, the growth stops when the crystals come into contact with each other, and so-called spherulites are formed. PFA
It is known that the surface smoothness of a compact depends on the size of the spherulite. In conventional PFA, spherulites generally grow large, and as a result, a large number of irregularities are generated on the surface of a molded body. In a tube molded from such PFA,
Turbulence occurs in the fluid flowing along the inner peripheral surface, and the transport resistance at this time prevents smooth transport of the fluid. For example, when the flow velocity of the fluid is low, a portion where the flow does not occur occurs on the surface uneven portion. In the case of ultrapure water, the fluid stays in the portion for a long time, and bacteria and the like are generated in the portion. Therefore, there is a problem that the cleanliness of the fluid is impaired. Further, when used as a coating material for the inner surface of a container, there is also a problem that a coating film having a large spherulite tends to cause stress cracks and deteriorate durability. It is known that the size of spherulites depends on the cooling rate after melt molding, and the more rapid the cooling, the more fine spherulites are formed. However, rapid cooling may not be possible depending on the molding method. For example, when a thick-walled tube is obtained by an extrusion molding method, there is a problem that when the extruded tube is cooled from the outer surface, the inner surface of the tube is not rapidly cooled, so that large spherulites are generated and the inner surface of the tube is poor in smoothness. PFA having a low perfluoro (alkyl vinyl ether) content (Japanese Patent Laid-Open No. 8-4126)
7) A method has been proposed in which crystallization characteristics are improved and fine crystals are obtained by adding a low molecular weight tetrafluoroethylene polymer (hereinafter referred to as PTFE) (JP-A-7-70394). The additive becomes crystal nucleus,
It is considered that the large number of crystal nuclei causes the growth to stop and the spherulite size to decrease because the crystal nuclei come into contact with adjacent crystals before the crystals grow large. However, in these methods, the additive is PFA
When the kneading of PFA and the additive is too weak, the mixing property is poor and the additive becomes a lump when molded into a tube, resulting in a so-called fish eye. On the other hand, if the kneading is too strong, the PFA and the additive are uniformly mixed, and the additive cannot serve as a crystal nucleus, and the effect of reducing the spherulite size is significantly reduced. SUMMARY OF THE INVENTION The present invention relates to a modified PFA, which has a small spherulite size and crystallization characteristics without impairing the excellent physical properties and moldability of PFA itself. Provided is a PFA composition that can provide a molded article having excellent surface smoothness and stress crack resistance even when high-quality PTFE is kneaded with PFA in a wide operation range. [0010] That is, the present invention provides a P
The following modified PTFE was added in an amount of 0,0 per 100 parts by weight of FA.
PFA and modified PT contained in a proportion of 0.5 to 20 parts by weight
And FE. Modified PTFE: tetrafluoroethylene and perfluoro (divinyloxyalkane)
Wherein the molar ratio of the polymerized units based on tetrafluoroethylene to the polymerized units based on perfluoro ( divinyloxyalkane ) is 99 to 99.999 / 1 to 1
0.001, and the volume flow rate X is 0.01-20 m
A copolymer having a m ³ / sec. However, the volume flow rate X was measured at a temperature of 380 ° C. and a load of 20 using a Koka type flow tester.
It is the volume of the polymer that melts and flows out per unit time from a nozzle having a diameter of 2 mm and a length of 8 mm in kg / cm ² . DETAILED DESCRIPTION OF THE INVENTION In the present invention, the volume flow rate Y of PFA is preferably 0.5 to 100 mm ³ / sec. However, the volume flow rate Y was measured using a Koka type flow tester at a temperature of 380 ° C., a load of 7 kg / cm ² and a diameter of 2 kg.
melt PFA from a nozzle with a length of 8 mm and a length of 8 mm,
This is the volume of PFA flowing out per unit time. If the volume flow rate Y is too small, the moldability is not sufficient, and if it is too large, the strength decreases. The more preferable volumetric flow rate Y of PFA is 1 to 50 mm ³ / sec. Perfluoro (alkyl vinyl ether), which is a copolymer component in PFA, has a general formula CF ₂ ＣC
N is preferably an integer of 0 to 6 in that it is represented by FO (CF ₂ ) _n CF ₃ and PFA has excellent mechanical strength at high temperatures. Perfluoro (propyl vinyl ether) wherein n is 2 is particularly preferred. The content of the polymerized unit based on perfluoro (alkyl vinyl ether) in PFA is preferably about 1.0 to 3.0 mol% from the moldability of PFA. In the present invention, the modified PTFE comprises tetrafluoroethylene and perfluoro (divinyloxyalka).
A copolymer of perfluoro (divinyloxy)
The content of the polymerized unit based on ( alkane) is 0.001 to 1
Mol%, the content of the polymerized unit based on tetrafluoroethylene is 99 to 99.999 mol%, and the volume flow rate X is PTFE having a volume flow rate of 0.01 to 20 mm ³ / sec. Pell
If the content of the polymerized units based on fluoro (divinyloxyalkane) is more than 1 mol%, it becomes difficult to knead with PFA. Similarly, if the volume flow rate X is less than 0.01 mm ³ / sec, it becomes difficult to knead with PFA. [0015] Bae Rufuruoro (divinyloxyethyl carboxylate alkanes)
Is preferred from the viewpoint of polymerizability and thermal stability of the polymer.
Perfluoro (divinyloxyalkane) is highly reactive and forms a crosslinked structure by copolymerizing with tetrafluoroethylene. In the composition of the present invention, the modified PTFE
Is from 0.05 to 2 per 100 polymerized parts of PFA.
It is selected from the range of 0 polymerization parts. In particular, it is preferable to add about 0.5 to 10 parts by weight. If the amount of the modified PTFE is too small, the effect of reducing the spherulite size is small, while if it is too large, the moldability of the PFA composition is impaired, which is not preferable. As a method for producing the composition of the present invention, a known method is employed. A PFA composition, in which PFA pellets and modified PTFE powder are mixed in advance, is supplied to a single-screw or twin-screw kneading extruder, and the melting temperature of the modified PTFE or higher,
For example, a method of kneading under a wide kneading condition of 340 to 400 ° C., a residence time of 1 to 30 minutes, and a rotation speed of 10 to 100 rpm, adding modified PTFE to molten PFA by heating it to a melting temperature or higher and stirring. While mixing. In addition, PFA and modified PT supplied during mixing are used.
The shape of the FE is also not particularly limited, and may be a pellet, a bead,
A powder form can be adopted. The composition of the present invention has a spherulite size of 10 μm.
The following molded articles are provided, and an extruded tube having an inner surface roughness of 0.3 μm or less is provided. Furthermore, since it has a crystallization characteristic that easily produces fine spherulites even at a relatively slow cooling rate, a tube having excellent inner surface smoothness can be obtained smoothly even when forming a thick-walled tube by an extrusion molding method. . In the present invention, spherulite size, inner surface roughness,
And the crystallization temperature is defined as follows. Spherulite Size: A sample of the composition is compression molded at 340 ° C. into a 200 μm thick film, and then quenched to near room temperature in about 5 minutes with a cooling press to produce a test film. Spherulite size is measured by observing the surface of the test film with a polarizing microscope. Inner surface roughness: Using a single screw extruder, a sample of the composition is extruded at 380 ° C. into a tube having an inner diameter of 8 mm and an outer diameter of 10 mm, and then water-cooled from the outside of the tube to prepare a test tube. . Roughness meter for surface roughness of test tube (Surfcoder SE-30H, trade name, manufactured by Kosaka Laboratory)
Measure with. Crystallization temperature: Scanning differential calorimeter (DSC)
To determine the exothermic peak when the temperature was lowered at 10 ° C./min,
The temperature at that time is defined as the crystallization temperature. Example 1 640 g of water, 10 g of methanol, 1.3 g of ammonium perfluorooctanoate, Fluorinert FC-4 as a solvent were placed in a 1 liter degassed autoclave.
3 (manufactured by Sumitomo 3M Limited, trade name), 30 g, perfluoro (1,4-divinyloxybutane) CF ₂ ＣＦCFO
0.35 g of (CF ₂ ) ₄ OCF = CF ₂ and 23 g of tetrafluoroethylene were charged and maintained at 75 ° C., and 2.5 g of ammonium persulfate was added as a polymerization initiator.
The reaction was started. The reaction pressure was maintained at 10 kg / cm ² , and an amount of tetrafluoroethylene corresponding to the amount of tetrafluoroethylene consumed during the reaction was continuously introduced into the reactor.
The reaction was stopped when 100 g of tetrafluoroethylene was introduced, and about 105 g of white modified PTFE powder was obtained.
The crystallization temperature of this modified PTFE is 315 ° C., and the volume flow rate X
Was 1.5 mm ³ / sec. Next, the polymerization unit based on tetrafluoroethylene / perfluoro (propyl vinyl ether) is 98.7 / 1.3 (molar ratio), and the volume flow rate Y is 2 m
m ³ / sec, 100 parts by weight of PFA beads having a crystallization temperature of 280 ° C., and 5 parts by weight of the previously obtained modified PTFE powder were subjected to a cylinder temperature C by a twin-screw kneading extruder.
1 / C2 / C3 / C4 / C5 / C6 / H = 200 ° C./3
50 ° C / 380 ° C / 380 ° C / 380 ° C / 385 ° C / 3
85 ° C, feed rate 20kg / hour, screw rotation speed 8
The mixture was kneaded at 0 rpm to obtain pellets of the PFA composition. The average spherulite size of a 200 μm thick film formed by compression molding the pellets was 6 μm. The inner surface roughness of the tube (inner diameter 8 mm, outer diameter 10 mm) produced by the extruder was 0.06 μm. Cylinder temperature is C1 / C2 / C3 / C4 / C5 / C6 / H =
200 ° C / 390 ° C / 390 ° C / 390 ° C / 390 ° C /
Even when the feed amount was changed to 395 ° C./395° C. and the feed amount was changed to 10 kg, the spherulite size and the inner surface roughness of the tube were the same. Comparative Example 1 Tetrafluoroethylene was polymerized in the same manner as in Example 1 except that perfluoro (1,4-divinyloxybutane) was not used, to obtain 103 g of white PTFE powder. The crystallization temperature of this white PTFE powder was 316 ° C., and the volume flow rate X was 2.3 mm ³ / sec. 5 parts by weight of this PTFE powder and 100 parts by weight of the beads of PFA used in Example 1 were subjected to a cylinder temperature C1 / C2 / C3 / C4 /
C5 / C6 / H = 200 ° C./350° C./380° C./38
0 ° C / 380 ° C / 385 ° C / 385 ° C, feed amount 20
kg / hour, kneading at a screw rotation speed of 80 rpm,
A pellet of the FA composition was obtained. The average spherulite size of a 200 μm thick film formed by compression molding of the pellets was 6 μm. The inner surface roughness of the tube made by the extruder is 0.1.
It was 06 μm. Set the cylinder temperature to C1 / C2 / C3 /
C4 / C5 / C6 / H = 200 ° C / 390 ° C / 390 ° C
/ 390 ° C / 390 ° C / 395 ° C / 395 ° C and the feed amount was changed to 10 kg. As a result, the spherulite size of the compressed film was 32 µm, and the inner surface roughness of the extruded tube was 0.22 µm. The PFA composition of the present invention has a small spherulite crystallization characteristic without impairing the excellent physical properties and moldability of PFA itself, and is a modified additive. Quality P
Even if TFE is kneaded with PFA in a wide range, surface smoothness,
A molded article having excellent stress crack resistance can be provided.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-41267 (JP, A) JP-A-8-73689 (JP, A) JP-A-6-136218 (JP, A) JP-A-62-162 59610 (JP, A) JP-A-5-230151 (JP, A) JP-A-9-316266 (JP, A) JP-A-5-509433 (JP, A) US Patent 3,310,606 (US, A) UK Patent 1,106,344 (GB, B) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 27/18 C08L 29/10

Claims (1)

(57) [Claim 1] The following modified tetrafluoroethylene polymer is added to 100 parts by weight of the tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer.
A composition containing a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer and a modified tetrafluoroethylene polymer, contained in a proportion of from 0.5 to 20 parts by weight. Modified tetrafluoroethylene polymer: a copolymer of tetrafluoroethylene and perfluoro ( divinyloxyalkane) , wherein the molar ratio of the polymerized units based on tetrafluoroethylene to the polymerized units based on perfluoro (divinyloxyalkane) Is 99-99.999 / 1-0.
001 and the volume flow rate X is 0.01 to 20 mm ³
Per second. However, the volume flow rate X was measured at a temperature of 380 ° C. and a load of 20 kg using a Koka type flow tester.
/ Cm ² is the volume of the polymer that melts and flows out from a nozzle having a diameter of 2 mm and a length of 8 mm and flows out per unit time.