JPH0735424B2 - Method for producing soft fluororesin - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a flexible fluororesin, more specifically, a crystalline fluorine-containing copolymer having a melting point of 130 ° C. or higher. In the step of graft-copolymerizing the polymer, a homogeneous mixed solvent of a soluble solvent (good solvent) of the elastic copolymer and a non-soluble organic solvent (poor solvent) is used as a polymerization solvent. It is about.

(Prior Art) Soft fluororesin (Japanese Patent Publication No. 62-34324) that has both flexibility and molding processability is used in a wide range of applications such as tubes, sealing materials, films, wire coatings and injection molded products. .

According to the publication, as a first step, a fluorine-containing elastic copolymer containing unsaturated peroxide (hereinafter abbreviated as a trunk resin) is produced, and an aqueous emulsion of the trunk resin obtained in the first step in the second step is produced. A soft fluororesin is obtained by a method of decomposing peroxy groups in a liquid or a dispersion solvent to initiate polymerization of a branch resin.

In this case, when an aqueous emulsion (water latex) of the trunk resin is used, the residual initiator used during the production of the trunk resin also acts in the second-stage polymerization, resulting in the decomposition of the peroxy group in the trunk resin. A mixture of the graft copolymer and a linear fluororesin resulting from the decomposition of residual initiator is formed.
Generally, the aqueous emulsion is the water latex itself obtained by emulsion polymerization. That is, the trunk resin obtained by suspension polymerization or solution precipitation polymerization, and the trunk resin obtained by precipitating solids by an operation such as salting out of latex can remove residual initiator by washing. However, it is extremely difficult to make them into a water latex by adding a surfactant or the like.

On the other hand, the trunk resin from which the residual initiator has been removed by washing can be graft-copolymerized in a dispersion solvent such as an organic solvent. In this case, a graft copolymer based on only the decomposition of peroxy groups in the trunk resin is produced, so that the graft efficiency of the monomer is higher than the above, and a soft fluororesin having excellent tensile strength and tensile elongation can be obtained. However, in general, the decomposition temperature of the peroxy group is high, and there are some that easily undergo chain transfer in organic solvents and the like, so a graft copolymer having a high molecular weight cannot be obtained depending on the type of the monomer to be graft-copolymerized, In some cases, appropriate physical properties may not be obtained in terms of mechanical properties and workability.

As described above, industrially, graft copolymerization is carried out in an aqueous emulsion or dispersion solvent of a trunk resin to obtain a soft fluororesin. It depends on the physical properties of the coalescence. However, it can be said that this method is superior in physical properties if an appropriate dispersion solvent is selected as described above.

(Problems to be Solved by the Invention) The present invention solves the problems of the graft copolymerization carried out in the dispersion solvent.

That is, when performing graft copolymerization in a dispersion solvent,
The graft copolymerization rate is mainly determined by (1) particle diameter of the trunk resin in the dispersion medium, (2) monomer solubility in the dispersion medium, (3) peroxy group content in the trunk resin, and (4) polymerization temperature. If a trunk resin with a constant peroxy group content is used at a certain temperature, the above items (1) and (2) become important. These items are based on the fact that the contact between the peroxy group in the trunk resin and the monomer affects the polymerization rate.

It is preferable that the particle size of the trunk resin in the dispersion medium is porous or small. From this aspect, if the dispersion medium completely dissolves the trunk resin, the molecular trunk resin and the monomer come into contact with each other, and ideal graft copolymerization can be performed. Generally, this method is limited to the method of using a non-crystalline fluorine-based polymer, for example, a fluorine-containing elastic copolymer as a trunk resin, since a crystalline fluorine-based polymer is hardly dissolved in an organic solvent or the like. .

However, the graft copolymerization method has many industrial problems in practical use. That is, the solution of the trunk resin has a considerable viscosity, which makes stirring difficult during the graft copolymerization. Further, when the graft ratio is increased, the graft copolymer is often precipitated in the solution, but in order to obtain the soft fluororesin of the gist of the present invention, the graft copolymer is usually used at a high proportion of the trunk resin. Since the polymerization is stopped, a solution of the graft copolymer or a swelling solution thereof is obtained. This hinders the subsequent precipitation and separation of the graft copolymer.

Therefore, as the dispersion medium, the trunk resin is swollen moderately,
It is preferable that the trunk resin can be made finer to some extent by stirring, and the graft copolymer produced by the graft copolymerization does not swell in the dispersion medium at all and can be easily separated by filtration.

On the other hand, a dispersion medium that can dissolve the fluorine-based monomer well to increase the monomer concentration in the polymerization system is preferable. In particular, monomers such as tetrafluoroethylene and vinylidene fluoride, which have a critical temperature of about 30 ° C, are gaseous at normal graft copolymerization temperatures (40 ° C or higher), so the solubility of the gas in the dispersion medium is important. Is.

The conditions to be possessed by a suitable dispersion medium for the above graft copolymerization are summarized as follows.

(1) Moderately swell the trunk resin.

(2) The polymerization rate of the trunk resin can be reduced.

(3) Does not dissolve or swell the graft copolymer.

(4) The solubility of the monomer is large.

As a dispersion medium suitable for such a condition, there is a CFC type medium found in JP-B-62-34324. In particular, 1,1,2-trichloro 1,2,2-trifluoroethane (R113), 1,1-trichloro 1,1,2,2-trifluoroethane (R114) and the like are typical examples.

Such a medium is optimum as a graft polymerization solvent, but has a low boiling point, which makes it difficult to handle in industrial use. Moreover, since the vapor pressure at room temperature is high, it easily scatters during separation of the graft polymer, and a solvent recovery device is required. And

Furthermore, as the ozone layer depletion problem of chlorofluorocarbon solvents has recently been raised, it has become socially indispensable to find alternative solvents.

(Means for Solving Problems) The present inventors searched for many solvents in order to solve the above problems, but were unable to find a single medium that could substitute for a Freon-based medium.

However, it is necessary to return to the above requirements for the dispersion medium and mix a soluble solvent (good solvent) and a non-soluble solvent (poor solvent) for the trunk resin to come up with a search for a medium that behaves similarly to a CFC-based medium. Thus, the present invention has been completed.

That is, a ketone, an ester, a chlorine-based organic medium or the like, which is a good solvent for the trunk resin and which dissolves a fluorine-based monomer well, is mixed with an alcohol, a saturated hydrocarbon, or the like, which is a poor solvent,
Graft copolymerization was carried out by observing the degree of swelling of the trunk resin and the solubility of the graft copolymer produced in a fluorocarbon solvent, and assuming an appropriate combination and mixing ratio of them. The results of these experiments have revealed that the ester-alcohol mixed solvent behaves like a chlorofluorocarbon-based solvent most closely and that a soft fluororesin having excellent physical properties is obtained.

Naturally, the mixed solvent is required to be a homogeneous system. That is, in a heterogeneous mixed medium that does not dissolve in each other, the trunk resin dissolves or swells significantly in a good solvent, which is not preferable.

The trunk resin in the present invention is an elastic copolymer having a composition of fluororubber having a glass transition temperature of room temperature or lower, and having a peroxide bond in the side chain of the polymer.
The production method is similar to the example described in JP-B-62-34324, but the composition thereof is not particularly limited.

On the other hand, as the fluorine-containing crystalline polymer produced by graft copolymerization having a melting point of 130 ° C. or higher, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene and Examples thereof include a copolymer with ethylene, a copolymer with chlorotrifluoroethylene and ethylene, and a copolymer with tetrafluoroethylene and perfluorovinyl ether, but the composition thereof is not particularly limited.

The ratio of the fluorine-containing elastic copolymer and the fluorine-containing crystalline polymer is
A soft fluororesin having excellent physical properties and processability can be obtained at a weight ratio of 50:50 to 90:10.

As the organic medium in the graft copolymerization, a mixture of a soluble organic medium of the trunk resin (good solvent: including a medium having a large swelling property) and a non-soluble organic medium (poor solvent) is used. In addition, it is a necessary condition that the two kinds of solvents dissolve in each other to form a homogeneous mixed solvent.

Examples of good solvents include ketones, esters and chlorine-based organic compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, n-butyl acetate, t-butyl acetate, ethyl formate, methyl propionate, ethyl propionate, Ethane dichloride, ethylene tetrachloride, trichloroethylene, trichloroethane,
Examples include chloroform, methylene chloride and chlorobenzene.

Examples of the poor solvent include alcohols and saturated hydrocarbons such as methanol, ethanol, n-butanol, t-butanol (tertiary butyl alcohol), amyl alcohol, ethylene glycol, butanediol, n-pentane, n-hexane and n. -Heptane, n-octane and the like.

A proper weight ratio of the good solvent and the poor solvent is 5 to 50:95 to 50, and in these ranges, the solid surface of the trunk resin is slightly swelled in the medium and is dispersed in the medium by agitation by stirring. . Moreover, the soft fluororesin produced by the graft copolymerization exists in the medium as fine particles, and the handling of the slurry and the filtration of the resin can be carried out very easily.

Next, reference examples, comparative examples and examples are shown, but the present invention is not limited thereto.

Reference example 1 300 kg stainless steel autoclave 120 kg pure water, 0.4 kg potassium persulfate, ammonium perfluorooctanoate
After degassing by adding 0.036 kg, potassium dihydrogen phosphate 0.168 kg and sodium borate 0.373 kg, the temperature of the autoclave was raised to 50 ° C. Then, 20% by weight of t-butylperoxyallyl carbonate, 0.168 kg of a Freon 113 solution, 3.4 kg of chlorotrifluoroethylene, and 4.2 kg of vinylidene fluoride were charged to initiate polymerization. Further, 0.112 kg of a chlorofluorocarbon 113 solution of t-butylperoxyallyl carbonate, 1.8 kg of chlorotrifluoroethylene, and 2.2 kg of vinylidene fluoride were each divided into 6 portions, and the mixture was stirred at 11.5 to 12.7 kg / c.
Polymerization was performed at m ² (G) and 50 ° C. for 10 hours. After that, the stirring speed is increased and polymerization is carried out for 5 hours, and the final pressure is 7.4 kg / cm.
² (G) was cooled to 40 ° C. or lower to remove unreacted monomer.

The product was a water slurry of elastic copolymer. This slurry was filtered, washed with water three times, and vacuum dried. The yield of elastic copolymer was 32.0 kg.

Elemental analysis revealed that the molar composition ratio of vinylidene fluoride and chlorotrifluoroethylene in this copolymer was 72:28. Further, by DSC measurement, an exothermic peak due to the decomposition of the peroxy group in the t-butylperoxyallylcarbonate chain was observed at about 160 ° C.

The intrinsic viscosity of this copolymer in dimethylformamide at 30 ° C. was 1.66 dl / g.

The copolymer was kneaded with a 4-inch double roll (roll temperature 200 ° C.) and then press-molded (press temperature 200 ° C.) to prepare a 2 mm-thick smooth sheet. 23 of this sheet
Tensile strength at ℃ 26kgf / cm ² , tensile elongation 1550%, J
The IS-A hardness was 61. (Measured according to JIS-K7210.) Comparative Example 1 To a 2 l stainless steel autoclave, 200 g of the peroxy group-containing elastic copolymer of Reference Example 1 and 113 cc of Freon 113 were added, deaerated, and then 133 g of vinylidene fluoride was added. Polymerization was started at 98 ° C with stirring. Performed 15 hours graft polymerization, the pressure was reduced 19.4 kg / cm ² from (G) 11.0kg / cm ² to (G).

The product was an R113 slurry of the graft copolymer. This slurry was filtered and dried at 90 ° C. to obtain 253.3 g of a graft copolymer. The vinylidene fluoride fraction in the graft copolymer was 21% by weight.

The results of the graft copolymerization and the physical properties of the graft copolymer are shown in Table 1.

Comparative Examples 2 to 5 In the same manner as in Comparative Example 1, graft copolymerization was carried out for 24 hours by using t-butanol, n-heptane, ethyl acetate and 1,1,1-trichloroethane instead of Freon 113. The results are shown in Table 1.

Examples 1 to 3 In the same manner as in Comparative Example 1, a mixed solution of ethyl acetate-t-butanol (2: 8 weight ratio) instead of CFC 113, 1,1,1-trichloroethane-t-butanol (4: 6 weight%) was used. (Ratio) mixed solution and methylene chloride-t-butanol (4: 6 weight ratio) mixed solution were used for graft copolymerization for 24 hours. The results are shown in Table 1.

Comparative Examples 6 to 7 In the same manner as in Comparative Example 1, a mixed solution of ethyl acetate-t-butanol (6: 4 weight ratio) instead of CFC 113, 1,1,1-trichloroethane-t-butanol (6: 4) was used. Graft copolymerization was carried out for 24 hours using the mixed solution (weight ratio). The results are shown in Table 1.

As shown in Table 1, graft copolymerization does not proceed in a poor solvent of a peroxy group-containing elastic copolymer such as t-butanol or n-heptane. On the other hand, a good solvent such as ethyl acetate or 1,1,1-trichloroethane undergoes graft copolymerization, but the graft copolymer swells in the solvent, which causes problems in filterability and polymer separation from the solvent. Further, since the polymerization system is gelled, sufficient stirring efficiency cannot be obtained and the polymerization is slow depending on the degree of stirring.

(Effect of the Invention) By using the mixed solvent for graft polymerization in a suitable ratio of the good solvent and the poor solvent according to the present invention, a polymer having an excellent polymerization rate and physical properties superior to conventional solvents can be obtained. Further, the mixed solvent is easy to handle and no special solvent recovery device is required.

Claims (4)

[Claims] 1. A crystalline fluorine-containing copolymer having a melting point of 130 ° C. or higher in the presence of a fluorine-containing elastic copolymer (stem resin) containing a peroxy group in the molecule, which gives at least one fluorine-containing monomer. In the step of graft copolymerizing one or more kinds of monomers containing, a soft fluorine resin characterized by using a homogeneous mixed medium of a soluble organic medium and an insoluble organic medium of the elastic copolymer as a polymerization solvent. Manufacturing method. 2. A soluble organic medium 5 of a fluorine-containing elastic copolymer.
The method for producing a soft fluororesin according to claim 1, wherein a homogeneous mixed medium of -50% by weight and an insoluble organic medium of 95-50% by weight is used. 3. The method for producing a soft fluororesin according to claim 1, wherein a mixed solvent of acetic acid ester and tertiary butyl alcohol is used as a polymerization solvent. 4. A chlorine-based organic compound and a third organic solvent as a polymerization solvent.
The method for producing a soft fluororesin according to claim 1, wherein a mixed solvent of primary butyl alcohol is used.