JP2008019377A - Vinylidene fluoride-based resin composition and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vinylidene fluoride resin composition, excellent in heat stability and especially excellent in the resistance to discoloring in the low melting temperature range of 175-210°C. <P>SOLUTION: The vinylidene fluoride-based resin composition comprises 100 pts.wt. of vinylidene fluoride polymer having not less than 55% of stable terminal groups and 0.01-0.1 pt.wt. of at least one compound selected from hydroxides and oxides of magnesium and zinc. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vinylidene fluoride resin composition excellent in thermal stability, in particular, low temperature melting region (175 to 210 ° C.) and subsequent coloring resistance to heating in aging, and further low elution, and a method for producing the same.

Depending on the type of polymerization method, polymerization initiator, chain transfer agent, etc., the thermal stability of fluororesins (fluorinated polymers) containing vinylidene fluoride polymers can cause unstable end groups to form. For this reason, it is well known that bubbles and voids are formed or colored in a molded product produced by melt processing. For example, in Patent Documents 1 to 3, for example, a copolymer (FEP) of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP), a copolymer (PFA) of TFE and perfluoroalkyl vinyl ether (PAVE), When the polymerization initiator is a persulfate (ammonium persulfate, potassium persulfate, etc.) often used in the production by emulsion polymerization of a melt-processable fluoropolymer such as a copolymer of TFE and ethylene (ETFE), Carboxylic acid end groups are generated, and these carboxylic acid end groups change to vinyl end groups (—CF═CF ₂ ) and acid fluoride end groups (—COF) when the fluoropolymer is melt-kneaded; The group is thermally unstable and produces volatile substances that can cause bubbles and voids in the final product; Furthermore, in these patent documents, the unstable terminal group as described above is changed to a stable —CF ₂ H group by treatment with water and heat (patent document 1); treated in an oxygen atmosphere in the presence of water. It is disclosed that it is changed to a stable —CF ₂ H group by performing (Patent Document 2) or is stabilized by acting an alkali metal or an alkaline earth metal in an atmosphere containing moisture (Patent Document 3).

  Furthermore, vinylidene fluoride polymers obtained by suspension polymerization using diisopropyl peroxydicarbonate as a polymerization initiator also for vinylidene fluoride polymers that are more crystalline than the above-mentioned fluoropolymers. In addition, it is also known to improve thermal stability by mixing a kind of compound obtained from Ca, Ba, Zn, Mg hydroxide, carbonate or Sn, Al hydroxide (patent) Reference 4). Furthermore, it is also known to add a phosphite compound and a phenol compound as an anti-coloring agent (Patent Document 6). However, the thermal stability of the vinylidene fluoride polymer thus obtained is not necessarily sufficient.

  The vinylidene fluoride polymer is a crystalline polymer and is used in various molded articles as a polymer having good mechanical strength. At this time, sufficient heat treatment (hereinafter referred to as “aging”) is performed before use so that the molded product maintains good dimensional stability for the purpose of use, and distortion during molding and new crystallization are performed. It is usually done to proceed. Aging in a normal molded product is performed under conditions of about 1 to 24 hours at 50 to 170 ° C., depending on the shape of the molded product. In addition, aging may be performed by controlling the rate of temperature increase from room temperature to a predetermined temperature and the rate of temperature decrease from a predetermined temperature to room temperature at about 5 to 20 ° C./hour. However, after this aging operation, the molded body is often colored yellow to brown, resulting in a problem that the commercial value of the molded body is lowered. For this reason, a vinylidene fluoride polymer resin that is difficult to be colored is required.

  The vinylidene fluoride polymer obtained by the method of Patent Document 4 shows considerably good color resistance when aging is performed after melt molding in a high temperature range of 220 to 270 ° C., but at a lower temperature. When aging is performed after melt molding in the region (175 to 210 ° C.), there is a difficulty in coloring. Melt molding in a high temperature range is not preferable in terms of energy efficiency. In particular, in the case of injection molding, molding in a high temperature range is not preferable from the viewpoint of production efficiency because it takes a long time to take out the cooling.

On the other hand, as an influence of a polymerization initiator, Patent Document 5 discloses that a vinylidene fluoride polymer obtained by polymerization using di-t-butyl peroxide at 100 to 150 ° C. is excellent in thermal stability. . Non-Patent Document 1 discloses that vinylidene fluoride using t-butyl peroxybivalate (tBuO-OCO-tBu; where tBu is a tertiary butyl group) or di-t-butyl peroxide (tBuO-OtBu). It discloses a polymerization mechanism in which a tBu end group and a tBuO end group are formed in polymerization of a polymer. However, it does not disclose the characteristics of the product polymer of the polymerization system.
US308503 JP 2000-198813 A WO99 / 46307 Japanese Patent Publication No.44-19153 US Pat. No. 3,193,539 JP-A-9-208784 J. Guiot et al., Macromolecules 2002, 35, 8694-8707

  The main object of the present invention is a vinylidene fluoride resin composition having further improved thermal stability, in particular, coloring resistance in a low temperature melting region (175 to 210 ° C.), and also excellent low elution properties. It is in providing a thing and its manufacturing method.

  The vinylidene fluoride resin composition of the present invention has been developed to achieve the above-mentioned object, and more specifically, 100 parts by weight of a vinylidene fluoride polymer having a stable end group of 55% or more, magnesium and It consists of 0.01-0.1 weight part of at least 1 type of compound chosen from the hydroxide and oxide of zinc.

  The inventors have studied for the above-mentioned purpose, and a little will be added about the background to the present invention.

  The reason why the vinylidene fluoride polymer obtained in Patent Document 4 shows coloration properties not shown in the molding in the high temperature melting region in the molding in the low temperature melting region is not necessarily clear. Currently, I am thinking as follows. That is, the coloration of the vinylidene fluoride polymer is considered to be caused mainly by the generation of a conjugated double bond by dehydrofluoric acid from the main chain. In addition, the molded product melt-molded in the low-temperature region, whereas the molded product melt-molded in the high-temperature region due to some cause (difference in higher order structure, etc.) does not proceed with chain dehydrofluorination during aging. So I think that chain dehydrofluorination may occur during aging. Further, it is considered that the catalyst that initially causes the dehydrofluorination reaction in the main chain is a low molecular compound such as hydrofluoric acid generated by thermal degradation of unstable terminal groups generated by polymerization of the vinylidene fluoride polymer. Furthermore, compared to carboxylic acid end groups, isopropyl carbonate groups or normal propyl carbonate groups, which were previously considered stable end groups, are also considered unstable end groups, and there is a need for more advanced end group control. Recognizing and increasing the proportion of stable end groups by using a polymerization initiator such as t-butyl peroxypivalate or di-t-butyl peroxide disclosed in Patent Document 5 or Non-Patent Document 1 above. In addition, if a substance that effectively captures hydrofluoric acid generated by dehydrofluorination reaction by decomposition of remaining unstable end groups is added, dehydrofluorination reaction that causes coloring of vinylidene fluoride polymer is possible as much as possible. The usefulness of various compounds was screened based on the idea that they can be suppressed to a low level. Mg and Zn hydroxides and oxides (hereinafter, for convenience) The, often referred to as "coloring preventing agent") has found that it is extremely effective. That is, in the vinylidene fluoride resin composition of the present invention, the start of the dehydrofluorination reaction due to the increased stable end groups, and the suppression of the dehydrofluorination reaction chain by the effective capture of the generated hydrofluoric acid, Are functioning synergistically to improve coloration resistance.

Moreover, the improvement of the dissolution resistance is the increase of stable end groups, the fixing of MgF ₂ or ZnF ₂ which is a hardly soluble salt by the anti-coloring agent of hydrofluoric acid generated by dehydrofluorination, and the polymerization initiator and chain transfer agent. It is understood that it is obtained as a result of fixation as a sparingly soluble salt by the anti-coloring agent of the organic acid generated from use.

  In addition, the chain dehydrofluorination reaction described above is considered to include some radical generation process, and the radical generated in the reaction process by adding a phenol-based stabilizer having a radical scavenging action. It is thought that the chain dehydrofluorination reaction is inhibited by trapping in a stable form. Since the mechanism of action of the phenol-based stabilizer is different from the above-described reduction of the amount of hydrofluoric acid generated by the stable end group and the capture of hydrofluoric acid by the anti-coloring agent, it functions synergistically to improve the color resistance. It is understood.

  The vinylidene fluoride resin composition and the method for producing the same of the present invention are based on the above knowledge.

  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, and vinylidene fluoride containing vinylidene fluoride as a main component, preferably 50% by weight or more, more preferably 65% by weight or more. Copolymers with polymerizable monomers are 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.

  The vinylidene fluoride polymer used in the present invention is a vinylidene fluoride alone or a monomer copolymerizable therewith (hereinafter collectively referred to as “vinylidene fluoride monomer”). Emulsion polymerization or suspension polymerization, preferably in the presence of a polymerization initiator and a chain transfer agent for adjusting the molecular weight added as necessary and a solvent for improving the compatibility of the vinylidene fluoride monomer with the polymerization initiator, preferably Is obtained by suspension polymerization, and at this time, a stable end group and an unstable end group are formed mainly depending on the polymerization initiator and chain transfer agent used.

According to the study by the present inventors, the group that can be judged as a stable end group from the viewpoint of preventing coloring during foaming, as well as foaming or remaining / colored bubbles during melt molding, is inherent in vinylidene fluoride. In addition to the methyl group (CH ₃ —) and difluoromonohydromethyl group (CHF ₂ —) produced by polymerization, an alkyl group (eg t-butyl peroxypivalate or di-t-butyl peroxide as an initiator) An alkoxy group that forms an ether bond between the tertiary butyl group (t-Bu-) and the polymer chain carbon (for example, when di-t-butyl peroxide is used as an initiator) The resulting tertiary butyloxy group (t-BuO-)) is included.

On the other hand, groups that are classified as unstable terminal groups in terms of foaming at the time of melt molding, residual or coloring of bubbles, or coloring in aging include carboxylic acid terminals as disclosed in Patent Documents 1 to 3 and the like. In addition to the groups and fluorovinyl groups derived therefrom (CF ₂ ═CF—), acid fluoride groups (FCO—), most groups other than those listed above as stable end groups, such as alkyl carbonate groups (for example as initiators) Isopropyl peroxycarbonate group (i-Pr-O-CO-O-) or normal propyl peroxycarbonate group (n-Pr-O-CO-) produced when diiso (or dinormal) propyl peroxydicarbonate is used O-)), and further the ethyl acetate group produced when ethyl acetate is used as the chain transfer agent ( _{H 3 COOCH (CH 3) -} ) or a chain transfer agent as diethyl carbonate group formed when using diethyl carbonate _{(C 2 H 5 -O-CO} -O-CH (CH 3) -), moving the other chain Examples include agent-derived groups.

The vinylidene fluoride polymer used in the present specification has a stable terminal group according to the above classification of 55 (all stable terminal groups + unstable terminal groups) identified by ¹ H-NMR and ¹⁹ F-NMR. Mol)% or more. The use of a vinylidene fluoride polymer having a stable end group of less than 55% is effective even when a compound selected from hydroxides and oxides of Mg and Zn (ie, “anti-coloring agent”) is blended. An improvement in coloring resistance cannot be obtained (Comparative Examples 6 and 7 described later). It is preferable to use a vinylidene fluoride polymer having a stable end group of 58% or more, particularly 60% or more.

  The vinylidene fluoride polymer having 55% or more of the stable end groups as described above is preferably produced by suspension polymerization as follows. That is, 100 parts by weight of vinylidene fluoride monomer (in addition to batch addition in the initial stage, only a part thereof, for example, only 35 to 80 parts by weight is initially added, and the pressure inside the system that decreases with the continuation of polymerization exceeds the critical pressure. And a relatively small amount of a polymerization initiator are preferably added in an amount of 200 to 500 parts by weight of an aqueous medium (which may contain various auxiliary agents such as a dispersion stabilizer, However, it is preferably dispersed in 250 to 350 parts by weight, and the suspension polymerization is started while the temperature is raised to the polymerization temperature.

As the polymerization initiator, 10 hours half-life temperature T ₁₀ is 30 ° C. (about the critical temperature of vinylidene fluoride) of to 140 ° C. ones are preferably used, and preferred examples thereof to give a stable end groups in a high proportion Known are t-butyl peroxypivalate (T ₁₀ = 54.6 ° C.) and di-t-butyl peroxide (T ₁₀ = 123.7 ° C.). Conventionally, di-i-propyl peroxydicarbonate (T ₁₀ = 40.5 ° C.) and di-n-propyl peroxycarbonate (T ₁₀ = 40) which are known to give vinylidene fluoride polymers having good heat resistance. .3 ° C.), it is difficult to realize 55% or more of stable end groups, which is not preferable.

  The amount of the polymerization initiator used is as small as possible in accordance with the object of the present invention to obtain a vinylidene fluoride polymer having good thermal stability, but if it is too small, the polymerization time becomes extremely long, so an appropriate amount is used. It is desirable to do.

  In addition, since the decomposition rate varies depending on the 10-hour half-life temperature of the polymerization initiator, the amount used is small when a polymerization initiator having a relatively low 10-hour half-life temperature is used, and the 10-hour half-life temperature is relatively high. When using a polymerization initiator, it is necessary to use a large amount.

  Specifically, in the polymerization initiator having a 10-hour half-life temperature of 90 ° C. or less, the range of 0.001 to 0.12 wt% is preferable with respect to the vinylidene fluoride monomer, and more preferably 0.001 to 0 A range of 0.09% by weight, more preferably 0.001 to 0.06% by weight is used. In the polymerization initiator having a 10-hour half-life temperature exceeding 90 ° C., the range of 0.01 to 3% by weight is preferable with respect to the vinylidene fluoride monomer, more preferably 0.01 to 1% by weight, and still more preferably. Is used in the range of 0.01 to 0.6% by weight.

  If a polymerization initiator is used beyond these ranges, it will be difficult to use it up effectively in the polymerization reaction, and the resulting polymer will tend to deteriorate in coloration resistance and elution. It is desirable to add a step of removing the unreacted polymerization initiator by washing the polymer with an organic solvent such as ethanol.

  In the present invention, it is also preferable to form a dispersion using a relatively small amount of suspending agent. Cellulose compounds such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, partially saponified polyvinyl acetate, The suspending agent such as an acrylic acid polymer is preferably 0.01 to 0.1% by weight, more preferably 0.01 to 0.07% by weight, based on the initially added vinylidene fluoride monomer. Used. A cellulosic suspension is preferred from the viewpoint of thermal stability.

  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. Although it does not give a stable end, it is preferable to use ethyl acetate and diethyl carbonate from the viewpoint that the thermal stability is not impaired by adjusting the amount 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. As mentioned above, it is preferable to set it as the range of 0.7-1.3 dl / g especially.

The polymerization temperature T (° C.) is preferably set to a temperature that satisfies the condition of T ₁₀ ≦ T ≦ T ₁₀ +25 with respect to the 10-hour half-life temperature T ₁₀ (° C.) of the polymerization initiator.

If the polymerization temperature T is lower than T ₁₀ is ensured because 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, the amount of the polymerization initiator used must be increased. As a result, the polymerization initiator that did not contribute to the polymerization and the residue thereof remain in the polymer, and the coloration resistance and the low elution property are deteriorated. On the other hand, when the polymerization temperature T is higher than T ₁₀ +25 (° C.), the polymerization rate suddenly decreases during the polymerization, and the polymerization must be stopped during the polymerization, resulting in the vinylidene fluoride weight formed as a result. The coloration resistance and low elution property of the coalesce also deteriorate. This is presumably because the radical generation rate becomes too fast and contributes to the polymerization of vinylidene fluoride, and more side reactions such as disproportionation reaction between radicals and hydrogen abstraction reaction occur.

  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, product polymer productivity). After completion of the polymerization, the polymer slurry is dehydrated, washed with water and dried to obtain a polymer powder.

  A vinylidene fluoride polymer having 55% or more of stable terminal groups obtained as described above according to the present invention, and at least one compound (anti-coloring agent) selected from Mg and Zn hydroxides and oxides Mix.

At least one of the hydroxides and oxides of Mg and Zn used as the coloring inhibitor in the present invention is CaCO ₃ as a representative example disclosed in Patent Document 4 in combination with the vinylidene fluoride polymer (comparison described later). Example 2) Ca, Ba, Zn, Mg hydroxides, carbonates or Sn, Al hydroxides in general (but excluding overlapping Zn and Mg hydroxides) low temperature melting The coloring resistance in an area | region is shown (after-mentioned Examples 1-8). The same applies to an alkali metal compound typically used in Patent Document 3.

  The anti-coloring agent is added in a proportion of 0.01 to 0.1 parts by weight with respect to 100 parts by weight of the vinylidene fluoride polymer. If the amount is less than 0.01 parts by weight, the effect of addition is poor. If the amount exceeds 0.1 parts by weight, the action of the coloring inhibitor as an alkali becomes strong, and on the other hand, dehydrofluorination is promoted and coloring is not preferable. The amount added is more preferably in the range of 0.02 to 0.8 parts by weight.

  The composition of this invention is obtained by mixing the said vinylidene fluoride polymer and a coloring inhibitor. In addition to powder mixing in a dry state, the mixture of the two is obtained by adding a coloring inhibitor to the slurry, latex, or wet dehydrated vinylidene fluoride polymer obtained by polymerization to obtain a mixture. It is also possible to dry.

  In this case, the coloring inhibitor can be added in the form of powder, solution or dispersion, and in order to help mixing with the vinylidene fluoride polymer, an organic solvent such as methanol or ethyl acetate, a surface activity An agent or a dispersion aid can also be added.

  When mixing the vinylidene fluoride and the color-preventing agent, a normal stirring tank can be used in the case of a liquid, and in the case of a wet state and a powder, a mixing tank having a stirring device, a normal powder such as a Henschel blender, etc. A blender used to blend can be used. In any case, it is preferable to stabilize the composition after mixing by, for example, an extruder or the like after melt-kneading at 200 to 270 ° C. and then granulating into a shape such as pellets. When using an extruder, a single screw extruder, a same direction twin screw extruder, a different direction twin screw extruder, etc. can be used. Various methods can be used for pelletization, and cold cut, mist cut, hot cut, underwater cut, and the like can be employed.

  It is also preferable to further add a phenol compound (phenolic stabilizer) in a proportion of 0.01 to 0.1 parts by weight to the vinylidene fluoride polymer composition of the present invention. Example 6 below). It is understood that the phenol-based stabilizer suppresses generation of a conjugated double bond by chain dehydrofluoric acid due to its radical stabilizing action. If the amount of the phenol-based stabilizer added is less than 0.01 parts by weight, the effect is poor.

  As the phenol-based stabilizer, those similar to those disclosed in Patent Document 6 can be used. That is, a compound having 1 to 4 benzene rings substituted with 1 to 3 alkyl groups and a hydroxyl group in the molecule and having a phenolic OH group is preferred. Specifically, tetrakis- [methylene-3- (3 ′, 5′-di-tert-butyl-4-hydroxyphenyl) propionate] methane, 4,4′-isopropylidenediphenol, stearyl (3,5-di-tert-butyl-4-hydroxyphenyl) propionate Thiodiethylene glycol bis [(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 1,6-hexamethylene bis [(3.5-di-tert-butyl-4-hydroxyphenyl) propioic acid Amide], 2,2′-methylenebis (4-ethyl-6-tert-butylphenol, 4,4′- Tylidenebis (6-tert-butyl-cresol), 2.2'-ethylidenebis (4,6-di-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert- Butylphenyl) butane, bis [2-tert-butyl-4-methyl-6- (2-hydroxy-3-tert-butyl-5-methylbenzyl) phenyl] terephthalate, 1,3,5-tris (3,5 -Di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) -2,4,6-trimethylbenzene, 2- tert-butyl-4-methyl-5-methylbenzyl) phenol, 2,6-diphenyl-4-octadecyloxyphenol, etc. .

  In general, these phenol-based stabilizers are mixed at the same time when the vinylidene fluoride polymer and the color-preventing agent are mixed, but they may be mixed successively.

  The vinylidene fluoride resin composition of the present invention obtained as described above is preferably used as a raw material resin for forming various molded articles by utilizing its excellent heat stability and low elution characteristics.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Including the following description, the proportion of stable end groups in the polymer described in the present specification and the characteristics of the composition are based on the results of the evaluation methods described below.

(Proportion of stable end groups in the polymer)
A solution prepared by using acetone-d ₆ as a solvent and adjusting the polymer concentration to about 10% by weight was dissolved by heating, and then the insoluble matter was removed with a filter to prepare a sample. Using this sample, the terminal composition was determined by ¹ H-NMR under the following conditions.
Measuring machine: “AVANCE 400” manufactured by Bruker
Resonance frequency: 400.13 MHz
Integration count: 5000 times

For identification, the chemical shift using tetramethylsilane as a reference signal was expressed in ppm, and Non-Patent Document 1 was used as a reference. For the calculation of the ratio of stable ends, a value obtained by dividing the integrated value of the peak derived from each terminal structure obtained by measurement by the number of corresponding protons was used. For example, the peak attributed to (CH ₃ ) ₃ C—CH ₂ CF ₂ — of 1.06 ppm corresponds to 9 protons of the tertiary butyl group, so that the integral value divided by 9 was used. The sum of the non-polar terminal values such as (CH ₃ ) ₃ C—CH ₂ CF ₂ —, CHF ₂ —, CH ₃ CF ₂ CF ₂ CH ₂ —, etc. obtained based on this method was After dividing by the sum of the terminal structure values and multiplying by 100, the ratio of stable ends was obtained.

The breakdown of the stable end groups and unstable end groups in the polymers obtained in Examples 1 and 8 and Comparative Examples 6 and 7, for example, measured by the above method is as follows.

(Colorability-color tone)
14 g of the sample pellet was put into a Teflon (registered trademark) crucible container and left in a gear oven at 190 ° C. for 2 hours to obtain a melt. After the crucible was air-cooled to room temperature, the lump was taken out, and the color tone was measured by applying the center of the bottom of the solidified product to the opening of a color difference meter (“Color Meter ZE2000” manufactured by Nippon Denshoku Industries Co., Ltd.). Standard of b value of bottom of solidified product (b value in L * a * b * color system, higher yellow value means higher yellowness, higher negative value means higher blueness) The difference Δb value from the b value of a white plate (XYZ color system characteristic values as X = 92.29, Y = 94.28, Z = 110.66) was measured.

  About the said solidified material, two same kind solidified materials were prepared, and (DELTA) b value was calculated | required like the above about what aged at 170 degreeC for 2 hours or 170 degreeC for 6 hours. Based on the three measured values of these Δb values, four-step comprehensive color tone determinations of “very excellent”, “excellent”, “slightly inferior”, and “inferior” were performed in descending order of the absolute value of −.

(conductivity)
After putting 50 g of sample pellets in 50 g of pure water and immersing them at 85 ° C. for 7 days, the conductivity (unit: μS / cm) of water was measured with an ion conductivity meter (“DS-51” manufactured by Horiba, Ltd.). did.

(TOC (total organic carbon))
About the water after immersion of the sample pellet on the same conditions as the above-mentioned conductivity measurement, the TOC concentration is measured with a total organic carbon meter (“TOC-5000” manufactured by Shimadzu Corporation), and the measured value is the total surface area of the pellet. By dividing, the TOC value per unit surface area of the pellet (unit: μg / m ² ) was obtained.

(Example 1)
An autoclave having an internal volume of 20 liters was charged with ion exchange water 10,894 g, methyl cellulose 4.19 g, diethyl carbonate 108.9 g, t-butyl peroxypivalate 4.19 g, and vinylidene fluoride 4,190 g. After the temperature increase, the temperature was maintained at 55 ° C. The maximum pressure reached during this period was 6.97 MPa. Further, after 0.5 hour, 5.447 g of vinylidene fluoride was gradually added so that the polymerization pressure was maintained at 6.59 to 6.61 MPa. Thereafter, polymerization was continued at 55 ° C. for about 7 hours, and suspension polymerization was carried out for a total of 27.8 hours from the start of the temperature increase until the pressure dropped to 2.5 MPa. After completion of the polymerization, the polymer slurry was dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a polymer powder. The polymerization rate was 95%, and the inherent viscosity of the obtained polymer was 0.97 dl / g.

0.05 parts by weight of Mg (OH) ₂ is added to 100 parts by weight of the obtained polymer, and the temperature condition (C1 / C1) is determined by the same direction twin screw extruder (TEM-26 manufactured by Toshiba Machine Co., Ltd.). C2 / C3 / C4 / C5 / C6 / DH = 200/210/210/210/190/190/190) was extruded (resin temperature at the die part = 217 ° C.) to obtain a pellet-shaped composition.

(Example 2)
1333 g of wet polymer (dry polymer weight 1000 g) having a water content of 25% (wet polymer base) obtained by dehydrating the slurry obtained by polymerization in Example 1 was supplied to a screw feeder, and powdered Mg (OH) ₂ A slurry-like liquid in which 0.5 g was dispersed in 100 g of water was added dropwise to the screw portion of the screw feeder little by little. While the wet polymer exiting from the screw feeder outlet was returned to the feed part of the screw feeder as needed, the entire amount of the Mg (OH) ₂ -containing slurry was dropped in small portions. After completion of the dropping, the entire amount of the wet polymer was recovered, dried at 80 ° C. for 20 hours to obtain a powder, and pelletized in the same manner as in Example 1.

(Examples 3 to 7)
Instead of 0.05 parts by weight of Mg (OH) ₂ with respect to 100 parts by weight of the polymer, 0.02 parts by weight of MgO (Example 3), 0.03 parts by weight of Zn (OH) ₂ (Examples) 4), 0.03 parts by weight of ZnO (Example 5), 0.05 parts by weight of Mg (OH) ₂ and a phenolic stabilizer (n-octadecyl-3- (3 ′, 5′-t-butyl- 4-hydroxyphenyl) propionate; “Irganox 1076” from Ciba Specialty Chemicals) 0.05 part by weight (Example 6) or 0.05 part by weight Mg (OH) ₂ and 0.03 part by weight ZnO Example 7) was obtained in the same manner as in Example 1 except that each of them was added.

(Example 8)
An autoclave with an internal volume of 2 liters was charged with 1,024 g of ion-exchanged water, 1.0 g of methyl cellulose, 4 g of ethyl acetate, 16 g of di-tert-butyl peroxide, and 400 g of vinylidene fluoride, heated to 85 ° C. in 2 hours, then 85 C was maintained. The maximum ultimate pressure was 10.31 MPa. Further, after 0.5 hour, 400 g of vinylidene fluoride was gradually added so that the polymerization pressure was maintained at 6.99 to 7.01 MPa. Thereafter, polymerization was continued at 85 ° C. for about 7 hours, and suspension polymerization was carried out for a total of 22.0 hours from the start of temperature increase until the pressure dropped to 2.5 MPa. After dehydration, it was washed with methanol, further washed with water, and then vacuum dried at 80 ° C. for 20 hours to obtain a polymer powder. The polymerization rate was 97%, and the inherent viscosity of the obtained polymer was 1.22 dl / g.

0.05 parts by weight of Mg (OH) ₂ was added to 100 parts by weight of the polymer thus obtained, and pelletized in the same manner as in Example 1 to obtain a composition.

(Comparative Example 1)
Without adding Mg (OH) ₂ , only the polymer obtained in Example 1 was pelletized in the same manner as in Example 1 to obtain a composition.

(Comparative Examples 2 to 5)
Instead of 0.05 parts by weight of Mg (OH) ₂ , 0.05 parts by weight of CaCO ₃ (Comparative Example 2), 0.05 parts by weight of a phosphite-based stabilizer (diester) per 100 parts by weight of the polymer Stearyl pentaerythritol diphosphite; “PEP-8W” manufactured by Adeka Corporation) (Comparative Example 3), 0.05 parts by weight of the same phenol-based stabilizer as in Example 6 and 0.05 parts by weight of Comparative Example 3 The same phosphite-based stabilizer (Comparative Example 4) or 0.05 parts by weight of the same phenol-based stabilizer (Comparative Example 5) as in Example 6 was added in the same manner as in Example 1 except that 4 types were added. A pellet-like composition was obtained.

(Comparative Example 6)
An autoclave with an internal volume of 2 liters was charged with 1,024 g of ion-exchanged water, 0.20 g of methyl cellulose, 11.2 g of ethyl acetate, 2.0 g of diisopropyl peroxydicarbonate, and 400 g of vinylidene fluoride, and the temperature was raised to 26 ° C. in 1 hour. Thereafter, 26 ° C. was maintained until the pressure dropped to 1.2 MPa. The polymerization time was 25.5 hours. It was dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a polymer powder. The polymerization rate was 90%, and the inherent viscosity of the obtained polymer was 0.99 dl / g.

0.05 parts by weight of Mg (OH) ₂ was added to 100 parts by weight of the polymer thus obtained, and pelletized in the same manner as in Example 1 to obtain a composition.

(Comparative Example 7)
An autoclave with an internal volume of 2 liters was charged with 1,024 g of ion-exchanged water, 0.33 g of methylcellulose, 7.8 g of ethyl acetate, 4.8 g of a 50% methanol-diluted solution of dinormalpropyl peroxydicarbonate, and 400 g of vinylidene fluoride, The temperature was raised to 26 ° C. in 1 hour. After 5.5 hours from the start of polymerization, the temperature was raised to 40 ° C. over 5 hours, and then maintained at 26 ° C. until the pressure decreased by 2.5 MPa. The polymerization time was 13 hours. The polymerization rate was 89%, and the inherent viscosity of the obtained polymer was 1.02 dl / g.

0.05 parts by weight of Mg (OH) ₂ was added to 100 parts by weight of the polymer thus obtained, and pelletized in the same manner as in Example 1 to obtain a composition.

The outlines of the examples and comparative examples, the ratio of stable end groups in the polymer obtained by the above method and the evaluation results of the compositions are summarized in Tables 2 and 3 below.

  As described above, according to the present invention, a vinylidene fluoride polymer having an increased stable end group is obtained mainly by selecting a polymerization aid including a polymerization initiator, and from this, hydroxides and oxides of Mg and Zn are obtained. By adding the obtained anti-coloring agent, a vinylidene fluoride resin composition excellent in heat resistance and elution resistance in a low-temperature melting region (175 to 210 ° C.) where coloration tends to occur due to a chain of dehydrofluorination reaction. Things are obtained.

Claims (9)

Fluorination comprising 100 parts by weight of a vinylidene fluoride polymer having 55% or more of stable end groups and 0.01 to 0.1 parts by weight of at least one compound selected from hydroxides and oxides of magnesium and zinc Vinylidene resin composition. Furthermore, the vinylidene fluoride resin composition of Claim 1 containing 0.01-0.1 weight part of phenolic stabilizers. The vinylidene fluoride resin composition according to claim 1 or 2, wherein the vinylidene fluoride polymer is obtained by polymerization using t-butyl peroxypivalate or di-t-butyl peroxide as an initiator. object. Fluorination in which 100 parts by weight of vinylidene fluoride polymer having a stable end group of 55% or more and 0.01 to 0.1 part by weight of at least one compound selected from hydroxides and oxides of magnesium and zinc are mixed A method for producing a vinylidene resin composition. Furthermore, the manufacturing method of Claim 5 which mixes 0.01-0.1 weight part phenol type stabilizer. The production method according to claim 4 or 5, wherein the mixing is performed by melt kneading and granulation. The production method according to claim 6, wherein at least the vinylidene fluoride polymer and the compound are mixed in a dry state and then melt-kneaded. The production method according to claim 6, wherein at least the vinylidene fluoride polymer and the compound are mixed in a wet state, dried and then melt-kneaded. The method according to any one of claims 4 to 8, wherein the vinylidene fluoride polymer is obtained by polymerization using t-butyl peroxypivalate or di-t-butyl peroxide as an initiator.