JPH0559214A - Method for molding fluoropolymer - Google Patents

Abstract

PURPOSE:To prevent the viscosity of a fluoropolymer melt from decreasing with time during melt molding even at high temp. and to prevent the molding from having impaired mechanical strength by conducting the melt molding in the presence of an antioxidant. CONSTITUTION:A melt-moldable fluoropolymer is melt-molded at 300-430 deg.C in the presence of an antioxidant. An example of the polymer is a copolymer of tetrafluoroethylene with a fluorinated alkyl vinyl ether represented by the formula CF2=CFOCH2(CF2)nX (wherein X is a hydrogen atom or a halogen atom selected from among fluorine, chlorine and bromine, and n is 1-12).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for molding a fluoropolymer. More specifically, the presence of an antioxidant during melt molding of the fluoropolymer prevents a decrease in melt viscosity during melt molding of the fluoropolymer,
It is intended to provide a method capable of excellent molding.

[0002]

2. Description of the Related Art Conventionally, fluororesins have been used in a wide range of industrial fields because they are excellent in chemical resistance, heat resistance, melt moldability and electrical characteristics.

The inventors of the present invention have also proposed a fluororesin. Among them, CF ₂ = CFOCH ₂ (CF ₂ ) nX
(However, X is a hydrogen atom or each halogen atom of fluorine, chlorine and bromine, and n is an integer of 1 or more.) The vinyl ether (hereinafter, simply abbreviated as FVE) is tetrafluoroethylene ( Below, simply TFE
Is omitted. ) Shows a very good copolymerizability with
The content of the monomer unit based on VE has a characteristic that a desired fluoropolymer can be obtained (Japanese Patent Laid-Open No. HEI-2).
No. 276808). The fluoropolymer has excellent chemical resistance, mechanical strength and electrical characteristics equivalent to those of conventional fluororesins.

[0004]

However, when the above-mentioned fluorine-containing polymer is melt-molded, the melt viscosity is gradually reduced to cause defective molding, and the mechanical strength of the obtained molded body is deteriorated. There was a problem.

As a result of investigations by the present inventors regarding this cause, it was found that the above-mentioned fluoropolymer partially decomposed during molding because the molding temperature and the decomposition temperature were close to each other.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies as to a method for molding a fluoropolymer which has solved the above-mentioned drawbacks, and as a result, have found that an antioxidant is allowed to coexist during molding of the fluoropolymer. As a result, it was found that melt molding is possible even at a high temperature of 300 to 430 ° C., there is no significant decrease in melt viscosity and no decrease in mechanical strength of the molded body, and the present invention has been completed.

That is, the present invention is a method for molding a fluoropolymer characterized in that the fluoropolymer capable of melt molding is melt-molded at 300 to 430 ° C. in the presence of an antioxidant.

The fluorine-containing polymer used in the present invention is 3
Any known polymer having a fluorine atom can be used without any limitation as long as it can be melt-molded in the range of 00 to 430 ° C.

Examples of the fluorine-containing polymer to be used in the present invention include copolymers of TFE and hexafluoropropylene, copolymers of TFE and fluoroalkyl vinyl ether, and copolymers of TFE and ethylene. ..

In particular, in comparison with a perfluoropolymer in which all carbon-hydrogen bonds in the molecule are replaced with carbon-fluorine bonds, a fluoropolymer in which carbon-hydrogen bonds remain in the molecule is melt-molded. Because it is prone to thermal deterioration,
The effect of the present invention is great. In particular, the following general formula [I] CF ₂ ═CFOCH ₂ (CF ₂ ) nX [I] (where X is a hydrogen atom or each halogen atom of fluorine, chlorine and bromine, and n is 1 to 12, preferably 1 to
It is an integer of 8. The copolymer of fluoroalkyl vinyl ether and TFE shown in () requires a high temperature for melt molding, and the heat deterioration during melt molding is remarkable, so that the effect of the present invention is remarkable.

Specific examples of the fluoroalkyl vinyl ether represented by the above general formula [I] are as follows.

CF ₂ = CFOCH ₂ CF ₃ , CF ₂ = CFO
CH ₂ CF ₂ CF ₃ , CF ₂ = CFOCH ₂ CF ₂ CF ₂ H,
CF ₂ = CFOCH ₂ (CF ₂ ) ₂ CF ₃ , CF ₂ = CFOC
H ₂ (CF ₂ ) ₃ CF ₃ , CF ₂ = CFOCH ₂ (CF ₂ ) ₄ C
_{F 3, CF 2 = CFOCH 2} (CF 2) 5 CF 3, CF 2 = C
FOCH ₂ (CF ₂ ) ₆ CF ₃ , CF ₂ = CFOCH ₂ (CF
₂ ) ₇ CF ₃ , CF ₂ = CFOCH ₂ CF ₂ Cl, CF ₂ = C
FOCH ₂ CF ₂ Br, CF ₂ = CFOCH ₂ CF ₂ CF ₂ B
r, CF ₂ = CFOCH ₂ CF ₂ CF ₂ Cl, CF ₂ = CF
OCH ₂ (CF ₂ ) ₂ CF ₂ Br, CF ₂ = CFOCH ₂ (C
F ₂ ) ₂ CF ₂ Cl, CF ₂ = CFOCH ₂ (CF ₂ ) ₃ CF ₂
Br, a _{CF 2 = CFOCH 2 (CF 2} ) 3 CF 2 Cl and the like.

The composition of the copolymer of fluoroalkyl vinyl ether and TFE is 0.5 to 40 mol% of the monomer unit based on the fluoroalkyl vinyl ether, preferably 0. 5-1
It is in the range of 0 mol%, and TFE is in the range of 60 to 99.5 mol%, preferably 90 to 99.5 mol%. Further, in addition to the above-mentioned monomer components, a monomer unit based on a monomer copolymerizable with these monomer components may be contained within a range that does not impair the effects of the present invention.

As the antioxidant in the present invention, those used in conventional general-purpose resins can be used without any limitation.
In the present invention, particularly a phenol-based antioxidant and a phosphite-based antioxidant are preferable in order to favorably prevent a decrease in viscosity during melt molding of the fluoropolymer and a decrease in mechanical strength of the molded body. Can be used.
Furthermore, since the obtained fluoropolymer is scarcely colored, the phosphite antioxidant can be most preferably used.

Specific examples of the above-mentioned phenolic antioxidant are as follows.

[0016]

[Chemical 1]

[0017]

[Chemical 2]

[0018]

[Chemical 3]

[0019]

[Chemical 4]

[0020]

[Chemical 5]

[0021]

[Chemical 6]

[0022]

[Chemical 7]

[0023]

[Chemical 8]

[0024]

[Chemical 9]

[0025]

[Chemical 10]

[0026]

[Chemical 11]

[0027]

[Chemical formula 12]

(However, R ₁ , R ₂ , R ₄ , R ₅ , R ₆ , R ₇ ,
R ₈ and R ₉ are alkyl groups, R ₃ is a hydrogen atom or an alkyl group, and n is a positive integer. ) Further, specific examples of the phosphite-based antioxidant are as follows.

[0029]

[Chemical 13]

[0030]

[Chemical 14]

[0031]

[Chemical 15]

(However, R ₁ , R ₂ , R ₃ and R ₄ are alkyl groups, and R ₅ is a hydrogen atom or an alkyl group.) The alkyl group in the above formula is generally a methyl group or an ethyl group. , Propyl, t-butyl and t
-Amyl group or the like is adopted.

The antioxidant is present in an amount of 0.001 to 1% by weight, which is a proportion of the total amount of the fluorine-containing polymer, and a sufficient effect can be obtained.
It is in the range of 0.1% by weight.

Melt molding of the fluoropolymer in the presence of an antioxidant is carried out in the range of 300 to 430 ° C.
If the molding temperature is less than 300 ° C., it becomes difficult to mold a fluoropolymer having a high melting point, and a fluoropolymer having a low melting point has a small thermal deterioration due to a low molding temperature.
Good melt molding is possible without using the present invention. On the other hand, when the molding temperature exceeds 430 ° C., it is difficult to sufficiently prevent thermal degradation of the fluoropolymer even by the present invention. The present invention provides a method of 36% for the reason that the effect is sufficiently exerted in melt molding in a relatively high temperature range.
Suitable for melt molding at 0-430 ° C.

As the melt-molding method, the conventional melt-molding method of a thermoplastic resin is adopted as it is. For example, a well-known molding method such as injection, extrusion, compression or the like is employed after thoroughly mixing the fluoropolymer and the antioxidant with a mixing device such as a Henschel mixer.

[0036]

[Effect] According to the present invention, the presence of an antioxidant during the melt molding of the fluoropolymer results in 300 to 430.
Despite the molding at a temperature of ° C., good molding is possible because the melt viscosity of the fluoropolymer does not decrease with time during melt molding, and the molded body obtained is
It is a good one without any decrease in mechanical strength due to molding.

In the case of a general-purpose resin such as polypropylene, its heat deterioration mechanism has been clarified, and a method of preventing heat deterioration at the time of molding is adopted by adding a stabilizer for preventing the heat deterioration. However, in the case of the fluoropolymer used in the present invention, a molding temperature in the vicinity of 300 to 430 ° C. is required. Under such a temperature, the fluoropolymer undergoes thermal deterioration by any mechanism, and has a melt viscosity. I do not know at all if it changes.

Moreover, the antioxidant used in the present invention is used for general-purpose resins such as polypropylene, and the thermal decomposition temperature of these antioxidants is a maximum of 260 as will be apparent from the reference examples described later. It is about ℃. This thermal decomposition temperature is considerably lower than the molding temperature of the fluoropolymer used in the present invention. Therefore, it is considered that these antioxidants cannot be used as heat stabilizers for fluoropolymers that require a molding temperature higher than their decomposition temperature.

However, by using such an antioxidant, it was possible to effectively prevent the thermal deterioration of the fluoropolymer, whose mechanism is unknown, in the melt molding at a temperature higher than its decomposition temperature. Is totally amazing.

[0040]

EXAMPLES Examples will be given below for illustrating the present invention in detail, but the present invention is not limited to these examples.

The measured value was obtained as follows.

1. Mechanical strength (1) Preparation of test sample After mixing the fluoropolymer and the antioxidant, pellets were prepared by extrusion molding, and the pellets were compression molded at a temperature of 340 ° C to obtain a sheet having a thickness of 1-2 mm. A test piece was prepared and a test piece subjected to the following test method was prepared.

(2) Measurement of tensile strength It was measured according to JIS K7113.

2. Pyrolysis temperature SSC5200-TG / DTA320 (manufactured by Seiko Instruments Inc.) was used to measure the temperature rising rate at 10 ° C / min in an air stream.

3. Shear rate The shear rate was measured using a high-grade melt viscosity measuring device (manufactured by Shimadzu Corporation).

As a die, the diameter is 0.5 mm and the length is 5 mm.
The shear rate was measured by applying a load of 50 kg / cm ² at a temperature of 370 ° C.

4. Yellowness (YI) (1) Preparation of test sample 1 mm by the same method as the test sample of mechanical strength
A thick sheet was created.

(2) Measurement The measurement was carried out by the transmission method according to JIS K7103.

The antioxidants used in the following examples are the following compounds.

[0050]

[Chemical 16]

[0051]

[Chemical 17]

[0052]

[Chemical 18]

[0053]

[Chemical 19]

[0054]

[Chemical 20]

[0055]

[Chemical 21]

[0056]

[Chemical formula 22]

[0057] Example 1 CF ₂ = CF ₂ and CF ₂ = CFOCH ₂ CF ₂ copolymer of _{CF 3 (CF 2 = CFOCH 2} CF 2 CF 3 monomeric units 3.
0 mol%) and various antioxidants were put into a mixer at a ratio shown in Tables 1 and 2 and mixed.

The mixture was taken out, melt-kneaded at 390 ° C. for 20 minutes, extruded, and then measured for shear rate, tensile strength and yellowness. The results of shear rate and tensile strength obtained are shown in Table 1, and the results of yellowness are shown in Table 2.

[0059]

[Table 1]

[0060]

[Table 2]

Comparative Example 1 Only the copolymer used in Example 1 was extrusion-molded for the times shown in Table 3 and then the shear rate and the tensile strength were measured. The results are shown in Table 3.

[0062]

[Table 3]

Example 2 A copolymer of CF ₂ ═CF ₂ and a fluoroalkyl vinyl ether having the structure shown in Table 4 (3.0 mol% of fluoroalkyl vinyl ether monomer units) and an antioxidant N
O5 was added to a 0.01 wt% mixer and mixed.

The mixture was taken out, melt-kneaded at 390 ° C. for 20 minutes and extruded, and then the shear rate and the tensile strength were measured. The shear rate and tensile strength obtained are shown in Table 4.

[0065]

[Table 4]

[0066] A copolymer of Example 3 CF ₂ = CF ₂ and _{CF 2 = CFOCH 2 CF 2 CF} 3, CF 2 = CFOCH 2 CF 2 CF based on ₃ monomer units in Table 5 The copolymer and the antioxidant No. 5 having the indicated contents were put into a 0.01% by weight mixer and mixed.

The mixture was taken out, melt-kneaded at 390 ° C. for 20 minutes, extruded, and then measured for shear rate and tensile strength. The results of shear rate and tensile strength obtained are shown in Table 5.

[0068]

[Table 5]

Comparative Example 2 After extruding only the copolymer used in Example 3, the shear rate and the tensile strength were measured, and the results are shown in Table 6.

[0070]

[Table 6]

Reference Example The thermal decomposition temperature of the antioxidant used in the examples was measured, and the results are shown in Table 7.

[0072]

[Table 7]

Claims (1)

[Claims] 1. A method for molding a fluoropolymer, which comprises melt-molding a melt-moldable fluoropolymer at 300 to 430 ° C. in the presence of an antioxidant.