JPS63286410A - Fluorine-containing elastomer suitable for compression molding - Google Patents

Abstract

PURPOSE:To obtain the titled novel elastomer, consisting of vinylidene fluoride units, hexafluoropropylene units and tetrafluoroethylene units and having specific physical properties, excellent fluidity, compression set characteristics, etc. CONSTITUTION:The aimed elastomer, consisting of 65-100wt.% (A) vinylidene fluoride units and (B) hexafluoropropylene units and (C) 35-0wt.% tetrafluoroethylene units at 80:20-40:60 weight ration of the components (A) to (B) and having 80-100(ml/g) intrinsic viscosity and 2-3.5 ratio of the weight- average molecular weight (MW) to the number-average molecular weight (MN) and the relation (F, M5) between the fraction (wt.%) (hereinafter referred to as M5) having <=50,000mol.wt. and fluorine content (wt.%) (hereinafter referred to as F) existing within the range surrounded by points (A) (63.5, 15), (B) (63.5, 2), (C) (71, 2) and (D) (68, 15).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel fluorine-containing elastomer having a specific molecular weight distribution. More specifically, the present invention relates to a fluorine-containing elastomer having a small intrinsic viscosity and having extremely excellent compression set resistance and mechanical properties regardless of the fluorine content.

[Conventional technology]

Fluorine-containing elastomers have excellent heat resistance and chemical resistance, and are used in O-rings that are used under harsh conditions.

! It is used for sealing materials such as seals, gaskets, and diaphragms.

It is important that sealing materials molded primarily by compression molding have low compression set. On the other hand, due to technological innovation, the usage conditions for sealing materials are becoming increasingly harsh.
There is a growing demand for fluorine-containing elastomers that have not only compression set resistance but also chemical resistance and solvent resistance. However, when the fluorine content is increased in order to improve chemical resistance and solvent resistance, there is a problem in that compression set increases.

Furthermore, the moldability of fluorine-containing elastomers is becoming increasingly important as mechanical parts become smaller and more complex in shape. In other words, it is important to improve wall flow, reduce cracks, and facilitate cutting. It is difficult to develop a fluorine-containing elastomer that has fluidity over a wide range of fluorine content, can be molded into small, complex-shaped sealing materials, and has excellent compression set resistance and mechanical properties. there were.

Various compositions of fluorine-containing elastomers have been proposed so far. For example, a manufacturing method (Japanese Patent Publication No. 33-1972) in which polymerization is carried out at a charging ratio of 60 to 15% by weight of vinylidene fluoride (hereinafter abbreviated as VdF) units and 40 to 85% by weight of hexafluoropropylene (hereinafter abbreviated as RFP) units. 7394
3 to 35% by weight of tetrafluoroethylene (hereinafter abbreviated as TFE) units and 97 to 65% by weight of VdF units and HFP units;
The ratio of FP unit to No1i amount is 2.33:1 to 0.667:1
Copolymers within the range of (Japanese Patent Publication No. 36-3495)
, TFf! 10 to 30% by weight of units, 90 to 70% by weight of VdF units and HFP units, and VdF
The weight ratio of the unit to the HFP unit is 1.6:1.0 to 4.0
: Copolymer in the range of 1.0 (Japanese Patent Publication No. 48-1895
Publication No. 7).

A copolymer consisting of 57 to 61% by weight of VdF units, 1i% by weight of 27 to 31% HFP units, and 10 to 14% by weight of TFE units (Japanese Patent Laid-Open Publication No. 149291/1983) is known.

On the other hand, methods have also been proposed for adjusting the molecular weight distribution of fluorine-containing elastomers. A method for producing copolymers with two molecular weight distributions through polymerization (Japanese Patent Publication No. 51-25279) A method for producing copolymers or terpolymers with low Mooney viscosity and excellent processability by suspension polymerization (Japanese Patent Publication No. 49-1989) -29630, Japanese Patent Publication No. 51-8432) and high molecular weight fluorine-containing elastomers with bimodal molecular weight distribution (EPC0186180^2), which have extremely good fluidity and a wide range of fluorine content. However, it is still not sufficient from the viewpoint of having both compression set resistance and mechanical properties.

[Problem that the invention seeks to solve]

Under these circumstances, the object of the present invention is to provide a material that has extremely excellent fluidity, excellent moldability, and excellent compression set resistance, mechanical properties, and chemical and solvent resistance. An object of the present invention is to provide a fluorine-containing elastomer that has the following properties.

[Means for solving problems]

As a result of extensive research, the present inventors have discovered that the molecular weight distribution is extremely narrow within a specific intrinsic viscosity number (s+l/g) (hereinafter abbreviated as [η]), and the fluorine content (weight% )(
When the relationship between the weight percent (hereinafter referred to as F) and the fraction with a molecular weight of 50,000 or less (hereinafter referred to as -3) is within a specific range, it has excellent fluidity, excellent moldability, and has excellent compression set resistance and mechanical properties. The inventors discovered that a fluorine-containing elastomer with excellent physical properties, chemical resistance, and solvent resistance could be obtained, and based on this knowledge, they reached the goal of completing the present invention.

That is, the present invention provides a fluorine-containing elastomer comprising 65 to 100% by weight of vinylidene fluoride units and hexafluoropropylene units and 35 to 0% by weight of tetrafluoroethylene units, including (a) the weight of vinylidene fluoride units and hexafluoropropylene units; The ratio is 8
0:20 to 40:60, (b) the intrinsic viscosity number (-m!/g) is 80 to less than 100, and (c) the weight average molecular weight (curve) and number average molecular weight (M
W) is less than 2 to 3.5, and the relationship between (F, MS) and F is the following four points A (
63,5,15).

B (63,5,2), C (71,2) and D (68,
15) The present invention relates to a fluorine-containing elastomer characterized in that it falls within the range of 15).

The characteristics of the fluorine-containing elastomer of the present invention are that it is optimal for polyol vulcanization, has a low molecular weight, and has a compression set of 21 to 26% (at 200°C 72 hr).

The composition of the fluorine-containing elastomer of the present invention is VdP units and H
65 to 100% by weight of FP units and 35% of TFE units
~0% by weight, and the weight ratio of VdF units to HFP units is 80:20 to 40:60.

If the TFE unit is 35% by weight or more, the fluorine-containing elastomer becomes resin-like, which is undesirable. Similarly, if the VdF unit is 80% by weight or more, the fluorine-containing elastomer becomes resin-like, which is not preferable. On the other hand, if the HPP content is 60% by weight or more, the polymerization rate becomes extremely slow, which is not preferable. A preferred range that satisfies both chemical resistance and solvent resistance is a TFE unit of 25 to 5% by weight, [η] of 80 to less than 100, and a VdF unit to HFP unit (7) fEt ratio of 45:65 to 75: There are 25 te.

[η] is an index that indicates the molecular weight of the fluorine-containing elastomer, and when it is less than 80, there is a lot of bulge, which deteriorates the compression set resistance,
Mechanical properties deteriorate and adhesion to the roll occurs, which is undesirable. On the other hand, if it is more than 100, the dispensing roll processability becomes poor especially in a range where the fluorine content is large. Another feature of the invention is that the molecular weight distribution is very narrow.

%Iw/iln is in the range of 2 to less than 3.5. Therefore, it has become possible to control h within a certain range without reducing workability.

The MS range is related to the fluorine content. The relationship between F and h can be expressed using the F-Ms coordinate axis as A (63, 5, 15),
B(63,5,2) C(71,2) and D(68,1
5). The compression set tends to increase as the fluorine content increases, so in order to reduce the compression set, h is decreased as the fluorine content increases. If the fluorine content is more than 15% by weight, the compression set resistance and mechanical properties will deteriorate, and adhesion to the roll will occur, which is undesirable. On the other hand, if the fluorine content is less than 2% by weight, it is a limit that is currently difficult to achieve technically. The preferred range is 8-2% by weight.

The effect of reducing compression set by reducing JS is particularly remarkable for fluorine-containing elastomers having a fluorine content (F) of 66 to 71% by weight or more.

Next, the polymerization method that made the present invention possible will be described.

The general manufacturing method for fluorine-containing elastomers is generally emulsion polymerization, and suspension polymerization or solution polymerization may be adopted in very special cases. Legal is chosen. As mentioned above, patents related to suspension polymerization of fluorine-containing elastomers include Japanese Patent Publication No. 49-29630 and Japanese Patent Publication No. 51-8432, but the characteristics of the polymerization conditions of the present application are mainly for hydrocarbon-based dialkyl peroxydicarbonates. The method is to charge a catalyst at once at a high temperature of 50° C. or higher, to make the polymerization pressure relatively low, and to lengthen the polymerization time. That is, under such polymerization conditions, the formation of ultra-high molecular weight components is suppressed, and at the same time, the low molecular weight components, that is, h, are relatively reduced, and the fluorine-containing elastomer of the present invention can be obtained. In addition, the polymerization rate is fast and the rubber properties are excellent.

The physical properties of the vulcanized rubber are that it has a small 100% modulus, low hardness, elongation, and low compression set, making it similar to what is called an elastic body. There is little mill shrinkage during roll forming, and Mooney viscosity (ML).

(121°C)) The fluorine-containing elastomer of the present invention also has H
Even though the fluorine content is small, it ranges from about 40 to 120 over a wide range of fluorine contents, and has good wall flow even in complex compression molding molds, and is effective in reducing flash.

Compared to the polymerized product obtained by the polymerization method described above, the same [η
It has also been discovered that passing the fluorine-containing elastomer through an extruder, for example, produces a good effect as a method of reducing the size of the fluorine-containing elastomer.

As a result, the extruded fluorine-containing elastomer was [η]
decreases, but H3 hardly increases, and high molecular weight components decrease, so processability is improved, but the physical properties of vulcanized rubber are
It was surprising that there was almost no change or warpage before and after extrusion. As a result, the invention of the present application can be more reliably achieved by extruding a fluorine-containing elastomer that is 10 to 100 larger than the desired [η] using an extruder in order to suppress H3 as much as possible.

The extruder is not limited in type or type as long as it has a structure that is heated and subjected to shear stress.

- As an example, the operating conditions of a twin-screw extruder with a die diameter of 4 inches will be outlined. Twin-screw extruder with at least one seal ring, barrel heating temperature 140-280℃, screw rotation speed 120-400 rpm, discharge speed 20-50kg/H
When the fluorine-containing elastomer is extruded by the preferred polymerization method of the present invention at r, the temperature of the elastomer becomes 280 to 350°C, and the objective is achieved. Next, a preferred suspension polymerization method of the present application will be described. First, an inert organic solvent in which a predetermined mixed monomer (preparation monomer) is dissolved is dispersed in an aqueous medium, and a suspension stabilizer and an oil-soluble catalyst are added.While stirring mechanically, the temperature is kept at 50-60℃ and the pressure is But 5-10k
g/cjG (10 to 15 when further processed with an extruder
You can select up to kg/cjG. ) with a new composition of mixed monomers (additional twist monomers) so that the pressure remains constant at a relatively low pressure.
is added to proceed with polymerization. The charging composition is determined so that the amount of the fluorine-containing elastomer to be produced is equal to the amount of the continuous monomer added, and the composition of the fluorine-containing elastomer is the same as the composition of the additional twist monomer.

The charged monomer composition and the continuous addition composition are measured by gas chromatography (G, C,), and the composition of one monomer unit in the fluorine-containing elastomer is measured by F NMR after dissolving the elastomer in acetone.

The inert organic solvent used in this suspension polymerization method is selected from organic solvents that do not have carbon-hydrogen bonds that easily cause chain transfer, such as 1.1.2-trichloro, 1.
,2,2. ) Lifluoroethane is preferred in terms of performance and economy; methylcellulose may also be used as the suspension stabilizer. As the oil-soluble catalyst, dialkyl peroxy carbonate is preferred as long as it can be used at high temperatures.

Although the fluorine-containing elastomer of the present invention can be vulcanized with a polyamine compound or a polyhydroxy compound, the improved performance of the fluorine-containing elastomer of the present invention is particularly exhibited when vulcanized with a polyhydroxy compound.

°The polyol vulcanization method will be explained below.

The fluorine-containing elastomer is mixed with an acid binder, a polyhydroxy compound, a vulcanization accelerator and, if necessary, a filler, and then kneaded, followed by heating and vulcanization.

As compounding agents, divalent metal oxides or hydroxides such as oxides or hydroxides of magnesium, calcium, zinc, lead, etc. are used, and the amount used is 1 to 30 parts by weight per 100 parts by weight of the elastomer. It is preferably selected in a range of 2 to 20 parts by weight.

As a polyhydroxy compound, hydroquinone, 2.2
-Bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)
Perfluoropropane (bisphenol AP), 4.
4'-dihydroxydiphenyl ether, 4,4'
-dihydroxydiphenylmethane, 2゜2-bis(
0.1 to 10 parts by weight, preferably 0.6 parts by weight of 4-hydroxyphenyl)butane, etc., per 100 parts by weight of elastomer.
It is used in a proportion of ~5 parts by weight.

As the vulcanization accelerator, quaternary onium salt compounds, quaternary phosphonium salts, quaternary ammonium salts or iminium salts, such as tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, tetrabutylammonium chloride, tetrabutyl Ammonium bromide, bis(benzyldiphenylphosphine)iminium chloride, tetrabutylphosphonium chloride, benzyltriphenylphosphonium chloride, benzyltrioctylphosphonium chloride, etc. are suitable, preferably 0.05 to 2 parts by weight per 100 parts by weight of elastomer. It is used in a proportion of .1 to 1 part by weight. As the filler reinforcing agent, for example, carbon black, silica, clay, talc, etc. are used as necessary. The mixture of the fluorine-containing elastomer, acid bond site, polyhydroxy compound, vulcanization accelerator, and filler is kneaded using rolls or a Banbury mixer, then put into a mold and pressurized for primary vulcanization, and then secondary vulcanization. do. Generally, the conditions for primary vulcanization are a temperature of 100 to 200℃ and a vulcanization time of 10 to 18℃.
The conditions for secondary vulcanization are selected from the range of temperature 150 to 300°C and vulcanization time of 0 to 30 hours.

Note that (1) intrinsic viscosity number (2) molecular weight distribution M5 measurement conditions and (3) standard conditions for polyol vulcanization of the fluorine-containing elastomer of the present invention are as follows.

(1) Intrinsic viscosity: Measure a solution of methyl ethyl ketone at a concentration of 0.1 g/100 m at 35° C. using a capillary viscometer.

(2) Molecular weight distribution measurement conditions Detector: ERC-751O3 (manufactured by Elma Optical) Developing solvent: Tetrahydrofuran concentration: 0.1% by weight Temperature: 35°C Standard polymer for molecular weight calibration curve: Various types of monodisperse polystyrene (Toyo Co., Ltd.) Made by Soda ■) (MW/1ilN-1,2 (wax)) Based on the above results, 6
Calculate.

(3) Polyol vulcanization standard conditions Fluorine-containing elastomer: 100 parts by weight Highly active magnesium oxide: 3 parts by weight Calcium hydroxide = 6 parts by weight Bisphenol AF: 2 parts by weight Kneading method Two-roll primary heat press vulcanization: 177°C x 10 Secondary oven vulcanization for minutes = 232°C x 24 hours The mechanical properties of the polyol vulcanized product were determined by punching out No. 3 dumbbell-shaped specimens from a 2 kg thick vulcanized sheet and testing them using a tensile tester according to JIS-6301. (manufactured by Toyo Seiki KK), tensile speed 50
Measured in cm+/min.

On the other hand, the compression set is 25% according to JIS-K 6301 using polyol-cured P-24 type rolling.
After holding the temperature at 200℃ for 72 hours under pressure and compression,
After cooling in a greenhouse for 0 minutes, the thickness was measured using a thickness gauge (manufactured by Kyoto Kobunshi Needle).

Example 1 An autoclave equipped with an electromagnetic induction stirrer and having an internal volume of approximately 151 cm was sufficiently purged with nitrogen gas, vacuum-N and filling were repeated three times, the air was replaced with nitrogen, and deoxygenated pure water was prepared under reduced pressure. 5800 g, 1.1.2-) Rechloro1.
2.2-) 2670 g of refluoroethane (hereinafter referred to as Freon 113) and 2.9 g of methyl cellulose (viscosity 50CP) as a suspension stabilizer were charged, and the mixture was heated at 500 r.
The temperature was maintained at 50°C while stirring at p+m. Next, a monomer mixture consisting of 33.7% by weight of VdF, 59.7% by weight of RFP, and 6.6% by weight of TFE was charged as a charging gas until it reached 7.0 kg/cj-G.
Next, 153 g of a Freon 113 solution containing 10.5% by weight of diisopropyl peroxydicarbonate was charged as a catalyst to initiate polymerization. Due to polymerization, pressure increases
VdF 5 with Q decreasing to 6.5 kg/c+J-G
3.0% by weight, RFP 29.0% by weight, TFE 18
．． A mixed monomer containing 0% by weight was used as additional gas, and the pressure was returned to 7.0 kg/csJ-G again. After repeating these operations and carrying out the polymerization reaction for 14 hours, the remaining mixed monomers were scavenged, the resulting suspension was dehydrated using a centrifugal separator, and thoroughly washed with water.
About 5 kg of elastomer was obtained by vacuum drying at 0°C. When the obtained fluorine-containing elastomer was analyzed by F NMR, it was found that VdF units were 54.1% by weight and RFP units were 2%.
The content of TFE units was 9.0% by weight and 16.9% by weight.

Also, [η] is 82), 9.1, and phase/F4N is 2.5.
MS was 11.6%. MLl, lo (120℃)
was 40.

When the fluorine-containing elastomer was polyol-vulcanized under standard conditions, a vulcanized product exhibiting excellent mechanical properties was obtained. Table 1 shows the physical properties of the vulcanized rubber.

Table 1 Examples 2 to 5 The polymerization results were carried out in the same manner as in Example 1 except as described in the polymerization conditions column of Table 2. The elastomer physical properties and vulcanization physical properties were also
Shown in the table.

(The following is a blank space) Example 5 Pure water and 113% Freon were added in the same manner as in Example 1. and suspension stabilizer were charged, and the temperature was maintained at 50° C. while stirring at 500 rpm. Then VdF 4.6% by weight, RF
A mixed monomer consisting of 91.8% by weight of P and 3.6% by weight of TFE was charged as a monomer until it reached 15kg/cd G, and then a fluorocarbon containing 10.5% by weight of diisovyl peroxydicarbonate as a catalyst was added. 113
Polymerization was started by charging 51 g of the solution. At this time, the pressure decreases to 14.5 kg/ajG due to polymerization (7) TeV
dF 39.4% by weight, HFP 40.0% by weight, TFE
A mixed gas consisting of 20.6% by weight was added as an additional monomer, and the pressure was returned to 15 kg/aJG. This operation was repeated to carry out polymerization for 17 hours. Approximately 5 kg of elastomer was obtained.

The composition of this elastomer was 39.1% by weight of VdF units;
The HFP unit was 41.4% by weight, the TFIli unit was 19.5% by weight, and [η] was 109.

The fluorine-containing elastomer was extruded under the following conditions, cut with a hot cutter, and left to cool to form pellets.

[Extruder]

Type 2 Tt manufactured by Nippon Steel Corporation! X-44, PS-30AW-2V (2 axes)
[Extrusion conditions] Heating temperature: 170°C Screw rotation speed: 30 rpm Sample feeding rate: 30 kg/hr [η] of the obtained pellet-like fluorine-containing elastomer is 8
7. MN is 13.2 x 10'l, phase/sleeves are 2.
5. Ms was 6.7%.

ML+++. (120°C) was 100.

When the pelletized fluorine-containing elastomer was polyol-vulcanized under standard conditions, a vulcanized product with excellent mechanical properties was obtained. The physical properties of this vulcanized rubber are shown in Table 3.

Table 3 Comparative Example 1 An autoclave with an internal volume of 151 and equipped with a mechanical stirrer is sufficiently purged with nitrogen gas, and the process of depressurization and nitrogen filling is repeated three times, and finally the pressure is reduced as much as possible. Next, 7500 g of pure water degassed with nitrogen gas, 1 ammonium persulfate
5 g and 22.5 g of ammonium perfluorooctanoate as an emulsifier were charged, and the temperature was maintained at 85°C. “Next”
i' A mixed monomer consisting of 38.3% by weight of VdP, 39.2% by weight of RFP and 39.2% by weight of TFE was charged and the pressure was 8.
kg/aj-G. The pressure is 7k due to polymerization.
g/cd-G, VdF 44.7% by weight,
Additional monomer consisting of 31.6% by weight RFP and 23.7% by weight TFH was added and the pressure was increased again to 8 kg/c.
Returned to d-G.

After repeating this operation for 1 hour, the remaining mixed monomers were scavenged to stop the polymerization.

An aqueous magnesium chloride solution was added to the resulting emulsion to salt out the polymer, followed by sufficient water washing and vacuum drying at 100°C to obtain about 1.3 kg of a fluorine-containing elastomer. According to P NMR measurements, the elastomer composition was 45.8% by weight VdF units, 32.7% by weight RFP units, and 21.5% by weight TPE units.

Also, [η] is 84m/g, and Mn is 7. IX
10'F4II4/touch is 13.0. Ms was 15.3%.

The fluorine-containing elastomer was polyol-vulcanized under standard conditions. Mooney viscosity was 62. Table 4 shows the physical properties of the vulcanized rubber.

Table 4

[Brief explanation of drawings]

Figure 1 shows the fraction with a molecular weight of 50,000 or less (wt%)
The coordinate axes are MS and fluorine content (weight %) F, and the ranges (A, B, C, D) of the fluorine-containing elastomer of the present invention are shown.

Claims (3)

[Claims] (1) In a fluorine-containing elastomer consisting of vinylidene fluoride units, 65 to 100% by weight of hexafluoropropylene units, and 35 to 0% by weight of tetrafluoroethylene units, (a) the weight ratio of vinylidene fluoride units to hexafluoropropylene units is (b) Intrinsic viscosity number (ml/g) is from 80 to less than 100, (c) Weight average molecular weight (@M@W) and number average molecular weight (@
(d) the fraction (weight%) with a molecular weight of 50,000 or less (hereinafter abbreviated as M_5) and the fluorine content (weight%) (hereinafter F
It is abbreviated as ) relationship (F, M_5) is the following four points A(
63.5, 15), B (63.5, 2), C (71, 2
) and D(68, 15). (2) A fluorine-containing elastomer according to claim 1, which is composed of vinylidene fluoride units and hexafluoropropylene units in an amount of 75 to 95% by weight and tetrafluoroethylene units in an amount of 25 to 5% by weight; Weight ratio with proprene unit is 45:5
Fluorine-containing elastomer characterized by having a ratio of 5 to 75:25 (3) The fluorine-containing elastomer according to claim 1, characterized in that M_5 is 8 to 2% by weight.