JP3931382B2 - Polytetrafluoroethylene powder and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polytetrafluoroethylene powder and a method for producing the same, and more particularly to a polytetrafluoroethylene powder excellent in water and oil repellency and a method for producing the same.
[0002]
[Prior art]
Polytetrafluoroethylene (PTFE) is commercially available in the form of powder as a raw material for molding, and has heat and cold resistance, flame resistance, slidability, non-adhesiveness, antifouling properties, chemical resistance, weather resistance, electrical properties, etc. Therefore, various molded products are used in various fields. In addition, PTFE fine particles and powder are dispersed in other materials or blended with other materials and used as a modifier.
[0003]
The PTFE powder for molding is obtained by agglomerating a polymer from a powder (molding powder or granular) obtained by finely pulverizing a granular resin produced by a suspension polymerization method and a latex obtained by an aqueous dispersion (emulsion) polymerization method. There are two types of powders (fine powders) that are obtained, and both are in practical use. These two types of powders are processed by completely different forming methods. For example, the former is processed by compression molding or ram extrusion, and the latter is processed by paste extrusion molding or rolling (calender) molding performed by mixing a liquid lubricant.
[0004]
PTFE fine powders and molding powders as molding raw materials usually have an extremely high molecular weight and are not used for modification of other materials by dispersion or blending except in special cases. The biggest reason these powders are unsuitable for dispersion or blending is that they cause fibrillation during dispersion or blending.
The fibrillation property of PTFE is a property that appears strongly in a virgin polymer that has not been subjected to a heat treatment at or above its melting point after polymerization, and is particularly strong in colloidal particles and fine powders produced by emulsion polymerization.
[0005]
Fine powder is usually formed by “paste extrusion” in which a paste containing a lubricating aid is filled into a cylinder with a narrow orifice and extruded cold, and the extrudate is fired into a tube or wire coating. Alternatively, it is rolled into a film to be used as a seal tape, and further rolled and used as a porous film after rolling. Paste extrusion processing is established by the fibrillation characteristics of colloidal PTFE fine particles, and the fine particles are fibrillated during extrusion and entangled with each other, thereby imparting a certain degree of mechanical strength to the molded product before heat treatment.
[0006]
However, since fibrillation easily occurs even with extremely small shearing force, when fine powder or molding powder is dispersed or blended with other materials, fibrils are generated by the shearing force received during blending, and PTFE particles once aggregate. It becomes difficult to re-disperse, and a uniform dispersed state cannot be maintained. In addition, the occurrence of fibrils causes problems such as abnormal high viscosity and inability to mix uniformly. Even with high molecular weight PTFE, once subjected to a heat treatment (usually a treatment at a melting point or higher), the fibrillation characteristics are almost lost. However, unless special pulverization such as freeze pulverization is performed, an ordinary fine pulverizer is more than 70 μm. It is difficult to obtain a fine powder, and a fine powder that is practical for dispersion or blending cannot be obtained, for example, since the shape of the particles has increased anisotropy.
[0007]
However, the fibrillation characteristics of virgin PTFE depend on the molecular weight of PTFE and are expressed at a certain molecular weight or higher, and fibrillation characteristics do not appear with low molecular weight PTFE. Therefore, low molecular weight PTFE fine particles and powders have been commercially available for dispersion or blending.
When the low molecular weight PTFE is seen from the particle form, it is roughly classified into agglomerated powder of colloidal particles, or a powder that is once melted and densified and then pulverized. For applications requiring submicron fine dispersion such as paint, the use of agglomerated powder of colloidal particles is particularly suitable. In general, the particle diameter of the aggregated powder is 1 to 30 μm, but the aggregated powder is redispersed by the shearing force during blending, so that it can be easily finely dispersed in submicron units. On the other hand, the particle size of the densified powder depends on the particle size in the pulverization, and generally 1 μm or less is impossible, and is inappropriate for applications requiring submicron fine dispersion.
[0008]
Various techniques have been proposed as a method for producing low molecular weight PTFE fine particles and powder.
For example, in Japanese Patent Publication No. 57-22043 and Japanese Patent Publication No. 51-25275, in a general emulsion polymerization of PTFE, a low molecular weight PTFE is obtained by using a chain transfer agent, and the obtained colloidal PTFE aqueous dispersion is obtained. A method for obtaining a powder by coagulating and drying the powder is disclosed.
In addition, a method for reducing the molecular weight by thermal decomposition of high molecular weight PTFE (for example, Japanese Patent Publication No. 50-15506 and Japanese Patent Publication No. 38-20970) and a method for reducing the molecular weight by irradiating high molecular weight PTFE with radiation (for example, JP-B-52-25419 and JP-B-49-48671) are known.
[0009]
However, the above-mentioned low molecular weight PTFE fine particles and powders do not provide a sufficient effect in applications requiring water and oil repellency. On the other hand, PTFE having a fluorinated molecular end is known to be suitable, and various coating compositions and water-repellent treatment compositions have been proposed.
[0010]
Japanese Patent Laid-Open No. 7-26169 discloses a paint in which a tetrafluoroethylene (TFE) oligomer fluorinated up to the molecular end is dispersed in a paint material, and describes that water repellency is improved.
In addition, JP-A-8-3477, JP-A-8-3479 and JP-A-8-3544 disclose a coating material and a treatment in which low molecular weight PTFE having a molecular weight of 500 to 20000 and fluorinated to the terminal is added. An agent is disclosed that describes improved water repellency and anti-snow properties.
However, the molecular weights of these disclosed PTFEs are very low and volatilize on heating and cannot be used in baking paints.
[0011]
Various techniques have also been proposed for a method for producing PTFE having molecular ends fluorinated.
Japanese Examined Patent Publication No. 46-23245 discloses a method of stabilizing a terminal group of a high molecular weight perfluorocarbon polymer excluding a low molecular weight wax with a fluorine radical source.
Japanese Patent Publication No. 1-49403 and Japanese Patent Publication No. 1-49404 disclose a method for producing a fluorine-containing resin in which a fluorine-containing polymer is brought into contact with a fluorine radical source at 250 to 550 ° C. Since PTFE is a lump, a pulverization step is required to obtain a powder. Moreover, even if pulverized, the particle diameter remains at a few μm, and fine dispersion of submicron is difficult.
[0012]
Japanese Patent Publication No. 6-67859 discloses that a fluorine-containing resin is heated to a melting point to 600 ° C. and reacted with a fluorine radical source at an atmospheric temperature of 200 to 600 ° C. for the purpose of further reducing the molecular weight and increasing the yield. Although the method of cooling the reaction product gas to 100 ° C. or lower is disclosed, the disclosed production method has a poor yield, and the molecular weight of the obtained PTFE is extremely low and easily volatilizes by heating. Addition to polyacetal, etc., tends to cause mold deposits (adhesion to the mold) during molding, resulting in poor appearance of the molded product, and baked coating at high temperature, volatile components adhere to the coating surface and gloss There is a problem such as losing.
[0013]
Furthermore, in Japanese Patent Publication No. 7-5744, in some cases, the heat treatment is performed in the presence of a fluorine radical source, and after pulverization, the average particle size is 1 to 30 μm and the specific surface area is 2 to 6 m.²/ G of PTFE powder is disclosed, but the particle diameter of PTFE by the disclosed production method is large, and fine dispersion in a paint or the like is difficult.
[0014]
[Problems to be solved by the invention]
In general, paint coating methods include a method of curing at normal temperature and a method of baking by heating, but the baking temperature ranges from about 150 to about 400 ° C. depending on the type of matrix resin. On the other hand, fluorinated PTFE is used as a water-repellent coating component, however, the PTFE has a low molecular weight, so that it has a high volatile content due to heating, or the powder has a large particle size, so the fine dispersibility is poor.
An object of the present invention is to provide a PTFE powder having good water repellency and oil repellency, capable of being baked on, and having excellent fine dispersibility, and a method for producing the PTFE powder.
[0015]
[Means for Solving the Problems]
  In order to solve the above problems, the present invention provides a number average molecular weight of 40000 to 600000, 7 to 20 m.²A polytetrafluoroethylene powder having a specific surface area of / g, an average particle diameter of 1 to 30 μm, and a contact angle with water of 110 to 125 ° is provided.
  Furthermore, the present invention provides, as one method for producing the PTFE powder of the present invention, a number average molecular weight of 40,000 to 600,000 and a specific surface area of 7 to 20 m.²Agglomerated powder of colloidal polytetrafluoroethylene particles having an average particle diameter of 1 to 30 μm,At a temperature of 100 to 300 ° C.Provided is a production method comprising reacting with a fluorine radical source.
[0016]
As described above, low molecular weight PTFE that does not exhibit fibrillation properties is generally used for dispersion or blending. However, since the molecular weight measurement method common to the low molecular weight body and the high molecular weight body of PTFE has not been used so far, the boundary of the molecular weight at which fibrillation characteristics are manifested is unclear.
[0017]
As a conventional method for measuring the molecular weight of PTFE, for example, a method of obtaining the number average molecular weight from the melting point is known, but this method can be applied only to PTFE having a melting point of less than 327 ° C. The molecular weight of the high molecular weight PTFE is Cannot be measured.
For the high molecular weight PTFE for molding, a method for obtaining the number average molecular weight from the standard specific gravity (SSG) is known. This method is based on the premise that a molded body having a standard specific gravity can be obtained. However, since low molecular weight PTFE has a low melt viscosity, it cannot melt and flow during firing to obtain a molded product, or even if a molded body is obtained, cracks and foaming often occur, and the standard specific gravity cannot be measured. It is almost impossible to measure the molecular weight of low molecular weight PTFE by this method.
Therefore, by using a common molecular weight measurement method from low molecular weight to high molecular weight and quantitatively examining the molecular weight and fibrillation characteristics of PTFE having different molecular weights, the boundary between the molecular weights where the fibrillation characteristics are manifested can be clarified.
[0018]
Number average molecular weights obtained by polymerizing PTFE having different molecular weights by aqueous dispersion (emulsion) polymerization method, aggregating and drying the resulting latex to prepare powders, and measuring dynamic viscoelasticity at the time of melting (of the measurement method) Details are described by S. Wu in Polymer Engingering & Science, 1988, Vol. 28, 538, 1989, Vol. 29, 273) and the elongation of green beads obtained by paste extrusion. Looking at the relationship between the average molecular weight and the elongation, even if the number average molecular weight is 500,000 or less, even a continuous paste extrusion bead cannot be obtained. In the range of 500,000 to 600,000, a continuous paste extrusion bead is not obtained, or even if it is obtained, there is almost no elongation of the unfired bead and fibrillation characteristics do not appear. However, when the number average molecular weight exceeds 600,000, elongation clearly appears and fibrillation characteristics are exhibited.
[0019]
The PTFE powder of the present invention has a number average molecular weight of 40,000 to 600,000 (preferably 60000 to 500,000), and those having less than 40,000 have a large amount of volatile components at high temperatures and are used for heat resistant paints such as paints that require baking. Inappropriate. Moreover, when the number average molecular weight exceeds 600,000, the fibrillation characteristics are manifested, and the cohesive strength between colloidal particles is strong, so that the fine dispersibility is poor.
The above number average molecular weight range corresponds to about 324 to 333 ° C. at the melting point as a conventional measuring method, and about 1 × 10 5 at a melt viscosity at 380 ° C.^Three~ 7 × 10^FiveCorresponds to PaS.
[0020]
The specific surface area of the PTFE powder of the present invention correlates with the particle diameter. The larger the specific surface area, the smaller the particle diameter, and it is used as a measure of the particle diameter (primary particle diameter) of the basic unit constituting the aggregated powder.
Specific surface area is 7-20m²/ G, preferably 9-15 m²/ G. Specific surface area is 7m²When the particle size is less than / g, the primary particle size is large and the fine dispersibility is poor. 20m²When the amount exceeds / g, it is necessary to use a special dispersant during polymerization or use a large amount of dispersant, which is not economical.
[0021]
The average particle size of the PTFE powder of the present invention is 1 to 30 μm, preferably 2 to 20 μm. When the average particle size is less than 1 μm, the bulk density of the powder is small and the handleability is poor. Moreover, since the cohesion force between primary particles is strong, what exceeds 30 micrometers is hard to disperse | distribute finely.
[0022]
The PTFE powder of the present invention is obtained by reacting unsintered PTFE obtained by coagulating and drying a colloidal PTFE aqueous dispersion with a fluorine radical source at 100 to 300 ° C, preferably 150 to 250 ° C. Can be manufactured by.
When the reaction temperature is less than 100 ° C., the reaction rate is low and the productivity is inferior. Moreover, when it exceeds 300 degreeC, since primary particles fuse | melt, it cannot disperse | distribute finely. Moreover, volatile matter increases and productivity is inferior.
[0023]
Any fluorine radical source conventionally used in fluorination can be used. For example, molecular fluorine (F₂); ClF, ClF_Three, BrF_Three, IF_ThreeHalogenated fluorides such as XeF₂, XeF_Four, KrF₂Noble gas fluoride such as NF_Three, NF₂A nitrogen-containing fluorine compound such as can be used.
[0024]
The addition amount of the fluorine radical source depends on the reaction time and the reaction temperature, but is 0.01 to 1 part by weight, preferably 0.1 to 0.5 part per 100 parts by weight of the raw material powder in terms of fluorine atoms. Parts by weight. If it is less than 0.01 parts by weight, it is necessary to lengthen the reaction time, resulting in poor productivity. The upper limit of the amount added is not particularly limited, and the unreacted component existing in excess can be recovered and reused, but up to 1 part by weight is sufficient.
[0025]
As the reactor to be used, any reactor can be used as long as it has a heating device and is in a form in which a gas and a solid are in contact with each other. For example, those having a reaction shelf in an air circulation furnace or those capable of achieving good gas-solid contact such as a fluidized bed are preferable.
[0026]
The green PTFE used in the production method of the present invention is obtained by coagulation and drying of an aqueous colloidal PTFE dispersion. This colloidal PTFE aqueous dispersion can be produced, for example, by the following production method.
Examples of the water-soluble fluorine-containing dispersant include a general formula:
X (CF₂)_aCOOH
(Wherein, X represents a hydrogen atom, a fluorine atom or a chlorine atom, and a represents an integer of 6 to 12),
General formula:
Cl (CF₂(CFCl)_bCF₂COOH
(Wherein b represents an integer of 2 to 6),
General formula:
(CF_Three)₂CF (CF₂CF₂)_cCOOH
(Wherein c represents an integer of 2 to 6), or
General formula:
F (CF₂)_dO (CFYCF₂O)_eCFYCOOH
(In the formula, Y is a fluorine atom or CF._Three, D represents an integer of 1 to 5, and e represents an integer of 1 to 5. )
Or an ammonium salt or an alkali metal salt thereof (for example, potassium salt, sodium salt) or the like can be used. In particular the general formula:
C_nF_{2n + 1}COOX or
C_ThreeF₇O (CF (CF_ThreeCF₂O)_lCF (CF_ThreeCOOX
(In the formula, n represents an integer of 6 to 9, l represents an integer of 1 to 2, and X represents an ammonium group or an alkali metal atom.)
It is preferable to use the compound shown by these.
[0027]
The usage-amount of a water-soluble fluorine-containing dispersing agent is 0.02-0.5 weight% with respect to the aqueous medium used for reaction, Preferably it is 0.03-0.5 weight%.
[0028]
As the polymerization initiator, any of those conventionally used in the polymerization of TFE can be used, for example, persulfates such as ammonium persulfate and potassium persulfate, water-soluble water such as disuccinic acid peroxide and diglutaric acid peroxide. Organic peroxides can be used. Of these, persulfate is preferable.
[0029]
The polymerization temperature can be selected from a wide range of 10 to 95 ° C. When using a persulfate as a polymerization initiator, 40 to 80 ° C. is appropriate. When the reaction is performed at a low temperature, it is preferable to add a reducing agent such as sulfite or acidic sulfite to the persulfate to make a redox system.
The polymerization reaction is usually allowed to proceed while maintaining a pressure in the range of 0.6 to 3.9 MPa, preferably 0.9 to 3.0 MPa by gas pressurization of TFE itself.
[0030]
TFE and at least one other olefin of 1% by weight or less may be copolymerized. Other olefins include, for example, the general formula:
X (CF₂)_nO_yCF = CF₂
(In the formula, X represents a hydrogen atom, a fluorine atom or a chlorine atom, n represents an integer of 1 to 6, and y represents 0 or 1.)
And the general formula:
C_ThreeF₇(OCF₂CF₂CF₂)_m[OCF (CF_ThreeCF₂]_pOCF = CF₂
(In the formula, m and p each represent an integer of 0 to 4. However, these are not 0 at the same time.)
A compound represented by the formula: chlorotrifluoroethylene (CTFE), vinylidene fluoride (VdF), trifluoroethylene (TrFE) and the like can be used.
[0031]
If necessary, as chain transfer agents, hydrogen and hydrocarbons such as methane, ethane, propane, butane; CH_ThreeCl, CH₂Cl₂, CH₂CF₂Halogenated hydrocarbons such as water-soluble organic compounds such as methanol and ethanol can be used.
[0032]
In some cases, as a dispersion stabilizer in the reaction system, 2 to 10 parts by weight of a hydrocarbon having a carbon number of 12 or more which is substantially inert to the reaction and liquid under the reaction conditions may be used. it can. In order to adjust the pH during the reaction, for example, ammonium carbonate or ammonium phosphate may be added as a buffering agent.
[0033]
The resulting colloidal PTFE particles usually have a particle size of 0.05 to 0.5 μm, and the polymer concentration of the PTFE particle aqueous dispersion is usually 10 to 45% by weight based on the aqueous medium. The resulting colloidal PTFE aqueous dispersion (referred to as polymer latex or simply latex) is removed from the reaction vessel and transferred to the next step, namely the coagulation and drying step.
[0034]
Coagulation is usually carried out by diluting the polymer latex with water to a polymer concentration of 10 to 20% by weight and, in some cases, adjusting the pH to neutral or alkaline and then reacting in a vessel equipped with a stirrer. Stir more vigorously than stirring. At this time, stirring may be performed while adding a water-soluble organic compound such as methanol or acetone, an inorganic salt such as potassium nitrate or ammonium carbonate, or an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid as a coagulant. Further, coagulation may be performed continuously using an inline mixer or the like.
[0035]
The wet powder obtained by coagulation is usually dried using means such as vacuum, high frequency, and hot air. The drying temperature is 10 to 250 ° C, preferably 100 to 200 ° C. Since the PTFE powder at this point is a powder in which colloidal particles are aggregated, the specific surface area is usually 7 to 20 m.²/ G value.
[0036]
The number average molecular weight of PTFE obtained by the polymerization reaction is adjusted to 40000-600000, preferably 60000-500000. Those having a number average molecular weight of less than 40,000 are not preferable because they have a high volatile content at high temperatures. Further, those exceeding 600,000 exhibit fibrillation characteristics, and are therefore unsuitable for blends that require fine dispersion.
[0037]
The PTFE powder of the present invention is preferably used for dispersion or blending, and is suitably used for a water- and oil-repellent paint, particularly a baking type water- and oil-repellent paint. It can also be used as a water / oil repellency imparting agent for thermoplastic resins and thermosetting resins.
In addition, secondary batteries using primary or secondary batteries, especially secondary batteries using nickel compounds as positive electrode active materials, and electrode materials such as battery active materials and conductive carbonaceous materials for imparting water repellency to fuel cells. It can also be used as an additive, or as a water / oil repellency or lubricity imparting agent for thermoplastic resins and thermosetting resins. Typical secondary batteries include nickel-hydrogen secondary batteries and nickel-cadmium batteries. Since the PTFE powder of the present invention is easy to finely disperse and rich in water repellency, the addition thereof efficiently forms a gas-liquid-solid three-phase interface in the electrode, and the gas generated by the electrode reaction diffuses quickly, The reaction back to oxide or hydride is promoted.
[0038]
The analysis method and test method of polymer latex and PTFE powder in this specification are as follows.
1) Number average molecular weight
S. The method of Wu (Polymer Engingering & Science, 1988, Vol. This method is a method for calculating the number average molecular weight, weight average molecular weight, and molecular weight distribution from the elastic modulus at the time of melting of the resin, and is particularly useful for measuring the molecular weight of a resin insoluble in a solvent represented by PTFE.
The measuring apparatus used the rheometrics viscoelasticity measuring machine RDS-2, and measured the dynamic viscoelasticity in 380 degreeC. However, a parallel plate is used as a jig for holding the sample, the thickness when the sample is melted is 1.4 to 1.5 mm, and the frequency range is 0.001 to 500 rad / sec.
The deformation amount of the sample at the time of melting is selected from a range of 0.8 to 3% on the circumference with respect to the thickness of the sample when the frequency is 1 rad / second or more, and 2 to 2 when the frequency is 1 rad / second or less. Select from a range of 10%. The sampling frequency of the measurement values is 5 points per digit at regular logarithmic intervals.
Further, in two consecutive measurements, the measurement is repeated until the average deviation of the storage elastic modulus (G ′ (ω)) at each measurement frequency (ω) is 5% or less.
Using the frequency (ω) and storage elastic modulus (G ′ (ω)) obtained by measurement, S.P. The number average molecular weight (Mn) was determined according to the method of Wu (Polymer Engineering & Science, 1988, Vol. 28, 538, 1989, Vol. 29, 273). However, time t = 1 / ω and G (t) = G ′ (ω).
[0039]
2) Elongation of unfired beads
50 g of PTFE powder and 9.2 g of hydrocarbon oil (trade name ISOPER-E, manufactured by Exxon Chemical Co., Ltd.) as an extrusion aid are mixed in a glass bottle and aged at room temperature (25 ± 2 ° C.) for 1 hour. Next, the above mixture was filled in an extrusion die with a cylinder (inner diameter: 25.4 mm) (with an aperture angle of 30 degrees and an orifice having an inner diameter of 2.54 mm and a land length of 7 mm), and the piston inserted into the cylinder was charged with 5 Apply a 7 MPa load and hold for 1 minute. Immediately thereafter, the mixture is extruded from the orifice at room temperature at a ram speed of 20 mm / min to obtain a rod. The obtained rod-like extrudate is dried at about 100 ° C. for about 10 hours, and 5 samples having a length of about 7 cm are cut from the latter half where the extrusion pressure is stable. About 15 mm of each end of each sample is fired in a 380 ° C. salt bath, and a scale with a spacing of 20 mm is marked in the center of the surface in the longitudinal direction. Next, both ends of the sample are grasped with a clamp of a tensile tester, the sample is pulled at a constant speed of 200 mm / min, and the length between the graduations (E_l) And calculate elongation (%) using the following formula.
[0040]
[Expression 1]
Elongation (%) = (E_l(mm) -20 (mm)) / 20 (mm) × 100
The number of tests is 5 times, and the value of 3 times excluding the maximum value and the minimum value is averaged to obtain the elongation (%). During the tensile test, the room temperature is adjusted to 24 ± 0.5 ° C.
[0041]
3) Polymer concentration
10 g of polymer latex is collected in a petri dish, dried at 150 ° C. for about 3 hours, and evaporated to dryness. The solids are weighed and from this the polymer concentration is calculated.
[0042]
4) Number average particle diameter of polymer latex
For a known sample, the transmittance of 550 nm projection light with respect to the unit length of the polymer latex diluted with water to a solid content of 0.15% by weight, and the number reference length determined by measuring the fixed direction diameter with a transmission electron micrograph Using a calibration curve prepared by measuring the average particle diameter, the average transmittance is determined from the transmittance measured for each sample.
[0043]
5) Average particle size of powder
Particles corresponding to 50% of the integrated particle size distribution are measured using a laser diffraction particle size distribution measuring device (HELOS & RODOS) manufactured by JEOL Ltd., without using a cascade, with a pressure of 0.1 MPa and a measurement time of 3 seconds. Let the diameter be the average particle diameter.
[0044]
6) Specific surface area of powder
According to the BET method, measurement is performed using MONOSORB manufactured by QUANTA CHROME as an apparatus. A mixed gas of 30% nitrogen and 70% helium is used as a carrier gas, and cooling is performed with liquid nitrogen. The sample amount is 2 g, and the measurement is performed three times to obtain the average value as the specific surface area.
[0045]
7) High temperature volatiles
10g of sample is put in an aluminum cup (capacity 50ml, upper diameter 61mm, lower diameter 42mm, depth 33mm), and kept in an atmosphere of 300 ± 2 ° C for 1 hour in a hot air circulating electric furnace adjusted to the heating temperature in advance. The weight is measured, and the high temperature volatile content is obtained by the following formula.
[0046]
[Expression 2]
High temperature volatile content (% by weight) = (10 (g) −weight after heat treatment (g)) / 10 (g) × 100
[0047]
8)Preparation of contact angle measurement data from powder
In accordance with ASTM D4894-89 (the mold uses a mirror-finished surface), an unfired PTFE compression molded body for SSG (standard specific gravity) measurement is prepared, and this is used as a sample for contact angle measurement.
9)Contact angle
The contact angle of the surface of the molded body or coating film was measured with a droplet having a diameter of 3 mm using a contact angle meter (CA-DT • A type manufactured by Kyowa Interface Science Co., Ltd.). The measurement is performed three times, and the average value is taken as the contact angle.
[0048]
【Example】
Example 1
A stainless steel (SUS316) anchor-type stirring blade and a temperature control jacket are provided, and a stainless steel (SUS316) autoclave with an internal volume of 100 liters is charged with 54 l of deionized water and 11.6 g of ammonium perfluorooctanoate, While heating to 55 ° C., the inside of the system was replaced with nitrogen gas three times and TFE gas twice to remove oxygen. Then CH_ThreeCharge 330 g of Cl, bring the internal pressure to 0.83 MPa with TFE gas, stir at 80 rpm, and keep the internal temperature at 55 ° C.
[0049]
Next, when an aqueous solution in which 14.3 g of ammonium persulfate is dissolved in 1 liter of water is injected with TFE and the internal pressure of the autoclave is set to 0.88 MPa, the reaction proceeds at an accelerated rate. Meanwhile, the reaction temperature is maintained at 55 ° C. and the stirring speed is maintained at 80 rpm. TFE is continuously supplied so that the internal pressure of the autoclave is always kept at 0.88 ± 0.05 MPa.
The reaction was terminated when 10.3 kg of TFE monomer was consumed, stirring and monomer supply were stopped, and the gas in the autoclave was immediately released to normal pressure.
The total reaction time was 5.3 hours, and the number average particle size was 0.18 μm. Further, the polymer concentration of the obtained latex was 15.8% by weight.
[0050]
The obtained latex was coagulated and washed, and then the polymer powder was dried at 140 ° C. for 18 hours. The raw material powder obtained has a specific surface area of 11 m.²The number average particle diameter of the powder was 5 μm. Moreover, the number average molecular weight of the polymer was 140000.
After charging 5 kg of the obtained raw material powder into a stainless steel (SUS316) reaction vessel provided in an air circulation furnace, the inside of the reaction vessel was replaced with nitrogen to remove air, and the reaction vessel was adjusted to 240 ° C. The temperature inside the furnace was raised. Next, fluorine (F₂) 12 g was charged in a reaction vessel and held at 240 ° C. for 2 hours to complete the fluorination reaction. Immediately after the reaction, the inside of the system was replaced with nitrogen to remove fluorine (F2), the temperature of the reaction vessel was cooled to room temperature, and the powder was taken out.
[0051]
The specific surface area of the obtained powder is 11 m.²/ G, the number average particle diameter of the powder was 5 μm, and the number average molecular weight of the polymer was 140000. The high-temperature volatile component was extremely low at 0.09% by weight, and the contact angle with water was 119 °, indicating excellent water repellency.
[0052]
Paint addition test
39.2 g of the obtained PTFE powder and 4.7 g of carbon black (Seast 116 manufactured by Tokai Carbon Co., Ltd.), 39.2 g of polyethersulfone (Victrex 4100P manufactured by Sumitomo Chemical Co., Ltd.) in advance, and N-methyl-2 -178 g of pyrrolidone (Dainippon Ink Chemical Co., Ltd.), 66.6 g of methyl isobutyl ketone (Futaba Chemical Co., Ltd.), 39.2 g of methyl ethyl ketone (Futaba Chemical Co., Ltd.) and toluene (Osaka Petrochemical Co., Ltd.) ) It was mixed and dispersed in a solution dissolved in 39.2 g of a mixed solvent to obtain a paint.
[0053]
The obtained paint was spray-coated on a degreased aluminum plate (thickness: 2 mm), dried at 120 ° C. for 15 minutes, and further baked at 380 ° C. for 15 minutes to obtain a coated plate.
The surface of the resulting coating film had a water contact angle of 118 °, indicating excellent water repellency. In addition, n-hexadecane (CH_Three(CH₂)₁₄CH_Three, Manufactured by Tokyo Chemical Industry Co., Ltd.) was 43 °, indicating excellent oil repellency.
[0054]
Example 2
Fluorination was performed under the same conditions as in Example 1 except that the raw material powder obtained in Example 1 was used and the fluorination reaction temperature was changed to 280 ° C. The specific surface area of the obtained powder is 9m²/ G, the number average particle diameter of the powder was 7 μm, and the number average molecular weight of the polymer was 140000. The high-temperature volatile component was extremely low at 0.08% by weight, and the contact angle with water was 117 °, indicating excellent water repellency.
[0055]
Example 3
A stainless steel (SUS316) anchor-type stirring blade and a temperature control jacket are provided, and a stainless steel (SUS316) autoclave with an internal volume of 6 liters is mixed with 2960 ml of deionized water, 3.0 g of ammonium perfluorononanoate and liquid paraffin ( 120 g of Kishida Chemical Co., Ltd., reagent grade 1) was charged, and the system was replaced with nitrogen gas three times and TFE gas twice while heating to 70 ° C. to remove oxygen. Thereafter, 75 cc of ethane gas is charged, the internal pressure is adjusted to 0.83 MPa with TFE gas, the mixture is stirred at 250 rpm, and the internal temperature is maintained at 70 ° C.
[0056]
Next, when an aqueous solution obtained by dissolving 60 mg of ammonium persulfate in 40 ml of water is injected with TFE and the internal pressure of the autoclave is set to 0.88 MPa, the reaction proceeds at an accelerated rate. During this time, the reaction temperature is maintained at 70 ° C. and the stirring speed is maintained at 250 rpm. TFE is continuously supplied so that the internal pressure of the autoclave is always kept at 0.88 ± 0.05 MPa.
The reaction was terminated when 1260 g of TFE monomer was consumed, stirring and monomer supply were stopped, and the gas in the autoclave was immediately released to normal pressure. The total reaction time was 11.5 hours, and the number average particle size was 0.15 μm. The polymer concentration of the obtained latex was 29.6% by weight.
[0057]
The obtained latex was coagulated and washed, and then the polymer powder was dried at 140 ° C. for 18 hours. The specific surface area of the obtained raw material powder is 15 m.²The number average particle diameter of the powder was 10 μm. The number average molecular weight of the polymer was 420,000.
[0058]
The amount of raw material powder is 500 g, and fluorine (F₂) Was fluorinated under the same conditions as in Example 1 except that the amount charged was 1.2 g. The specific surface area of the obtained powder is 15 m.²/ G, the number average particle diameter of the powder was 10 μm, and the number average molecular weight of the polymer was 420,000. The high-temperature volatile content was extremely small at 0.07% by weight, and the contact angle with water was 120 °, indicating excellent water repellency.
[0059]
Example 4
The reaction was carried out in the same procedure as in Example 3 except that the amount of ethane charged was 68 cc and the consumption of TFE monomer was 1290 g. The total reaction time was 10.4 hours, and the number average particle size was 0.16 μm. Further, the polymer concentration of the obtained latex was 30.1% by weight.
The obtained latex was treated in the same manner as in Example 3 to obtain a raw material powder. The specific surface area of the obtained powder is 14 m.²The number average particle size of the powder was 12 μm. The number average molecular weight of the polymer was 530000.
The obtained raw material powder was fluorinated under the same conditions as in Example 3. The specific surface area of the obtained powder is 14 m.²/ G, the number average particle diameter of the powder was 12 μm, and the number average molecular weight of the polymer was 530000. The high-temperature volatile content was as extremely low as 0.07% by weight, and the contact angle with water was 121 °, indicating excellent water repellency.
[0060]
Comparative Example 1
The water contact angle of the raw material powder obtained in Example 1 was measured to be as small as 95 ° and the water repellency was inferior. The raw material powder obtained in Example 1 was subjected to the same paint addition test as Example 1. As a result, the water contact angle of the coating film was as small as 109 °, and the contact angle of n-hexadecane was also 33 °. The water repellency and oil repellency were inferior.
[0061]
Comparative Example 2
In an autoclave similar to that in Example 3, 2960 ml of deionized water and 4.5 g of ammonium perfluorooctanoate were charged, and the system was replaced with nitrogen gas three times and TFE gas twice while heating to 70 ° C. Oxygen was removed. Then CH_Three30 g of Cl is charged, the internal pressure is adjusted to 0.83 MPa with TFE gas, the mixture is stirred at 250 rpm, and the internal temperature is kept at 70 ° C.
[0062]
Next, when an aqueous solution obtained by dissolving 2.25 g of ammonium persulfate in 40 ml of water is injected with TFE and the internal pressure of the autoclave is set to 0.88 MPa, the reaction proceeds at an accelerated rate. During this time, the reaction temperature is maintained at 70 ° C. and the stirring speed is maintained at 250 rpm. TFE is continuously supplied so that the internal pressure of the autoclave is always kept at 0.88 ± 0.05 MPa.
The reaction was terminated when 540 g of TFE monomer was consumed, stirring and monomer supply were stopped, and the gas in the autoclave was immediately released to normal pressure.
The total reaction time was 8.2 hours and the number average particle size was 0.17 μm. Further, the polymer concentration of the obtained latex was 15.3% by weight.
[0063]
The obtained latex was coagulated and washed, and then the polymer powder was dried at 140 ° C. for 18 hours. The obtained raw material powder has a specific surface area of 13 m.²The number average particle diameter of the powder was 4 μm. The number average molecular weight of the polymer was 30000.
The obtained raw material powder was fluorinated under the same conditions as in Example 3. The specific surface area of the obtained powder is 11 m.²/ G, the number average particle diameter of the powder was 6 μm, and the number average molecular weight of the polymer was 30000. The contact angle with water was 119 °, indicating excellent water repellency, but the high-temperature volatile content was extremely high at 0.59% by weight.

Claims (4)

A polytetrafluoroethylene powder having a number average molecular weight of 40,000 to 600,000, a specific surface area of 7 to 20 m ² / g, an average particle diameter of 1 to 30 μm, and a contact angle with water of 110 to 125 °. ^{2. The} polytetrafluoroethylene powder according to claim 1, having a number average molecular weight of 60,000 to 500,000, a specific surface area of 9 to 15 m ² / g, and an average particle diameter of 2 to 20 μm. An aggregated powder of colloidal polytetrafluoroethylene particles having a number average molecular weight of 40,000 to 600,000, a specific surface area of 7 to ²⁰ m ² / g, and an average particle diameter of 1 to 30 μm is obtained at a temperature of 100 to 300 ° C. The method for producing polytetrafluoroethylene powder according to claim 1, wherein the polytetrafluoroethylene powder is reacted with a fluorine radical source.   The manufacturing method of the polytetrafluoroethylene powder of Claim 3 made to react with a fluorine radical source at 150-250 degreeC.