JPH0730134B2 - Melt-processable tetrafluoroethylene copolymer and its production method - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to melt-pvocessible tetrafluoroethylene copolymers having good particle flow properties and thermal stability.

Such melt processable copolymers are extruded onto wire,
Alternatively, it can be extruded into a film or tube, or used as a coating, or it can be used in rotomolding or lining of barrels for making hollow products.

BACKGROUND OF THE INVENTION There are two types of tetrafluoroethylene polymers. One is a non-melt processable polymer, which has too high a melt viscosity to be processed by conventional melt extrusion methods. Instead, these polymers are usually sintered or paste extruded, depending on the type of polymer produced. Another class is melt-fabricable tetrafluoroethylene copolymers with melt viscosities in the range of melt extrusion possible.

Direct melt processable tetrafluoroethylene (TFE) copolymer resins from the polymerizer and / or coagulator are called fluffs or powders. Fluffs are usually stabilized by wet heat treatment and / or melt extrusion, as described in US Pat. No. 3,085,083. There are applications such as rotocasting when it is preferred to make a free-flowing powder (hereinafter referred to as granule) into melt-extruded pellets, or when a high purity resin is desired. Rotoring and rotation coating (ro
tocoating is from several technical points of view.
Although different from (olding), in this specification, the term rotary casting is used for the sake of convenience and to refer to these three inclusively unless otherwise specified.

It is desirable to improve the particle properties to facilitate handling of such granules. Melt-processible copolymers coagulated and dried from aqueous dispersions are friable and tend to produce fine powders which give poor handleability. It would be desirable to provide melt-processable copolymers that are stable and easy to handle with minimal processing steps. It would be particularly desirable to provide a copolymer that can be used both in conventional melt processing methods and in rotary casting methods where particle properties are important.

It is also desirable to obtain a thermally stable resin. Many stabilization methods are known in the art, most of which require melting of the resin. Thus, the resins stabilized by these methods are generally available only as pellets and, unless a cumbersome and costly re-milling step is used, are obtained as the free-flowing granules upon which the present invention is based. It is not possible.

Another desirable feature of such resins is that the metal contamination of the granules should be minimal. When granules are melted in conventional thermoplastic processing equipment, the corrosion-resistant alloys will form when the corrosive tetrafluoroethylene copolymer melt comes into contact with the internal metal surface of the thermoplastic processing equipment. Even when used, unavoidable contamination occurs. For applications in the semiconductor industry, copolymers with low levels of metal contamination are especially desirable.

SUMMARY OF THE INVENTION The usual product forms for melt-fabricable tetrafluoroethylene copolymers are either extruded pellets, i.e. strand cut right cylinders, or melt cut discs or cylinders. These pellets are used as a feedstock for thermoplastic processing equipment.

Another product form for melt-processible tetrafluoroethylene copolymers is a very fine powder. This product form is used as a feed for industrially known coating operations.

The subject of the invention is a new product form, namely a free-flowing, attrition-resistant, generally spherical, thermostable granule. These granules are of high purity and are thermally stable in air, and are produced by a process for producing freely upright rotomoulded products and defect-free polymer coatings or linings, especially metalworking equipment for rotolining. It has particular utility in providing what has been produced. The new composition has improved thermal stability and low foaming tendency. More specifically, the composition comprises 80-99.5 mol% tetrafluoroethylene.
A melt processable, substantially non-elastomeric tetrafluoroethylene copolymer comprising 0.5 to 20 mole% of at least one copolymerizable monomer, the copolymer comprising: (a) 0.1 × at 372 ° C. 10 melt viscosity of ⁴ to 100 × 10 ⁴ poise, (b) substantially spherical coefficient less than the particle morphology and 1.5 spherical (s
phere factor), (c) an attrition coefficient of less than 60, (d) less than 80 total unstable end groups per 10 ⁶ carbon atoms,
And (e) having an average particle size of 200 to 3000 micrometers.

The process of the present invention starts with a melt-fabricable tetrafluoroethylene copolymer which has been polymerized in an aqueous medium and which has labile end groups. When produced in an aqueous medium, the copolymer is isolated by solvent-assisted coagulation prior to gelation. The solidified granules thus obtained have a spherical shape that is easy to handle. The granules are then placed on a differential scanning calorimeter
Tial scanning calorimeter (DSC) Dry and harden (ie heat-treat the granules to harden it by exposing them to a high temperature between the melting point and 25 ° C below the melt onset temperatare) But do not completely melt or substantially deform it). Curing also facilitates sieving or mechanical sieving to the desired particle size and ease of handling to reduce friability. The unstable end groups are then converted to stable fluorinated end groups by exposing the granules to a fluorine-containing atmosphere, thereby reducing foaming or volatile generation during subsequent end-use thermal processing. Let

These granules are particularly well suited for rotary casting because of the optimum particle size and free-flowability combined with a low foaming tendency.

Another advantage of the stabilized free-flowing granules of the present invention is that such granules are not melt processed in conventional thermoplastic processing equipment and therefore have low metal contamination.

Description of the Invention Representative ethylenically unsaturated comonomers that can be copolymerized with tetrafluoroethylene are represented by the formula: In the formula, R ₁ is -Rf, -Rf-X, -O-Rf or -O-Rf-
X, where Rf is a perfluoroalkyl group having 1 to 12 carbon atoms, and -Rf- is a perfluoroalkylene divalent group having 1 to 12 carbon atoms having a bond at each end of the chain. There, and X is H or Cl; and R ₂ is -Rf or -Rf-X.

Specific copolymerizable fluorinated ethylenically unsaturated comonomers include hexafluoropropylene, perfluoro (methyl vinyl ether), perfluoro (n-propyl vinyl ether), perfluoro (n-heptyl vinyl ether), 3,3,3. -Trifluoropropylene-1,3,3,
4,4,5,5,6,6,6-nonafluorohexene-1,3-hydroperfluoro (propyl vinyl ether), or
Includes mixtures thereof, such as, for example, a mixture of hexafluoropropylene and perfluoro (propyl vinyl ether). Comonomers formula Rf-O-CF = CF ₂ perfluoro (alkyl vinyl ether); or hexafluoropropylene; it is preferably selected from or a compound of formula Rf-CH = CH _2, wherein -Rf 1 to 12 carbon Atomic perfluoroalkyl group.

The comonomer content can range from 0.5 mole percent to about 20 mole percent, and more than one comonomer can be present.

The comonomer content is such that the copolymer is a plastic rather than an elastomer, that is, the copolymer is partially crystalline and, after extrusion, stretches from room temperature to 2 times its original length to its initial length. It should be low enough so that it does not exhibit significant shrinkage.

Aqueous copolymers of TFE and various comonomers are known. The reaction medium consists of water, a monomer, a dispersant, a free radical polymerization initiator, optionally a chain transfer agent and, optionally, a water immiscible fluorocarbon phase as described, for example, in U.S. Pat.No. 3,635,926. ing.

Polymerization temperatures of 20-140 ° C and pressures of 1.4-7.0 MPa are commonly used. Generally higher temperatures and pressures are used to increase the rate of polymerization, especially when the comonomer is less reactive compared to TFE. Either the TFE and optionally the comonomer are continuously fed to the reactor to maintain the reaction pressure, or in some cases the comonomer is added initially and the pressure is maintained only by the TFE feed. The monomer (s) are fed until the desired final dispersion solids (15-50%) are achieved. The reactor agitation rate may be kept constant during the polymerization or it may be varied to control the polymerization rate.

Commonly used initiators are free radical initiators such as ammonium or potassium persulfate, or disuccinic acid peroxide. The dispersant is 0.01-0.5 percent, preferably 0.05, based on the weight of the aqueous medium.
Present in an amount of ~ 0.1 percent.

The term "melt processible" means that the copolymer can be processed (ie, processed into shaped articles such as films, fibers, tubes, wire coatings, etc.) by conventional melt processing equipment. This requires the melt viscosity of the copolymer at the processing temperature to be less than 10 ⁷ poise. Melt viscosity at 372 ℃ is 10 ⁴ to 10 ⁶
It is preferably in the range of poise.

Melt viscosities of polymers that can be melt processed are measured by American Society For Testing End Materials Method D-1238, modified as follows: Cylinder, Orifice and Piston Tips are, for example, Heinness Stellite (trade name) 19 or It is made of a corrosion-resistant alloy, such as Inconel ™ 625. 372
5.0g in a cylinder with an inner diameter of 9.53mm kept at ℃ ± 1 ℃
Insert the sample. Five minutes after charging the sample into the cylinder, it is extruded under a load (piston + weight) of 5,000 g through an orifice with a square edge 2.10 mm in diameter and 8.00 mm in length. This corresponds to a shear stress of 44.8 Kpa. Melt viscosity in Poise units is calculated as 53170 divided by the extrusion rate measured as grams per minute.

The copolymer produced by the above water-based polymerization method is colloidally dispersed in the polymerization medium. The polymer is recovered from this dispersion by coagulation. Normal coagulation of aqueous polymer dispersions by mechanical shear tends to give very fine powders with poor handling properties. Various methods may be used to obtain suitable relatively large particle sizes. It is possible to obtain relatively large spherical particles using a combination of mechanical stirring and certain scientific additives. In the method of the present invention, the aqueous dispersion is gelled with a gelling agent and a mineral acid with stirring. Nitric acid is preferably used as the gelling agent. Then a liquid that is immiscible with water is added to the gel while continuing to stir. The gel separates into separate phases of water and liquid wet polymer particles. The particles are then dried. The size of the granules is a function of the particle size of the dispersion, the ratio of liquid immiscible liquid to polymer, and stirring conditions. The size of the granules, as desired, is much larger than the size achieved if the dispersion is solidified by mechanical shearing alone. Usually, the amount of liquid immiscible with water is 0.25 per part of polymer, based on dry weight.
~ 1.0 copy. About 0.1-10 per 100 parts by weight of polymer
Some HNO ₃ can be used. Nitric acid is preferred because it is not corrosive to stainless steel and readily vaporizes during subsequent baking steps. Coagulated particles obtained by this method generally have a particle size of 200 to 3000 micrometers. The product is separated, washed and dried at 80-150 ° C for 4-30 hours.

Liquids that are immiscible with water preferably have a surface tension of 35 dynes / cm or less at 25 ° C and a normal boiling point in the range of 30 to 150 ° C. Typical examples of immiscible liquids that can be used in the present invention are, for example, hexane, heptane, gasoline and kerosene,
Or liquid hydrocarbon of aliphatic hydrocarbons such as mixtures thereof, for example aromatic hydrocarbons such as benzene, toluene and xylene, such as carbon tetrachloride, monochlorobenzene, trichlorotrifluoroethane, difluorotetrachloroethane and chlorotrifluoroethylene. It is a halogenated derivative such as an oligomer.

Other methods can also be used to obtain the preferred particle size in the present invention. A nucleating agent can also be added to the aqueous dispersion before coagulation, which gives a relatively large particle size. Small polymer particles obtained by mechanical coagulation can be redispersed in a two-phase liquid mixture, which can be aggregated into larger particles. The polymerization itself is water /
It is also possible to carry out with immiscible liquid mixtures, whereby particles of the desired particle size are obtained directly from the polymerization.

The dried particles are generally spherical and have a spheroidal coefficient of less than 1.5, preferably less than 1.2. The spherical coefficient is a measure of the degree of roughness of the particles. A sphere factor of 1 represents a geometrically spherical particle.

The particles then have a fineness factor of 60, as noted herein.
It is cured by heat treatment to less than 25, preferably less than 25 but before the granules agglomerate.

The term "before granulation agglomerates" means that the D50 as defined later does not increase by more than 20%.

The thermosetting of the granules formed in the solidification stage occurs at a temperature relatively close to the melting point of the copolymer. The temperature at which cure occurs depends not only on the melting point of the copolymer but also on other properties such as comonomers and molecular weight distribution. These properties affect the temperature at which the onset of melting occurs.

This thermosetting phenomenon occurs when the copolymer granules are kept at a temperature within the range of 25 ° C below the melting point and melting start temperature of the copolymer as measured by the differential scanning calorimeter (DSC) described below. Occurs in The granules must be exposed to temperatures in this range for a sufficient time to impart a useful degree of cure. The resulting thermoset granules do not melt completely but only partially sinter. When the heat of fusion ratio as defined below is less than 1.2,
The polymer granules are melting and beginning to fuse. After heat setting, the granules have a degree of hardness that is useful during subsequent steps in the manufacturing process and also during melt processing in preventing abrasion and particulate formation.

The manufacturing process for granules is sometimes screen granulation where the whole granules are mechanically pressed through a mesh of selected mesh size that destroys oversized particles while retaining useful particle properties.
It can also include sizing. Some lump formation occurs during heat curing and fluorination. Such sieving granulation is effective in removing these lumps, which adversely affect the rotary casting operation.

These particles have unstable end groups. The end groups present in the untreated polymer obtained directly from the polymerization are
It depends on the initiator used and the presence of pH and molecular weight regulators. For example, when using ammonium persulfate or potassium as the initiator, the terminal groups of the polymers are essentially all the carboxylic acid groups (-CO ₂ H). Acid end groups are found in both monomeric and dimeric forms. In the presence of pH regulators such as ammonium hydroxide, most of the carboxylic acid ends are amide ends (-CON
H ₂ ). Vinyl end (-CF
= CF ₂ ) is generally not a direct result of the polymerization, but is the result of decarboxylation of the initially formed carboxylic acid end. The acid fluoride end (-COF) is generally generated by air oxidation of the vinyl end. All of the terminal groups of the (except -CF ₂ H) is believed a thermally and / or hydrolytically unstable. This is what the term "labile end groups" means. These tend to create bubbles or voids during melt processing. These voids can adversely affect the physical or electrical properties of the manufactured product. It is desirable to have less than 80 of these labile end groups per 10 ⁶ carbon atoms in the polymer.

The labile end groups can be reduced by treatment of the polymer with fluorine. The fluorination can be carried out using various fluorine radical generating compounds, but it is preferable to bring the polymer into contact with fluorine gas. Since the reaction with fluorine is extremely exothermic, it is preferable to dilute fluorine with an inert gas such as nitrogen. The content of fluorine in the fluorine / inert gas mixture can be from 1 to 50% by volume, preferably from 10 to 30%. Although any reaction temperature between 0 ° C and the melting point of the polymer can be used, a temperature range of 130-200 ° C is practical for a reasonable reaction time (1-5 hours under fluorine). It appears to be. Agitation is preferred to continuously expose the polymer to fresh surfaces. The atmospheric pressure during fluorination can range from atmospheric pressure to 1 MPa. If a normal pressure reactor is used, it is expedient to continuously pass the fluorine / inert gas mixture through the reactor. After exposing the polymer for the desired time, excess fluorine is driven out of the sample and then the sample is cooled.

Perfluoromethyl most of unstable terminal groups by fluorine is converted to (-CF ₃₎ ends.

Suitable copolymers must have a heat of fusion ratio greater than 1.2. Heat of fusion ratio means the ratio of heat of fusion to the first melting to heat of fusion recorded for the second melting. These indicate that the particles are not completely melted.

Test Method Bubble Index The bubble index test described in the examples was carried out as follows: a 15 g sample of the copolymer was used, a diameter of about 50 mm, a depth of 16 mm,
Weigh into a new clean aluminum pan 0.08 mm thick. The sample (along with a control for comparison) is calcined in a hot recirculating air oven for 40 minutes at 50 ± 5 ° C. above its melting point. Baking time is defined as the sample exposure time between closing and opening the oven door. Set the oven air temperature in advance and recover the set temperature within 5-10 minutes after putting the sample. After cooling to room temperature, the polymer test piece is removed from the pan. The extent of bubble formation can be qualitatively observed and can be quantified by the percentage increase in the specific volume of the test piece relative to the bubble-free polymer. The bubble index is defined as: Where G = specific gravity of the bubble-free copolymer, measured by ASTM method D-792.

A = Net weight of sample in air.

W = Net weight of the sample in water due to the water displacement method.

The exposed total bubble index test piece is weighed in air and water by an electronic balance to an accuracy of 0.01 g. To determine the net weight of a test piece immersed in water, hang a stainless steel wire device with depth indicia from a small ring stand on a balance and tare the device into the device. Set to zero in water before dipping to a fixed depth. About 800 ml of deionized water containing 1 drop of Triton® X-100 or X-500 surfactant is used for immersion at room temperature. The specimen is observed in water to confirm a constant immersion depth and the absence of bubbles on the specimen surface.

Coefficient of Friction Particle hardness is measured by the following sieving test: Equipment: Fritsch Pulverisette, 24
-0217-000 (Techmer Company, Cincinnati, Ohio) Sieve (US standard test sieve) -Height 51mm x diameter 203mm x 30 mesh For D50 granules over 700 micrometers-Height 51mm x diameter 203mm × 80 mesh for D50 granules less than 700 micrometer Pan and lid, 203mm diameter 19mm diameter stainless steel balls (32g each) Method: 100.0g of polymer (Ws), pre-weighed (Wo) Place on a pan. Cover with a dome-shaped lid and put it in the flitch barberizette (trade name) device. Set the amplitude to 1.5 mm in advance (3 amplitude settings).

Attach the retaining band to the lid and tighten it securely. Set the timer to 10 minutes and start running. After 10 minutes the lid and sieve are removed and the polymer adhering to the inside of the bottom edge of the sieve is scraped into the pan. Weigh the bread (W ₁ ). 12
Place one stainless steel ball on the sieve, reassemble the pan / sifter / lid and place in the Parverisese.
After 10 minutes, the sieve is disassembled again, and the polymer adhering to the inside of the bottom edge is again slid into the pan. Reweigh the bread and contents (W ₂ ). Calculate the fineness factor as follows: Measurement of Spherical Coefficient A small amount of sample is placed on a glass slide of a microscope and dispersed in a single layer by slight shaking before taking a micrograph. On the print, the maximum and minimum diameters (a and b) of each particle were determined for more than 30 particles selected for the Rydam,
Accurately measure within ± 5%.

Calculate the sphericity coefficient according to the method of US Pat. No. 3,911,072 as follows: (n = number of particles measured) End group analysis The end groups in the fluorocarbon polymer are quantified by the infrared spectrum of the compression molded film. This method is described in existing patents such as US Pat. No. 3,085,083.

Quantitative measurement of the number of end groups is performed using the extinction coefficient measured for the model compound containing the end group of interest. Relationship is terminated group, a calibration factor determined from the absorption wavelength and model compounds, the following: wavelength calibration coefficients end groups micrometers _{(CF) -COF 5.31 406 -CO 2} H (M) 5.52 335 -CO 2 H ( D) 5.64 320 -CONH ₂ 2.91 914 -CF = CF ₂ 5.57 635 M = monomer, D = dimer The calibration rate is a mathematical conversion value for giving the end group value as the number of end groups per 10 ⁶ carbon atoms. . The concentrations of various end groups in polymer films are generally obtained by the formula: Where the film thickness is in millimeters (± 0.
003 mm).

Some of the peaks of _{absorbance, -CO 2 H (D),} - if the CO ₂ H (M), and -CF = CF ₂ end group are present all, there may interfere with each other. -CO ₂ H (D) (hydrogen-bonded carboxylic acid dimer) and -CF = correction for the absorbance of CF ₂ end groups have been developed. These are (where μ is the wavelength micrometer): The presence of -CONH ₂ also interfere with the absorbance of the acid and -CF = CF _2. Their presence is generally predictable, as these groups are generally the result of additives to the polymerization. The presence of −CONH ₂ absorbance near 5.6 micrometers is 2.9.
It can be checked by searching for the CONH ₂ secondary absorption band at 1 micrometer.

Polymer films (thickness 0.25-0.30 mm) were transferred using a Perkin-Elmer 283B spectrophotometer containing a film of the same thickness known to contain no end groups under analysis during instrumental measurements. To scan. The device is set to a response time setting of 1, a scan time setting of 12 minutes, a vertical axis expansion of 2, a horizontal axis expansion of 2, a slit program of 7, and an auto-check gain control of 20%. The film is then scanned over the relevant region of the spectrum ensuring that a suitable baseline is established on both sides of the absorption concerned.

Polymer films are generally compression molded at 270-350 ° C. The presence of certain salts, especially alkali metals, can lead to decomposition of the end groups in this temperature range. When these salts are present, the film should be cast at the lowest temperature possible.

Determination of Hexafluoropropylene (HFP) Content H in the melt-processable TFE / HFP copolymers described herein
The FP content is the absorption at 10.18 μm in the infrared and 4.2
Quantify by measuring the ratio of absorption at 5 micrometers. This ratio is referred to as HFP index or HFPI. A control film of known HFP content, quantified by F ¹⁹ NMR for HFPI calibration, is also measured. HFP mole percent present is HFP
It is equal to 2.1 times I. A compression molded film having a thickness of about 0.10 to 0.11 mm is scanned under a nitrogen atmosphere.

Determination of Perfluoropropyl Vinyl Ether (PPVE) Content The PPVE content in the melt-processible TFE / PPVE copolymers described here is also quantified by infrared spectroscopy. The ratio of the absorbance at 10.07 micrometers to the absorbance at 4.25 micrometers is measured under a nitrogen atmosphere using a film about 0.05 mm thick. The film is compression-molded at 350 ° C and then immediately cooled in ice water. The PPVE content is then determined from this absorbance ratio using a calibration curve established with a control film of known PPVE content. F ¹⁹ NMR is used as the primary standard for calibration of control films.

Average Particle Size US Pat. No. 3,929,721 describes a method for dry sieve analysis. “Average particle size” refers to ASTM D-145 modified as follows:
Measure by the dry sieving method according to the method of 7-81a (12.3.3). A sieve set with a diameter of 203 mm is sequentially assembled with the largest mesh being the upper end. From the U.S. standard test sieve size table (ASTM E-11 standard), 4 to 8 contiguous sieves with a mesh between 6 and 200 mesh expected to have an average particle size within that range are selected. Choose.

Preferably obtained using a test splitter and 0.01 g
A 40-60 g representative portion of the sample to be tested, accurately weighed to, is placed in the topmost sieve. The set of sieves is shaken in a sieve shaker (typically a "Lotusup" brand shaker obtained from Fisher Scientific, Cat. No. 4-909). After shaking,
Accurately weigh 0.01 g of residual material on each sieve.

The weight average particle size was determined based on the results of plotting the cumulative residual percentage and the sieve mesh on log probability paper as described in the method of ASTM D-1921-63, or by equivalent computer writing of these data. decide. The average particle size in micrometers is read from the plot at the 50th percentile (D50) on the horizontal axis of the cumulative weight percentage remaining.

DSC Analysis DSC analysis is performed on a DuPont 1090 thermal analyzer using the 910 DSC cell base and the DuPont General Analysis Program, version 1.0. As the manufacturer recommends the device, 1
Calibrate with 0 mg indium standard. A sample amount of polymer is 6-10 mg, which is placed in an aluminum capsule. Different heating and cooling cycles are used depending on the melting point of the sample. The sample is 90 ± 5 ℃ below the melting endothermic peak temperature.
Scan twice over the melting endotherm from a low temperature to a high temperature of 40 ± 5 ° C at a heating rate of 10 ° C per minute. Between the highest and lowest scan temperature of the sample between the first and second endothermic scan
Cool at a rate of 10 ° C / min. “Melting endothermic peak temperature” is defined as the peak temperature of the first melting endotherm. The heats of fusion (H ₁ and H ₂ ) are calculated from the first and second melting scans, respectively. The "heat of fusion ratio" (Hm ratio) is defined as H ₁ / H ₂ .
Heats of fusion H ₁ and H ₂ range from 80 ° C below the peak temperature to 30 above the peak temperature.
Determined by instrumental integration using a baseline up to ° C. The "melting onset temperature" is determined graphically by plotting the derivative of the first melting scan using the DuPont General Analysis Program, version 1.0. This is defined as the temperature at which the extended derivative curve first increases by 0.2 mW / min from the zero baseline (on the cold end of the melting curve).

Example 1 TFE in aqueous media using ammonium persulfate and potassium initiators and ammonium perfumerocaprylate surfactant according to the general method of US Pat. No. 4,380,618.
And HFP are polymerized to produce tetrafluoroethylene / fuxafluoropropylene (TF
E / HFP) copolymer, HFP 7.6 mol% was obtained. This copolymer was diluted in 500 ml deionized water with 1250 ml dispersion in a 3.5 liter stainless steel beaker (diameter 152 mm) equipped with four equally spaced rectangular streak plates protruding 13 mm into a beaker. (Solid content 26.4%) was used to coagulate. The blades of the stirrer have a diameter of 17 ° at a pitch of 35-40 ° C that pushes upwards from the horizontal when rotating clockwise.
4 pieces of 34mm × 17mm × 3.2mm (thickness) welded on the axis of mm
Had a blade. The blade diameter was 85 mm. The contents were stirred at 900 rev / min and 3.0 ml of 70% by weight nitric acid was added to give a thick gel. After 3 minutes, 160 ml of Freon (trade name) 113 was added to break the gel to make the polymer powder. The stirring was stopped after 5 minutes. The aqueous phase was poured out, 1000 ml of deionized water was added and the polymer was stirred at 500 rpm for 5 minutes. The aqueous phase is poured out again and the polymer is
Dry in an air oven at 0 ° C. for 4 hours. This entire procedure was repeated 3 more times to obtain a total of 1500 g of polymer (melt viscosity 3
At 72 ° C. 6.2 × 10 ⁴ poise) was obtained. This copolymer
Sift on a 30-mesh screen to remove fines, 1210
A product with a D50 in micrometers and a spheroidal coefficient of 1.33 was obtained. About 1000 g of this polymer was divided into 8 essentially equal samples using a sample divider. Seven samples were fired under various conditions in an air oven to cure the granules. The eighth sample was left unfired for comparison. The attrition coefficient measured for all eight samples is shown below.

All temperatures for samples 1 to 7 are 2 from the DSC melting onset temperature
It is between 5 ℃ lower temperature and melting endothermic peak temperature.

Two samples of this polymer (125 g of each sample after sieving to remove fines), that is, a sample in which granules were hardened by firing at 239 ° C. for 4 hours and a second sample which was not fired were treated with nitrogen. Fluorination was performed in a stainless steel shaker tube at 160 ° C. for 4 hours at a gauge pressure of 0.69 MPa using 25% fluorine in the atmosphere. The total treatment time was just 5 hours. These samples were sieved on a 30 mesh screen and the amount of particulate produced during the shake tube treatment was measured with the following results: The results of DSC were as follows: Before calcination After calcination Peak temperature 262 ℃ 263 ℃ Melting heat ratio 1.45 1.56 Melting onset temperature 248 ℃ 244 ℃ Dry polymer has 440 unstable end groups per 10 ⁶ carbon atoms Was. No unstable end groups were observed after fluorination.

Example 2 A TFE / HEP copolymer (5.9 mol% HEP) was polymerized with ammonium perfluorocaprylate dispersant and ammonium persulfate initiator at 3.1 MPa cage pressure at 95 ° C. The resulting dispersion (19.0% polymer) was coagulated as in Example 1. On a dry basis, 6 parts of 60 wt% nitric acid per 100 parts of copolymer and 93 parts of Freon® 113 were used. The nitric acid was removed by washing the polymer several times with deionized water.
The freon was distilled off by washing with warm water (60 ° C.) under slight vacuum. The polymer was separated from the aqueous phase and dried / calcined in a 220 ° C. circulating air oven for 8 hours. Analysis was for 448 per 10 ⁶ carbon atoms -COF, -CO ₂ H (monomer), and -CO ₂ H
It showed the presence of unstable end groups consisting of (dimers).

A 22.7 kg portion of the calcined granules was treated with fluorine at 190 ° C. for 3 hours while rotating in a container as described below. The fluorination reactor was a 0.1 m ³ double cone mixer equipped with a gas inlet and exhaust connection and an electric heating mantle. The gas inlet was submerged in the particles and the outlet was towards the gas phase. A steady state was maintained when the lines were connected and the mixer was rotated. After placing the polymer granules in the reactor, they were sealed and spun at 5 rpm. The polymer was heated with both an electric heating mantle and a stream of preheated air flowing through the reactor. When the polymer reached the desired temperature, the air flow was interrupted and vacuum was applied. The pressure was raised to normal pressure using a mixture of fluorine / nitrogen (25% / 75% by volume) and this mixture was continuously fed into the reactor while maintaining the temperature with an electric mantle heater. Then use a damp starch-iodine paper and supply gas until no fluorine is detected in the exhaust gas.
Switched to 100% nitrogen and continued. The resin was then cooled using cold air leading into the reactor. The reactor was then opened and the resin collected. The granules had the following properties: Melt viscosity 12.6 × 10 ⁴ Poise Average particle size (D50) at 372 ° C 1480 micrometer Milling coefficient 54.4 Spherical coefficient 1.16 10 ⁶ Unstable end groups per carbon atom 21 DSC Heat of Melt Ratio 1.60 Fluorinated granules were fed to a 32 mm diameter Waldron-Hartig extruder having a 20: 1 length / width ratio barrel and coated onto AWG # 20 19/32 stranded copper wire.
No electrical defects were observed in the coating in either of the two extruder temperature profiles. 69kV for coated copper wire
It had an electrical strength of / mm (ASTM D-149).

Example 3 An aqueous dispersion of a copolymer of tetrafluoroethylene and 1.3 mol% purple oropropyl vinyl ether was prepared according to US Pat. No. 3,635,926. This dispersion, which contains 26.9% copolymer, uses ammonium persulfate initiator, ammonium perflucaprylate interfacial activator and ethane chain terminator, and ammonium hydroxide pH modifier and freon as a phase immiscible with water. Obtained by polymerizing the monomers in the presence of 113.

The above TFE / PPVE copolymer dispersion was coagulated at 35 ° C. in the same manner as in Example 2. With agitation, 5.8 parts of 60 wt% nitric acid and 85.5 parts per 100 parts of copolymer (dry basis) by polymerization
Part of Freon 113 was added.

The granules formed were washed with deionized water at 20 to 25 ° C three times with stirring, then once with wash water heated to 60 ° C to remove Freon 113, and finally once with water at 20 to 40 ° C. . The copolymer thus obtained was separated from the wash water and dried in a circulating air oven at 180 ° C. for 6 hours. The soft granule had the following properties.

Average particle size (D50) = 360 micrometers Fineness coefficient = 81.8 Spherical coefficient = 1.18 Melt viscosity = 3.9 × 10 ⁴ Poise at 372 ° C PPVE comonomer content = 1.3 mol% Melting heat ratio = 1.53 Melting endothermic peak temperature = 311 ° C melting initiation temperature = 287 ° C. bubble index = 26 infrared scan showed a slight vinyl and / or carboxylic acid end groups per 10 ⁶ amide end groups of carbon atoms per 93 and 10 ⁶ carbon atoms.

The resin was heat cured at about 285 ° C for 3 hours and then the granules were sieved through a 20 mesh screen.
It showed the following characteristic values: Average particle size (D50) = 340 micrometers Milling coefficient = 3.1 Melt viscosity = 7.9 x 10 ⁴ poise, PPVE comonomer content at 372 ° C = 1.3 mol% Melt heat ratio = 1.59 Melting endothermic peak temperature = 311 ° C Melting onset temperature = 289 ° C Bubble index = 66 The markedly reduced fineness shows a marked improvement in the hardness of the granules. Infrared analysis showed 88 amide end groups and few vinyl or carboxylic acid groups per 10 ⁶ carbon atoms.

The resin was fluorinated using a high pressure stainless steel cylindrical batch reactor equipped with a gas and vacuum connection, an electric heater and a shaker stirrer. The reactor was sealed by charging with polymer granules. First, after reducing the pressure, a gauge pressure of 1 MPa was applied with a fluorine / nitrogen mixture (25% / 75% by volume) at 190 ° C. The total processing time was just 5 hours including start-up, evacuation and cooling time. The granules were heated in a circulating air oven for 1 hour or more to remove traces of fluorine. The integrity of the particles was retained. The granules showed the following characteristic values: Average particle size (D50) = 285 micrometers Fineness factor = 6.3 Melt viscosity = 7.5 x 10 ⁴ Poise at 372 ° C Melting heat ratio = 1.60 Melting endothermic peak temperature = 311 ° C Melting onset temperature = 291 ° C Bubble index = 15 Infrared analysis showed the presence of less than 50 labile end groups per 10 ⁶ carbon atoms after fluorine.

Front Page Continuation (72) Inventor Richard Alan Morgan 26105 Vienna Apartment 3 Twenty Seventh Street 1013, West Virginia, United States 1013 (56) Reference JP-A-58-174407 (JP, A) JP-A-56- 131629 (JP, A) JP 50-161586 (JP, A) JP 46-23245 (JP, B1) JP 52-2428 (JP, B2) JP 55-45084 (JP, B2)

Claims (11)

[Claims] 1. A process for preparing granules of melt-processable, non-elastomeric, tetrafluoroethylene copolymer solidified particles prepared in an aqueous polymerization medium, the method comprising: Tetrafluoroethylene and 0.5-20
Mol% formula In the formula, R ₁ is Cl, —Rf, —Rf—X, —O—Rf or —O—
Rf-X, wherein Rf is a perfluoroalkyl group having 1 to 12 carbon atoms, and -Rf- is a perfluoroalkylene divalent group having 1 to 12 carbon atoms having a bond at each end of the chain. And X is H or Cl, wherein a melt-fabricable tetrafluoroethylene copolymer consisting of at least one copolymerizable comonomer of the formula: is solidified from its aqueous polymerization medium, where solidification is A liquid that is essentially immiscible with water, with mechanical stirring or the addition of a chemical gelling agent, to form a viscous gel of the copolymer and the medium, and then with mechanical stirring. B. separating the coagulated copolymer granules from the aqueous medium; C. removing the liquid from the separated copolymer granules by drying; D. drying Copolymerization Body granules at a temperature between 25 ° C below their differential scanning calorimeter melting onset temperature and their first melting endothermic peak temperature until the granule's attrition coefficient is less than 60 and co-weighted Partially sinter the coalesced granules before they become agglomerated; E. Copolymer granules in D above, in a fluorine gas containing atmosphere until the total number of labile end groups is less than 80 per 10 ⁶ carbon atoms. F. Then, the copolymer granules are separated from the fluorine gas-containing atmosphere. 2. A method according to claim 1, wherein the chemical gelling agent for coagulation is at least one mineral acid. 3. A method according to claim 2 wherein the chemical gelling agent is nitric acid. 4. A method according to claim 1, 2 or 3 in which steps D and E are carried out simultaneously. 5. 80 to 99.5 mol% tetrafluoroethylene and 0.5 to 20 mol% formula In the formula, R ₁ is Cl, —Rf, —Rf—X, —O—Rf or —O—
Rf-X, wherein Rf is a perfluoroalkyl group having 1 to 12 carbon atoms, and -Rf- is a perfluoroalkylene divalent group having 1 to 12 carbon atoms having a bond at each end of the chain. And X is H or Cl, consisting of at least one copolymerizable comonomer of, and melt-fabricable in which the majority of its labile end groups are converted predominantly into CF ₃ groups, A non-agglomerating granule of coagulated particles of a non-elastomeric tetrafluoroethylene copolymer, the copolymer comprising: (a) a melt viscosity at 372 ° C. of 0.1 × 10 ^{4 to} 100 × 10 ⁴ poise, (B) less than 80 total unstable end groups per 10 ⁶ carbon atoms,
Here it said distal Tanmoto is -COOH, -COF, -CF = CF ₂ or -CO
Including NH ₂ , and the granules have (c) a spherical morphology and a spheroidal coefficient of less than 1.5, (d) an attrition coefficient of less than 60, (e) an average diameter of 200 to 3000 micrometers. Granule characterized by that. 6. The granule according to claim 5, wherein the copolymer has a heat of fusion ratio of more than 1.20. 7. The copolymer is 0.5 × 10 ^{4 to} 20 at 372 ° C.
The granule according to claim 5 or 6, which has a melt viscosity of × 10 ⁴ poise and a weight average diameter of 200 to 500 micrometers. 8. The copolymer is 1 × 10 ^{4 to} 100 at 372 ° C.
The granule according to claim 5 or 6, having a melt viscosity of × 10 ⁴ poise and a weight average diameter of 700 to 3000 micrometers. 9. The granule according to claim 5, wherein the copolymerizable comonomer is hexafluoropropylene. 10. The method according to claim 5, wherein the copolymerizable comonomer is perfluoro (propyl vinyl ether).
Item or the granule according to item 6. 11. Claim 5 for use in rotary casting.
~ The granule according to any one of items 10.