JP5297140B2 - Method for producing vinylidene fluoride polymer having excellent acid resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a vinylidene fluoride polymer having excellent resistance to acid discoloration as well as favorable initial discoloration through a stable suspension polymerization. <P>SOLUTION: In the method for producing the vinylidene fluoride polymer, an N-vinyl carboxylic acid amide polymer is used as a suspending agent to perform suspension polymerization by dispersing a monomer composed mainly of vinylidene fluoride into an aqueous medium including the suspending agent. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

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 coloring of the polymer to be formed is inferior.
JP 59-174605 A JP 63-264603 A Japanese Patent Laid-Open No. 11-80216

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

As a result of researches for the above-mentioned purposes, the present inventors have been able to use a vinylidene fluoride polymer as a homopolymer of N-vinylcarboxylic acid amide , which has been conventionally known as a thickener or a dispersion stabilizer for inorganic particles and pigments. It has been found that by using it as a suspending agent in the suspension polymerization of the polymer, a vinylidene fluoride polymer having significantly improved acid resistance and good initial colorability can be obtained. That is, in the method for producing a vinylidene fluoride polymer of the present invention, N-vinylcarboxylic acid amide is used when suspension polymerization is performed by dispersing a monomer having vinylidene fluoride as a main component in an aqueous medium containing a suspending agent. These homopolymers are 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 masses. %, More preferably 65% by mass or more, and a copolymer of vinylidene fluoride and a copolymerizable monomer 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.

  According to the method of the present invention, vinylidene fluoride alone or a mixture thereof with a monomer copolymerizable therewith (hereinafter collectively referred to as “vinylidene fluoride monomer”) as a suspending agent, N-vinylcarboxylic Suspension polymerization is carried out by dispersing in an aqueous medium containing an acid amide polymer, 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 mass or more of water as a main component is preferably used, and 200 to 500 with respect to 100 parts by mass of the above-mentioned vinylidene fluoride monomer. Part by weight, preferably 250-350 parts by weight of an aqueous medium is used.

The N-vinylcarboxylic acid amide polymer used in the present invention includes N-vinylformamide, N-vinylacetamide, N-vinylpropionamide, N- (propenyl-2-yl) formamide, N- (propenyl-2-yl). ) acetamide, N- vinyl-2-pyrrolidone, a alone polymer of N- vinyl carboxylic acid amides such as N- vinyl-2-piperidone, among others from the viewpoint of the balance between hydrophilicity and lipophilicity of N- vinylacetamide poly -N- vinylacetamide is alone Polymerization body is preferably used. The suspension polymerization system is preferably added as an aqueous solution, for example, a viscosity of about 1500 to about 30,000 mPa · s as a 5 to 40% by mass aqueous solution, particularly about 10,000 to 25 as an about 8 to 25% by mass aqueous solution. Those exhibiting a viscosity of 1,000 mPa · s are preferably used.

  The N-vinylcarboxylic acid amide polymer is preferably used in a proportion of 0.01 to 2 parts by mass, particularly 0.01 to 1 part by mass as a solid content per 100 parts by mass of the above-mentioned vinylidene fluoride monomer. When the N-vinylcarboxylic acid amide polymer is less than 0.01 part by mass, the protective power of the suspended particles of vinylidene fluoride monomer is insufficient, and when it exceeds 2 parts by mass, the initial colorability tends to deteriorate. It is.

  It is possible to use other suspending agents in combination as long as the effect of improving the acid coloration resistance by using the N-vinylcarboxylic acid amide polymer is not impaired. Particularly, methylcellulose, hydroxyethylcellulose, which are effective in reducing initial coloration, It is also preferable to use a cellulose-based suspending agent such as hydroxypropylmethylcellulose in the range of 1 to 30% by mass of the N-vinylcarboxylic acid amide polymer.

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 mass% is preferable, more preferably 0.001 to 3 mass%, and more preferably 0.001 to 3 mass%, based on the amount of vinylidene chloride monomer (in the case of divided addition, the total amount of initial addition amount and late addition amount) Preferably the range of 0.001-1 mass% is used. If it is less than 0.001% by mass, it is difficult to complete the polymerization, and if it exceeds 5% by mass, it becomes difficult to use it effectively in the polymerization reaction, and the resulting polymer melt-molded product can be colored and dissolved. 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 preferable aspect, the initial charge amount of the above-mentioned vinylidene fluoride monomer is 100 parts by mass, and a relatively small amount of the polymerization initiator, for example, 0.001 to 0.12 parts by mass, preferably 0.001 to 0.1. 06 mass parts is dispersed in 200 to 500 mass parts, more preferably 250 to 350 mass parts of an aqueous medium (and various auxiliary agents such as suspending agents and chain transfer agents), and 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 mass, and more preferably 50 to 150 parts by mass with respect to 100 parts by mass 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, “part” representing the quantitative ratio means “part by mass”.

Example 1
In an autoclave having an internal volume of 2 liters, 1016 g (254 parts) of ion-exchanged water and an approximately 10% by weight aqueous solution of poly-N-vinylacetamide as a suspending agent (“GE191-103” manufactured by Showa Denko KK); viscosity = about 16 4,000 mPa · s, hereinafter sometimes abbreviated as “PVAA1”) 40 g (4 g as solids = 1 part), 18.4 g (4.6 parts) of ethyl acetate (EA) as chain transfer agent, and di as initiator -I-propyl peroxydicarbonate (IPP) 0.4g (0.1 part, 0.2 part as a solution in 50 mass% Freon 225cb) and vinylidene fluoride 400g (100 parts) were charged, and the pressure was 29 ° C. Suspension polymerization was performed for 27 hours until the initial pressure dropped from 4.2 MPa to 2.76 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 81%, and the inherent viscosity of the obtained polymer was 0.92 dl / g.

(Comparative Example 1)
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 as a solution in mass% methanol), 8.8 g (2.2 parts) of ethyl acetate as the chain transfer agent, and a pressure of 2 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 MPa. The polymerization rate was 80%, and the inherent viscosity of the obtained polymer was 0.90 dl / g.

(Comparative Example 2)
As a suspending agent, 1.2 g (0.3 part) of acrylic copolymer Na salt prepared as described below was used, and the polymerization temperature was 28 ° C. Turbid polymerization was performed. 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 2 was prepared as follows. That is, 150 g of ethyl acetate, 0.1 g of NPP as an initiator (0.2 g as a solution in 50 mass% methanol), 45 g of acrylic acid, and 5 g of 2-ethylhexyl acrylate were placed in a 500 ml Erlenmeyer flask and stirred at 40 to 50 ° C. for 85 minutes. . 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 3)
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 performed until the pressure dropped to 2.5 MPa in the same manner as in Comparative Example 1 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 to 5, Comparative Examples 4 to 5]
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 with an internal volume of 2 liters, 1040 g (260 parts) of ion-exchanged water, 20 g of an about 10% by weight aqueous solution of poly-N-vinylacetamide (“PVAA1”) used in Example 1 as a suspending agent (2 g as a solid content) = 0.5 part), 8.4 g (2.1 parts) of diethyl carbonate (DEC) as a chain transfer agent, and 0.48 g (0.12 parts, t-butyl peroxypivalate (PB-PV) as an initiator. 0.24 parts as a solution in 50% by mass Freon 225cb) and 400 g (100 parts) of vinylidene fluoride were charged, and the temperature was raised to 65 ° C. over 3 hours, and then maintained at 65 ° C. The maximum ultimate pressure was 8.07 MPa. Further, after 1 hour, 400 g (100 parts) of vinylidene fluoride was gradually added so as to maintain the polymerization pressure of 7.6 MPa. Thereafter, polymerization was continued at 65 ° C. for about 15 hours, and suspension polymerization was carried out for a total of 24 hours from the start of temperature increase until the pressure dropped to 2.5 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 0.96 dl / g.

(Example 3)
As in Example 2, except that the amount of PVAA1 added as a suspending agent was reduced to 8 g (0.8 g = 0.2 parts as a solid content) and the amount of post-added vinylidene fluoride monomer was reduced to 75 parts, respectively. Suspension polymerization was performed for a total of 24 hours. The polymerization rate was 93%, and the inherent viscosity of the obtained polymer was 0.92 dl / g.

Example 4
Suspension polymerization for a total of 23 hours was carried out in the same manner as in Example 2 except that the amount of “PVAA1” added as a suspending agent was increased to 40 g (4 g as solids = 1 part). The polymerization rate was 90%, and the inherent viscosity of the obtained polymer was 1.00 dl / g.

(Example 5)
About 20% by mass aqueous solution of poly-N-vinylacetamide as a suspending agent (“GE191-203” manufactured by Showa Denko KK; viscosity = about 12,000 mPa · s, hereinafter sometimes abbreviated as “PVAA2”) 40 g Suspension polymerization was carried out for a total of 24 hours in the same manner as in Example 4 except that (the solid content was 4 g = 1 part) and the amount of the post-added vinylidene fluoride monomer was reduced to 80 parts. The polymerization rate was 93%, and the inherent viscosity of the obtained polymer was 0.96 dl / g.

(Comparative Example 4)
0.4 g (0.1 part) of methylcellulose (“SM-100” manufactured by Shin-Etsu Chemical Co., Ltd. used in Comparative Example 3) as a suspending agent, and t-butyl peroxypivalate (BP-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 0.4 g (0.1 part, 0.2 part as a solution in 50% by mass of Freon 225cb) was used. The polymerization rate was 92%, and the inherent viscosity of the obtained polymer was 0.99 dl / g.

(Comparative Example 5)
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 The suspension polymerization was carried out for a total of 23 hours in the same manner as in Comparative Example 4 except that .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 mass 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.

  The summary of the polymerization and the evaluation results of the color tone are summarized in Table 1 (Example 1 and Comparative Examples 1 to 3) and Table 2 (Examples 2 to 5 and Comparative Examples 4 to 5).

  As can be seen from Table 1 and Table 2 above, according to the present invention, in the suspension polymerization of vinylidene fluoride monomer, by using an N-vinylcarboxylic acid amide polymer as a suspending agent, A vinylidene fluoride polymer having excellent acid resistance in addition to good initial colorability (rather, showing a tendency of increasing whiteness W after acid immersion) while allowing stable progress of the polymerization is obtained. Yes.

Claims (9)

In performing suspension polymerization is dispersed in an aqueous medium containing a monomer suspension consisting mainly of vinylidene fluoride, which comprises using the homopolymer of N- vinylcarboxamide as a suspending agent A method for producing a vinylidene fluoride polymer. The process according to claim 1 homopolymers of N- vinylcarboxamides is poly -N- vinylacetamide. The manufacturing method of Claim 1 or 2 using the homopolymer of 0.01-2 mass parts N-vinyl carboxylic acid amide with respect to 100 mass parts of monomers. 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 mass 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.