Manufacturing method for low odor emulsion

Abstract

A method of producing a low-odor emulsion, wherein the method comprises: a step for stocking an aqueous polymer emulsion in a treatment vessel that can be depressurized, bringing the temperature of the aqueous polymer emulsion into the range of 50-90°C, bringing the pressure inside the treatment vessel to the range of 12-57 KPa, keeping the inside of the treatment vessel in a state where water boils, and supplying pressurized water vapor through a supply passage into the treatment vessel; and a step for discharging, to the outside of the system, water vapor of a gas phase part inside the treatment vessel as well as volatile organic compounds that have been volatilized from the aqueous polymer emulsion. The ratio of the inner diameter of the treatment vessel to the opening diameter of a supply opening for supplying the pressurized water vapor to inside the treatment vessel from the supply passage is set to 30-3,000 relative to an opening diameter 1 of the supply opening.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2020-171389, filed on October 9, 2020, the contents of which are incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to a method for producing a low-odor emulsion, and more particularly to a technique for efficiently removing volatile organic compounds from an aqueous polymer emulsion obtained by an emulsion polymerization method or the like. [Background technology]

[0003] Aqueous polymer emulsions obtained by emulsion polymerization of monomers such as styrene, vinyl acetate, acrylonitrile, butadiene, and alkyl (meth)acrylate in an aqueous medium are widely used as raw materials for rubber-like elastomer materials, paints, coating agents, adhesives, pressure-sensitive adhesives, binders, thickeners, cosmetic compositions, pharmaceutical compositions, and the like.

[0004] Aqueous polymer emulsions (hereinafter simply referred to as "emulsions") usually contain trace amounts of volatile organic compounds, the main components of which are unreacted monomers and decomposition products generated during polymerization. These volatile organic compounds may generate unpleasant odors and affect the workability of workers who handle them.

[0005] Methods for removing volatile organic compounds in emulsion include a method of blowing pressurized steam into the emulsion to expel the volatile organic compounds together with the steam (see, for example, Patent Document 1).Other methods that have been proposed include a method of adding a redox initiator after polymerization to perform additional polymerization (see, for example, Patent Document 2), a method of feeding an emulsion from the top of a plate tower stripper while feeding pressurized steam from below (see, for example, Patent Document 3), and a method of blowing air or an inert gas into a heated emulsion (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2002-60415 A [Patent Document 2] JP 2002-212207 A [Patent Document 3] Japanese Unexamined Patent Publication No. 58-213003 [Patent Document 4] Japanese Patent Application Publication No. 53-41387 Summary of the Invention [Problem to be solved by the invention]

[0007] In the methods of Patent Documents 1 to 4, the emulsion is subjected to a high-temperature, long-term thermal history, which raises concerns about the likelihood of polymer particle agglomeration. Furthermore, the resulting polymer particle agglomerates may adhere to the walls of the processing vessel, the agitator shaft, and other surfaces, potentially reducing the temperature control function within the processing vessel. In addition to adhering to the walls of the processing vessel, these agglomerates may also exist in minute form within the emulsion. Removing the agglomerates from the emulsion requires significant effort and time, which raises concerns about potential problems such as reduced productivity during industrial-scale production. Furthermore, the emulsion's stability over time may be reduced, resulting in the formation of sediment at the bottom of the container during long-term storage, raising concerns about insufficient quality.

[0008] The present disclosure has been made in view of the above-mentioned problems, and has as its main object to provide a method for producing a low-odor emulsion that can suppress the amount of aggregates generated during deodorization treatment, has good stability over time, and has a sufficiently reduced amount of volatile organic compounds in the emulsion. [Means for solving the problem]

[0009] As a result of intensive research to solve the above problems, the inventors have found that by setting the ratio of the diameter of the supply port for supplying pressurized steam into the treatment vessel to the inner diameter of the treatment vessel within a specific range, it is possible to reduce the thermal history of the aqueous polymer emulsion and to easily remove volatile organic compounds in a short period of time.

[0010] That is, a first aspect of the present disclosure relates to a method for producing a low-odor emulsion, comprising the steps of: charging an aqueous polymer emulsion into a treatment vessel capable of reducing pressure; adjusting the temperature of the aqueous polymer emulsion to a range of 50°C to 90°C; adjusting the pressure inside the treatment vessel to a range of 12 KPa to 57 KPa; and maintaining the treatment vessel in a state where water boils; and supplying pressurized steam into the treatment vessel through a supply passage; and discharging the steam in the gas phase inside the treatment vessel and the volatile organic compounds volatilized from the aqueous polymer emulsion to the outside of the system, wherein the ratio of the diameter of a supply port for supplying the pressurized steam from the supply passage into the treatment vessel to the inner diameter of the treatment vessel is 30 to 3,000. [Effects of the Invention]

[0011] According to the present disclosure, an aqueous polymer emulsion with sufficiently reduced volatile organic compounds can be produced in a short treatment time (for example, within 10 hours) using a general-purpose apparatus capable of reducing pressure. Therefore, the aqueous polymer emulsion obtained by the method of the present disclosure has low odor and a small amount of aggregates, making it excellent in terms of the environment and safety and hygiene. Furthermore, since the amount of aggregates generated during deodorization treatment can be kept low, it is excellent not only in quality but also in terms of productivity and production costs. Furthermore, the aqueous polymer emulsion produced by the method of the present disclosure has excellent stability over time, making it less likely to cause problems even after long-term storage and allowing it to be used safely. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a batch-type deodorizing treatment device. [Figure 2] FIG. 2 is a vertical cross-sectional view showing a schematic configuration of a continuous deodorizing treatment device. [Figure 3] FIG. 3 is a cross-sectional view of the end of the supply pipe on the supply port side. [Figure 4] FIG. 4 is a cross-sectional view of the end of the supply pipe on the supply port side. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present disclosure will be described in detail below. In this specification, "(meth)acrylic" means acrylic or methacrylic. "Aqueous polymer emulsion" means an emulsion in which a polymer is dispersed in a solvent mainly composed of water. "A solvent mainly composed of water" means a liquid containing water in an amount of 70% by mass or more, preferably 80% by mass or more, based on the total amount of the solvent.

[0014] <<Method for producing low-odor emulsion>> The method for producing a low-odor emulsion of the present disclosure (hereinafter also referred to as "the present production method") produces a low-odor aqueous polymer emulsion (hereinafter also referred to as "low-odor emulsion") by performing a treatment (deodorization treatment) to remove volatile organic compounds contained in the aqueous polymer emulsion. The present production method includes the following steps A and B. Step A: A step in which the emulsion is placed in a deodorizing treatment vessel capable of reducing the pressure, and pressurized steam is supplied to the emulsion under reduced pressure. Step B: A step of discharging the water vapor in the gas phase within the deodorizing treatment vessel and the volatile organic compounds that have evaporated from the emulsion to the outside of the system. In the present production method, the timing of carrying out step B is not particularly limited as long as it is a timing at which the water vapor in the gas phase part in the deodorization treatment container and the volatile organic compounds volatilized from the emulsion can be discharged to the outside of the system. That is, the present production method may be an embodiment in which step B is carried out after step A is carried out, or an embodiment in which step A and step B are carried out simultaneously.

[0015] This production method may be applied to a batch system or a continuous system. When this production method is applied to a batch system, a low odor emulsion can be produced by a method including the above steps A and B. When this production method is applied to a continuous system, it is preferable to produce a low odor emulsion by a method including the following step C in addition to the above steps A and B. Step C: A step of withdrawing the emulsion from which the volatile organic compounds have been removed by step B from the deodorizing treatment container, and supplying undeodorized emulsion to the deodorizing treatment container at a rate equal to the rate at which the emulsion is withdrawn from the deodorizing treatment container. This manufacturing method will now be described.

[0016] <Water-based polymer emulsion> The emulsion from which volatile organic compounds are removed is preferably an emulsion containing polymer particles produced by emulsion polymerization in an aqueous medium. A vinyl monomer can be preferably used as the monomer constituting the polymer particles. Examples of the vinyl monomer include (meth)acrylic acid ester compounds, aromatic vinyl compounds, unsaturated carboxylic acids, unsaturated acid anhydrides, hydroxyl group-containing vinyl compounds, amino group-containing vinyl compounds, amide group-containing vinyl compounds, alkoxy group-containing vinyl compounds, nitrile group-containing vinyl compounds, vinyl ether compounds, sulfonic acid group-containing vinyl compounds, and polyoxyalkylene group-containing vinyl compounds. As the vinyl monomer, one of these may be used alone, or two or more may be used in combination.

[0017] Emulsion polymerization to obtain an emulsion can be carried out according to a conventionally known method. Emulsion polymerization is preferably carried out in the presence of at least one of a surfactant and a protective colloid. Examples of ionic surfactants include anionic, cationic, and nonionic surfactants, with anionic and / or nonionic surfactants being more preferred. A radical polymerization initiator is preferably used for emulsion polymerization. Known oil-soluble or water-soluble polymerization initiators can be used as the radical polymerization initiator. A water-soluble polymerization initiator is preferred.

[0018] In emulsions produced by emulsion polymerization in an aqueous medium, the aqueous medium after polymerization typically contains approximately 1,000 to 3,000 ppm of volatile organic compounds. Examples of volatile organic compounds include unreacted monomers, alcohols produced by hydrolysis of unreacted monomers, alcohols produced by hydrolysis of ester bonds in the copolymer, and impurities contained in the monomers and emulsifiers. To suppress odors caused by these volatile organic compounds, the present production method involves steps A and B, which remove the volatile organic compounds from the emulsion.

[0019] <Step A: Supply of pressurized steam> In step A, the emulsion to be deodorized is placed in a deodorization treatment vessel capable of reducing the pressure, and pressurized steam is supplied to the emulsion in the deodorization treatment vessel under reduced pressure. This causes the volatile organic compounds contained in the emulsion to volatilize and move from the liquid phase to the gas phase. The deodorization treatment vessel (hereinafter also simply referred to as the "treatment vessel") is a treatment tank that contains the emulsion to be deodorized, and its interior has a storage section that stores the emulsion. The size and shape of the storage section are not particularly limited. Examples of the shape of the storage section include a cylindrical shape and a rectangular cross-section. The treatment vessel is provided with a supply pipe (hereinafter also referred to as the "steam supply pipe" or simply the "supply pipe") that supplies pressurized steam into the treatment vessel.

[0020] The treatment vessel may further be equipped with a heating unit for heating the emulsion in the vessel, a stirrer for stirring the emulsion in the vessel, a thermometer (e.g., a thermocouple) for measuring the temperature in the vessel (i.e., emulsion temperature), a pressure gauge for measuring the pressure in the gas phase in the vessel, and an exhaust pump for exhausting the gas phase in the vessel. From the viewpoint of efficiently releasing volatile organic compounds from the emulsion (more specifically, from the aqueous medium), it is preferable to uniformly stir the emulsion in the tank during deodorization treatment. Therefore, it is preferable to use an agitator with blades suitable for stirring, such as three-blade swept-back blades, paddle blades, propeller blades, anchor blades, or large blades. Examples of large blades include Fullzone (manufactured by Kobelco Solutions Co., Ltd.), Maxblend (manufactured by Sumitomo Heavy Industries Process Equipment Co., Ltd.), and Bend Leaf Blades (manufactured by Hakko Sangyo Co., Ltd.). The size of the agitator blade is not particularly limited. However, to ensure sufficient stirring, the blade diameter of the agitator blade relative to the inner diameter of the treatment vessel is preferably 0.3 or more, more preferably 0.4 or more.

[0021] 1 and 2 show schematic configuration diagrams of the processing vessel. FIG. 1 shows a batch type, and FIG. 2 shows a continuous type. As shown in FIGS. 1 and 2, the processing vessel 10 is a bottomed vessel with a storage section 11 provided therein. In the processing vessel 10, undeodorized emulsion Em is stored in the lower part of the storage section 11, and a gas phase section Gs is formed in the upper part of the storage section 11, and the emulsion Em is deodorized in this state. The storage section 11 is provided with an agitator 12. The agitator 12 is arranged within the storage section 11 so that the agitator blades 13 provided at the lower end of the agitator shaft are positioned at the bottom of the storage section 11. The processing vessel 10 shown in FIGS. 1 and 2 is provided with an agitator 12 having three swept-back blades as the agitator blades 13.

[0022] The treatment vessel 10 is provided with a supply pipe 15 that supplies pressurized steam from a supply port 14 into the storage section 11. In the treatment vessel 10 of FIG. 1, the supply pipe 15 is inserted into the storage section 11 from the bottom of the treatment vessel 10. In the treatment vessel 10 of FIG. 2, the supply pipe 15 is inserted into the storage section 11 from the top of the treatment vessel 10. An exhaust pipe 16 is provided at the top of the treatment vessel 10 to discharge gas in the gas phase section Gs at the top of the storage section 11 to the outside of the system. The continuous treatment vessel 10 further has an extraction hole 17 at the bottom of the treatment vessel 10 that extracts the emulsion after deodorization from the storage section 11.

[0023] While the use of an agitator can increase the contact efficiency between the emulsion and pressurized steam in the treatment vessel and improve the removal effect of volatile organic compounds, excessive agitation may be more likely to cause foaming. Therefore, an appropriate amount of antifoaming agent may be used to suppress foaming. Furthermore, during the deodorization treatment, if necessary, the emulsion may be extracted from the liquid phase (i.e., the lower part of the treatment vessel) to the outside of the system, circulated by a circulation pump, and flash-sprayed from the gas phase (i.e., the upper part of the treatment vessel) in the treatment vessel.

[0024] By supplying pressurized steam to the emulsion stored in the treatment vessel, the volatile organic compounds contained in the emulsion are separated from the liquid phase and become contained in the gas phase. As the pressurized steam to be supplied into the treatment vessel, steam with a gauge pressure of about 0.05 to 0.50 MPa (temperature 110 to 160°C) is preferably used, more preferably steam with a gauge pressure of 0.05 to 0.30 MPa, and even more preferably steam with a gauge pressure of 0.10 to 0.30 MPa.

[0025] When supplying pressurized steam into the treatment vessel, the pressurized steam may be supplied directly into the emulsion in the treatment vessel. Alternatively, the pressurized steam may be supplied to the gas phase portion of the treatment vessel, thereby indirectly supplying the pressurized steam to the emulsion in the treatment vessel. Of these, directly supplying pressurized steam into the emulsion stored in the treatment vessel is preferred, more preferably supplying pressurized steam directly from the bottom of the treatment vessel into the emulsion in the treatment vessel, and even more preferably supplying pressurized steam directly from the bottom of the treatment vessel near the stirring blade into the emulsion in the treatment vessel. By directly supplying pressurized steam into the emulsion, the thermal history of the emulsion can be further reduced, and volatile organic compounds in the emulsion can be efficiently removed while suppressing destruction of the polymer particles.

[0026] In step A, the temperature of the emulsion in the treatment vessel is maintained within a predetermined temperature range so that volatile organic compounds are sufficiently removed from the emulsion. There are no particular limitations on the method for maintaining the temperature of the emulsion in the treatment vessel within the predetermined range, but a treatment in which the emulsion to be deodorized is heated is preferred, as this allows for simple and highly accurate temperature control. This heating treatment can be carried out using a heating jacket, a heat exchanger provided outside the treatment vessel, or the like. If necessary, the emulsion may be preheated by batch treatment using a heating treatment vessel or continuous treatment by line heating using a heat exchanger before being supplied to the treatment vessel.

[0027] During the period when pressurized steam is supplied into the treatment vessel, the temperature of the emulsion in the treatment vessel (i.e., the temperature inside the vessel) is adjusted so that it is in the range of 50 to 90°C. If the emulsion temperature exceeds 90°C, a relatively large amount of polymer film is likely to form on the inner wall surface of the vessel, particularly at the interface between the gas and liquid phases, causing the temperature inside the vessel to become non-uniform and reducing the accuracy of temperature control. In addition, ester bonds in the polymer and unreacted monomers are likely to be hydrolyzed to newly generate alcohol, which tends to require a long time to remove volatile organic compounds from the emulsion. If the temperature inside the vessel is less than 50°C, the rate of removal of volatile organic compounds will be slow, resulting in reduced productivity. The temperature inside the vessel is preferably 50 to 85°C, more preferably 50 to 80°C.

[0028] In this step, the emulsion temperature and the pressure inside the treatment vessel are controlled so that the pressure inside the treatment vessel (more specifically, the gas phase inside the treatment vessel) is saturated water vapor pressure, i.e., the water inside the treatment vessel is boiling, at the above emulsion temperature. Specifically, during deodorization, the pressure in the gas phase inside the treatment vessel is set to a range of 12 KPa (90 mmHg) to 57 KPa (430 mmHg). The pressure inside the vessel is preferably 12 KPa (90 mmHg) to 40 KPa (300 mmHg), more preferably 12 KPa (90 mmHg) to 30 KPa (225 mmHg), since this allows the emulsion temperature during deodorization to be set at a lower temperature and the occurrence of polymer particle agglomerates can be suppressed to a low level.

[0029] <Step B: Discharge of volatile organic compounds and water vapor> In step B, after and / or simultaneously with the supply of pressurized steam into the processing vessel in step A, the gas in the processing vessel is exhausted to the outside of the system. This reduces the pressure in the system and maintains it within a predetermined pressure range. Specifically, after and / or simultaneously with the supply of pressurized steam into the processing vessel, the volatile organic compounds decomposed by the supply of pressurized steam and an amount of water vapor equal to the amount of water vapor supplied into the processing vessel are exhausted to the outside of the system. While the exhaust method is not particularly limited, it is preferable to provide an exhaust pump in the processing vessel and perform the exhaust using the exhaust pump. It is more preferable to reduce the pressure by exhausting the gas from the top of the processing vessel through exhaust pipe 16 using the exhaust pump. Alternatively, a condenser may be provided midway between the processing vessel and the exhaust pump, and the gas may be condensed and removed using the condenser.

[0030] In this production method, in step A, pressurized steam is supplied to the emulsion in a processing vessel, and in step B, volatile organic compounds and an amount of steam equal to the amount of steam supplied into the processing vessel are discharged out of the system. The amount of pressurized steam supplied into the processing vessel is preferably 5 to 100 parts by mass, more preferably 5 to 90 parts by mass, and even more preferably 15 to 70 parts by mass per 100 parts by mass of emulsion. By setting the amount of pressurized steam within the above range, it is possible to suppress the thermal history of the emulsion and prevent destabilization of the emulsion. It is also possible to sufficiently increase the efficiency of removing volatile organic compounds.

[0031] In the case of a batch process, the time for deodorizing the emulsion in step A and step B varies depending on the amount of pressurized steam supplied and other conditions, but from the viewpoint of productivity, it is preferably 10 hours or less, and from the viewpoints of productivity and low odor, it is more preferably 1 to 8 hours, and even more preferably 2 to 6 hours.

[0032] <Step C: Withdrawal and Supply of Emulsion> In step C, the emulsion from which the volatile organic compounds have been removed by steps A and B is continuously withdrawn from the treatment vessel into another vessel (e.g., a tank) at the same time, or before or after the withdrawal, undeodorized emulsion is supplied at a rate equal to the rate at which the deodorized emulsion is continuously withdrawn from the treatment vessel, thereby maintaining a constant amount of emulsion in the treatment vessel in a steady state.

[0033] In the case of a continuous process, the average residence time of the emulsion in the treatment vessel can be appropriately selected by selecting the feed rate relative to the internal volume of the treatment vessel. The residence time of the emulsion is preferably 10 hours or less, and from the viewpoints of productivity and low odor, 1 to 8 hours is more preferable, and 2 to 6 hours is even more preferable. A sufficiently long residence time (for example, 1 hour or more) is preferable because it allows for sufficient removal of volatile organic compounds.

[0034] In order to sufficiently remove volatile organic compounds from the emulsion, it is preferable to maintain the temperature of the emulsion in the treatment vessel within a predetermined temperature range. Therefore, if the temperature of the emulsion in the treatment vessel decreases when the emulsion that has not been deodorized is supplied to the treatment vessel, it is preferable to preheat the emulsion that has not been deodorized. Examples of this heat treatment method include batch treatment using a heat treatment vessel and continuous treatment by line heating using a heat exchanger.

[0035] Before and / or during the deodorization treatment, the emulsion may be neutralized to an appropriate pH range, as necessary. A suitable pH range is 5 to 10, more preferably 6 to 10, even more preferably 6.5 to 9.5, and even more preferably 7 to 9. A pH of 10 or less can suppress the hydrolysis of ester bonds in the polymer and unreacted monomers to produce new alcohols, thereby shortening the time required to remove volatile organic compounds from the emulsion. On the other hand, a pH of 5 or more can suppress the formation of aggregates of polymer particles, improving productivity. Furthermore, the emulsion's stability over time can be ensured, and the emulsion's quality can be maintained at a high level.

[0036] Examples of basic compounds used for neutralization include ammonia, alkylamines such as trimethylamine, triethylamine, and butylamine, etheramines such as 2-dimethylaminoethanol, diethylaminoethanol, diethanolamine, triethanolamine, triisopropanolamine, 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, and morpholine, and metal hydroxides such as potassium hydroxide and sodium hydroxide. Methods for adjusting the pH of the emulsion (specifically, adding a basic compound) include adding the compound before deodorizing treatment, adding the compound in portions during deodorizing treatment, and adding the compound continuously during deodorizing treatment.

[0037] <Pressurized steam supply> Next, an embodiment of supplying pressurized steam into the processing vessel will be described with reference to FIGS.

[0038] Supply pipe 15 has a supply passage as a passage through which pressurized steam flows, and is connected to processing vessel 10 so that the supply passage communicates with the interior of processing vessel 10 (i.e., storage section 11) (see FIGS. 1 and 2). Supply pipe 15 may be any pipe capable of supplying pressurized steam into processing vessel 10, and its shape, material, etc. are not particularly limited. Supply pipe 15 is, for example, a pipe made of resin or metal.

[0039] A supply port 14 is provided at the tip of supply pipe 15 for supplying pressurized steam into processing vessel 10 from a supply passage within supply pipe 15. The shape and number of supply ports 14 are not particularly limited. Examples of the shape of supply port 14 include a rectangular shape, a circular shape, an elliptical shape, and a star shape. In one embodiment of supply port 14, as shown in FIG. 3, an opening portion of a pipe serving as supply pipe 15 constitutes supply port 14. In this case, supply port 14 has a diameter corresponding to the diameter of the pipe.

[0040] Another embodiment of supply port 14 is a configuration in which a porous member having a large number of holes (for example, a wire mesh or a flat plate with a large number of through holes in the thickness direction) is arranged in the supply passage, thereby providing a large number of supply ports 14 in the supply passage, as shown in FIG. 4. In this case, each hole in the wire mesh or the flat plate corresponds to one supply port 14. FIG. 4 shows a case in which wire mesh 18 is arranged as a large number of members at the opening of supply pipe 15. The end of supply pipe 15 on the side where supply port 14 is provided may be expanded or contracted in diameter toward supply port 14.

[0041] The position where the supply port 14 is disposed in the processing vessel 10 is not particularly limited, and the supply port 14 may be disposed in at least one of the side wall, ceiling, and bottom of the processing vessel 10. From the viewpoint of directly supplying pressurized steam to the emulsion in the processing vessel 10 and thereby efficiently bringing the volatile organic compounds in the emulsion into contact with the pressurized steam, the supply port 14 is preferably disposed at least in the bottom of the processing vessel 10.

[0042] When the agitator 12 is provided inside the processing vessel 10, the supply port 14 is preferably located near the agitator blade 13. In particular, a configuration in which the agitator 12 is provided so that the agitator blade 13 is located at the bottom of the processing vessel 10, and the supply port 14 is provided at the bottom of the processing vessel near the agitator blade 13, and pressurized steam is directly supplied from the bottom of the processing vessel 10 into the emulsion, is preferred because it allows efficient contact between the volatile organic compounds in the emulsion and the pressurized steam. From the above perspective, the position of the supply port 14 relative to the agitator blade 13 is preferably 0.5 × d1 [m] or less, more preferably 0.4 × d1 [m] or less, and even more preferably 0.3 × d1 [m] or less from the surface (outer edge) of the agitator blade 13, where d1 [m] is the blade diameter of the agitator blade 13. Furthermore, the supply port 14 is preferably located at a height equivalent to or lower than the upper end of the agitator blade 13, and more preferably lower than the upper end of the agitator blade 13.

[0043] If supply pipe 15 is made of metal, the surface temperature of supply pipe 15 is likely to become high, which may cause the emulsion to dry out instantly and form a coating. Therefore, if necessary, the metal portion of supply pipe 15 may be covered with a resin or the like to prevent the heat of supply pipe 15 from directly contacting the emulsion. Examples of resins include fluororesins such as polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer, and ethylene / tetrafluoroethylene copolymer.

[0044] The size of the bubbles of pressurized steam relative to the scale in the treatment vessel 10 can be adjusted by adjusting the ratio between the diameter of the supply port 14 and the inner diameter (tank diameter) of the treatment vessel 10. Here, the inner diameter of the treatment vessel 10 refers to the maximum inner diameter of the storage section 11 into which the undeodorized emulsion is placed.

[0045] The ratio of the diameter of the supply port 14 to the inner diameter of the processing vessel 10 is determined as follows. The diameter of the supply port 14 is D1 [m], the inner diameter of the processing vessel 10 is D2 [m] (see FIGS. 1 to 4), and the ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the processing vessel 10 is defined as "D2 / D1." When the supply port 14 and the processing vessel 10 have a circular cross section, the diameter of the supply port 14 is the diameter D1, and the diameter of the inside of the processing vessel 10 (i.e., the vessel diameter) is the inner diameter D2. On the other hand, when the supply port 14 and the processing vessel 10 do not have a circular cross section, the equivalent diameter is used as the diameter and / or inner diameter. The equivalent diameter is calculated by dividing the opening area of ​​the supply port 14 and the cross-sectional area of ​​the opening of the processing vessel 10 by S [m 2 ] and the circumferential length is L [m], and the value is calculated by the following formula (3). Equivalent diameter [m]=(4×S) / L…(3)

[0046] In this production method, the ratio (D2 / D1) of the diameter D1 of the supply port 14 to the inner diameter D2 of the treatment vessel 10 is set to 30 to 3000. This allows the emulsion to have improved stability over time through deodorization using pressurized steam. If the ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the treatment vessel 10 is less than 30, a large amount of polymer particle aggregates is generated, which is likely to result in reduced productivity and reduced quality. Furthermore, the stability over time of the emulsion after deodorization is reduced, and the emulsion quality is likely to deteriorate. On the other hand, if the ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the treatment vessel 10 exceeds 3000, the bubbles of the pressurized steam become too fine, causing foaming on the liquid surface, which tends to make the deodorization difficult. From this perspective, the ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the treatment vessel 10 is preferably 200 to 3000, more preferably 350 to 3000.

[0047] The configuration for achieving the ratio D2 / D1 within the above range is not particularly limited. For example, a pipe having a diameter D1 such that the ratio D2 / D1 satisfies the above range may be used as the supply pipe 15, and the pipe may be connected to the processing vessel 10 as is without attaching anything to the opening of the pipe (see FIG. 3). In this configuration, for example, the diameter of the opening at the tip of the pipe may be narrowed toward the downstream side, thereby setting the diameter of the supply port 14 to D1. Alternatively, a wire mesh 18 having a mesh size D1 such that the ratio D2 / D1 satisfies the above range may be disposed at the tip of the supply pipe 15, and the supply pipe 15 with the wire mesh 18 attached may be connected to the processing vessel 10 (see FIG. 4). Among these, a configuration in which multiple supply ports 14 are provided in the supply passage and pressurized steam is supplied from the supply passage into the processing vessel 10 through the multiple supply ports 14 is preferred because it is easy to design the ratio D2 / D1 to satisfy the above range and because it allows a sufficient amount of pressurized steam to be efficiently supplied to the emulsion in a short time.

[0048] According to the production method described above, by selecting various conditions, a low-odor aqueous polymer emulsion having a volatile organic compound concentration of preferably 300 ppm or less can be produced by deodorizing for a short period of time, such as 1 to 10 hours. In the emulsion after deodorizing using this production method, the concentration of volatile organic compounds is preferably 100 ppm or less, more preferably 50 ppm or less, even more preferably 35 ppm or less, and preferably closer to 0 ppm. The concentration of volatile organic compounds in the emulsion is a value measured by gas chromatography according to the method described in the Examples.

[0049] In particular, in aqueous polymer emulsions containing (meth)acrylic acid ester monomer units as constituent monomers, it may be preferable to reduce the odor of alcohol produced by hydrolysis of the ester bonds in the polymer or unreacted monomers rather than the odor of the unreacted monomers themselves. To suppress such alcohol-derived odor, the concentration of alcohol in the emulsion is preferably 100 ppm or less, more preferably 30 ppm or less, and preferably as close to 0 ppm as possible.

[0050] According to the present disclosure, a low-odor aqueous polymer emulsion with low amounts of volatile organic compounds and aggregates and excellent stability over time can be obtained by a simple operation using a general-purpose apparatus capable of reducing pressure. Such an emulsion can be used in a wide range of applications that require strict environmental, safety, and quality requirements, such as rubber-like elastomer materials, paints, coating agents, adhesives, pressure-sensitive adhesives, binders, thickeners, cosmetic compositions, and pharmaceutical compositions. [Example]

[0051] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0052] 1. Synthesis of aqueous polymer emulsion <Production Example 1> <Emulsion polymerization> In a flask equipped with a stirrer, a thermometer, a condenser, a nitrogen inlet tube, and two dropping funnels, 45 parts of water and 2 parts of a surfactant (manufactured by Kao Corporation, trade name: Neopelex G-15, sodium dodecylbenzenesulfonate, hereinafter also referred to as "G-15") were charged, and the temperature was raised to 80°C. A monomer pre-emulsion was prepared by mixing 35 parts of methyl methacrylate (MMA), 40 parts of n-butyl acrylate (BA), 17 parts of 2-ethylhexyl acrylate (HA), 5 parts of styrene (St), 3 parts of methacrylic acid (MAA), 10 parts of G-15, and 45 parts of water. The resulting monomer pre-emulsion and 20 parts of a 5% aqueous ammonium persulfate solution as a polymerization initiator were each added dropwise to a flask over a period of 4 hours using separate dropping funnels. Emulsion polymerization was carried out while maintaining the liquid temperature at approximately 80°C. After the addition was completed, the liquid temperature was maintained at 80°C for an additional 2 hours while the mixture was aged. During the aging period, 5 parts of a 5% aqueous ammonium persulfate solution were added. The mixture was then cooled to 50°C to terminate the polymerization. To the resulting emulsion, 0.1 parts of a defoamer (manufactured by San Nopco Ltd., product name: SN Deformer PC) was added to obtain an aqueous polymer emulsion (A) with a solid content of 45.0% and a pH of 2.1. The amounts of main volatile organic compounds contained in the resulting aqueous polymer emulsion (A) were measured by gas chromatography, and the results were as follows: MMA: 211 ppm, BA: 277 ppm, HA: 104 ppm, St: 82 ppm, methanol: 5 ppm, n-butanol: 264 ppm, 2-ethylhexanol: 70 ppm

[0053] 2. Deodorization treatment Example 1 A water vapor supply pipe and an exhaust pipe were attached to a cylindrical flask (inner diameter: 120 mm) containing the aqueous polymer emulsion (A) obtained in Production Example 1 above. The supply pipe was a pipe with a pipe diameter of 1 mm, and a 100-mesh wire mesh (opening size: 0.154 mm) was attached to the end of the pipe. The end of the pipe with the wire mesh attached was inserted into the bottom of the flask. The water vapor supply port was located near the stirring impeller (below the stirring impeller with a blade diameter of 90 mm, at a position where the distance D3 from the bottom end of the stirring impeller was 20 mm, and where the stirring impeller and the pressurized water vapor supply port (hereinafter also referred to as the "water vapor supply port") of the water vapor supply pipe overlapped when viewed from above and below the stirring impeller) (see Figure 1). A three-blade swept-back impeller was used for the stirring impeller. Note that supply port 14 in Figure 1 corresponds to the water vapor supply port. The diameter of the water vapor supply port corresponds to the mesh size of the wire mesh and is 0.154 mm. After raising the liquid temperature to 55°C, the pH was adjusted to 8.0 with 25% aqueous ammonia while stirring. Pressurized steam at 0.2 MPa was then blown into the liquid through the steam supply tube at a rate of 0.1 part / min per 100 parts of aqueous polymer emulsion (A). The steam in the system was then evacuated through the exhaust tube using an exhaust pump, reducing the pressure in the flask to 15 KPa and maintaining the system in a boiling water state. During the deodorization treatment, 25% aqueous ammonia was added as needed to maintain the pH in the range of 7 to 9. Pressurized steam was blown in over a 5-hour period, supplying a total of 30 parts of steam.

[0054] <Example 2> Deodorization treatment was carried out in the same manner as in Example 1, except that the steam supply pipe was changed to a pipe with a diameter of 1 mm and a 300-mesh wire mesh attached to the tip (diameter of steam supply port: 0.05 mm). Example 3 Deodorization treatment was carried out in the same manner as in Example 1, except that the steam supply pipe was changed to a pipe with a diameter of 1 mm and a 50-mesh wire net attached to the tip (diameter of steam supply port: 0.3 mm). Example 4 Deodorization treatment was carried out in the same manner as in Example 1, except that the steam supply pipe was changed to a pipe with a diameter of 1 mm and a 30-mesh wire net attached to the tip (diameter of steam supply port: 0.5 mm). <Example 5> Deodorization treatment was carried out in the same manner as in Example 1, except that the steam supply pipe was changed to a pipe with a diameter of 4 mm (diameter of steam supply port: 4 mm, no wire mesh attached).

[0055] Example 6 The deodorizing treatment was carried out in the same manner as in Example 1, except that the treatment time was changed from 5 hours to 3 hours. <Examples 7 to 10> The deodorization treatment was carried out in the same manner as in Example 1, except that the supply amount of pressurized steam was changed as shown in Tables 1 and 2. <Examples 11, 12, 14 and 15> The deodorizing treatment was carried out in the same manner as in Example 1, except that the pH during the deodorizing treatment was changed as shown in Table 2. Example 13 The deodorization treatment was carried out in the same manner as in Example 1, except that the pH was not adjusted before the deodorization treatment and 25% aqueous ammonia was not added during the deodorization treatment.

[0056] Example 16 A heat treatment vessel (internal volume: 5 L) equipped with a stirrer, a thermometer, and a condenser was charged with 3,000 g of the aqueous polymer emulsion (A) obtained in Production Example 1 above, and the liquid temperature was raised to 55°C while stirring with three swept-back impellers, after which the pH was adjusted to 8 with 25% aqueous ammonia. Meanwhile, the aqueous polymer emulsion (A) was continuously fed from the heat treatment vessel at a feed rate of 3.3 g / min to a cylindrical deodorization treatment vessel (inner diameter: 200 mm) equipped with a stirrer, a thermometer, a condenser, a water vapor supply pipe, and an exhaust pipe. The steam supply pipe was a pipe with a diameter of 1 mm, and a 100-mesh wire mesh (opening size: 0.154 mm) was attached to the end of the pipe. The end of the pipe with the wire mesh attached was inserted into the deodorization container from the top of the container, and a steam supply port was placed near the agitator impeller (to the side of the agitator impeller with a blade diameter of 90 mm, at a distance D4 of 10 mm from the outer edge of the agitator impeller, and below the top surface of the agitator impeller) (see Figure 2). Note that supply port 14 in Figure 2 corresponds to the steam supply port. The diameter of the steam supply port corresponds to the opening size of the wire mesh, which is 0.154 mm. When the liquid volume in the deodorization vessel reached 100 g (0.5 hours after the start of supply), stirring was initiated. When the liquid volume in the deodorization vessel reached 500 g (2.5 hours after the start of supply), pressurized steam at 0.2 MPa was blown into the liquid through the steam supply pipe at a supply rate of 0.1 part / min per 100 parts of aqueous polymer emulsion (A). The steam in the system was evacuated through the exhaust pipe using an exhaust pump, reducing the pressure in the flask to 15 KPa and maintaining the system in a boiling water state. When the liquid volume in the deodorization vessel reached 1,000 g (5 hours after the start of supply), an amount of liquid (emulsion) equal to the amount of aqueous polymer emulsion (A) supplied was withdrawn from the system, and deodorization was continued. During the deodorization, 25% aqueous ammonia was added as needed to maintain the pH in the range of 7 to 9.

[0057] <Examples 17 to 24> The deodorization treatment was carried out in the same manner as in Example 1, except that the pressure inside the container, the temperature inside the container, and the position of the steam supply port during the deodorization treatment were changed as shown in Table 3.

[0058] Example 25 A water vapor supply pipe and an exhaust pipe were attached to a reaction vessel (inner diameter: 1200 mm) containing the aqueous polymer emulsion (A) from Production Example 1, and the liquid temperature was raised to 55°C. The water vapor supply pipe was a pipe with a diameter of 50 mm, and a flat plate with 30 1 mm holes was attached to the end of the pipe. The end of the pipe with the plate attached was inserted into the deodorization vessel from the bottom. The water vapor supply port was located near the stirring impeller (below the stirring impeller with a blade diameter of 680 mm, at a position where the distance D3 from the bottom of the stirring impeller was 150 mm, and where the stirring impeller and the water vapor supply port overlap when viewed from above and below the stirring impeller) (see Figure 1). A three-blade swept-back impeller was used for the stirring impeller. The diameter of the water vapor supply port, which corresponds to the diameter of the holes in the flat plate, was 1 mm. Next, the pH was adjusted to 8 with 25% aqueous ammonia, and then pressurized steam at a pressure of 0.2 MPa was blown into the liquid at a rate of 0.1 part / min per 100 parts of aqueous polymer emulsion (A). The steam in the system was evacuated with an exhaust pump, reducing the pressure in the treatment vessel to 15 KPa and maintaining the system in a boiling water state. During the deodorization treatment, 25% aqueous ammonia was added as needed to maintain the pH in the range of 7 to 9. Pressurized steam was blown in over a period of 5 hours, resulting in a total of 30 parts of steam.

[0059] <Comparative Example 1> The deodorization treatment was carried out in the same manner as in Example 1, except that the pressure inside the container during the deodorization treatment was changed to 20 KPa (a state where water does not boil). <Comparative Example 2> The deodorization treatment was carried out in the same manner as in Example 1, except that pressurized steam was not supplied during the deodorization treatment. <Comparative Example 3> The deodorization treatment was carried out in the same manner as in Example 1, except that the pressure and temperature inside the container during the deodorization treatment were changed as shown in Table 4. However, there was a lot of foaming and it was difficult to control the vacuum, so the treatment was stopped after 1 hour.

[0060] <Comparative Example 4> The deodorization treatment was carried out in the same manner as in Example 1, except that the pressure and temperature inside the container during the deodorization treatment were changed as shown in Table 4. <Comparative Example 5> Deodorization treatment was carried out in the same manner as in Example 1, except that the steam supply pipe was changed to a pipe with a diameter of 10 mm (diameter of steam supply port: 10 mm, no wire mesh attached). <Comparative Example 6> Deodorization treatment was carried out in the same manner as in Example 1, except that the steam supply pipe was changed to a pipe with a diameter of 1 mm and a 400-mesh wire net attached to the tip (diameter of steam supply port: 0.034 mm).

[0061] 3. Evaluation The aqueous polymer emulsions after deodorization treatment obtained in Examples 1 to 25 and Comparative Examples 1 to 6 and the conditions during the deodorization treatment were measured and evaluated as follows. <Liquid level in the treatment container during deodorization treatment> The state of the liquid surface during the deodorizing treatment was visually evaluated. (Evaluation criteria) ○: Little foaming on the liquid surface and no floating aggregates (good) △: There is a lot of foaming on the liquid surface, but no floating aggregates (fair) ×: Vacuum control impossible due to severe foaming on the liquid surface, or aggregates floating on the liquid surface (bad)

[0062] <Amount of aggregates> 500 g of the aqueous polymer emulsion after deodorization was sampled and filtered through a 100-mesh (mesh size: 0.154 mm) wire mesh whose weight had been measured in advance [weight of 100-mesh wire mesh = N (g)]. The residue on the wire mesh was washed with distilled water and left to stand for one day in a hot air circulation dryer at 50°C. After leaving it to stand for one day at 23°C and 50% RH, the mass [M (g)] of the 100-mesh wire mesh was measured. The amount of aggregates in the aqueous polymer emulsion (A) after deodorization was calculated using the following formula (4): Amount of aggregates (ppm) = [(MN) / 500] x 10 6 …(4)

[0063] <Contamination on the treatment vessel wall> After the deodorizing treatment, the aqueous polymer emulsion was removed from the treatment container, and the container was washed with distilled water, after which the degree of contamination on the wall surface of the treatment container was visually observed and evaluated. (Evaluation criteria) ◎: Aggregates adhere to less than 10% of the total surface area of ​​the emulsion immersed part (very good) ○: Aggregates adhere to 10% or more but less than 50% of the total surface area of ​​the emulsion immersed part (good) △: Aggregates adhere to 50% to less than 70% of the total surface area of ​​the emulsion immersed part (OK) ×: Aggregates adhered to 70% or more of the surface area of ​​the part immersed in the emulsion (bad)

[0064] <Stability over time> Distilled water was added to the deodorized aqueous polymer emulsion to adjust the solids concentration to 20%. 50 g of this aqueous polymer emulsion (solids concentration: 20%) was placed in a 100 mL glass container, sealed, and left to stand in a hot air circulating dryer at 50°C for 7 days, and then left to stand at 23°C and 50% RH for 1 day, after which the appearance was visually inspected. (Evaluation criteria) ◎: No change (very good) ○: There is slight change such as aggregation and sedimentation, but this is resolved by shaking (good) △: Slight changes such as aggregation and sedimentation occur, and are not resolved even after shaking (fair) ×: Coagulation and sedimentation occurred (bad)

[0065] <Odor of treatment liquid> 80 g of the deodorized aqueous polymer emulsion was placed in a 100 mL glass container, sealed with a lid, and left to stand in a hot air circulation dryer at 40°C for 1 hour. Immediately after removing the lid, the container was removed and the odor was evaluated by a sensory test. (Evaluation criteria) ◎: Almost no odor (very good) ○: Slight odor is detected (good) △: Odor is noticeable (fair) ×: Strong odor (bad)

[0066] <Volatile organic compound concentration> The content of volatile organic compounds (unreacted monomer and alcohol) was measured by gas chromatography (Shimadzu Corporation GC-2014, column: GL Sciences Inc. DB-1, carrier gas: nitrogen, detector: hydrogen flame ionization detector) to determine the respective concentrations of unreacted monomer and alcohol. For the gas chromatography measurement, 0.5 g of emulsion, 4.0 g of ethanol, and 0.3 g of 20% calcium chloride aqueous solution were mixed and left to stand for 10 minutes, then centrifuged at 12,000 rpm for 10 minutes. 1.5 g of the supernatant was collected, and 0.05 g of a 1% aqueous solution of ethylene glycol monomethyl acetate was added to this as an internal standard. This solution was used as the gas chromatography injection solution.

[0067] The aqueous polymer emulsions of Examples 1 to 25 and Comparative Examples 1 to 6 were evaluated for the liquid level in the treatment container during deodorization, the amount of aggregates, the degree of contamination on the wall surface of the treatment container, the stability over time, the odor due to volatile organic compounds, and the concentration of volatile organic compounds. The results are shown in Tables 1 to 4.

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3]

[0071] [Table 4]

[0072] As is clear from the results in Tables 1 to 4, Examples 1 to 25, which were subjected to deodorization treatment using this production method, demonstrated that low-odor aqueous polymer emulsions in which the volatile organic compounds in the aqueous polymer emulsions were reduced to trace amounts could be easily obtained using a general-purpose apparatus capable of reducing pressure, at a relatively low temperature, and in a short period of time. It was also revealed that the aqueous polymer emulsions obtained by this production method also have excellent stability over time, and are less likely to deteriorate in quality even after long-term storage. Furthermore, Examples 1 to 25 showed little staining on the interior walls of the container during and after the deodorization treatment, indicating excellent temperature controllability and productivity within the treatment container.

[0073] On the other hand, in Comparative Examples 1 and 2, the reduction of volatile organic compounds in the emulsion was insufficient. In Comparative Example 3, the pressure inside the vessel was low at 10 KPa, which resulted in a lot of foaming when blowing in pressurized steam, making it difficult to control the vacuum. In Comparative Example 4, the temperature inside the vessel was high at 95°C, which resulted in a lot of agglomerates due to emulsion skinning. In addition, the emulsion was subjected to excessive thermal history, which reduced its stability over time. In Comparative Example 5, a lot of polymer particle agglomerates occurred. In Comparative Example 6, the ratio D2 / D1 was large, and the pressurized steam bubbles became too fine, causing foaming from the liquid surface and staining the wall of the treatment vessel.

[0074] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. 1. A method for producing a low odor emulsion, comprising: a step of charging an aqueous polymer emulsion into a treatment vessel capable of reducing pressure, adjusting the temperature of the aqueous polymer emulsion to a range of 50°C to 90°C, adjusting the pressure inside the treatment vessel to a range of 12 KPa to 57 KPa, and maintaining the inside of the treatment vessel in a state where water boils, and supplying pressurized steam into the treatment vessel through a supply passage; and a step of discharging the water vapor in the gas phase portion in the treatment vessel and the volatile organic compounds volatilized from the aqueous polymer emulsion to the outside of the system, a ratio of a diameter of a supply port for supplying the pressurized steam from the supply passage into the processing vessel to an inner diameter of the processing vessel is 30 to 3000, where 1 is the diameter of the supply port and 1 is the inner diameter of the processing vessel.

2. 2. The method according to claim 1, wherein the ratio of the amount of the aqueous polymer emulsion to the total amount of pressurized steam supplied into the treatment vessel is 5 to 100 parts by mass of the pressurized steam per 100 parts by mass of the aqueous polymer emulsion.

3. 3. The method of claim 1 or 2, wherein the concentration of the volatile organic compounds in the low odor emulsion is 300 ppm or less.

4. The method according to any one of claims 1 to 3, wherein the pressurized steam is supplied while maintaining the pH of the aqueous polymer emulsion in the range of 5 to 10.

5. The method according to any one of claims 1 to 4, wherein a ratio of the diameter of the supply port to the inner diameter of the processing vessel is 350 to 3000.

6. A stirrer is provided inside the processing vessel, The method according to any one of claims 1 to 5, wherein the supply port is arranged near an agitation blade in the agitator.

7. The method according to any one of claims 1 to 6, wherein the concentration of the volatile organic compounds in the low odor emulsion is 100 ppm or less.

8. The method according to any one of claims 1 to 7, wherein the alcohol concentration in the low odor emulsion is 100 ppm or less.

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