JP5320227B2 - Method for producing vinylidene fluoride polymer having excellent acid resistance - Google Patents

Description

  The present invention relates to a method for producing a vinylidene fluoride polymer that is less colored by contact with an acid, that is, excellent in acid-coloring resistance.

  Manufacture of vinylidene fluoride polymer (vinylidene fluoride homo- or copolymer) by suspension polymerization of vinylidene fluoride alone or a monomer mixture mainly composed of vinylidene fluoride in an aqueous suspension medium containing a suspending agent The method is well known. As the suspending agent, cellulose derivatives, polyvinyl alcohol, and the like are known, and among them, cellulose derivatives such as methyl cellulose are most commonly used (Patent Documents 1 and 2). However, the vinylidene fluoride polymer obtained by suspension polymerization using a cellulose derivative has a problem of being colored brown or black when contacted with an acid.

  On the other hand, in order to solve the above problem, it has been proposed to use a salt of an acrylic copolymer as a suspending agent (Patent Document 3). As a result, although improvement in acid-coloring resistance can be obtained to some extent, it is inadequate, and the salt of acrylic copolymer is insufficient in the protective power of suspended particles of vinylidene fluoride monomer, and it is difficult to set polymerization conditions In addition, there is a problem that the initial coloration of the produced polymer is inferior (Comparative Example 3 described later). Further, there is a document that mentions polyethylene oxide (that is, polyethylene glycol) as a suspending agent used in the production by suspension polymerization of a vinylidene fluoride polymer (Patent Document 4). However, polyethylene glycol lacks the suitability for suspension polymerization of vinylidene fluoride, and more specifically, the protective ability of suspended particles is insufficient, so the produced polymer adheres to the polymerization can and yields. Is significantly reduced (Comparative Example 5 described later).

JP 59-174605 A JP 63-264603 A Japanese Patent Laid-Open No. 11-80216 JP 2005-310747 A

  Therefore, the main object of the present invention is to provide a vinylidene fluoride polymer that uses a compound exhibiting stable suspending agent performance, has an industrially reasonable yield, excellent acid coloration resistance, and good initial colorability. There is to get.

  As a result of the above research, the present inventors have used a polyethylene glycol / polypropylene glycol block copolymer having a specific polyethylene glycol content as a suspending agent in suspension polymerization of a vinylidene fluoride polymer. The present inventors have found that a vinylidene fluoride polymer can be obtained with an industrially reasonable yield and markedly improved acid resistance and good initial colorability. That is, in the method for producing a vinylidene fluoride polymer of the present invention, when the polymerization is performed by dispersing a monomer having vinylidene fluoride as a main component in an aqueous medium containing a suspending agent, the ethylene oxide content is 75 to 75%. 85% by weight of polyethylene glycol / polypropylene glycol block copolymer is used as a suspending agent.

  Hereinafter, preferred embodiments of the present invention will be sequentially described.

  The vinylidene fluoride polymer referred to in the present invention includes a homopolymer of vinylidene fluoride (critical temperature Tc = 30.1 ° C., critical pressure Pcr = 4.38 MPa), and vinylidene fluoride as a main component, preferably 50 wt. A copolymer of vinylidene fluoride and a copolymerizable monomer having a concentration of at least%, more preferably at least 65% by weight is included. Examples of monomers copolymerizable with vinylidene fluoride include, but are not necessarily limited to, vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. is not. Further, ethylene, monomethyl maleate, allyl glycidyl ether, and the like can be used as monomers not containing fluorine, but are not necessarily limited thereto.

  In accordance with the method of the present invention, the above-mentioned vinylidene fluoride alone or a mixture thereof with a copolymerizable monomer (hereinafter collectively referred to as “vinylidene fluoride monomer”) is used as a suspending agent in polyethylene glycol. / Suspension polymerization is carried out by dispersing in an aqueous medium containing a polypropylene glycol block copolymer and further adding a polymerization initiator and a chain transfer agent for adjusting the molecular weight of the vinylidene fluoride polymer to be produced.

  As the aqueous medium, water or a mixed medium of water and a halogenated hydrocarbon medium containing 70% by weight or more of water as a main component is preferably used, and 200 to 500 with respect to 100 parts by weight of the above-mentioned vinylidene fluoride monomer. Part by weight, preferably 250-350 parts by weight of an aqueous medium is used.

  The polyethylene glycol / polypropylene glycol block copolymer used as a suspending agent in the present invention is a polyethylene glycol / polypropylene glycol block copolymer (hereinafter referred to as “EO / PO block copolymer”) having polyethylene glycol blocks at both ends. ", And examples of commercially available products are commercially available from NOF Corporation as" Pronon "series. Among them, those having an ethylene oxide (EO) content of 75 to 85% by weight are used from the viewpoint of the balance between hydrophilicity and lipophilicity. As an example of a particularly preferable commercial product, there is a product commercially available from NOF Corporation as “Pronon # 208” (EO content: 80% by weight, Mw: about 10,000). When the EO content is less than 75% by weight, the polymerization is significantly delayed. On the other hand, when it exceeds 85% by mass, the protective power of the suspended particles becomes insufficient, and the adhesion to the polymerization can becomes remarkable. In some cases, adhesion to the polymerization can causes poor stirring, and the polymerization reaction must be stopped halfway. In addition to the EO / PO block copolymer having an EO content of 75 to 85% by weight within the range of maintaining the overall ethylene oxide (EO) content of 75 to 85% by weight, the EO content is 75 to 85% by weight. A small amount of EO / PO block copolymer, polyethylene oxide, polypropylene oxide and the like which are out of the range can be used in combination. Further, those having a weight average molecular weight of 1000 to 20000, particularly 3000 to 15000 are preferably used. When the suspending agent is added to the polymerization system, it may be used as it is or as an aqueous solution.

  The EO / PO block copolymer is preferably used in a ratio of 0.01 to 3 parts by weight, particularly 0.01 to 1.5 parts by weight, per 100 parts by weight of the above-mentioned vinylidene fluoride monomer. If the EO / PO block copolymer is less than 0.01 parts by weight, the protective power of the suspended particles of the vinylidene fluoride monomer is insufficient. On the other hand, if it exceeds 3 parts by weight, the initial colorability tends to deteriorate. is there.

  It is possible to use other suspending agents in combination as long as the effect of improving the acid coloration resistance by the use of the EO / PO block copolymer is not inhibited. For example, it is possible to control the polymerization by adjusting the ethylene oxide (EO) content. For fine adjustment, it is also possible to dilute with polyethylene glycol up to the same amount as the EO / PO block copolymer. In addition, it is also preferable to use a cellulose-based suspending agent such as methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, etc., which is particularly effective for reducing initial coloring, in the range of 1 to 30% by weight of the EO / PO block copolymer.

As the polymerization initiator, those having a 10-hour half-life temperature T ₁₀ of 30 ° C. (approximately the critical temperature of vinylidene fluoride) to 90 ° C. are preferably used, and preferred examples thereof include diisopropyl peroxydicarbonate (T ₁₀ = 40). .5 ° C.), dinormalpropyl peroxydicarbonate (T ₁₀ = 40.3 ° C.), and tertiary butyl peroxypivalate (T ₁₀ = 54.6 ° C.).

  The amount of the polymerization initiator used is preferably as small as possible in order to obtain a vinylidene fluoride polymer having good thermal stability, but if it is too small, the polymerization time becomes extremely long. The range of 0.001 to 5% by weight is preferable, more preferably 0.001 to 3% by weight, based on the amount of vinylidene chloride monomer (in the case of divided addition, the total amount of initial addition and late addition) A range of 0.001 to 1% by weight is preferably used. If it is less than 0.001% by weight, it is difficult to complete the polymerization, and if it exceeds 5% by weight, it becomes difficult to effectively use the polymer in the polymerization reaction. Tend to get worse.

  In the polymerization of the present invention, a known chain transfer agent can be used for the purpose of adjusting the molecular weight of the resulting polymer, and for example, ethyl acetate, propyl acetate, acetone, diethyl carbonate, etc. can be used. The vinylidene fluoride polymer has an inherent viscosity (logarithmic viscosity at 30 ° C. of a solution obtained by dissolving 4 g of resin in 1 liter of N, N-dimethylformamide) in order to obtain a molecular weight suitable for molding applications. In particular, the range of 0.8 to 1.5 dl / g is particularly preferable.

The polymerization temperature T (° C) is 10 hours half-life temperature T ₁₀ (° C) of the polymerization initiator,
It is preferable to set the temperature that satisfies the conditions of the _{T 10 -25 ≦ T ≦ T 10} +25.

If the polymerization temperature T is lower than T _{10 -25,} since the radical generation rate from the polymerization initiator is slow, reasonable productivity of the polymer (e.g., a polymer yield of 80% or more within the polymerization time 30 h) Therefore, it is necessary to increase the amount of the polymerization initiator used in order to ensure the above. On the other hand, when the polymerization temperature T is higher than T ₁₀ +25 (° C.), the radical generation rate becomes too fast and the number of side reactions increases, so that the polymerization rate is suddenly lowered during the polymerization and the polymerization is stopped during the polymerization. No longer get. In either case, the utilization efficiency of the initiator is deteriorated, and the initial color or high-temperature colorability is increased.

By increasing the polymerization temperature T (° C.), in particular in the range of T ₁₀ ≦ T ≦ T + 25, and performing the polymerization under a high pressure, the utilization efficiency of the polymerization initiator is increased and the thermal stability (heat-resistant coloring property) is improved. It is preferable to obtain a good vinylidene fluoride polymer.

  According to a particularly preferred embodiment of the present invention, “when a monomer having vinylidene fluoride as a main component is subjected to suspension polymerization as described in WO 2006 / 061988A, the monomer is first fluorinated in a polymerization system containing a polymerization initiator. A method for producing a vinylidene fluoride polymer, characterized in that the polymerization is started by supplying the vinylidene fluoride at a pressure lower than the critical pressure Pcr (= 4.38 MPa), and continuing the polymerization by additionally supplying it at a pressure higher than the Pcr. Is adopted.

  According to this preferred embodiment, the initial charge amount of the above-mentioned vinylidene fluoride monomer is 100 parts by weight, and a relatively small amount of the polymerization initiator, for example, 0.001 to 0.12 parts by weight, preferably 0.001 to 0.1. 06 parts by weight in 200 to 500 parts by weight, more preferably 250 to 350 parts by weight of an aqueous medium (and various auxiliary agents such as suspending agents, chain transfer agents, etc.) until the polymerization temperature T (° C.) is reached. Suspension polymerization is started while raising the temperature.

  When the system rises to the polymerization temperature T as described above, the pressure inside the system exceeds Pcr due to the initially added vinylidene fluoride monomer, but the system pressure tends to decrease as the polymerization proceeds. Here, preferably, the additional vinylidene fluoride monomer is continuously supplied so as to keep the system pressure P substantially constant before the system pressure (polymerization pressure) falls below Pcr. Incidentally, the polymerization conversion rate of the initially added monomer at the time when the system pressure first reaches Pcr as the temperature rises is less than 20%, that is, to suppress the progress of polymerization at a pressure less than Pcr, It is preferable in increasing the effect of high pressure polymerization.

  The polymerization pressure P when adding the vinylidene fluoride monomer in the middle is preferably not less than the critical pressure of vinylidene fluoride (4.38 MPa). In other words, it is considered that by supplying and polymerizing the monomer in a supercritical state, the movement of the monomer to the reaction field is accelerated, and the efficient polymerization can proceed with respect to the radical. When the polymerization pressure P exceeds the critical pressure of vinylidene fluoride + 5 (MPa), it becomes a so-called overfilled state, which not only affects the granulation such as coalescence of the polymers but also increases the danger at high pressure. Therefore, it is preferable to keep the polymerization pressure P substantially constant (within ± 10%, more preferably within ± 7%) within the above-described range of Pcr to Pcr + 5 (MPa) during the midway addition of the additional monomer.

  The intermediate addition of the vinylidene fluoride monomer is preferred after the initially charged monomer is polymerized to some extent to form polymerization nuclei and form stable particles. More specifically, it is preferably added when the polymerization conversion rate of the initially charged monomer reaches 0.1 to 70%, more preferably 0.5 to 50%, and still more preferably 1 to 40%.

  The intermediate addition amount of the vinylidene fluoride monomer is preferably 20 to 200 parts by weight, more preferably 50 to 150 parts by weight with respect to 100 parts by weight of the initial charge.

  The polymerization end point is appropriately selected in consideration of the balance between the decrease in the amount of unreacted monomer and the lengthening of the polymerization time (that is, the productivity of the product polymer). After completion of the polymerization, the polymer slurry is dehydrated, washed with water and dried to obtain a polymer powder.

  The vinylidene fluoride polymer of the present invention thus obtained can be contacted with various molded body forming resins, particularly strong acids, using its excellent acid resistance and good initial colorability. It is preferably used as a resin for forming a molded article having Here, the strong acid means acids represented by hydrochloric acid, sulfuric acid and the like and mixtures thereof, but is not necessarily limited thereto.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following description, “parts” representing the quantity ratio means “parts by weight”.

Example 1
In an autoclave with an internal volume of 2 liters, 1016 g (254 parts) of ion-exchanged water, 4 g of EO / PO block copolymer (EO content: 80% by weight, weight average molecular weight (Mw): about 10,000) as a suspending agent Part), diethyl carbonate 6 g (1.5 parts) as a chain transfer agent, di-i-propyl peroxydicarbonate (IPP) 2.4 g (0.6 parts as a 50 wt% CFC 225cb solution as an initiator) 1.2 parts) and 400 g (100 parts) of vinylidene fluoride were charged, and suspension polymerization was carried out for 25 hours at 29 ° C. until the pressure dropped from the initial pressure of 4.29 MPa to 2.98 MPa. After completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 30 minutes, dehydrated and washed with water, and further dried at 80 ° C. for 20 hours to obtain a polymer powder. The polymerization rate was 86%, and the inherent viscosity of the obtained polymer was 0.91 dl / g.

(Comparative Example 1)
Polymerization was carried out in the same manner as in Example 1 except that 4 g (1 part) of an EO / PO block copolymer (EO content: 70% by weight, Mw: about 10,000) was used as a suspending agent. As a result, no significant drop in pressure was observed indicating that the polymerization had progressed even after 50 hours had elapsed from the start of polymerization, and stirring was stopped at that time.

(Comparative Example 2)
As a suspension, 0.4 g (0.1 part) of gelatin powder (manufactured by Kanto Chemical Co., Ltd.) and 4.8 g (1.2 parts, 50) of di-n-propyl peroxydicarbonate (NPP) as an initiator 2.4 parts by weight as a methanol solution with a concentration by weight), 8.8 g (2.2 parts) of ethyl acetate as a chain transfer agent, and the pressure is the same as in Example 1 except that the polymerization temperature is 28 ° C. Suspension polymerization was performed for 23 hours until the pressure dropped to 2.2 MPa. The polymerization rate was 80%, and the inherent viscosity of the obtained polymer was 0.90 dl / g.

(Comparative Example 3)
As a suspending agent, 1.2 g (0.3 parts) of an acrylic copolymer Na salt prepared as described below, and 0.4 g (0.1 parts) of di-i-propyl peroxydicarbonate (IPP) as an initiator. , 0.2 parts as a 50 wt% CFC solution of 225 cb), 18.4 g (4.6 parts) of ethyl acetate as a chain transfer agent, and the polymerization temperature is 28 ° C. For 40 hours. The granidity of vinylidene fluoride was slightly poor and polymerization was possible, but the rate was somewhat slow. The obtained polymer powder had few pearl-like spherical particles and contained irregularly shaped particles and crushed particles. The polymerization rate was 73%, and the inherent viscosity of the obtained polymer was 0.85 dl / g.

<Preparation of acrylic copolymer salt>
The acrylic copolymer salt used in Comparative Example 3 was prepared as follows. That is, 150 g of ethyl acetate, 0.1 g of NPP (0.2 g as a 50 wt% methanol solution), 45 g of acrylic acid, and 5 g of 2-ethylhexyl acrylate were placed in a 500 ml Erlenmeyer flask and stirred at 40-50 ° C. for 85 minutes. did. Then, while increasing the temperature stepwise, stirring was continued at 50 to 55 ° C. for 2 hours and at 55 to 70 ° C. for 45 minutes. After completion of the reaction, ethyl acetate was distilled off, and overnight at 60 ° C. using a vacuum dryer. The acrylic copolymer was dried almost quantitatively. 2.7 g of this acrylic copolymer was placed in a 300 ml flask, 180 g of water and 11 g of a 10% aqueous solution of sodium hydroxide were added, and the mixture was heated and stirred at 60 ° C. to neutralize 95% of the carboxyl groups of the acrylic copolymer with NaOH. Then, it adjusted by adding water so that the whole quantity might be set to 200 g, and obtained the 1.5 mass% aqueous solution of the salt of an acrylic copolymer.
(Comparative Example 4)
As a suspending agent, 0.2 g (0.05 parts) of methyl cellulose (methyl substitution number 1.8, 2% solution having a viscosity of 100 mPa · s at 20 ° C .; “SM-100” manufactured by Shin-Etsu Chemical Co., Ltd.) Suspension polymerization for 23 hours was carried out until the pressure dropped to 2.5 MPa in the same manner as in Comparative Example 2 except that 10.8 g (2.7 parts) of ethyl acetate was used as the chain transfer agent and the polymerization temperature was 26 ° C. went. The inherent viscosity of the polymer obtained at a polymerization rate of 83% was 0.97 dl / g.

[Examples 2-6, Comparative Examples 5-11]
Suspension polymerization of vinylidene fluoride polymer by monomer split addition-high temperature polymerization system, which can produce vinylidene fluoride polymer with good heat-resistant coloring property through improvement in utilization efficiency of polymerization initiator, is as follows. went.

(Example 2)
In an autoclave having an internal volume of 2 liters, 1040 g (260 parts) of ion-exchanged water and 2 g of an EO / PO block copolymer (EO content: 80% by weight, Mw: about 10,000) used in Example 1 as a suspending agent ( 0.5 part), diethyl carbonate (DEC) 4 g (1 part) as a chain transfer agent, t-butyl peroxypivalate (PB-PV) 2 g as an initiator (0.5 part, chlorofluorocarbon 225 cb at a concentration of 50% by weight) 4 g) as a solution and 400 g (100 parts) of vinylidene fluoride were charged, the temperature was raised to 65 ° C. over 3 hours, and then maintained at 65 ° C. The maximum ultimate pressure was 7.8 MPa. Further, after 1 hour, 400 g (100 parts) of vinylidene fluoride was gradually added so as to maintain the polymerization pressure of 7.7 MPa. Thereafter, polymerization was continued at 65 ° C. for about 15 hours, and suspension polymerization was carried out for a total of 23 hours from the start of temperature increase until the pressure dropped to 4.8 MPa. After completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 30 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a polymer powder. The polymerization rate was 92%, and the inherent viscosity of the obtained polymer was 1.17 dl / g.

(Example 3)
Suspension polymerization was carried out in the same manner as in Example 2 except that 2 g (0.5 parts) of an EO / PO block copolymer (EO content: 75% by weight, Mw: about 10,000) was used as the suspending agent. It was. The polymerization rate was 93%, and the inherent viscosity of the obtained polymer was 1.14 dl / g.

Example 4
Suspension polymerization was carried out in the same manner as in Example 2 except that 2 g (0.5 parts) of an EO / PO block copolymer (EO content: 85% by weight, Mw: about 10,000) was used as the suspending agent. It was. The polymerization rate was 90%, and the inherent viscosity of the obtained polymer was 1.14 dl / g.

(Example 5)
Suspension polymerization was carried out in the same manner as in Example 2 except that 1 g (0.25 part) of an EO / PO block copolymer (EO content: 80% by weight, Mw: about 10,000) was used as the suspending agent. It was. The polymerization rate was 90%, and the inherent viscosity of the obtained polymer was 1.16 dl / g.

(Example 6)
Suspension polymerization was carried out in the same manner as in Example 2 except that 6 g (1.5 parts) of an EO / PO block copolymer (EO content: 80 wt%, Mw: about 10,000) was used as the suspending agent. It was. The polymerization rate was 92%, and the inherent viscosity of the obtained polymer was 1.12 dl / g.

(Comparative Example 5)
Polymerization was carried out in the same manner as in Example 2 except that 2 g (0.5 parts) of polyethylene glycol (“PEG # 20000” manufactured by NOF Corporation; Mw: about 20,000) was used as the suspending agent. As a result, since the agitation became poor during polymerization due to remarkable adhesion to the polymerization can, the polymerization was stopped midway.

(Comparative Example 6)
Polymerization was carried out in the same manner as in Example 2 except that 2 g (0.5 parts) of an EO / PO block copolymer (EO content: 70% by weight, Mw: about 10,000) was used as a suspending agent. . As a result, no significant drop in pressure was observed indicating that the polymerization had progressed even after 50 hours had elapsed from the start of polymerization, and stirring was stopped at that time.

(Comparative Example 7)
Polymerization was carried out in the same manner as in Example 2 except that 2 g (0.5 parts) of an EO / PO block copolymer (EO content: 40% by weight, Mw: about 3300) was used as a suspending agent. As a result, no significant drop in pressure was observed indicating that the polymerization had progressed even after 50 hours had elapsed from the start of polymerization, and stirring was stopped at that time.

(Comparative Example 8)
As a suspending agent, 4.8 g (1.2 parts) of polyethylene glycol (manufactured by NOF Corporation “PEG # 20000”; Mw: about 20,000) and polypropylene glycol (“UNIOL D-2000” manufactured by NOF Corporation): Mw: about 2000) Polymerization was carried out in the same manner as in Example 2 except that 1.2 g (0.3 parts) of the mixture was used. As a result, since the agitation became poor during polymerization due to remarkable adhesion to the polymerization can, the polymerization was stopped midway.

(Comparative Example 9)
As a suspending agent, 2 g (0.5 parts) of an EO / PO block copolymer (EO content: 40% by mass, Mw .: about 3300) and polyethylene glycol (“PEG # 20000” manufactured by NOF Corporation; Mw: Polymerization was carried out in the same manner as in Example 2 except that a mixture of about 20,000) 4 g (1 part) was used. As a result, no significant drop in pressure was observed indicating that the polymerization had progressed even after 50 hours had elapsed from the start of polymerization, and stirring was stopped at that time.

(Comparative Example 10)
0.4 g (0.1 part) of methyl cellulose (manufactured by Shin-Etsu Chemical Co., Ltd. “SM-100”) as a suspending agent, and 0.4 g (0. 0 of t-butyl peroxypivalate (PB-PV) as an initiator. Suspension polymerization was carried out for a total of 24 hours in the same manner as in Example 2 except that 1 part and 0.2 part as a 50 wt% concentration CFC 225cb solution were used. The polymerization rate was 92%, and the inherent viscosity of the obtained polymer was 0.99 dl / g.

(Comparative Example 11)
Hydroxypropyl methylcellulose as a suspending agent (hydroxypropyl substitution number 0.20, methyl substitution number 1.4, 2% solution having a 20 ° C. viscosity of 100 mPa · s; “SH-100” manufactured by Shin-Etsu Chemical Co., Ltd.) 0 A total of 23 hours of suspension polymerization was carried out in the same manner as in Comparative Example 10, except that 0.4 g (0.1 part) was used. The polymerization rate was 91%, and the inherent viscosity of the obtained polymer was 0.97 dl / g.

<Acid resistance test>
For each of the vinylidene fluoride polymer sample powders obtained in the above Examples and Comparative Examples, after preheating at 240 ° C. for 6 minutes using a press molding machine (“AYSR-5” manufactured by Shinfuji Metal Industry Co., Ltd.) A test piece of 11 × 6.4 × 0.6 cm was prepared by holding at a press pressure of 10 MPa for 2 minutes. The test piece thus prepared was immersed in 35% by weight hydrochloric acid and kept at 60 ° C. for 1 week.

<Color tone evaluation>
The color tone of the test piece before and after immersion in hydrochloric acid was measured using a color difference meter (“ZE6000” manufactured by Nippon Denshoku Industries Co., Ltd.). Was measured. The larger the W value, the more white, W = 100 indicates true white, and W = 0 indicates true black. The smaller the YI value, the lower the yellowness, and the b value the higher the + (plus) value, the higher the yellowness, and the greater the-(minus) value, the higher the blueness.

<Productivity evaluation>
About the said Example and comparative example, the productivity evaluation regarding polymerization time, the stirring behavior at the time of superposition | polymerization, the recovery rate of a polymer, and the rational productivity by the combination of these evaluations were evaluated in three steps according to the following criteria, respectively. .

(Polymerizability)
A: The polymerization time is within 30 hours.
B: Polymerization time exceeds 30 hours.
C: Stirring failure occurs due to remarkable adhesion to the polymerization can in the middle of the polymerization, and the polymerization must be stopped in the middle.

(Polymer recovery rate)
A: 80% or more B: 50% or more, less than 80% C: less than 50%.

(Rational productivity)
A: No problem in industrial implementation. Specifically, both the above-described evaluation of polymerizability and polymer recovery rate are A ratings.
B: Although industrial implementation is possible, there is a problem. Specifically, in the above-described polymerization evaluation and polymer recovery rate, C evaluation is not included, but at least one of them is B evaluation.
C: Industrial implementation is not possible. Specifically, at least one of the polymerizability evaluation and the polymer recovery rate is C evaluation.

Tables 1 to 3 summarize the polymerization and the evaluation results of the above items for the above Examples and Comparative Examples.

  As can be seen from Table 1 and Table 2, according to the present invention, in the suspension polymerization of vinylidene fluoride monomer, the ethylene oxide (EO) content as a suspending agent is 75 to 85% by weight. By using a narrow range of polyethylene glycol / polypropylene glycol block copolymers, stable polymerization of suspension polymerization is possible, and in addition to good initial colorability, vinylidene fluoride having excellent acid coloration resistance Coalescence is obtained.

Claims (9)

A polyethylene glycol / polypropylene glycol block copolymer having an ethylene oxide content of 75 to 85% by weight when suspension polymerization is carried out by dispersing a monomer mainly composed of vinylidene fluoride in an aqueous medium containing a suspending agent. As a suspending agent, and a method for producing a vinylidene fluoride polymer. The method according to claim 1, wherein the polyethylene glycol / polypropylene glycol block copolymer has a weight average molecular weight of 1,000 to 20,000. The production method according to claim 1 or 2, wherein 0.01 to 3 parts by weight of a polyethylene glycol / polypropylene glycol block copolymer is used with respect to 100 parts by weight of the monomer. The process according to claim 1, 10 hours half-life temperature _{T 10} uses a polymerization initiator is 30 to 90 ° C.. In suspension polymerization of a monomer having vinylidene fluoride as a main component, the monomer is first supplied to a polymerization system containing a polymerization initiator at a pressure lower than the critical pressure Pcr (= 4.38 MPa) of vinylidene fluoride. The production method according to any one of claims 1 to 4, wherein the polymerization is started and the polymerization is continued by further supplying at a pressure of Pcr or higher. The production method according to claim 5, wherein suspension polymerization is performed using 0.001 to 5% by weight of a polymerization initiator based on the total amount of monomers added to the polymerization system. The production method according to claim 5 or 6, wherein the polymerization conversion rate of the initially supplied monomer to the polymerization system when the polymerization system pressure first reaches Pcr is less than 20%. Polymerization within the range of T _{10 to} T ₁₀ +25 (° C.) by adding a monomer mainly composed of vinylidene fluoride in the middle so that the pressure P is maintained within the range of Pcr (MPa) to Pcr + 5 (MPa). The production method according to claim 7, wherein suspension polymerization is performed at a temperature T. The production method according to any one of claims 1 to 8, wherein the monomer comprises only vinylidene fluoride.