DE1720479A1 - Process for the production of polytetrafluoroethylene - Google Patents

Description

The invention also relates to a method of manufacture τοη polytetrafluoroethylene duroh Polyaerieatlon τοη tetrafluoroethylene in watery mediua.

Polytetrafluoroethylene (hereinafter referred to as ale FTPE) for ForaTWecke is generally known by polyaerleation τοη tetrafluoroethylene (hereinafter referred to as TPS) at a temperature τοη ο bla 150 ° C under a pressure τοη 3 bia ICK »t in the presence of an aqueous medium using inorganic or organic peroxy de obtained as polymerization initiators. When pressure and temperature are selected to be low at this Polyaerisatlonsreaktion that Polymerlsationsgesohwindlgkeit (polymerization rate) low · Usually, the polymerization is therefore τοη at a temperature τοη JW to 100 ⁰ C under a Druok Ziirn lndeet 20 executed at.

In such a polymerization according to known processes, there is a tendency that some of the polymer tends to enlarge Pieces clumped together or on the wall of the reaction vessel or

81-POS.11.083-N8E (5)

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the stirring blades or paddles · Inside dleaee thaws aggregated polymers or polymers adhering to surfaces eloh then the Polymerisatlonswärme, which is not only disadvantageous affects the physical properties of the polymer obtained, but also poses a risk of explosion, so that polymerization on a large scale is difficult to carry out 1st. Welter makes the removal of the on the surfaces adhering polymers much trouble and the method is therefore for the industrial production of FTFE is unsuitable.

In order now to this co-operation or addition of the polymer ▼ prevent, is known to be a perfluorocarboxylic acid or a sal "added to such a stture. 80 became a procedure found in which the adhesion of the polymer by the addition of Ferfluorooctanoic acid or one of its salts (Japanese patent, Publication no. 11,985 / 61) or from ammonium perfluoroeaprylate (Japanese Patent Publication No. 1,539 / 64) is prevented. Because of the relatively high price of these perfluoroarboxylic acids, this is the case Process catfish, however, uneconomical.

As is well known, is usually folytetrafluoräthylenpulver preformed at the molding by applying pressure and then sintered above the second transition point (327 ⁰ C). The shape, corrugation and physical properties of the i-ulver therefore influence the quality or properties of the resulting shaped object to a great extent.

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With a coarse-grained powder, there are gaps between the grains, thereby affecting the electrical and other physical properties of the reformed object.

To obtain a luokenfrelen dense molded article made of PTFE must therefore τοη during the polymerization TFE accumulating particles are crushed or ground. At the Comminution of those obtained by a conventional polymerization process Polymer particles form a fibrous pulrer, which gives a dense molded article, such as in the Jap. Patent, Publication «-No. 10 177/59 described 1st. However, the flowability of this powder is impaired and the powder tends to form lumps or agglomerates for the handling of the powder »are disadvantageous. Welter loses an object preformed from such a powder if he is cooled after sintering without applying pressure, its surface smoothness as a result of shrinkage pads.

The aim of the invention is therefore an economical process for the polymerization of TFE, in which the formation of coagulated and adhering polymers is prevented and, in particular, coarse, soft tolymertellchen are obtained, even when comminuting form a non-fibrous (easy to handle) powder

One of the inventors, Yutaka Kometani, collaborated with others have already found that by polymerizing TFE, relative what particles do not become fibrous even if crushed and a method of making them

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of non-fibrous FTH powder is prepared in the nooh soh-looming Jap. Patent application Mr. 36 621/65 ^a deuteohe application D 44 954 rVd / 39c indicated. However, this non-fibrous, fine FTFK-FuIver could only be produced by crushing relatively soft, coarse PTFB particles, which are obtained by polymerizing TFB at low temperatures and pressure in the oasis phase with subsequent delivery of TFB to keep the druoke practically constant. at a temperature of 0 to 40 ° C, a pressure of up to 10 atm and in the presence of an aqueous medium with a known polymerization initiator. Even with this method, however, the polymer particles floating in the aqueous medium tend to agglomeration and adhesion, which causes difficulties in the production in industrial corn sticks.

Be has now been found dal agglomeration and adhesion of the polymer can be duroh ™ surprisingly prevents simple means, namely when powert holds the aqueous medium during polymerization uniform within a "certain range.

The process according to the invention for the production of polytetrafluoroethylene by polymerizing tetrafluoroethylene in an aqueous medium is therefore essentially characterized in that the polymerisation at a temperature of 0 to 20 ⁰ C and at a pressure of 0 to 0 at in an aqueous medium with an inorganic Polymerization

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BATH ORIGINAL

1720478

initiatorsyatem is performed and with a _pH value in the range 5.0 to 10.0 with the addition of a buffer in the necessary amount for maintaining a certain p "value in the aqueous medium during the polymerization.

According to the invention, polymer particles are obtained in a particularly economical manner which, when comminuted, do not have a ' fibrous granular polytetrafluoroethylene powder with a NaB sieve size of not more than 40 / U, a form factor of not more than 15, a factor for anisotropic expansion in the area from 1.02 to 1.26 and a surface smoothness of at least 15 seconds (a more detailed explanation of these Measurements follow below). The comminution takes place preferably through impact effects.

The Ρττ value of the aqueous medium is preferably between 6.5 and 9.5. If the _pH value is lower than 5.0, relatively soft coarse grains are obtained which coalesce au lumps and stick to the walls of the polymerization vessel. If the p _H "value is above 10.0, while agglomeration and adhesion of the polymer particles can be prevented, however, they are relatively hard and result in crushing a powder having a surface smoothness of less than 15 seconds.

The buffer can be added in an amount which is sufficient to maintain a given pn value during the reaction in the aqueous medium. For a given P _H value of 6.5, for example, 0.0j> to 1 part of potassium dihydrogen phosphate (KH ₂ PO /,) and 0.12 to 4 parts of disodium hydrogen phosphate (Na ₂ HPOu) and for one

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P _H -Vert yon 9.0 can "water can be used from 0.2 to 5 parts of borax per 1,000 part. The change in the p _H value within the above range is preferably within τοη +0.5, us to maintain the coarse grains of a defined hurt.

^ An inorganic leroxy compound, such as persulfate, is used as the polymerization initiator system. The addition lersulfatmenge depends tob from selected _pH value. For example, the used beträft Menpe of ammonium persulfate Torzugsweise 0.2 to 60 parts per 10 parts of water, when the _pH value at 6.5 and 9.0 However, is should 0.2 to 20 parts or from 2 to 40 T ? ll be used. If necessary, the initiator system can comprise one or more reducing agents. Alkali metal sulphite or alkali metal sulphite are used as reducing agents.

Welter can act as a beaktlons accelerator (promoter) hetalllon can be added. Silver or silver are effective as metal ions Elsenions.

The polymerization of TFB is carried out according to the invention a temperature of O and

20 ⁰ C and carried out at a pressure of 0 to 30 at, preferably between 0 and 1 at. The pressure during the polymerization is kept essentially constant by introducing TFB. TFE is preferably filled in the gas phase.

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BATH ORIGINAL

At temperatures above ⁴ ° C., as occur in known processes, relatively hard polymer particles are formed, regardless of the setting of the other conditions, which become fibrous during comminution. At pressures above 30 at, agglomerated and adherent polymers are formed. That is to say, the object of the present invention is only achieved if all conditions, ie temperature, pressure and p n value, are kept strictly within the appropriate ranges.

When PTPE grains obtained according to the invention are crushed using a crushing device having a fine crushing effect mainly by impact effects such as an "UltramlEer" (manufactured by Fuji Denk! KK), a fine PTPE powder having a NaS life size of not is obtained more than ko , u, a form factor of not more than 15, an anisotropic expansion factor of 1.02 to 1.26, and a surface smoothness of at least 15 seconds. NaBslebgr '^ e, forafactor, factor for the anisotropic expansion and surface area are defined as follows and c-emessem

The Na "8iebsrr ^ !? e is determined by actual sieving of the powder. JIS standard sieves of 20? 6Bh (clear mesh size 840 / u), 250 mesh (clear mesh size 62 / u), 2? 0 are used for the measurement mesh (clear mesh size 53 / u) _v of 325 mesh (clear mesh size kk m) and of 4oo mesh (clear mesh size 37 / ti).

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First, the 20 mesh sieve is put on the 250 me · h sieve. Then 5 β of a powder sample was placed on the 20 mesh slab and carefully sprayed carbon tetrachloride onto the upper sieve for about 50 seconds at a rate of about 3 liters / ml using an effervescent sprayer (according to the Korngräfie) the lower 81eb was similar. After the sample has been completely "washed out", the upper sieve is removed and the lower sieve is also sprayed simultaneously for about 4 minutes in the same catfish. This sieve or its contents are then air-dried and the dry powder that has fused in it is loaded.

These operations are repeated bit every 5 β of fresh powder, using the 20 mesh screen with the other three finer screens. The weight of the powder remaining on the finer sieve is multiplied by 20 and provides eo values for the "cumulative" weight percentages, which are then plotted on (logarithmic) true-to-life stackers against the clear mesh size. A straight line is drawn through the drawn points, and from this curve one takes _{the TellohengrBeen corresponding to a "cumulative" percent eat ε of 50 (^ 0} ) and 84 (dg ^) for the calculation of the NaPsleb size (d _we ) according to the following equation

■ 1

e 50 2

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The form factor is obtained by using the wet screen tube divided by the "subsleb size". He gives a MaP for how far. the shape of the particles Ib means deviates from the spherical shape. Oils designation "SubsiebfröBe" means a particle diameter, which is defined by the customizable surface, which with a surface * · Svorrlchtung according to Shlmazu Selsakusho is determined according to the principle of permeability for air «

The anisotropic expansion factor becomes as follows Catfish definitely!

4.1 g of powder are weighed into a rectangular mold cavity with a 3.2 cm ² base area and compressed at a temperature of 23 ° C. The pressure is on within a minute

r Λ

ΐΛο kg / c ^ increased and this pressure is then sustained as long as length, width and height (ie X «, X and Z axes, with the Z axis indicating the application of pressure during preforming) ύ τ resulting substantially cubic preform are measured. This measured preformed object is sintered for 30 minutes at 380 + 0.5 ° C., allowed to cool to room temperature and measured again as already stated. The anisotropic expansion factor is a value obtained by dividing Z ^ Z by

X + Y
is obtained, where X, Y and ?. dl «axis dimension

ren the preformed part and X ₈ , Y ₁ and 2 _f the aohtabsessungen

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the peeinterten part (measured at 23 ° C) elnd.

The surface quality is determined by the following method:

18 κ FoIyt «trafluoroethylene tea powder is perforated under a pressure of 300 kg / cm in a metal mold with a diameter of 100 with a smoothly machined, flawless surface. The preformed part will take two hours? sintered without application of pressure at 36O ⁰ C, producing a sur Polytetrafluoräthylenplatte of about 1.5 η Dleke al · sample · The Gberfläohengltttte this specimen is old should be OK-Glättomeaser naoh JI8 · P sat elnea 8119-1963. The surface smoothness is represented by the tent (in seconds) which is needed for the passage of 10 cs ^ air as well as the sample plate

rTobenaufnahoetlech of the test device (made of optical glass with; polished surface1 effective surface 10 ± 0.05 es ² ) at | a pressure difference of 380 ns Bg * The measurement is carried out at 23 ° C and the surface smoothness is an average of the values obtained when each surface of the test plate is durobaiat 3 times in the specified Heise.

The invention is explained in more detail below using τοη examples.

Examples 1 to 7

10 Great oxygen-free deionized water are placed in a stainless steel AutoklaTen from a sit Bauslnhalt,

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BAD ORJCiNAL

▼ on 2 χ 10 parts of the old one provided with a drilling device 1st. The air inside the autoclave is «Toff is replaced and after that, TFE and a calculated amount a buffer for setting the pg value of the system is added. The temperature is kept at 3 ° C and TPE under pressure fed into the autoclave until the pressure betrttgt 8 at. Thereafter are an I olymerisatloneinitiator, a reducing agent and an accelerator was added to initiate the polymerization. When the pressure decreases from 8 at to 7 * t, TFE becomes under pressure fed in to readjust the pressure to β at. This work cycle is repeated 25 times.

After termination of the polymerization, the resulting polymer was washed and dried. It was then with the help of a • Ultramlzer "(manufactured by Fuji Denkl K.K.) finely chopped and the physical properties of the finely divided PTPS powder certainly.

The above working regime was changed the conditions repeated] The table below summarizes the values obtained.

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Table: Results of examples and comparison tests

example 1 Polymer conditions (at the start)
PH
(at the end) * Vü ₄ Na ₂ HiO ₄ Na ₂ B ₄ O ₇ (NH ₄ J ₂ S ₂ O ₃ NaHSC ₃ - 2.0 5.0 l.o pressure
YatJ temperature duration
ptdj commercially available PTFE See-Versuc
to 6.2
6.2 Parts per million parts of water - 2.0 5.0 1.0 7-8 3 6th Example 2 h *, T
I 4. * 3 180 72C 2.0 5.0 1.0 7-8 3 6th See experiment
the U 6.5 - - - 2.6 - ■ - 7-8 3 6th Example 3 6.5
6.5 360 i.Wo 600 2 * 6.7 1.3 7-8 60 6th 209 Example 4 7.0
7.0 360 !.Where - - 2.7 5.8 1.2 7-8 3 6th 813 / Example 5 7.2
7.2 590 - - - 4.7 1 1.7 2.3 7-8 3 6th Ί32 Example 6 8.0
8.0 66. 1,870 1,000 18.0 k 7.0 9.0 7-8 3 6th Compare verse,
to
At*". 5 9.0
9.0 3,200 - 3.0 7.5 1.5 7-8 3 6th Cf. «Versnob 8.0
8.0 - - 19th
turned
feeds
in rivers
siger
Fora 3 6th 3,200

1 example 1 Nature of the polymer lumpy
Toy kidney s adherent
Polymer commercial ίTFE physical sig €
Matter « NaSsleb-
fn ° / u society of the repulvert »
Is factor
* .d. aniso
tropics
expansion surfaces
•smoothness
(in seconds
the) Remark
gene Jk
<J See experiment
to yield
(Thousand
stel) no easy Shape d.
Powder 20th shape
factor 1.12 100 Example 2 30th many Klum
pen of 10
- 50 mni ρ Lump on
the stir
shovel not
fiber! dd 25th 6th 1.12 120 be
buffer 209813 / See experiment
to 30th no easy m 18th 8th 1.12 120 IO
-a. Example 3 30th Lump-of
2C mm j> Lump on
the Rtthr
shovel η 22nd 6th 1.30 2 high tempe
rature Example J * 30th no easy fibrous 22nd 7th 1.16 110 Example 5 30th no easy not
fibrous 23 7th 1.18 100 Example 6 30th traces ■ - 25th 8th 1.20 80 Compare verse.
for example 5 30th no ■ 28 8th 1.24 60 See Verreueh 30th traces m W. 2 * 9 1.21 2 30th Il 28 8th 1.20 2 fibrous Q l- high pressure known
procedure

Claims (3)

Patent claims 1. A process for the production of polytetrafluoroethylene dureh polymerization of tetrafluoroethylene in an aqueous medium, characterized in that the polymerization is carried out at a temperature of 0 to 20 ⁰ C and a pressure of 0 to 30 atm in an aqueous medium which has an inorganic polymerization initiator system and has a p "value within the range of 5 * 0 to 10.0. 2. The method naoh claim 1, characterized in that dai the change in the Pg value during the polymerization is kept within a range of +0.5. 3. A process for the production of fine-grained polytetrafluoroethylene powder, characterized in that the coarse polytetrafluoroethylene parts obtained according to one of claims 1 or 2 are comminuted at a temperature of up to ⁰ C, mainly by impact effects. BATH ORIGINAL 209813/1327