WO2023190793A1

WO2023190793A1 - Method for producing resin solution

Info

Publication number: WO2023190793A1
Application number: PCT/JP2023/013030
Authority: WO
Inventors: 大樹森光
Original assignee: 日東電工株式会社
Priority date: 2022-03-31
Filing date: 2023-03-29
Publication date: 2023-10-05
Also published as: TW202402893A

Abstract

The present disclosure provides a method for producing a resin solution in which a resin is dissolved in a solvent, the method involving: stirring a mixture 100 of the solvent and the resin by convection of the solvent, and dissolving the resin into the solvent. The convection of the solvent includes convection generated by circulating the solvent.

Description

Method for manufacturing resin solution

The present disclosure relates to a method for producing a resin solution.

The quality of resins used for optical applications, such as photosensitive resins used in lithography and resin materials used in optical components such as plastic optical fibers, may be degraded by foreign substances mixed in. Therefore, it is desirable that resins used for optical applications do not contain foreign substances. Therefore, in order to remove foreign substances from resin, a method has conventionally been used in which a resin solution is prepared by dissolving the resin in a solvent, and the solution is filtered. For example, Patent Document 1 proposes a method of circulating and filtering a photosensitive resin solution using a filter as a purification method for removing foreign substances from a photosensitive resin used in lithography.

International Publication No. 2017/163922

As described above, conventionally, in order to remove foreign substances from resin, a method has been used in which a resin solution in which resin is dissolved in a solvent is filtered. When using this method, it is first necessary to obtain a resin solution. The resin solution is produced by dissolving the resin from which foreign substances are removed in a solvent, but at this time, it is necessary to sufficiently stir the mixture of the resin and the solvent. For such stirring, a stirrer having stirring blades is generally used.

However, when a stirrer is used to dissolve the resin, sliding foreign objects and metal ions generated when the stirring blade rotates may mix into the solvent. Sufficient stirring is required to dissolve the resin in the solvent, so if a resin solution is produced only by stirring with a stirrer, the amount of foreign substances such as the above-mentioned sliding foreign substances and metal ions mixed into the solvent will be large. Become. Therefore, it becomes difficult to sufficiently remove these foreign substances even in the subsequent filtration step.

An object of the present disclosure is to provide a novel method for producing a resin solution that can obtain a resin solution with fewer foreign substances than a conventional resin solution obtained only by stirring with a stirrer.

The present disclosure provides a method for producing a resin solution in which a resin is dissolved in a solvent, the method comprising:
The manufacturing method includes:
stirring the mixture of the solvent and the resin by convection of the solvent to dissolve the resin in the solvent;
including;
The convection of the solvent includes convection caused by refluxing the solvent.

According to the present disclosure, it is possible to provide a novel method for producing a resin solution that can obtain a resin solution with less foreign matter than a conventional resin solution obtained only by stirring with a stirrer.

FIG. 1 is a schematic diagram illustrating an example of a method for manufacturing a resin solution in an embodiment. FIG. 2 is a graph showing the number of foreign substances in resin solutions obtained by the manufacturing methods of Examples and Comparative Examples.

A first aspect of the present disclosure is a method for producing a resin solution in which a resin is dissolved in a solvent, comprising:
The manufacturing method includes:
stirring the mixture of the solvent and the resin by convection of the solvent to dissolve the resin in the solvent;
including;
The convection of the solvent includes convection caused by refluxing the solvent.
Method for producing resin solution.

In the second aspect of the present disclosure, for example, in the manufacturing method according to the first aspect, the convection of the solvent further includes convection caused by boiling of the solvent.

In the third aspect of the present disclosure, for example, in the manufacturing method according to the first or second aspect, the resin is solid.

In a fourth aspect of the present disclosure, for example, in the manufacturing method according to any one of the first to third aspects, when stirring the mixture by causing convection of the solvent, the mixture is heated to a boiling point of the solvent. Heat to above temperature.

In the fifth aspect of the present disclosure, for example, in the manufacturing method according to any one of the first to fourth aspects, the resin includes a fluoropolymer.

In the sixth aspect of the present disclosure, for example, in the manufacturing method according to the fifth aspect, the solvent is a fluorine-based solvent, and the boiling point of the solvent is 50°C or more and 80°C or less.

In a seventh aspect of the present disclosure, for example, in the manufacturing method according to the fifth or sixth aspect, the solvent is a fluorine-based solvent, and the viscosity of the solvent at 25° C. is 1 mPa·s or more and 10 mPa·s or less. It is.

In the eighth aspect of the present disclosure, for example, in the manufacturing method according to any one of the first to seventh aspects, the resin is an optical resin.

Hereinafter, embodiments of the method for producing a resin solution of the present disclosure will be described.

The method for manufacturing a resin solution of this embodiment is a method for manufacturing a resin solution in which a resin is dissolved in a solvent. The method for manufacturing the resin solution of this embodiment is as follows:
agitating the mixture of solvent and resin by convection of the solvent to dissolve the resin in the solvent;
including.

In the resin solution manufacturing method of the present embodiment, the convection of the solvent includes convection caused by refluxing the solvent. That is, in the method for producing a resin solution of the present embodiment, the mixture is stirred by the convection of the solvent generated by volatilizing the solvent, cooling and condensing the volatilized solvent, and returning the condensed solvent to the mixture of the solvent and the resin. . Here, convection caused by refluxing a solvent includes, for example, the temperature difference (i.e., density These include natural convection of the solvent caused by the condensed solvent (difference) and forced convection of the solvent caused by the falling of the condensed solvent.

In the method for producing a resin solution of the present embodiment, a mixture of a resin and a solvent is stirred by convection of the solvent, including convection generated by refluxing the solvent as described above. Stirring by such convection does not cause contamination of foreign matter (for example, contamination of sliding foreign matter or metal ions generated when the stirring blade rotates) unlike stirring using a stirrer. Therefore, according to the method for producing a resin solution of this embodiment, it is possible to obtain a resin solution with less foreign matter than a conventional resin solution obtained only by stirring with a stirrer.

For example, a mixture of a solvent and a resin is heated in order to cause the convection of the solvent as described above. The heating temperature can be appropriately selected depending on the type of resin, the boiling point of the resin, and the like.

Furthermore, in the method for producing a resin solution of the present embodiment, the solvent volatilized as described above can be returned to the mixture by reflux. Therefore, according to the resin solution manufacturing method of the present embodiment, even if the resin solution is manufactured in an unsealed container, the amount of the solvent decreases due to solvent volatilization, and the concentration of the resin solution changes significantly. No problems occur. In addition, since there is no need to seal the container, there is no need to take measures to prevent the internal pressure of the container from increasing due to the solvent that evaporates during the production of the resin solution, such as pressure design of the container and valve, thereby suppressing increases in manufacturing costs. I can do it.

In the resin solution manufacturing method of the present embodiment, the convection of the solvent may further include convection caused by boiling of the solvent. Here, the convection caused by the boiling of the solvent refers to forced convection caused by vapor bubbles of the solvent generated from the solvent due to the boiling of the solvent. In this case, in addition to the convection generated by refluxing the solvent, the mixture is stirred by convection generated by boiling the solvent, so that the mixture can be stirred more efficiently and sufficiently.

In order to generate convection due to boiling of the solvent, it is desirable to heat the mixture to a temperature equal to or higher than the boiling point of the solvent when stirring the mixture by causing convection of the solvent.

The duration of stirring by convection of the solvent is not particularly limited, as the appropriate time varies depending on various conditions such as the type of resin, the type of solvent, the amount of resin, the amount of solvent, and the heating temperature during stirring. . As an example, the time for stirring the solvent by convection generated by refluxing the solvent may be, for example, 0.5 hours or more, or 1 hour or more. The upper limit of the time for stirring the solvent by convection generated by refluxing the solvent is not particularly limited, but may be, for example, 30 hours or less. When stirring the solvent by combining convection caused by refluxing the solvent and convection generated by boiling the solvent, the stirring time may be, for example, 0.5 hours or more, or 1 hour or more. There may be. When stirring the solvent by combining convection caused by refluxing the solvent and convection generated by boiling the solvent, the upper limit of the stirring time is not particularly limited, but may be, for example, 30 hours or less.

FIG. 1 is a schematic diagram illustrating an example of a method for producing a resin solution in an embodiment. A mixture 100 of resin and solvent is contained inside the container 1 and stirred. The container 1 has an exhaust port 2, a liquid feed port 3 for feeding the solvent into the inside of the container 1, and a liquid drain port 4 for draining the prepared resin solution to the outside of the container 1. are doing. A temperature controller 5 such as a heater for heating the container 1 is provided around the outer periphery of the container 1 . A heat exchanger 6 is installed at the exhaust port 2 of the container 1 . The exhaust port 2 is open to external space via the heat exchanger 6. An air filter 7 is installed in a passage open to the outside from the heat exchanger 6 to prevent foreign matter from entering from the outside. Further, a safety valve 8 for regulating the pressure inside the container 1 is provided in a passage opened from the heat exchanger 6 to the outside. The volatilized solvent vapor is exhausted from the exhaust port 2 and enters the heat exchanger 6, where it is cooled and condensed, and the condensed solvent returns to the container 1 and is dripped into the mixture. A refrigerant cooled by a cooler 9 is circulated through the heat exchanger 6, and the volatilized solvent vapor exchanges heat with the refrigerant to be cooled and condensed, returning to liquid.

An example of the method for producing a resin solution of this embodiment will be described with reference to FIG. A resin is placed inside a container 1, and a solvent is fed therein through a liquid feeding port 3. The mixture 100 in the container 1 is heated to a predetermined temperature by the temperature controller 5 via the container 1 to volatilize the solvent. The vaporized solvent vapor enters the heat exchanger 6 through the exhaust port 2 of the container 1, where it is cooled and condensed. The condensed solvent returns to the container 1 and is dripped into the mixture 100. Convection is generated by repeating such reflux of the solvent, that is, volatilization of the solvent → cooling and condensation of the volatile solvent → the condensed solvent returns to the container 1 and drips into the mixture, and the mixture 100 is stirred by the convection. . Further, when the mixture 100 is heated to a temperature equal to or higher than the boiling point of the solvent, convection also occurs due to the boiling of the solvent, and the mixture 100 is also stirred by the convection.

Note that the resin solution manufacturing method of the present embodiment can be applied to a one-time resin solution manufacturing method, that is, a resin solution manufacturing method in a batch process, or can be applied to a resin solution manufacturing method for removing foreign substances from the resin. It can also be applied as a resin solution manufacturing process, which is one process in an integrated line. The resin solution manufacturing method of the present embodiment can reduce foreign substances mixed into the solution when manufacturing the resin solution, and furthermore, the concentration of the obtained resin solution is less likely to change, and the internal pressure of the container increases too much. There is also little risk of such. Therefore, the method for producing a resin solution according to the present embodiment is a method suitable for use as one process in an integrated line, and improves the workability of the process for removing foreign substances from the resin. It is possible to guarantee the quality of resin and improve mass productivity. When the resin solution manufacturing method of this embodiment is used as one process in an integrated line, the resin solution discharged from the drain port 4 in FIG. Sent.

The method for producing a resin solution of the present embodiment can be applied to any resin for any purpose as a method for dissolving the resin in a solvent. The method for producing a resin solution according to the present embodiment can be particularly suitably used for resins used for optical applications (optical resins) in which contamination of foreign substances is strictly restricted. In particular, this embodiment is used as a method for manufacturing a resin solution used in a pre-treatment for removing foreign substances from a raw material resin, which is performed as a pre-treatment for an optical resin used in an optical fiber. The method for producing a resin solution can be suitably used.

The resin used in the method for producing a resin solution of this embodiment is not particularly limited. The resin may be solid at room temperature (25° C.), for example. For example, solid resin powder may be used as the resin.

For example, the resin may be a resin containing a fluoropolymer. Fluorine-containing polymers are useful as resins used in optical applications, such as photosensitive resins used in lithography and resin materials used in optical components such as plastic optical fibers (hereinafter referred to as "POF"). It is a substance. Therefore, the resin solution obtained by the resin solution manufacturing method of the present embodiment using a resin containing a fluoropolymer is suitable for pretreatment for removing foreign substances from a resin for optical applications such as POF. It can be used for Therefore, for example, in a POF manufacturing method, by applying the resin solution manufacturing method of the present embodiment to pretreatment for removing foreign substances from the POF material, a high-quality POF with reduced foreign substances can be obtained. be able to.

The fluorine-containing polymer may have, for example, a fluorine-containing alicyclic structure. The fluorine-containing aliphatic ring structure may be included in the main chain of the fluoropolymer, or may be included in the side chain of the fluoropolymer. The fluoropolymer has, for example, a structural unit (A) represented by the following structural formula (1).

In formula (1), R _ff ¹ to R _ff ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. R _ff ¹ and R _ff ² may be connected to form a ring. "Perfluoro" means that all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. In formula (1), the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1. The perfluoroalkyl group may be linear or branched. Examples of the perfluoroalkyl group include a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group.

In formula (1), the number of carbon atoms in the perfluoroalkyl ether group is preferably 1 to 5, more preferably 1 to 3. The perfluoroalkyl ether group may be linear or branched. Examples of the perfluoroalkyl ether group include perfluoromethoxymethyl group.

When R _ff ¹ and R _ff ² are linked to form a ring, the ring may be a 5-membered ring or a 6-membered ring. Examples of this ring include a perfluorotetrahydrofuran ring, a perfluorocyclopentane ring, and a perfluorocyclohexane ring.

Specific examples of the structural unit (A) include structural units represented by the following formulas (A1) to (A8).

The structural unit (A) may be the structural unit (A2) among the structural units represented by the above formulas (A1) to (A8), that is, the structural unit represented by the following formula (2).

The fluoropolymer may contain one or more structural units (A). In the fluoropolymer, the content of the structural unit (A) may be 20 mol% or more, or 40 mol% or more, based on the total of all structural units. By containing 20 mol% or more of the structural unit (A), the fluoropolymer tends to have higher heat resistance. When the structural unit (A) is contained in an amount of 40 mol % or more, the fluoropolymer tends to have higher transparency and higher mechanical strength in addition to high heat resistance. In the fluoropolymer, the content of the structural unit (A) may be 95 mol% or less or 70 mol% or less based on the total of all structural units.

The structural unit (A) is derived from, for example, a compound represented by the following formula (3). In formula (3), R _ff ¹ to R _ff ⁴ are the same as in formula (1). The compound represented by formula (3) can be obtained by a known production method, such as the production method disclosed in Japanese Patent Publication No. 2007-504125.

Specific examples of the compound represented by the above formula (3) include compounds represented by the following formulas (M1) to (M8).

The fluoropolymer may further contain other structural units in addition to the structural unit (A).

The fluoropolymer may be a fluoropolymer containing a structural unit (B) represented by the following formula (4).

(In formula (4), m and n are arbitrary integers)

The solvent is not particularly limited, as it may be selected according to the type of resin as long as it can dissolve the resin. The solvent used in the resin solution manufacturing method of this embodiment is preferably a solvent that easily causes convection due to reflux. For example, a solvent that is liquid at room temperature (25° C.) and has a lower boiling point is preferably used.

For example, when the resin contains a fluorine-containing polymer, the solvent is preferably a fluorine-based solvent. As the fluorine-based solvent, for example, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, hexafluorobenzene, and perfluorohexane are preferably used.

When the solvent is a fluorine-based solvent, the boiling point of the solvent is preferably 50° C. or higher and 80° C. or lower, for example, so that convection due to reflux can easily occur.

When the solvent is a fluorine-based solvent, the viscosity of the solvent at 25° C. is preferably 1 mPa·s or more and 10 mPa·s or less so that convection due to reflux can easily occur.

In the method for producing a resin solution of this embodiment, it is also possible to use stirring using a stirring blade. That is, in the method for producing a resin solution of the present embodiment, stirring by convection of the solvent, including convection generated by refluxing the solvent, and blade stirring using a stirring blade may be used in combination. According to such a method, for example, even if the amount of the resin solution to be produced is increased, sufficient stirring can be performed without significantly increasing the stirring time. Even when using a stirring blade in this way, stirring is also performed by convection generated by refluxing the solvent, so it is possible to suppress the mixing of sliding foreign objects and metal ions into the solvent that are generated when the stirring blade rotates to a small amount. can. Therefore, even when a stirring blade is used in conjunction with the method for producing a resin solution of this embodiment, it is possible to produce a resin solution with fewer foreign substances than a conventional resin solution obtained only by stirring with a stirrer. can.

(Example)
[Preparation of resin solution]
As a resin, a polymer of perfluoro-4-methyl-2-methylene-1,3-dioxolane (compound of formula (M2) above, "PFMMD") was prepared. Perfluoro-4-methyl-2-methylene-1,3-dioxolane is obtained by first synthesizing 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane and fluorinating it. It was synthesized by decarboxylating the carboxylic acid salt. Perfluorobenzoyl peroxide was used as a polymerization initiator in the polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane.

The following describes the synthesis of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, the fluorination of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, and the perfluorinated The synthesis of -4-methyl-2-methylene-1,3-dioxolane and the polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane will be explained in detail.

<Synthesis of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane>
Prepare a 3L three-neck flask equipped with a water-cooled condenser, a thermometer, a magnetic stirrer, and an isobaric dropping funnel, and add 139.4 g (total) of a mixture of 2-chloro-1-propanol and 1-chloro-2-propanol. 1.4 mol) was charged into the flask. The flask was cooled to 0°C, methyl trifluoropyruvate was slowly added thereto, and the mixture was further stirred for 2 hours. After adding thereto 100 mL of dimethyl sulfoxide (DMSO) and 194 g of potassium carbonate over 1 hour, the mixture was further stirred for 8 hours to obtain a reaction mixture. The resulting reaction mixture was mixed with 1 L of water, the aqueous phase was separated, it was further extracted with dichloromethylene, the dichloromethylene solution was mixed with the organic reaction mixture phase, and the solution was dried over magnesium sulfate. After removing the solvent, 245.5 g of crude product was obtained. This crude product was fractionally distilled under reduced pressure (12 Torr) to obtain 230.9 g of purified 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane. The boiling point of the purified product was 77-78°C, and the yield was 77%. It was confirmed by HNMR and ¹⁹ FNMR that the obtained purified product was 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane.

HNMR (ppm): 4.2-4.6, 3.8-3.6 (CHCH ₂ , multiplet, 3H), 3.85-3.88 (COOCH ₃ , multiplet, 3H), 1.36-1 .43 (CCH ₃ , multiplet, 3H)
¹⁹ FNMR (ppm): -81.3 (CF ₃ , s, 3F)

<Fluorination of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane>
4L of 1,1,2-trichlorotrifluoroethane was injected into a 10L stirred reactor. In a stirred reaction tank, nitrogen was flowed at a flow rate of 1340 cc/min and fluorine was flowed at a flow rate of 580 cc/min to create a nitrogen/fluorine atmosphere. After 5 minutes, 290 g of the previously prepared 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane was dissolved in 750 mL of 1,1,2-trichlorotrifluoroethane solution, and this solution was reacted. Added to the bath at a rate of 0.5 ml/min. The reaction vessel was cooled to 0°C. After all the dioxolane had been added in 24 hours, the fluorine gas flow was stopped. After purging nitrogen gas, an aqueous potassium hydroxide solution was added until the mixture became slightly alkaline.

After removing volatile substances under reduced pressure, the surroundings of the reaction vessel were cooled, and then dried under reduced pressure at 70° C. for 48 hours to obtain a solid reaction product. The solid reaction product was dissolved in 500 mL of water and excess hydrochloric acid was added to separate the organic and aqueous phases. The organic phase was separated and distilled under reduced pressure to obtain perfluoro-2,4-dimethyl-1,3-dioxolane-2-carboxylic acid. The boiling point of the main distillate was 103°C-106°C/100mmHg. The yield of fluorination was 85%.

<Synthesis of perfluoro-4-methyl-2-methylene-1,3-dioxolane>
The above distillate was neutralized with an aqueous potassium hydroxide solution to obtain potassium perfluoro-2,4-dimethyl-2-carboxylate-1,3-dioxolane. This potassium salt was vacuum dried at 70° C. for 1 day. The salts were decomposed at 250°C to 280°C and under nitrogen or argon atmosphere. It was condensed in a cold trap cooled to -78°C to obtain perfluoro-4-methyl-2-methylene-1,3-dioxolane in a yield of 82%. The boiling point of the product was 45°C/760mmHg. The product was identified using ¹⁹ FNMR and GC-MS.

¹⁹ FNMR: -84ppm (3F, CF ₃ ), -129ppm (2F, = CF ₂ )
GC-MS: m/e244 (Molecular ion) 225, 197, 169, 150, 131, 100, 75, 50.

<Polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane>
100 g of perfluoro-4-methyl-2-methylene-1,3-dioxolane obtained by the above method and 1 g of perfluorobenzoyl peroxide were sealed in a glass tube. The glass tube was refilled with argon after the oxygen in the system was removed by freeze degassing and heated at 50° C. for several hours. The contents became solid, but upon further heating at 70° C. overnight, 100 g of a transparent rod was obtained.

The obtained transparent rod was dissolved in Fluorinert FC-75 (manufactured by Sumitomo 3M), and the obtained solution was poured onto a glass plate to obtain a thin film of the polymer. The obtained polymer had a glass transition temperature of 117° C. and was completely amorphous. The product was purified by dissolving the transparent rod in hexafluorobenzene and adding chloroform to the solution for precipitation. The glass transition temperature of the purified polymer was about 131°C. This polymer was used as a resin for preparing a resin solution.

1,1,1,2,2,3,4,5,5,5-decafluoropentane was used as the solvent.

The resin and solvent prepared as described above were mixed so that the resin concentration was 7% by mass, and the mixture was placed in a glass flask. The total amount of the mixture was 6100 g. A cooling pipe was attached to the mouth of the glass flask as a heat exchanger, and 5°C cooling water was circulated through the heat exchanger.

The glass flask was heated to a surface temperature of 75° C. using a mantle heater, and the mixture of resin and solvent was stirred for 9 hours by convection generated by refluxing the solvent. A resin solution was prepared by such a method.

[Foreign substance evaluation]
50 mL of the prepared resin solution was taken out into a container and used as a sample for a foreign matter evaluation test. A transparent container that is transparent to laser light with a wavelength of 520 nm was used as the container. A resin solution sample in a container in a dark room is irradiated with laser light (PL201 manufactured by THORLABS, wavelength: 520 nm, laser power: 1 mW) from one direction, and the progress of the laser light irradiated on the sample is measured. The sample irradiated with light was imaged using a microscope (optical microscope VHX7000 (lens: VH-Z00R)) at a shutter speed of 100 ms from a direction perpendicular to the direction, and image data was obtained. Using the acquired image data, the number of foreign objects that could be confirmed was counted. FIG. 2 is a graph showing the number of foreign particles determined from each image obtained by photographing 50 images of the resin solution obtained by the manufacturing method of the example. Among the graphs in FIG. 2, the graph labeled "reflux" is the result of the example. Note that the results shown in FIG. 2 are the results obtained by extracting three 50 mL samples from the prepared resin solution and obtaining the number of foreign substances. The numerical values in the bar graph shown in FIG. 2 show the average value of three times, and the error bars show the maximum and minimum values of three times.

(Comparative example)
[Preparation of resin solution]
A resin solution was prepared using the same resin, solvent, and stirring method as in the example. The solution was additionally stirred using a stirring blade without being refluxed. Specifically, the mixture was stirred for 9 hours at a rotational speed of 300 rpm using a stirring blade having pitched paddle-shaped blades.

[Foreign substance evaluation]
The prepared resin solution was evaluated for foreign substances in the same manner as in the examples. The graph of FIG. 2 shows the number of foreign substances in the resin solution obtained by the manufacturing method of the comparative example. Among the graphs in FIG. 2, the graph labeled "blade stirring" is the result of the comparative example.

As shown in the graph of Figure 2, the resin solution obtained in the example in which stirring was performed by refluxing the solvent contained less foreign matter than the resin solution in the comparative example in which the stirring blade was used. .

The method for producing a resin solution of the present disclosure is for obtaining a resin solution for pretreatment (e.g., filtration treatment) for removing foreign substances from the resin, for example, when dissolving the resin in a solvent while suppressing the contamination of foreign substances. It is useful as a method.

Claims

A method for producing a resin solution in which a resin is dissolved in a solvent, the method comprising:
The manufacturing method includes:
stirring the mixture of the solvent and the resin by convection of the solvent to dissolve the resin in the solvent;
including;
The convection of the solvent includes convection caused by refluxing the solvent.
Method for producing resin solution.
The convection of the solvent further includes convection caused by boiling of the solvent.
The manufacturing method according to claim 1.
the resin is solid;
The manufacturing method according to claim 1.
heating the mixture to a temperature equal to or higher than the boiling point of the solvent when stirring the mixture by convection of the solvent;
The manufacturing method according to claim 1.
The resin includes a fluorine-containing polymer,
The manufacturing method according to claim 1.
The solvent is a fluorine-based solvent,
The boiling point of the solvent is 50°C or more and 80°C or less,
The manufacturing method according to claim 5.
The solvent is a fluorine-based solvent,
The manufacturing method according to claim 5, wherein the viscosity of the solvent at 25° C. is 1 mPa·s or more and 10 mPa·s or less.
The resin is an optical resin,
The manufacturing method according to claim 1.