JP2001048922A - Stable modified polytetrafluoroethylene resin powder for molding and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable modified polytetrafluoroethylene resin powder which is used for molding and scarcely corrodes the surfaces of Si, SiO2 and metals. SOLUTION: This stable modified polytetrafluoroethylene resin powder which is used for molding, has non-melting processability and contains perfluorovinyl ether units in an amount of 0.01 to 1 wt.% has the following characteristics (a), (b) and (c). (a) The content of a perfluorovinyl ether monomer left in the resin is <=50 ppb; (b) the content of fluoride ions capable of being extracted from the resin is <=100 ppb; and (c) the melt-viscosity of the resin at 380 deg.C is 1×108 to 1×1012 poises.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a modified polytetrafluoroethylene molding resin powder modified with perfluorovinyl ether. More specifically, the present invention relates to a stable modified polytetrafluoroethylene molding resin powder obtained by reacting a modified polytetrafluoroethylene resin with a fluorine radical.

[0002]

2. Description of the Related Art Perfluorovinyl ether (0.01%)
Polytetrafluoroethylene resin modified with １1% by weight) has excellent heat resistance, chemical resistance, bending fatigue resistance, and creep resistance.
It is used as a raw material for various molded products such as tubes, pipes, diaphragms, bellows and inner linings of tanks.

[0003] Conventional modified polytetrafluoroethylene resin has an acid odor or a metal corrosive H
It has the disadvantage that F is released and the inside of the molded article is colored.

Further, when a modified polytetrafluoroethylene resin is used as a lining material or a sealing material for a storage tank, a container or a holder for transporting or treating a chemical substance such as styrene monomer or chlorine gas, the modified polytetrafluoroethylene resin becomes chemically modified. Reacts with the substance, and the reaction product adheres to the surface of the resin molded product. Conventional modified polytetrafluoroethylene resins have the disadvantage that they cannot be used in applications that come into contact with the chemicals.

There has been no report on fluorination of a modified polytetrafluoroethylene resin used for molding.

[0006]

[Invention is to Solve An object of the present invention, (1) Si, to provide a stable modified polytetrafluoroethylene resin powder is less corrosive to SiO ₂ and metal surfaces (2) further improved the water and oil repellency Provide modified polytetrafluoroethylene resin powder (3) When used as a lining material or a sealing material for a container or a holder for storage, transportation or treatment of a chemical substance, it does not react with the chemical substance. It is an object of the present invention to provide a modified polytetrafluoroethylene resin powder which is extremely stable.

[0007]

Means for Solving the Problems The present inventors have found that resin powder emits acid odor, releases HF having metal corrosiveness,
The main cause of the coloring of the inside of the molded article was found to be oxidation, hydrolysis and / or thermal decomposition of the unreacted perfluorovinyl ether monomer adsorbed in the resin powder and modified, and the non-melt processability was modified. The above disadvantages have been overcome by contacting the polytetrafluoroethylene resin with a source of fluorine radicals.

The present invention relates to a modified polytetrafluoroethylene molding resin powder containing 0.01 to 1% by weight of a perfluorovinyl ether unit, wherein a) the residual amount of the perfluorovinyl ether monomer remaining in the resin is B) The content of fluoride ions that can be extracted from the resin is 10
0 ppb or less; and c) the resin has a melt viscosity at 380 ° C. of 1 × 10 ⁸ to 1 × 1.
Provided is a non-melt-processable modified polytetrafluoroethylene molding resin powder characterized by having a diameter of 0 ¹² poise.

The content of extractable fluoride ions in the modified polytetrafluoroethylene molding resin powder is 100
ppb or less, especially 80 ppb or less, for example, 30 to 80 p
pb. The residual amount of the perfluorovinyl monomer remaining in the molding resin powder is 50 ppb or less,
It is 0 ppb or less, for example, 10 ppb or less. The melt viscosity is 1 × 10 ⁸ to 1 × 10 ¹² poise at 380 ° C., for example, 1 × 10 ⁹ to 1 × 10 ¹¹ poise.

The molding resin powder is a molded product obtained by molding a powder (for example, SS based on ASTM D 4894).
G sample) has a contact angle with water of 100 ° or more, particularly 110
° or more. Additional polymerization reaction of tetrafluoroethylene monomer using molding resin powder, for example, at a temperature of 5
When an additional polymerization reaction is performed under the conditions of 0 ° C. and a pressure of 7 to 8 kgf / cm ² G, tetrafluoroethylene monomer newly reacting for 1 minute per 1 g of powder is 1 × 10 ^−5.
mol or less, for example, 0.5 × 10 ⁻⁵ mol or less. Since the adsorbed residual monomer is decomposed and removed from the powder molded article, the internal coloring is eliminated. For example, if the Z value measured by a colorimeter is 9
It may be 0 or more, for example, 92 or more.

[0011] The modified polytetrafluoroethylene resin is
Equation (1):

Embedded image [In the formula, X is a perfluoroalkyl group having 1 to 6 carbon atoms or a perfluoroalkoxyalkyl group having 4 to 9 carbon atoms. ] (Modified polytetrafluoroethylene resin) containing 0.01 to 1% by weight of a perfluorovinyl ether unit represented by the formula:

[0012] The modified polytetrafluoroethylene resin is
Tetrafluoroethylene and formula (2) CF ₂ ＣＦCF-OX (2) [wherein, X is the same as described above. And a perfluorovinyl ether represented by the formula (1), using an initiator (for example, a persulfate).

The perfluorovinyl ether of the formula (2) includes, for example, perfluoro (methyl vinyl ether), perfluoro (ethyl vinyl ether), perfluoro (propyl vinyl ether), perfluoro (butyl vinyl ether), perfluoro (pentyl vinyl ether), Perfluoro (hexyl vinyl ether)
Perfluoro (alkyl vinyl ether); perfluoro (2-methoxypropyl vinyl ether), perfluoro (alkoxyalkyl vinyl ether) such as perfluoro (2-propoxypropyl vinyl ether)
And the like.

When the perfluorovinyl ether is a perfluoro (alkyl vinyl ether),
(Propyl vinyl ether).

The number average molecular weight of the modified polytetrafluoroethylene resin may be from 1,000,000 to 10,000,000, for example, from 2,000,000 to 8,000,000. The form of the resin to be reacted with the fluorine radical may be a form such as powder, granules, flakes and the like.

The modified polytetrafluoroethylene resin is reacted with fluorine radicals. After the modified polytetrafluoroethylene resin powder is brought into contact with a reactive gas containing a fluorine radical source, the fluorine radical source is replaced with an inert gas. As a method of generating fluorine radicals, a method of heating a reactive gas to 100 ° C. or higher, or
There is a method of irradiating the reactive gas with light having a wavelength of 150 to 700 nm. The reactive gas containing the fluorine radical source is
It may be composed of only a fluorine radical source or a mixture of a fluorine radical source / an inert gas (for example, fluorine (F ₂ ) / nitrogen (N ₂ ) (weight ratio) = 1/99 to 99 /
1 mixture).

The reaction conditions are closely related to the reaction temperature, the reaction pressure, the reaction time, and the concentration of the fluorine radical source.
Each condition is not exact, and the relationship between the conditions is important. When higher temperatures are used, shorter reaction times can be used and the concentration of the fluorine radical source can be lower. The reverse is also possible. Similarly, when using high pressure, the reaction temperature can be lowered and the time can be reduced.

Each reaction condition is selected from conditions under which substantially no perfluorovinyl ether monomer remains after the treatment and unstable radical terminals are reduced. When a fluorine radical is generated and reacted by heating, the reaction temperature is preferably 100 ° C. or higher. If the reaction temperature is lower than 100 ° C., a decomposition product of an unreacted monomer may remain. The upper limit is not particularly limited, but if it exceeds 500 ° C., the resin is decomposed with a decrease in weight. The heating temperature may be 120 ° C. or higher, especially 150 ° C. or higher.

In the case of generating fluorine radicals by light irradiation, irradiation is performed with light having a wavelength of 150 to 700 nm.
A light source that emits high energy, such as a mercury lamp or a xenon lamp, is preferable as the light source. If the wavelength exceeds 700 nm, the reaction is insufficient and unreacted perfluorovinyl ether monomer may remain. The lower limit of the wavelength is not particularly limited.
m or more is preferable. Particularly in the ultraviolet region (wavelength 200 to 40
0 nm) is preferred.

The reactor to be used is provided with a heating device at 100 ° C. or higher and / or a light generation device at 150 to 700 nm, and any device can be used as long as it is in a form in which gas and solid are in contact. For example, it is preferable to use a circulating furnace having a reaction shelf or a fluidized bed capable of performing good gas-solid contact.

Examples of the fluorine radical source (fluorine-containing gas) include fluorine (F ₂ ) (molecular fluorine), halogenated fluoride (ClF, ClF ₃ , BrF ₃ , IF)
₃ ), rare gas fluorides (XeF ₂ , XeF ₄ , KrF ₂
Etc.) and nitrogen-containing fluorine compounds (NF ₃ , NF ₂ etc.).

The amount of the fluorine radical source added depends on the reaction time,
Although it depends on the reaction pressure, the reaction temperature or the wavelength of the light, it is converted to fluorine atoms and 0.1 parts by weight with respect to 100 parts by weight of the raw material powder.
It is preferably at least 05 parts by weight, for example, 0.1 to 10 parts by weight. Unreacted components present when the fluorine radical source is added in excess can be recovered and reused.

Since the reaction of the modified polytetrafluoroethylene with fluorine radicals generates a great deal of heat, it is preferable to dilute it with an inert gas such as nitrogen. Immediately after the completion of the reaction, a fluorine radical source remains, which is extremely dangerous. In addition, the remaining fluorine radicals react with moisture in the air to generate HF. Therefore, it is necessary to sufficiently replace the fluorine radical source with an inert gas while heating and / or irradiating with light.

The minimum time to complete the displacement is to contact the effluent inert gas with the starch / iodide solution.
It can be known by ordinary bubbling or by passing over starch / iodide paper. If there is no coloring of the indicator, it can be seen that there is no fluorine radical source in the inert gas.

The perfluorovinyl ether monomer remaining adsorbed by the reaction with the fluorine radical is
It is decomposed and removed from the resin, and most of the radical terminals (—CF ₂ —CF _2. ) Are converted to the most stable —CF ₂ —CF ₃ .

The modified polytetrafluoroethylene molding resin powder can be used for piston rings, power steering seal materials, various mechanical seal materials, bearings, gaskets, valve seats, packings, bearing pads, and the like. The molding method of the modified polytetrafluoroethylene molding resin powder may be the same as that of the conventional polytetrafluoroethylene powder that cannot be melt-molded, and examples thereof include (automatic) compression molding, ram extrusion molding, and isostatic molding. No.

[0027]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. Test method <Quantification of residual perfluorovinyl ether monomer>
1 vial and seal. The bottle is placed in a 180 ° C. electric furnace and held for 30 minutes. Immediately after the removal, 1 ml of gas is collected from the gas phase with a syringe, and the amount of residual monomer is determined by gas chromatography. The concentration (ppb) of the perfluorovinyl ether monomer generated from 1 g of the modified polytetrafluoroethylene resin powder is shown.

<Quantitative Determination of Fluoride Ion Concentration> ASTM D 4 using modified polytetrafluoroethylene resin powder
Based on 894, an SSG sample is created. This SS
The G sample is immersed in a 50 ml beaker containing 25 ml of pure water. The beaker is kept under pressurized steam at 121 ° C. (0.206 MPa) for 1 hour. Fluoride ions extracted into pure water are quantified by ion chromatography. Shows the fluoride ion concentration (ppb) extracted from 1 g of the SSG sample.

<Measurement of Melt Viscosity> A creep test is performed according to the following procedure using “Thermoflex sample lower position TMA” (manufactured by Rigaku Corporation) and measured. First, a sample is prepared by the following method. 8 in a cylindrical mold with an inner diameter of 50 mm
Fill with 0 g of powder and gradually apply pressure for about 30 seconds to a final pressure of about 352 kg / cm ² and hold at this pressure for 2 minutes. Next, the molded body is taken out of the mold, and
Baking for 90 minutes in an air electric furnace heated to
The temperature is lowered to 250 ° C. at a rate of ° C./min. This cylindrical fired body is cut along the side surface to obtain a 0.5 mm-thick strip-shaped sheet.

From this sheet, a width of 4 mm to 5 mm and a length of 1
A 5 mm piece is cut out, the width and thickness are measured accurately, and the cross-sectional area is calculated. Attach the sample mounting bracket to both ends of the small piece so that the mounting distance is 1.0 cm. The metal-sample assembly is placed in a cylindrical furnace, and the temperature is raised from room temperature to 380 ° C. at a rate of 20 ° C./min, and the temperature is maintained. After holding for about 5 minutes, a load of about 15 g is applied.
From the curve of the time change of the elongation, the elongation between 60 minutes and 120 minutes after loading is read, and the ratio to the time (60 minutes) is obtained. The melt viscosity is calculated from the following relational expression.

(Equation 1) Where η = melt viscosity (poise), W = tensile load (g), Lt = length of sample at 380 ° C. (cm), g =
Constant of gravity 980 cm / sec ² , dLt / dT = ratio of elongation between 60 minutes and 120 minutes to time (cm /
Second), At = 380 ° C. cross-sectional area of sample (cm ² ) Here, Lt / At can be calculated using the following equation from the measurement of thermal expansion obtained separately. Lt / At = 0.80 × L (length at room temperature) / A (cross-sectional area at room temperature)

<Evaluation of Amount of Residual Radical> 500 g of pure water and 40 g of modified polytetrafluoroethylene resin powder were put in a pressure-resistant polymerization vessel, and sealed, and the temperature was adjusted to 50 ° C. After the inside of the vessel is replaced with nitrogen and evacuated, the pressure is increased to 8 kgf / cm ² G with a tetrafluoroethylene monomer. Stirring is started, and the consumption amount of tetrafluoroethylene monomer is calculated from the reduced pressure in the vessel. Per minute, the amount of the tetrafluoroethylene monomer reacted with the residual radical in 1 g of the modified polytetrafluoroethylene resin (mol
/ (G · min)).

<Contact Angle with Water> An SSG sample is molded using a modified polytetrafluoroethylene resin powder according to ASTM D 4894. The contact angle of water on the surface of the SSG sample was measured with a droplet having a diameter of 1.5 mm using a contact angle meter.

<Evaluation of Residual Organic Substance by Coloring> 210 g of the modified polytetrafluoroethylene resin powder is weighed. Using a mold having a diameter of 50 mm, a molding ram speed of 13 mm /
min, holding at a molding pressure of 29.4 MPa for 5 minutes, 50 mm
A block of (diameter) × 50 mm (height) is created. The block is fired at 370 ° C. for 1.5 hours. Using a lathe, divide the block horizontally and measure the coloring of the center part according to JIS
It is measured with a colorimetric colorimeter based on Z 8722 and evaluated with the value of Z.

Production Example 1 Production of Modified Polytetrafluoroethylene Resin Powder A solution of 3.3 g of ammonium carbonate dissolved in 54.8 liters of pure water was charged into a 170 liter autoclave and stirred (110 rpm). . After degassing, tetrafluoroethylene was charged to 0.5 kg / cm ² (gauge pressure). After repeating this operation three times, 85 g of perfluoro (propyl vinyl ether) was injected by using tetrafluoroethylene, and the temperature of the reaction system was reduced to 50 ° C.
After raising the pressure to tetrafluoroethylene, the internal pressure of the reaction system becomes 8
It was press-fitted until it reached kg / cm ² . To this, ammonium persulfate (having a half-life of 46.3 hours at 55 ° C. The amount of ammonium persulfate decomposed up to 3 hours after the initiation of the polymerization was 1.2 × 10 ^-6 mol / liter at a polymerization temperature of 50 ° C). (Water) 0.2 l of an aqueous solution of 715 mg was added to initiate polymerization.

In the polymerization, tetrafluoroethylene is continuously injected so that the internal pressure of the reaction system is maintained at 8 kg / cm ^2, and 22.5% by weight of tetrafluoroethylene with respect to the weight of the aqueous medium is consumed. After that, the monomer was released. After cooling to room temperature, the obtained polytetrafluoroethylene bulk powder was taken out and coarsely pulverized. After the coarse powder was dried, it was pulverized with a fine pulverizer until the average particle size became about 30 μm to obtain a modified polytetrafluoroethylene resin powder.

Example 1 1 kg of the modified polytetrafluoroethylene resin powder obtained in Production Example 1 was placed in a reactor. The temperature inside the reactor was raised to 150 ° C., and the atmosphere in the reactor was removed by purging with nitrogen for 1 hour. While maintaining the temperature at 150 ° C., a mixed gas (fluorine / nitrogen (weight ratio) = 30/70) obtained by diluting fluorine gas (F ₂ ) with nitrogen gas as a fluorine radical source under atmospheric pressure at a flow rate of about 0.5 Nl / min. For 300 minutes (54-72 g of a fluorine radical source addition amount (that is, the amount of fluorine gas)). Immediately after the completion of the reaction, the inside of the system was replaced with nitrogen gas for 1 hour to remove fluorine gas. A starch / iodide test was performed to confirm the absence of fluorine in the inert gas by the presence or absence of coloring of the indicator. The temperature of the reaction vessel was cooled to room temperature, and various physical properties of the obtained resin powder were evaluated.
The results are shown in Table 1.

Example 2 The same operation as in Example 1 was carried out except that the reaction temperature was changed to 250 ° C., and various physical properties of the obtained resin powder were evaluated. The results are shown in Table 1.

Example 3 In Example 1, the concentration of the mixed gas was changed to fluorine / nitrogen (weight ratio) = 10/90 (a fluorine radical source addition amount of 18 to 2).
The same operation was performed except for changing to 4 g), and various physical properties of the obtained resin powder were evaluated. The results are shown in Table 1.

Example 4 In Example 2, the concentration of the mixed gas was changed to fluorine / nitrogen (weight ratio) = 10/90 (a fluorine radical source addition amount of 18 to 2).
The same operation was performed except for changing to 4 g), and various physical properties of the obtained resin powder were evaluated. The results are shown in Table 1.

Example 5 In Example 1, the concentration of the mixed gas was changed to fluorine / nitrogen (weight ratio) = 5/95 (fluorine radical source added amount 8 to 11).
Except for g), the same operation was performed, and various physical properties of the obtained resin powder were evaluated. The results are shown in Table 1.

Comparative Example 1 Various physical properties of a modified polytetrafluoroethylene resin powder which did not react with a fluorine radical were evaluated. The results are shown in Table 1.

Comparative Example 2 The same operation as in Example 1 was performed except that only nitrogen gas was used instead of the fluorine / nitrogen mixed gas, and various physical properties of the obtained resin powder were evaluated. The results are shown in Table 1.

Comparative Example 3 In Example 1, the concentration of the mixed gas was set to fluorine / nitrogen (weight ratio) = 5/95, and the concentration was 1 at a flow rate of about 0.5 Nl / min.
Keep flowing for 2 minutes (fluorine radical source added amount 0.32 ~
Except for 0.44 g), the same operation was performed, and various physical properties of the obtained resin powder were evaluated. The results are shown in Table 1.

[0044]

[Table 1]

The following results were obtained by fluorination according to the present invention. <Amount of Residual Perfluorovinyl Ether Monomer> The adsorbed residual monomer was decomposed and removed, and the absorption peak of the perfluorovinyl ether monomer was not detected by gas chromatography.

<Extractable Fluoride Ion> The remaining adsorbed monomer was decomposed and removed, and the thermally or chemically unstable terminal (-COF, -CF _2. , -C
Conversion of F ₂ CH ₂ OH, —COOH, etc.) to the most stable —CF ₃ terminus reduced the extractable fluoride ion by ２〜 to ６.

<Residual radical (tetrafluoroethylene consumption by additional polymerization)> Radical terminal (-CF _2. )
However, due to the conversion to the most stable —CF ₃ terminal, tetrafluoroethylene monomer was hardly consumed even when additional polymerization was performed using a resin powder as a starting species.

<Contact angle with water> Terminals having a large critical surface tension (-COF, -CF _2. , -CF ₂ CH ₂ OH, -COO
H etc.) were converted to -CF ₃ terminals having a remarkably low critical surface tension, whereby the contact angle with water was improved by 10 ° or more.

<Coloring degree (value of Z by colorimetric colorimeter)> The adsorbed residual monomer was decomposed and removed, so that the black color inside the fired product was eliminated.

[0050]

According to the present invention, (1) the amount of fluoride ions that can be extracted is reduced. (2) The radical terminal (-CF)_Two-CF_Two・) Is the most stable
-CF_Two-CF_Three(3) Perfluorovinyl ether monomer is decomposed and removed
Is obtained. The resulting modified polytetrafluoroethylene resin is stable
And Si, SiO _TwoAnd corrosiveness to metal surfaces
Less and has improved water and oil repellency. Also, resin powder
HF is not generated from the resin powder without acid odor.
The inside of the molded product is not colored and the resin powder is a reactive substance
Can be used in applications that come into contact with.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Takayuki Tanaka, Inventor 1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industries, Ltd. Yodogawa Works F-term (reference) 4J100 AC26P AE09Q BB18Q CA04 DA09 DA61 EA05 HA21 HB03 HC04 HC25 HE20

Claims (10)

[Claims] 1. The method according to claim 1, wherein the perfluorovinyl ether unit is contained in 0.1.
A modified polytetrafluoroethylene molding resin powder containing from 0.1 to 1% by weight, wherein: a) the residual amount of perfluorovinyl ether monomer remaining in the resin is 50 ppb or less; b) a fluorine extractable from the resin With a content of 10
0 ppb or less; and c) the resin has a melt viscosity at 380 ° C. of 1 × 10 ⁸ to 1 × 1.
A non-melt-processable modified polytetrafluoroethylene molding resin powder having a pore size of 0 ¹² poise. 2. The powder according to claim 1, wherein the amount of the tetrafluoroethylene monomer newly reacting in 1 minute per 1 g of the powder when the additional polymerization reaction is performed is 1 × 10 ⁻⁵ mol or less. 3. The powder according to claim 1, wherein a contact angle with water of a molded product obtained by molding the powder is 110 ° or more. 4. The powder according to claim 1, wherein the Z value of a molded product obtained by molding the powder is 90 or more as measured by a colorimeter. 5. The powder according to claim 1, wherein the perfluorovinyl ether is perfluoro (alkyl vinyl ether). 6. The powder according to claim 5, wherein the perfluoro (alkyl vinyl ether) is perfluoro (propyl vinyl ether). 7. The method according to claim 1, wherein the modified polytetrafluoroethylene resin powder is brought into contact with a reactive gas containing a fluorine radical source, and then the fluorine radical source is replaced with an inert gas. A method for producing a powder as described in 1. 8. The fluorine radical source is fluorine (F ₂ ),
The method of claim 7, wherein the method is selected from halogenated fluorides, rare gas fluorides, and nitrogen-containing fluorine compounds. 9. The method according to claim 7, wherein the reactive gas is heated to 100 ° C. or higher to generate fluorine radicals. 10. The reactive gas has a wavelength of 150 to 700 nm.
The method according to claim 7, wherein a fluorine radical is generated by irradiating light.