JPS5928211B2 - Tetrafluoroethylene - Hexafluoropropylene - Google Patents

Description

[Detailed description of the invention] The present invention uses tetrafluoroethylene (hereinafter referred to as TFE).

) and hexafluoropropylene (hereinafter referred to as HFP) copolymer, especially TFE-HF with excellent thermal stability.
The present invention relates to a method for efficiently producing a P copolymer. The main object of the present invention is to provide extremely thermally stable materials that do not cause a decrease in melt viscosity even in high-temperature regions reaching 400°C or higher.
It is an object of the present invention to provide an efficient method for producing a TFE-HFP copolymer that does not shrink in the stretching direction during molding even when a molded product is remelted.

Conventionally known TFE-HFP copolymers obtained by emulsion polymerization using ammonium persulfate as a polymerization initiator have defects due to instability of polymer terminals such as increased melt viscosity and coloration during heat molding. As a solution to these problems, for example, di(chlorofluoroacyl) peroxide [Japanese Patent Publication No. 47-44031] is used as a polymerization initiator.
No.] Yadi(fluoroacyl) peroxide [Special Publication Showa 4
No. 9-28675] has been proposed.

By the way, TFE-HFP copolymers generally have a molecular weight of 300 to
It is molded at temperatures as high as 380℃, and in some cases as high as 440℃. It is required that the melt viscosity does not change or decrease significantly.

Di(chlorofluoroacyl) as the polymerization initiator
The method using peroxide can avoid an increase in the melt viscosity of the obtained copolymer at a relatively low temperature range of 300 to 380°C, but decomposition of the polymer chain occurs at a high temperature range of 380°C or higher. This requirement cannot be fully satisfied because the melt viscosity decreases.
Furthermore, with the method of using di(fluoroacyl) peroxide as a polymerization initiator, it is difficult to obtain a copolymer with a desired melt viscosity under normal conditions. have no choice but to adopt disadvantageous conditions. In addition, when molded products made from this copolymer by injection molding or extrusion molding are remelted at temperatures above the melting point, they shrink significantly in the stretching direction during molding, and this property is second to none of the molded products. This becomes a major obstacle in the next processing.

The present inventors have conducted various studies to overcome the above defects observed in the production of TFE-HFP copolymers6.
The present inventors have discovered that the above object can be easily achieved by copolymerizing TFE and HFP in an aqueous medium in the presence of a specific polymerization initiator and molecular weight regulator, and have completed the present invention.

The gist of the present invention is to use a polymerization initiator of the general formula:
and X' mean H or F, respectively. When X is H, m is an integer of 4 to 10, and when X is F, m is an integer of 3 to 7. X/t) When 1H, n is an integer of 4 to 10, and when F, n is an integer of 3 to 7. ) A method for producing a TFE-HFP copolymer, which comprises copolymerizing TFE and HFP in an aqueous medium in the presence of a di(fluoroacyl) peroxide represented by the formula (2) and methanol or ethanol as a molecular weight regulator. Exists. The TFE-HFP copolymer obtained by using the above-mentioned polymerization initiator and molecular weight regulator in combination according to the method of the present invention exhibits sufficient thermal stability up to at least 400°C, It was able to withstand temperatures as high as 420°C in a short period of time, and also showed surprising results in that it did not shrink during secondary heating and melting after molding. Conventionally, for example, in Japanese Patent Publication No. 47-44031, in a copolymerization method of TFE and HFP using di(perfluorochloroacyl)peroxide, carbon tetrachloride, chloroform, etc. Although the addition of transfer agents has been described, such methods do not allow the above-mentioned drawbacks to be improved.

On the other hand, JP-A No. 50-145488 discloses that if a low molecular weight compound such as hydrogen or a lower alkane is added to the polymerization system as a modifier, the above-mentioned shrinkage property during secondary processing can be improved. has been revealed. However, the polymer produced by this method also suffers from accelerated thermal deterioration at high temperatures around 400 DEG C., and is unsatisfactory in this respect.

The methanol or ethanol used in the method of the present invention has both the functions of a molecular weight regulator and a shrinkage inhibitor in the above-mentioned known method, and can also provide a TFE-HFP copolymer with high thermal stability. Specific examples of the di(fluoroacyl) peroxide used as a polymerization initiator in the method of the present invention include di(ω-hydrododecafluoroheptanoyl) peroxide, di(
perfluoroheptanoyl) peroxide, di(ω-
Examples include hydrooctanoyl) peroxide and di(perfluorooctanoyl) peroxide.

The amount of methanol or ethanol used as a molecular weight regulator varies somewhat depending on the polymerization conditions, but it is usually at least 2 x 10-3 parts by weight of methanol and ethanol for 1 part by weight of monomers (TFE+HFP) in the polymerization system. It is necessary that the amount is at least 2×10 −8 parts by weight.

Therefore, if the molecular weight regulator is consumed as the polymerization progresses and the amount decreases below the above-mentioned amount, it must be added successively. However, in the case of methanol, since the rate of decrease is very slow, there is usually no need for additional charging if it is charged at the beginning of the polymerization. If the amount of the molecular weight regulator used is less than the above, the effects of the present invention cannot be achieved. Furthermore, if the amount of the molecular weight regulator used is too large, the resulting polymer will have a lower molecular weight and deteriorate various mechanical properties, as well as a lower melt viscosity, making it unsuitable for molding. Note that methanol and ethanol exist dissolved in both the liquid monomer and the aqueous medium in the polymerization system, and in the case of methanol, the blending ratio in both is approximately equal. The amount used is the total amount dissolved in both of these. The polymerization reaction of the present invention may be carried out by a conventional method. For example, water is placed in an autoclave equipped with a stirrer, and HFP is first added to the water.
After press-fitting, press-fit the required amount of TFE. Add a polymerization initiator and a molecular weight regulator, and start polymerization while stirring. As the pressure decreases as the polymerization progresses, TFE is injected to compensate for the decreased pressure, and the polymerization is continued until the desired amount of polymer is produced. If the stirring speed during polymerization is low, the TFE added under pressure will be insufficiently dissolved in the monomer liquid phase, so a very low stirring speed is not preferred. After the polymerization is completed, the remaining monomer is released, and the obtained polymer is thoroughly washed with warm water and dried. The TFE-HFP copolymer obtained as described above is in the form of granules, powder or fine powder. The above copolymerization can also be carried out in the presence of other additives such as emulsifiers, if necessary. In addition, even if the compound has a halogen atom other than fluorine, it does not have chain transfer ability under the reaction conditions, and even if it does have chain transfer ability, it does not impair the thermal stability of the resulting polymer. It can be added in moderate amounts.゛The copolymer obtained by the present invention can be processed by any melt processing method such as compression molding, extrusion molding, injection molding, fluidized dip coating, etc. It is stable under a wide range of temperature conditions, from high temperatures to extremely low temperatures, whether or not it comes into contact with chemicals, and can be used as molded products for electrical, mechanical, and chemical applications. EXAMPLES The present invention will be described in more detail below with reference to Examples, Comparative Examples, and Test Examples. Example 1~
4 Stirring type S with jacket that can contain water 31
A US-32 autoclave was charged with demineralized and deaerated pure water, and the internal space was sufficiently replaced with pure nitrogen gas, which was then removed, and first HFP and then TFE were pressurized into it.
Adjust the temperature to 20°C and start stirring.

Di(ω-hydrododecafluoroheptanoyl) peroxide as a polymerization initiator and methanol or ethanol as a molecular weight regulator are added to this. The reaction started immediately. During the reaction, TFE is successively added as the pressure decreases to maintain a constant pressure. After carrying out the reaction for a certain period of time, the monomer was purged and a granular powder was produced. Pure water was added to this powder, washed with a mixer, and dried in a dryer at a temperature of 120° C. for 24 hours to obtain a polymer. Table 1 shows detailed reaction conditions, polymer yield, and physical properties in the above polymerization. The physical properties of the polymer were measured by the following method: (1) HFP content (wt%) 980? The absorbance at the H wave number is 2350? It is expressed as a value obtained by multiplying the value divided by the absorbance at a wave number of -1 by 3.2.

(2) Specific melt viscosity (Boaz) refers to the apparent melt viscosity measured at 380° C. under a shearing force of 0.457 kg/Cd.

That is, this value was measured using a Koka type flow tester, and the inner diameter of the polymer was 9.5? It was loaded into a cylinder and held at 380°C for 5 minutes, then extruded through an orifice with an inner diameter of 2.1 mTn and a length of 8 mm under a piston load of 5k9, and at an extrusion speed (7/min) of 53150
This is the value obtained by dividing . (3) Shrinkage rate (%) Using a high-performance flow tester, load the polymer into a cylinder with an inner diameter of 9.5 mm, hold it at 340°C for 5 minutes, and then
Through an orifice with a length of 2mTfL, 25k9/
Push it vertically downward with the pressure of Cd.

In order to eliminate the difference in stretching due to its own weight, the extrudate is cut so that the length of the extrudate is always between about 100 and 70 m from the nozzle outlet, and an extrusion bar having a length of about 30 mm is cut from this. This plate was heat-treated at 350°C for 10 minutes,
The shrinkage rate is calculated from the length of the bar before and after the treatment using the following formula: L: Length of the bar before heat treatment (MIL) LH: Length of the bar after heat treatment (Mm) The polymer also gave an extruded product with a smooth surface and good transparency when extruded in a single batch in the above shrinkage measurement.

Comparative Examples 1 to 4 TFE and HFP were copolymerized in the same manner as in Examples 1 to 4, using the amounts of raw materials used and reaction conditions as shown in Table 2.

Table 2 shows the yield and physical properties of the obtained polymer. to
These comparative examples are similar to those of Example 1 in terms of the amount of raw materials used and reaction conditions.
Although it is similar to Example 4, it does not meet the requirements of the process of the present invention, and the resulting polymer is unsatisfactory, especially in that it has a large shrinkage during secondary processing.

Test Examples The polymers obtained in Examples 1 and 4 and Comparative Examples 1, 2, 3 and 4 were heated to 400° C. in air, and the changes in specific melt viscosity over time are shown in the drawing.

As shown in this figure, in the polymers of Comparative Examples 1, 2, 3, and 4, a decrease in specific melt viscosity due to thermal deterioration was observed,
It can be seen that the polymers of Examples 1 and 4 did not show such a decrease and could sufficiently withstand heat treatment for up to 1 hour.

[Brief explanation of the drawing]

The drawing is a graph showing changes in specific melt viscosity of TFE-HFP copolymers obtained in Examples and Comparative Examples at 400°C depending on heat treatment time.

Claims (1)

[Claims] 1 General formula for the polymerization initiator: ▲ Numerical formula, chemical formula, table, etc. ▼ (However, X and X' each mean H or F. When X is H, m is 4 to 10, and when F, m is an integer from 3 to 7. When X' is H, n is an integer from 4 to 10, and when F, n is an integer from 3 to 7.) di(fluoroacyl)peroxide shown, tetrafluoroethylene-hexafluoropropylene, characterized by copolymerizing tetrafluoroethylene and hexafluoropropylene in an aqueous medium in the presence of methanol or ethanol as a molecular weight modifier; Method for producing copolymer.