WO2014034178A1

WO2014034178A1 - Method for assessing polymer and process for producing polymer

Info

Publication number: WO2014034178A1
Application number: PCT/JP2013/061725
Authority: WO
Inventors: 真由美草野; 正臣 ▲吉▼田; 新弥笠間; 栄二穐田; 北村　秀樹
Original assignee: 株式会社クレハ
Priority date: 2012-08-27
Filing date: 2013-04-22
Publication date: 2014-03-06
Also published as: CN104285146B; JPWO2014034178A1; CN104285146A

Abstract

The present invention provides a method for detecting, easily and simply, iron and other metallic foreign particles which are contained in a polymer. This method comprises: a step for passing a polymer solution through a filter; a step for bringing a color-forming fluid which contains potassium hexacyanoferrate (II), potassium hexacyanoferrate (III) and an acid into contact with the filter; and a step for detecting foreign particles on the basis of the color developed on the filter, and measuring the number and/or sizes of the foreign particles. The pH of the color-forming fluid is 0.40 to +0.75.

Description

POLYMER EVALUATION METHOD AND POLYMER MANUFACTURING METHOD

The present invention relates to a method for evaluating a polymer and a method for producing a polymer. More specifically, the present invention relates to a method for evaluating a polymer by detecting foreign matters contained in the polymer, and a polymer including the evaluation method. It relates to a manufacturing method.

Vinylidene fluoride polymers are used in various applications because they are excellent in heat resistance, chemical resistance and electrochemical stability. In the manufactured vinylidene fluoride polymer, foreign components such as inorganic components such as metals and metal compounds and organic components such as other polymers may be mixed. In many applications, high-purity vinylidene fluoride polymers that are less contaminated with such foreign substances are required. In particular, when an inorganic component such as a metal is mixed into the vinylidene fluoride polymer, a decomposition reaction of the vinylidene fluoride polymer is induced at the time of melt molding, or a molded product of vinylidene fluoride polymer such as a pipe for ultrapure water is used. When used, the inorganic components and polymer decomposition products are eluted, which causes a problem. Therefore, quality control that reduces the content of foreign matter as much as possible is required.

As a method for analyzing a metal component in a polymer, for example, an ICP emission analysis method using a high frequency inductively coupled plasma (ICP) as a light source is known. In the ICP emission analysis method, a metal component in a polymer is extracted into a solvent such as water and acid, and the solution sample is applied to an ICP emission analysis device to detect an existing metal component.

In addition, as a method for inspecting foreign matters contained in a liquid material, Patent Document 1 discloses an image of foreign matter captured by a filter after filtering the liquid matter, detects the foreign matter from this image, and detects the foreign matter. A method for calculating the size and number is described.

In addition, Patent Document 2 uses a determination liquid containing potassium ferricyanide and potassium ferrocyanide to cause a color reaction between iron ions and an indicator, and the degree of mixing of iron ions in the resin-impregnated composition. It is described to know. It is known as a general chemical reaction that potassium ferricyanide reacts with divalent iron ions to give turn blue, and potassium ferrocyanide reacts with trivalent iron ions to give Berlin blue.

Japanese Patent Publication “Japanese Patent Laid-Open No. 2005-221291 (published on August 18, 2005)” Japanese Patent Publication “JP-A-5-172805 (published July 13, 1993)”

The analysis method of the metal component in the polymer by the ICP emission analysis method is complicated in operation because the metal component in the polymer is extracted into a solvent such as water and acid and the solution sample is applied to the emission analyzer. An ICP emission analyzer is required. In addition, although this analysis method can detect the presence of foreign matter, it has the disadvantage that the number and size of foreign matters cannot be measured.

In the method described in Patent Document 1, although the number and size of foreign substances can be confirmed, the type of foreign substances such as whether the foreign substances are metals, minerals other than metals, or carbides is distinguished. It is difficult to do.

Furthermore, the method described in Patent Document 2 does not consider the detection of metal foreign objects other than iron, and is not sufficient as a foreign object detection method when a metal other than iron is assumed as the foreign object. is there. For example, a general polymer production facility including a vinylidene fluoride polymer is made using SUS304 or SUS316 or an austenitic stainless steel according to these. Therefore, there is a high possibility that stainless steel is mixed as a foreign substance in the polymer. According to the result of confirming the foreign matter in the vinylidene fluoride polymer adhering to the iron remover using the iron remover, stainless steel and iron are mixed as foreign matters in the vinylidene fluoride polymer. .

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a method for easily detecting iron and metal foreign matters other than iron contained in a polymer.

In order to solve the above problems, the polymer evaluation method according to the present invention includes a filtration step of filtering a polymer solution in which the polymer is dissolved in a solvent, a hexacyanoiron (II) potassium, and a hexacyanoiron. (III) In the polymer solution captured by the filter by the contact step of bringing the color developing solution containing potassium and acid into contact with the filter after filtration, and color development on the filter caused by the color developing solution. A measuring step of detecting foreign matter and measuring at least one of the number and size of the foreign matter, and the pH of the color developing solution is in the range of −0.40 to +0.75. .

According to the above configuration, if foreign matter is mixed in the dissolved polymer, the foreign matter mixed in the polymer is captured by the filter by filtration of the polymer solution using a filter. If a foreign substance containing iron is present in the trapped foreign substance, the foreign substance exhibits a blue color due to the reaction with the color developing solution. By detecting foreign matter based on this color development and measuring at least one of the number and size, the production quality of the polymer from the viewpoint of the foreign matter mixed in the polymer can be evaluated. Here, since the pH of the color developing solution is lower than 0.75, even if the foreign material is, for example, stainless steel having high corrosion resistance, the color developing reaction proceeds and a blue color is exhibited. Therefore, even if the foreign material is a metal other than iron, it can be detected based on color development. Further, since the pH of the color developing solution is higher than −0.40, when the foreign material is iron, it can be prevented from being lost, and the foreign material can be detected while maintaining the size of the foreign material. it can.

Moreover, in order to solve the said subject, the manufacturing method of the polymer which concerns on this invention manufactures a polymer by polymerization reaction, the manufacturing process of obtaining the powder of this polymer by drying, and the obtained said polymer A part of the powder is dissolved in a solvent having a polymer dissolving ability and not having a foreign substance dissolving ability, and a filtration is performed by filtering the polymer solution in which the polymer is dissolved in the solvent with a filter. A step of contacting the color developing solution containing hexacyano iron (II) potassium, hexacyano iron (III) potassium and acid with the filter after filtration, and color development on the filter generated by the color developing solution, A foreign substance in the polymer solution captured by the filter is detected, and a measurement process for measuring at least one of the number and size of the foreign substance and a result of the measurement process are manufactured. And a determination step of determining the quality of the polymer, pH of the color developing solution has a structure in the range of -0.40 ~ +0.75.

According to the above configuration, a polymer is produced by a polymerization reaction and then dried to obtain a polymer powder. A part of the powder is dissolved in a solvent having the ability to dissolve the polymer and not the foreign substance, thereby preparing a polymer solution. If foreign matter is mixed in the polymer powder, the foreign matter mixed in the polymer powder is captured by the filter by filtration of the polymer solution using a filter. If a foreign substance containing iron is present in the trapped foreign substance, the foreign substance exhibits a blue color due to the reaction with the color developing solution. Foreign matter is detected based on this color development, and at least one of the number and size is measured. And based on the measurement result, the production quality of the polymer from the viewpoint of the foreign matter mixed in the polymer is determined. Here, since the pH of the color developing solution is lower than 0.75, even if the foreign material is, for example, stainless steel having high corrosion resistance, the color developing reaction proceeds and a blue color is exhibited. Therefore, even if the foreign material is a metal other than iron, it can be detected based on color development. Further, since the pH of the color developing solution is higher than −0.40, when the foreign material is iron, it can be prevented from being lost, and the foreign material can be detected while maintaining the size of the foreign material. it can. Therefore, the produced polymer can be sorted according to production quality, and a polymer having a desired production quality can be provided.

According to the polymer evaluation method of the present invention, the detection of foreign matter by color development caused by the reaction of a color developing solution containing hexacyano iron (II) potassium, hexacyano iron (III) potassium and an acid with foreign matter captured by a filter. The pH of the color developing solution is in the range of −0.40 to +0.75. Therefore, it is possible to easily detect iron and metal foreign matters other than iron contained in the polymer.

An embodiment of a polymer evaluation method according to the present invention will be described below. The polymer evaluation method according to the present invention is suitably incorporated as part of the polymer production method, and more suitably incorporated into the vinylidene fluoride polymer production method. Therefore, below, one Embodiment of the manufacturing method of the vinylidene fluoride polymer in which the evaluation method of the polymer based on this invention was integrated is described. However, the polymer evaluation method according to the present invention is not limited to the one incorporated in the polymer production method, and the polymer is not limited to the vinylidene fluoride polymer.

The manufacturing method of the vinylidene fluoride polymer in the present embodiment includes a manufacturing process of manufacturing a vinylidene fluoride polymer by a polymerization reaction and obtaining a vinylidene fluoride polymer powder by drying, and a manufactured vinylidene fluoride polymer. A dissolution step for dissolving in a solvent, a filtration step for filtering a polymer solution in which a vinylidene fluoride polymer is dissolved in a solvent, a hexacyano iron (II) potassium, a hexacyano iron (III) potassium and an acid are included. By detecting the foreign matter in the polymer solution trapped in the filter by the contact step of contacting the color developing solution with the filter after filtration and the color development on the filter caused by the color developing solution, at least the number and size of the foreign matter are detected. Determine the quality of the vinylidene fluoride polymer produced based on the measurement process that measures one and the results of the measurement process Configured to include a constant step.

(Manufacturing process)
In the production process, a vinylidene fluoride is polymerized in an aqueous medium together with a monomer capable of being copolymerized alone or copolymerized to produce a vinylidene fluoride polymer, and the powder is obtained by drying. Accordingly, in the present specification, the “vinylidene fluoride polymer” includes not only a homopolymer of vinylidene fluoride but also a copolymer of vinylidene fluoride and other monomers. The polymerization method of the vinylidene fluoride polymer is not particularly limited, and solution polymerization, emulsion polymerization, and suspension polymerization can be used. The slurry of the vinylidene fluoride polymer obtained by the polymerization reaction is subjected to dehydration treatment and water washing treatment, and then dried in an oven at a temperature of 50 ° C. or higher and lower than 150 ° C., for example. Thereby, the powder of a vinylidene fluoride polymer is obtained.

(Dissolution process)
In the dissolving step, a part of the produced vinylidene fluoride polymer powder is dissolved in a solvent to prepare a polymer solution in which the vinylidene fluoride polymer is dissolved.

The solvent has the ability to dissolve the polymer and does not have the ability to dissolve foreign matter, that is, can dissolve vinylidene fluoride polymer, dissolves iron and stainless steel mixed as foreign matter in the vinylidene fluoride polymer As long as it does not, there is no particular limitation, and N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide and the like can be used. Among these, it is preferable to use NMP from the viewpoint that it is excellent in solubility of vinylidene fluoride resin, is a general-purpose product, has relatively low toxicity, and has a boiling point and vapor pressure suitable for handling.

Although there is no restriction | limiting in the density | concentration of the vinylidene fluoride polymer in the polymer solution prepared, since the precision of evaluation can be raised by investigating the presence or absence of a foreign material about many amounts of vinylidene fluoride polymers, 1 mass% Preferably, it is preferably 3% by mass or more. Further, from the viewpoint of shortening the time required for dissolution and filtration, the concentration of the vinylidene fluoride polymer in the prepared polymer solution is preferably 20% by mass or less, and more preferably 10% by mass or less. .

The charging of the vinylidene fluoride polymer into the solvent may be either batch charging or split charging. Further, in order to disperse the vinylidene fluoride polymer in the solvent so that the vinylidene fluoride polymer can be easily dissolved, it is preferable that the vinylidene fluoride polymer is charged and dissolved while stirring the solvent.

The temperature at which the vinylidene fluoride polymer is dissolved in the solvent is not limited, but it is preferably dissolved at 60 ° C. to 80 ° C. By dissolving at 60 ° C. or higher, the dissolution time can be shortened. Accordingly, it is possible to shorten the time required from detection of the mixed foreign matter after the vinylidene fluoride polymer is obtained by the polymerization reaction.

(Filtration process)
In the filtration step, the polymer solution in which the vinylidene fluoride polymer is dissolved in the solvent is filtered by a filter, so that foreign matters mixed in the vinylidene fluoride are captured by the filter.

Filtration may be performed using a general filtration device, and suction filtration is preferable from the viewpoint of improving the filtration rate.

The filter may be any filter that does not contain a metal and has resistance to a solvent. For example, a known membrane filter formed of a fluororesin and cellulose acetate can be used.

The pore diameter of the filter may be appropriately determined according to the size of the foreign substance to be detected. For example, a filter having a pore diameter of 1 to 20 μm can be used, and a filter having a pore diameter of 5 to 15 μm is preferably used. It is done.

The temperature of the polymer solution in the filtration step is preferably 30 ° C. to 100 ° C., and more preferably 50 ° C. to 80 ° C.

When the solution temperature is 30 ° C. or higher in the filtration step, the solution viscosity decreases, thereby shortening the time required for filtration and improving the work efficiency. In addition, when the solution temperature is 100 ° C. or lower, the risk of burns when an operator touches the solvent is reduced, and the risk of the solvent igniting is also reduced.

After filtration, the filter is washed with a solvent and acetone, and then the filter is dried. Specifically, in order to remove the vinylidene fluoride polymer remaining on the filter, the solvent is further passed after filtration, and then acetone is passed to remove the solvent remaining on the filter. The solvent used for cleaning the filter may be any solvent that can dissolve the vinylidene fluoride polymer. For example, the same type of solvent as that used for preparing the polymer solution can be used. Further, acetone is used to remove the solvent remaining on the filter. However, the solvent is not limited to acetone as long as the solvent can be removed. For example, methanol and ethanol can be used.

(Contact process)
In the contact step, the coloring solution is brought into contact with the filter after filtration and drying. At this time, if foreign matter is trapped on the filter, the foreign matter and its surroundings are colored blue due to the reaction between the foreign matter and the coloring solution.

The color developing solution in the present embodiment is an aqueous solution containing hexacyano iron (II) potassium, hexacyano iron (III) potassium and an acid, and may contain other components as long as the effects of the present invention are not impaired.

The acid used in the color developing solution is not particularly limited, but for example, inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid are preferable, and hydrochloric acid is more preferable.

The color developing solution in this embodiment can be prepared, for example, by dissolving 0.1 to 5 parts by weight of a mixture of potassium hexacyanoiron (II) and hexacyanoiron (III) potassium in 100 parts by weight of an acidic aqueous solution. it can. The mixing ratio in the mixture of hexacyano iron (II) potassium and hexacyano iron (III) potassium is preferably in the range of hexacyano iron (II) potassium: hexacyano iron (III) potassium = 1: 5 to 5: 1.

In the present embodiment, the main foreign substances to be detected are iron and stainless steel. Stainless steel is known to have strong corrosion resistance. Therefore, when the acid concentration is low, even if the color developing solution comes into contact with stainless steel, hexacyano iron (II) potassium and hexacyano iron (III) potassium cannot react with sufficient iron ions and detection is possible. Color development does not occur to the extent. Therefore, stainless steel cannot be detected using color development as an index. In addition, if the acid concentration is too high, iron as a foreign matter is lost. As a result, the presence or absence of foreign matter or the size of foreign matter cannot be measured correctly. For this reason, the acid concentration in the color developing solution is within a range in which color development occurs due to the reaction with the stainless steel by contact with the color developing solution and iron is not lost. The concentration of the acid that satisfies such conditions varies depending on the type of acid. For example, when hydrochloric acid is used, the concentration of hydrochloric acid in the color developing solution is 0.5 to 4.0% by mass, preferably 1.0 to 4.0% by mass, and more preferably 2.0 to 3. 0% by mass. If the concentration of hydrochloric acid in the color developing solution is 0.5% by mass or more, color development occurs due to the reaction between the stainless steel as a foreign material and the color developing solution, so that the stainless steel contained as a foreign material can be detected. Further, if the concentration of hydrochloric acid is 4.0% by mass or less, iron melting can be prevented, and thus iron contained as foreign matter can be detected while maintaining the size as foreign matter. The color developing solution (potassium hexacyanoiron (II): 0.5% by mass, potassium hexacyanoiron (III): 0.5% by mass, hydrochloric acid: 0.5% by mass or 4.0% by mass, solvent: water) The pH was measured using a pH meter (manufactured by Toa Denpa Kogyo Co., Ltd., model: HM-30V). The pH of the color developing solution containing hydrochloric acid at a concentration of 0.5% by mass was 0.75. The pH of the color developing solution contained at a concentration of 0% by mass was −0.40. Therefore, a color developing solution that satisfies the above conditions can be defined as a color developing solution having a pH in the range of −0.40 to +0.75. Similarly, the pH of the color developing solution containing hydrochloric acid at a concentration of 2.0% by mass was 0.05, and the pH of the color developing solution containing a concentration of 3.0% by mass was −0.19. Therefore, a color developing solution having a pH in the range of −0.19 to +0.05 is more preferably used.

The method of bringing the color developing solution into contact with the filter is not particularly limited as long as the foreign matter captured by the filter can react with the color developing solution, but it is preferable to spray the color developing solution on the filter surface. According to the contact by spraying, the trapped foreign matter can be prevented from flowing away from the filter.

(Measurement process)
As described above, when foreign matter is trapped on the filter, the foreign matter and its surroundings develop color due to the reaction between the coloring solution and the foreign matter. In the measurement step, the foreign matter in the polymer solution trapped by the filter is detected based on the color developed by the reaction between the color developing solution and the foreign matter, and at least one of the number of detected foreign matters and the size of the foreign matter is measured. .

In the present embodiment, the colored portion is observed using a microscope, the foreign matter in the colored portion is observed, the number of the whole on the filter is measured, and the size of each is measured. It is not limited to this. For example, the foreign matter in the color development portion may be observed and the number thereof on the entire filter may be measured. Or the size of the foreign material in a color development part may be measured, and the presence or absence of the foreign material exceeding a specific size may be confirmed. The measurement object in the measurement process is appropriately determined by the user of the production method according to the present invention according to the use of the produced vinylidene fluoride polymer or the user's request to use the produced vinylidene fluoride polymer. That's fine.

(Decision process)
In the determination step, the production quality of the vinylidene fluoride polymer from the viewpoint of the foreign matter mixed in is determined based on the measurement result in the measurement step described above. That is, the quality of the produced vinylidene fluoride polymer is determined based on the number of foreign substances contained in the produced vinylidene fluoride polymer and / or the size thereof. For example, a threshold is set for the number or size of foreign matter to be detected, and when there is a foreign matter exceeding the threshold, the lot can be determined as a defective lot. Alternatively, a finer standard can be set and the quality can be determined based on the standard.

The threshold value or the standard for determining the quality is determined by the user of the production method according to the present invention according to the use of the produced vinylidene fluoride polymer or the user's request to use the produced vinylidene fluoride polymer. What is necessary is just to determine suitably. For example, when the number of foreign matters detected from 1 g of the produced vinylidene fluoride polymer exceeds 10, the lot is regarded as a defective product, and when the number of foreign matters is 4 to 10, the lot is usually As an example, the standard is that the lot is a high-purity product when the number of foreign materials is 2 or 3, and the lot is an ultra-high-purity product when the number of foreign materials is 1 or less. it can.

Another example of the threshold value or reference is, for example, when the size of a foreign material is measured in the measurement process and a foreign material larger than 50 μm is found, the lot is regarded as a defective product, and no foreign material exceeding 50 μm is found. In this case, it is possible to exemplify a standard for making the lot a normal product.

If the lot determined to be defective as described above is excluded from the final manufactured product, a vinylidene fluoride polymer having a desired quality can be provided as the final manufactured product.

As described above, the polymer evaluation method according to the present invention includes a filtration step of filtering a polymer solution in which a polymer is dissolved in a solvent, a hexacyanoiron (II) potassium, and a hexacyanoiron (III). A foreign substance in the polymer solution captured by the filter is detected by a contacting step in which a coloring solution containing potassium and an acid is brought into contact with the filter after filtration, and coloring on the filter caused by the coloring solution. And a measuring step for measuring at least one of the number and size of the foreign substances, and the pH of the color developing solution is in the range of −0.40 to +0.75.

In the polymer evaluation method according to the present invention, the acid is preferably hydrochloric acid, and the color developing solution preferably contains hydrochloric acid at a concentration of 0.5 to 4.0% by mass.

In the polymer evaluation method according to the present invention, in the contact step, it is preferable that the color developing solution is brought into contact with the filter by spraying the color developing solution.

In the polymer evaluation method according to the present invention, the foreign material is preferably at least one of iron and stainless steel.

In the polymer evaluation method according to the present invention, the polymer is preferably a vinylidene fluoride polymer.

In the polymer evaluation method according to the present invention, the solvent is a solvent having a polymer dissolving ability and a foreign substance dissolving ability, and the polymer powder is dissolved in the solvent to dissolve the polymer. It further includes a dissolution step of preparing a solution, and in the dissolution step, the powder is preferably dissolved at 60 to 80 ° C.

In the polymer evaluation method according to the present invention, the solvent is preferably N-methyl-2-pyrrolidone.

In the polymer evaluation method according to the present invention, the color developing solution is a mixture of the hexacyano iron (II) potassium and the hexacyano iron (III) potassium in an amount of 0.1 to 5 with respect to 100 parts by weight of the aqueous solution containing the acid. It is preferable that the part by weight is dissolved.

In the polymer evaluation method according to the present invention, the content ratio of hexacyano iron (II) potassium and hexacyano iron (III) potassium in the mixture is preferably in the range of 1: 5 to 5: 1.

Examples will be shown below, and the embodiments of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail. Further, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and the present invention is also applied to the embodiments obtained by appropriately combining the disclosed technical means. It is included in the technical scope of the invention. Moreover, all the literatures described in this specification are used as reference.

[Example 1: Confirmation of color development and erosion]
Using a plurality of color developing solutions containing hydrochloric acid as the acid and having different hydrochloric acid concentrations, color development in stainless steel and iron loss were compared between the color developing solutions. The concentration of hydrochloric acid in each color developing solution is 0.02, 0.25, 2.5, or 4.5 mass%. Each color developing solution contains potassium hexacyanoiron (II) and hexacyanoiron (III) at a concentration of 0.5% by mass. The solvent of the color developer is water.

First, each of a plurality of color developing solutions having different hydrochloric acid concentrations was sprayed on powdery SUS316 (hereinafter referred to as SUS powder), and it was confirmed using a microscope whether the SUS powder had a blue color.

As a result, when the color developing solution having a hydrochloric acid concentration of 0.02 or 0.25% by mass was sprayed, the SUS powder did not exhibit a blue color. On the other hand, it was observed that the SUS powder had a blue color when sprayed with a color developing solution having a hydrochloric acid concentration of 2.5 or 4.5% by mass.

Next, each of a plurality of coloring solutions having different hydrochloric acid concentrations was sprayed on the iron powder, and the state of the iron powder was confirmed using a microscope.

As a result, it was confirmed that bubbles were generated when a coloring solution having a hydrochloric acid concentration of 4.5 mass% was sprayed. That is, when a color developing solution having a hydrochloric acid concentration of 4.5% by mass was used, it was observed that the iron powder and the color developing solution reacted with gas generation. That is, when a color developing solution having a hydrochloric acid concentration of 4.5% by mass is used, the color developing solution and the iron powder react excessively, and the iron powder is lost. Color development also occurred in a color developing solution having a hydrochloric acid concentration of 0.02% by mass, and the area of the blue portion increased as the concentration of hydrochloric acid increased.

Next, using a color developing solution having a hydrochloric acid concentration of 2.5% by mass, changes in the sizes of SUS powder and iron powder due to contact with the color developing solution were observed. In order to observe the size of the specific powder before and after spraying the coloring liquid, SUS powder and iron powder were fixed on the tape and the coloring liquid was sprayed.

As a result, when the concentration of hydrochloric acid in the color developing solution was 2.5% by mass, there was almost no change in the size of the powder sprayed with the color developing solution before and after spraying the color developing solution. .

[Example 2: Production of vinylidene fluoride polymer]
(Preparation of vinylidene fluoride polymer powder)
An autoclave with an internal volume of 2 L is 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 is raised to 26 ° C. in 1 hour. Then, suspension polymerization was performed for 25.5 hours from the start of temperature increase. After completion of the polymerization, the polymer was washed with 5 L of ion exchange water while dehydrating the resulting polymer slurry. Then, it heated for 10 hours in 80 degreeC oven, and obtained the powder of the dried vinylidene fluoride polymer.

(Preparation of polymer solution)
Into a 1000 ml Erlenmeyer flask with a stopper, 475 g of NMP was added, and 25 g of vinylidene fluoride polymer powder was added little by little while stirring. The vinylidene fluoride polymer was dispersed in NMP by continuing stirring for 3 minutes after the addition. Subsequently, the vinylidene fluoride polymer was dissolved by heating at 70 ° C. for 4 hours while continuing stirring. As a result, a transparent polymer solution in which the vinylidene fluoride polymer was dissolved in NMP was obtained.

(Preparation of coloring solution)
An aqueous solution containing 2 g of hexacyano iron (II) potassium and hexacyano iron (III) potassium at a concentration of 1% by mass and 2 g of 5% HCl were placed in a sprayer and mixed to obtain a total of 4 g of a color developing solution. As a result of measuring the pH of the color developing solution with a pH meter (model: HM-30V) manufactured by Toa Denpa Kogyo Co., Ltd., the pH was -0.16.

(Measurement of foreign matter)
The prepared polymer solution was put into a funnel of a filtration device, and suction filtered using a membrane filter (pore diameter: 10 μm). After suction filtration, NMP and acetone were passed through the membrane filter in this order to wash the membrane filter. After washing, the membrane filter was dried. After the membrane filter was transferred to a petri dish, a coloring solution was sprayed on the membrane filter to cause a color reaction. Using a microscope, the number and size of foreign matters that were colored on the membrane filter were measured.

(Lot evaluation)
As a result of the measurement, when the number of foreign matters detected from 1 g of vinylidene fluoride polymer exceeded 10, the lot was excluded from the product as a defective product. On the other hand, when the number of foreign matters detected per gram of vinylidene fluoride polymer is 4 to 10, the lot is regarded as a normal product, and the number of foreign matters detected per gram of vinylidene fluoride polymer is 2 or If there are three, the lot is a high-purity product, and if the number of foreign matter detected per gram of vinylidene fluoride polymer is 1 or less, the lot is an ultra-high-purity product and the final product As a result, a vinylidene fluoride polymer was obtained.

The present invention can be used for the production of a vinylidene fluoride polymer and its quality evaluation.

Claims

A filtration step in which a polymer solution in which the polymer is dissolved in a solvent is filtered by a filter;
A contacting step in which a coloring liquid containing potassium hexacyanoiron (II), potassium hexacyanoiron (III) and an acid is contacted with the filter after filtration;
A step of detecting foreign matter in the polymer solution captured by the filter by color development on the filter caused by the coloring solution, and measuring at least one of the number and size of the foreign matter,
A method for evaluating a polymer, wherein the pH of the color developing solution is in the range of −0.40 to +0.75.
The acid is hydrochloric acid;
2. The method for evaluating a polymer according to claim 1, wherein the color developing solution contains hydrochloric acid at a concentration of 0.5 to 4.0% by mass.
3. The method for evaluating a polymer according to claim 1, wherein, in the contacting step, the color developing solution is brought into contact with the filter by spraying the color developing solution.
The polymer evaluation method according to any one of claims 1 to 3, wherein the foreign matter is at least one of iron and stainless steel.
The method for evaluating a polymer according to any one of claims 1 to 4, wherein the polymer is a vinylidene fluoride polymer.
The solvent is a solvent that has a polymer dissolving ability and does not have a foreign substance dissolving ability,
And further comprising a dissolution step of dissolving the polymer powder in the solvent to prepare the polymer solution,
The method for evaluating a polymer according to any one of claims 1 to 5, wherein, in the dissolving step, the powder is dissolved at 60 to 80 ° C.
The polymer evaluation method according to any one of claims 1 to 6, wherein the solvent is N-methyl-2-pyrrolidone.
The color developing solution is formed by dissolving 0.1 to 5 parts by weight of a mixture of the hexacyanoiron (II) potassium and the hexacyanoiron (III) potassium in 100 parts by weight of the aqueous solution containing the acid. The method for evaluating a polymer according to any one of claims 1 to 7, wherein:
9. The method for evaluating a polymer according to claim 8, wherein the content ratio of potassium hexacyanoiron (II) and hexacyanoiron (III) potassium in the mixture is in the range of 1: 5 to 5: 1.
A production process of producing a polymer by a polymerization reaction and obtaining a powder of the polymer by drying;
A dissolving step of dissolving a part of the obtained polymer powder in a solvent having a polymer dissolving ability and not having a foreign substance dissolving ability;
A filtration step of filtering the polymer solution in which the polymer is dissolved in a solvent with a filter;
A contacting step in which a coloring liquid containing potassium hexacyanoiron (II), potassium hexacyanoiron (III) and an acid is contacted with the filter after filtration;
A measurement step of detecting foreign matter in the polymer solution trapped by the filter by color development on the filter caused by the color developing solution, and measuring at least one of the number and size of the foreign matter;
A determination step for determining the quality of the produced polymer based on the result of the measurement step,
A method for producing a polymer, wherein the pH of the color developing solution is within a range of −0.40 to +0.75.