Process for the production of low-odor emulsions

Abstract

In a method for producing a low-odor emulsion, the following steps are included: a step of feeding an aqueous polymer emulsion into a treatment vessel capable of being depressurized, bringing the temperature of the aqueous polymer emulsion to a range of 50°C to 90°C, bringing the pressure in the treatment vessel to a range of 12 KPa to 57 KPa, and maintaining the treatment vessel in a state of water boiling, and feeding pressurized water vapor into the treatment vessel through a supply passage; and a step of discharging water vapor in the gas phase portion of the treatment vessel and volatile organic compounds volatilized from the aqueous polymer emulsion to the outside of the system, the ratio of the diameter of a supply port for feeding pressurized water vapor into the treatment vessel from the supply passage to the inner diameter of the treatment vessel being: relative to the diameter of the supply port 1, the inner diameter of the treatment vessel is set to 30 to 3000.

Description

[0001] Cross-referencing

[0002] 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

[0003] This invention relates to a method for manufacturing low-odor emulsions, and more specifically, to a technique for efficiently removing volatile organic compounds from aqueous polymer emulsions obtained by emulsion polymerization or the like. Background Technology

[0004] Aqueous polymer emulsions obtained by emulsion polymerization of monomers such as styrene, vinyl acetate, acrylonitrile, butadiene, and (meth)acrylate alkyl esters in an aqueous medium are widely used as raw materials for rubber-like elastomers, coatings, coating agents, adhesives, binders, thickeners, cosmetic compositions, pharmaceutical compositions, etc.

[0005] Aqueous polymer emulsions (hereinafter also referred to as "emulsions") typically contain trace amounts of unreacted monomers and volatile organic compounds, primarily composed of decomposition products generated during polymerization. Such volatile organic compounds can produce unpleasant odors or affect the operability of the operator.

[0006] Methods for removing volatile organic compounds from emulsions include blowing pressurized steam into the emulsion to expel the volatile organic compounds along with the steam (e.g., see Patent Document 1). Other methods proposed include adding a redox initiator after polymerization to induce further polymerization (e.g., see Patent Document 2), supplying pressurized steam from below while feeding the emulsion from the top of a multi-layer stripping tower (e.g., see Patent Document 3), and blowing air or inert gases into a heated emulsion (e.g., see Patent Document 4).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2002-60415

[0010] Patent Document 2: Japanese Patent Application Publication No. 2002-212207

[0011] Patent Document 3: Japanese Patent Application Publication No. 58-213003

[0012] Patent Document 4: Japanese Patent Application Publication No. 53-41387 Summary of the Invention

[0013] The technical problem that the invention aims to solve

[0014] In the methods of Patent Documents 1-4, the application of high temperature and prolonged thermal treatment to the emulsion raises concerns about the potential formation of polymer particle agglomerates. Furthermore, the resulting polymer particle agglomerates adhere extensively to the walls of the processing container, the shaft of the agitator, etc., sometimes reducing the effectiveness of temperature control within the processing container. These agglomerates, in addition to adhering to the walls of the processing container, sometimes exist in the emulsion in a tiny form. Removing these agglomerates from the emulsion requires significant labor and time, raising concerns about reduced productivity in industrial-scale production. Moreover, the emulsion's stability decreases over time, and sediment sometimes forms at the bottom of the container during long-term storage, raising concerns about insufficient quality.

[0015] The present invention was made in view of the above-mentioned problems, and its main objective is to provide a method for manufacturing a low-odor emulsion, wherein the low-odor emulsion can suppress the amount of coagulants generated during deodorization treatment to a low level and has good stability over time, and the volatile organic compounds in the emulsion are sufficiently reduced.

[0016] Means for solving technical problems

[0017] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that by setting the ratio of the diameter of the supply port for supplying pressurized steam into the processing container to the inner diameter of the processing container 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 time.

[0018] That is, the first embodiment of the present invention relates to a method for manufacturing a low-odor emulsion, comprising the following steps: adding an aqueous polymer emulsion to a depressurized treatment container, setting the temperature of the aqueous polymer emulsion to a range of 50°C to 90°C, setting the pressure inside the treatment container to a range of 12 kPa to 57 kPa, and maintaining the treatment container in a boiling state, and supplying pressurized steam to the treatment container through a supply passage; and discharging the steam in the gas phase of the treatment container and the volatile organic compounds volatilized from the aqueous polymer emulsion to the outside of the system, wherein the ratio of the diameter of the supply port for supplying the pressurized steam to the treatment container through the supply passage to the inner diameter of the treatment container is: relative to the diameter of the supply port 1, the inner diameter of the treatment container is 30 to 3000.

[0019] The effects of the invention

[0020] According to the present invention, a universal apparatus capable of depressurization can be used to manufacture an aqueous polymer emulsion with significantly reduced volatile organic compounds in a short processing time (e.g., within 10 hours). Therefore, the aqueous polymer emulsion obtained by the method of the present invention has low odor and low coagulant content, thus exhibiting excellent environmental and safety characteristics. Furthermore, the amount of coagulant formation can be suppressed to a low level during deodorization treatment, resulting in excellent quality, productivity, and manufacturing cost. In addition, the aqueous polymer emulsion manufactured by the method of the present invention exhibits excellent long-term stability, thus minimizing adverse effects even after long-term storage and ensuring safe use. Attached Figure Description

[0021] Figure 1 This is a longitudinal cross-sectional view showing the simplified structure of an intermittent deodorization treatment device.

[0022] Figure 2 This is a simplified longitudinal cross-sectional view showing the structure of a continuous deodorization treatment device.

[0023] Figure 3 This is a cross-sectional view of the end of the supply pipe on the supply port side.

[0024] Figure 4 This is a cross-sectional view of the end of the supply pipe on the supply port side. Detailed Implementation

[0025] The present invention will now be described in detail. It should be noted that, in this specification, "(meth)acrylic acid" refers to acrylic acid or methacrylic acid. "Aqueous polymer emulsion" refers to an emulsion formed by dispersing a polymer in a water-based solvent. "Water-based solvent" refers to a liquid containing 70% by mass or more, preferably 80% by mass or more, of water relative to the total solvent volume.

[0026] Method for manufacturing low-odor emulsions

[0027] The method for manufacturing the low-odor emulsion of the present invention (hereinafter also referred to as "the manufacturing method") is a method for manufacturing 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 manufacturing method includes the following steps A and B.

[0028] Process A: The process of adding emulsion into a deodorizing treatment container that can reduce pressure, and supplying pressurized water vapor to the emulsion under reduced pressure.

[0029] Step B: The process of removing water vapor and volatile organic compounds volatilized from the emulsion from the gas phase of the deodorization treatment container to the outside of the system.

[0030] In this manufacturing method, there is no particular limitation on the timing of step B, as long as it allows for the removal of water vapor from the gas phase of the deodorization treatment container and volatile organic compounds volatilized from the emulsion outside the system. That is, this manufacturing method can be performed after step A, or it can be performed simultaneously with step A.

[0031] This manufacturing method can be applied to both batch and continuous processes. When applied to a batch process, a low-odor emulsion can be manufactured by including steps A and B as described above. Furthermore, when applied to a continuous process, it is preferable to manufacture a low-odor emulsion by including step C in addition to steps A and B as described above.

[0032] Step C: The process of extracting the emulsion from the deodorization treatment container after the removal of volatile organic compounds in Step B above, and supplying the undeodorized emulsion to the deodorization treatment container at a rate equal to the rate at which the emulsion is extracted from the deodorization treatment container.

[0033] The manufacturing method is described below.

[0034] <Aqueous polymer emulsion>

[0035] The emulsion for removing volatile organic compounds is preferably an emulsion containing polymer particles manufactured by emulsion polymerization in an aqueous medium. Vinyl monomers are preferably used as monomers constituting the polymer particles. Examples of such vinyl monomers include (meth)acrylate compounds, aromatic vinyl compounds, unsaturated carboxylic acids, unsaturated anhydrides, hydroxyl-containing vinyl compounds, amino-containing vinyl compounds, amide-containing vinyl compounds, alkoxy-containing vinyl compounds, nitrile-containing vinyl compounds, vinyl ether compounds, sulfonic acid-containing vinyl compounds, and polyoxyalkylene-containing vinyl compounds. One of these vinyl monomers can be used alone, or two or more can be used in combination.

[0036] Emulsion polymerization for obtaining the emulsion can be carried out according to conventionally known methods. Emulsion polymerization is preferably carried out in the presence of at least one of a surfactant and a protective colloid. Among the surfactants, anionic, cationic, and nonionic species are mentioned, with anionic and / or nonionic species being more preferred. Emulsion polymerization preferably uses a free radical polymerization initiator. Known oil-soluble polymerization initiators and water-soluble polymerization initiators can be used as free radical polymerization initiators. Water-soluble polymerization initiators are preferred.

[0037] In emulsions produced by emulsion polymerization in an aqueous medium, the post-polymerization aqueous medium typically contains approximately 1000–3000 ppm of volatile organic compounds (VOCs). Examples of VOCs include unreacted monomers, alcohols generated from the hydrolysis of unreacted monomers, alcohols generated from the hydrolysis of ester bonds in copolymers, monomers, and impurities contained in the emulsifier. To suppress odors from such VOCs, steps A and B are performed in this manufacturing method to remove VOCs from the emulsion.

[0038] <Process A: Supply of pressurized steam>

[0039] In process A, the emulsion to be deodorized is placed into a deodorization treatment container capable of depressurization, and pressurized steam is supplied to the emulsion in the deodorization treatment container under reduced pressure. This causes the volatile organic compounds contained in the emulsion to evaporate and move from the liquid phase to the gas phase. The deodorization treatment container (hereinafter, also simply referred to as the "treatment container") is a treatment tank that internally holds the emulsion to be deodorized, and it has a storage section for holding 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. A supply pipe (hereinafter, also referred to as a "steam supply pipe" or simply a "supply pipe") is provided in the treatment container to supply pressurized steam into the treatment container.

[0040] The processing container may also be equipped with a heating unit for heating the emulsion inside the container, a stirrer for agitating the emulsion inside the container, a thermometer (e.g., a thermocouple) for measuring the temperature inside the container (i.e., the emulsion temperature), a pressure gauge for measuring the pressure of the gas phase inside the container, and an exhaust pump for venting the gas phase inside the container. 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 the deodorization treatment. Therefore, as the stirrer, it is preferable to use a stirrer with stirring blades suitable for stirring, such as three swept blades, paddle blades, propeller blades, anchor blades, or large blades. Examples of large blades include Fullzone (manufactured by Kobe Steel Solution), MaxBlend (manufactured by Sumitomo Heavy Industries), and BENDLEAF stirring blades (manufactured by Yako Sangyo). In addition, there is no particular limitation on the size of the stirring blades. From the viewpoint of ensuring sufficient stirring, it is preferable to set the blade diameter of the stirring blades to be 0.3 or more, more preferably 0.4 or more, relative to the inner diameter 1 of the processing container.

[0041] A simplified diagram of the processing container is shown below. Figure 1 and Figure 2 . Figure 1 It is intermittent. Figure 2 It is a continuous expression. For example... Figure 1 and Figure 2 As shown, the processing container 10 is a bottomed container with a storage section 11 inside. Undeodorized emulsion Em is stored in the lower part of the storage section 11 within the processing container 10, and deodorization treatment of the emulsion Em is performed with a gas phase section Gs formed in the upper part of the storage section 11. A stirrer 12 is installed in the storage section 11. The stirrer 12 is arranged inside the storage section 11 with stirring blades 13 located at the lower end of a stirring shaft, positioned at the bottom of the storage section 11. Figure 1 and Figure 2 In the processing container 10 shown, a mixer 12 with three swept blades is provided as the stirring blade 13.

[0042] The processing container 10 is provided with a supply pipe 15 that supplies pressurized steam from the supply port 14 into the receiving section 11. Figure 1 In the processing container 10, the supply pipe 15 is inserted from the bottom of the processing container 10 into the receiving section 11. Figure 2 In the processing container 10, the supply pipe 15 is inserted into the receiving section 11 from the top of the processing container 10. An exhaust pipe 16 is provided at the top of the processing container 10 to discharge the gas from the gas phase section Gs at the top of the receiving section 11 to the outside of the system. In the continuous processing container 10, an extraction hole 17 is also provided at the bottom of the processing container 10 to extract the deodorized emulsion from the receiving section 11.

[0043] It should be noted that while the use of a mixer can improve the contact efficiency between the emulsion and pressurized steam within the treatment container, thus enhancing the removal of volatile organic compounds, excessive stirring can easily lead to foaming. Therefore, an appropriate amount of defoamer can be used to suppress foam. Furthermore, during deodorization treatment, the emulsion can be further extracted from the liquid phase section (i.e., the lower part of the treatment container) to the outside of the system as needed, and then circulated using a circulation pump for flash evaporation spraying from the gas phase section (i.e., the upper part of the treatment container).

[0044] By supplying pressurized steam to the emulsion stored in the processing container, the volatile organic compounds contained in the emulsion are separated from the liquid phase and contained in the gas phase. The pressurized steam supplied to the processing container is preferably steam with a gauge pressure of about 0.05 to 0.50 MPa (temperature 110 to 160°C), 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.

[0045] When supplying pressurized steam to the processing container, the pressurized steam can be directly supplied to the emulsion within the container. Alternatively, pressurized steam can be indirectly supplied to the emulsion within the processing container by supplying pressurized steam to the gas phase section. Preferably, pressurized steam is directly supplied to the emulsion stored in the processing container; more preferably, it is supplied directly from the bottom of the processing container; and even more preferably, it is supplied directly from the bottom of the processing container near the stirring blades. By directly supplying pressurized steam to the emulsion, the thermal process of the emulsion can be further reduced, polymer particle damage can be suppressed, and volatile organic compounds in the emulsion can be efficiently removed.

[0046] In step A, to fully remove volatile organic compounds from the emulsion, the temperature of the emulsion in the treatment container is maintained within a specified temperature range. There are no particular limitations on the method for maintaining the temperature of the emulsion in the treatment container within the specified range; however, from the viewpoint of simple and highly accurate temperature control, heating the emulsion, which is the target of deodorization treatment, is preferred. This heating treatment can be performed using a heating jacket, a heat exchanger installed outside the treatment container, or the like. Alternatively, if necessary, the emulsion can be preheated by using batch processing in a heated treatment container or continuous processing based on pipeline heating using a heat exchanger, and then the emulsion can be supplied to the treatment container.

[0047] During the supply of pressurized steam to the processing container, the temperature of the emulsion inside the container is adjusted to be within a range of 50–90°C. If the emulsion temperature exceeds 90°C, a large amount of polymer film is easily formed on the inner wall of the container, especially at the gas-liquid interface, resulting in uneven temperature distribution and reduced temperature control precision. Furthermore, the ester bonds of polymers and unreacted monomers are easily hydrolyzed to form new alcohols, leading to a prolonged removal time for volatile organic compounds (VOCs) present in the emulsion. If the container temperature is below 50°C, the removal rate of VOCs slows down, reducing productivity. The preferred container temperature is 50–85°C, more preferably 50–80°C.

[0048] In this process, the emulsion temperature and the pressure inside the treatment container are controlled such that the vapor phase inside the treatment container (more specifically, the vapor phase inside the treatment container) reaches saturated water vapor pressure at the aforementioned emulsion temperature, i.e., the water inside the treatment container reaches a boiling state. Specifically, in the deodorization treatment, the pressure of the vapor phase inside the treatment container is set to a range of 12 kPa (90 mmHg) to 57 kPa (430 mmHg). From the viewpoint that a lower emulsion temperature can be set during the deodorization treatment, and the formation of polymer particle aggregates can be suppressed to a lower degree, the pressure inside the container is preferably 12 kPa (90 mmHg) to 40 kPa (300 mmHg), and more preferably 12 kPa (90 mmHg) to 30 kPa (225 mmHg).

[0049] <Process B: System-wide discharge of volatile organic compounds and water vapor>

[0050] In step B, after pressurized steam is supplied to the processing container in step A, and / or simultaneously with the supply of pressurized steam, the gas inside the processing container is discharged outside the system. This depressurizes the system and maintains it within a specified pressure range. Specifically, after supplying pressurized steam to the processing container, and / or simultaneously with the supply, volatile organic compounds decomposed by the pressurized steam and an amount of steam equal to the amount supplied to the processing container are discharged outside the system. The method of exhaust treatment is not particularly limited; preferably, an exhaust pump is installed in the processing container, and the exhaust is performed using the exhaust pump. More preferably, the exhaust is performed from the top of the processing container through exhaust pipe 16, and the gas is depressurized by the exhaust pump. Alternatively, a condenser can be installed between the processing container and the exhaust pump, and the gas is removed by condensation.

[0051] In this manufacturing method, in step A, pressurized steam is supplied to the emulsion in the processing container, and in step B, volatile organic compounds and an amount of steam equal to the amount of steam supplied to the processing container are discharged from the system. The amount of pressurized steam supplied to the processing container is preferably 5 to 100 parts by mass relative to 100 parts by mass of the emulsion, more preferably 5 to 90 parts by mass, and even more preferably 15 to 70 parts by mass. By maintaining the amount of pressurized steam within the above range, the thermal process applied to the emulsion can be suppressed, and the instability of the emulsion can be prevented. Furthermore, the removal efficiency of volatile organic compounds can be significantly improved.

[0052] In the case of intermittent operation, the deodorization treatment time of the emulsion based on process A and process B varies depending on the supply of pressurized steam and other conditions. From the viewpoint of productivity, it is preferably less than 10 hours, more preferably 1 to 8 hours, and even more preferably 2 to 6 hours.

[0053] <Process C: Emulsion Extraction and Supply>

[0054] In step C, while the emulsion from which volatile organic compounds have been removed through steps A and B is continuously drawn from the treatment container to another tank (e.g., a vessel), or before or after drawing it out, the undeodorized emulsion is supplied at a rate equal to the rate at which the deodorized emulsion is continuously drawn out of the treatment container. Thus, a certain amount of emulsion exists in a stable state in the treatment container.

[0055] In a continuous process, by selecting the supply rate relative to the internal volume of the processing container, the average residence time of the emulsion in the processing container can be appropriately selected. The residence time of the emulsion is preferably 10 hours or less, more preferably 1 to 8 hours from the viewpoint of productivity and low odor, and even more preferably 2 to 6 hours. If the residence time is long enough (e.g., more than 1 hour), volatile organic compounds can be sufficiently removed, and therefore this is preferred.

[0056] To ensure thorough removal of volatile organic compounds from the emulsion, it is preferable to maintain the temperature of the emulsion within the treatment container within a specified temperature range. Therefore, when the temperature of the emulsion within the treatment container is lowered by supplying the undeodorized emulsion to the treatment container, it is preferable to preheat the undeodorized emulsion. Examples of such heating treatment methods include batch processing using a heated treatment container and continuous processing based on pipeline heating using a heat exchanger.

[0057] Before and / or during deodorization treatment, the emulsion can be neutralized to a suitable pH range as needed. A preferred pH range is 5–10, more preferably 6–10, further preferably 6.5–9.5, and even more preferably 7–9. If the pH is below 10, the formation of new alcohols due to the hydrolysis of ester bonds in the polymer and unreacted monomers can be suppressed, thus shortening the time required to remove volatile organic compounds from the emulsion. On the other hand, if the pH is above 5, the formation of polymer particle aggregates can be suppressed, resulting in good productivity. Furthermore, the long-term stability of the emulsion can be ensured, and the quality of the emulsion can be well maintained.

[0058] Examples of alkaline compounds used for neutralization include alkylamines such as ammonia, trimethylamine, triethylamine, and butylamine; ether amines 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 emulsions (specifically, the addition of alkaline compounds) include adding them before deodorization treatment, adding them in batches during deodorization treatment, and adding them continuously during deodorization treatment.

[0059] <Supply of pressurized steam>

[0060] Next, use Figures 1-4 The method of supplying pressurized steam into the treatment container is explained.

[0061] The supply pipe 15 has a supply passage for pressurized steam flow, and is connected to the processing container 10 in a manner that communicates with the interior of the processing container 10 (i.e., the receiving part 11) (see reference). Figure 1 , Figure 2 The supply pipe 15 is only required to supply pressurized steam into the processing container 10, and its shape and material are not particularly limited. The supply pipe 15 may be, for example, a resin or metal pipe.

[0062] A supply port 14 is provided at the front end of the supply pipe 15 for supplying pressurized steam from the supply passage within the supply pipe 15 into the processing container 10. The shape and number of the supply ports 14 are not particularly limited. Examples of the shape of the supply ports 14 include rectangular, circular, elliptical, and star-shaped ports. Figure 3 As shown, one way the supply port 14 is formed is by the opening portion of the piping of the supply pipe 15. In this case, the supply port 14 has a diameter corresponding to the diameter of the piping.

[0063] In addition, as another way of supplying port 14, such as Figure 4 As shown, an example structure can be described as follows: a porous component with multiple holes (e.g., a metal mesh, a plate with multiple through holes in the thickness direction, etc.) is arranged in a supply passage, thereby providing multiple supply ports 14 in the supply passage. In this case, each hole of the metal mesh and the aforementioned plate corresponds to one supply port 14. Figure 4 The diagram shows a case where a metal mesh 18 is arranged as one of several components at the opening of the supply pipe 15. In the supply pipe 15, the end on the side where the supply port 14 is provided can be either enlarged or reduced in diameter toward the supply port 14.

[0064] The location of the supply port 14 in the processing container 10 is not particularly limited, as long as it is located on at least one of the side wall, top, or bottom of the processing container 10. From the viewpoint of directly supplying pressurized steam to the emulsion in the processing container 10, thereby efficiently contacting the volatile organic compounds in the emulsion with the pressurized steam, the supply port 14 is preferably located at least at the bottom of the processing container 10.

[0065] When a stirrer 12 is installed inside the processing container 10, it is preferable to arrange the supply port 14 near the stirring blade 13. In particular, it is preferable to arrange the stirrer 12 with the stirring blade 13 at the bottom of the processing container 10 and to arrange the supply port 14 at the bottom of the processing container and near the stirring blade 13, so that pressurized steam can be directly supplied to the emulsion from the bottom of the processing container 10, which can efficiently facilitate contact between the volatile organic compounds in the emulsion and the pressurized steam. From the above point of view, the position of the supply port 14 relative to the stirring blade 13, when the blade diameter of the stirring blade 13 is set to d1 [m], is preferably 0.5 × d1 [m] or less from the surface (outer edge) of the stirring blade 13, more preferably 0.4 × d1 [m] or less, and even more preferably 0.3 × d1 [m] or less. In addition, the supply port 14 is preferably arranged at the same height as the upper end of the stirring blade 13 or at a position lower than the upper end of the stirring blade 13, more preferably at a position lower than the upper end of the stirring blade 13.

[0066] It should be noted that when the supply tube 15 is made of metal, its surface temperature tends to rise rapidly, causing the emulsion to dry instantly and sometimes forming a film. Therefore, if necessary, the metal portion of the supply tube 15 can be coated with a resin or similar material to prevent the heat from the supply tube 15 from directly contacting the emulsion. Examples of resins include polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymers, and ethylene / tetrafluoroethylene copolymers, among other fluororesins.

[0067] The size of the pressurized steam bubbles relative to the scale in the treatment container 10 can be adjusted by varying the ratio of the diameter of the supply port 14 to the inner diameter (groove diameter) of the treatment container 10. Here, the inner diameter of the treatment container 10 refers to the maximum inner diameter of the receiving section 11 containing the undeodorized emulsion.

[0068] The ratio of the diameter of the supply port 14 to the inner diameter of the processing container 10 is determined as follows. The diameter of the supply port 14 is set as D1 [m], and the inner diameter of the processing container 10 is set as D2 [m] (refer to...). Figures 1-4The ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the processing container 10 is defined as "D2 / D1". When both the supply port 14 and the processing container 10 have circular cross-sections, the diameter of the supply port 14 is the diameter D1, and the inner diameter (i.e., the groove diameter) of the processing container 10 is the inner diameter D2. On the other hand, when the cross-sections of the supply port 14 and the processing container 10 are not circular, an equivalent diameter is used as the diameter and / or inner diameter. The equivalent diameter is defined as S[m], where the opening area of ​​the supply port 14 and the cross-sectional area of ​​the opening of the processing container 10 are set to S[m]. 2 Let the perimeter be L[m], and calculate the value using the following formula (3).

[0069] Equivalent diameter [m] = (4 × S) / L…(3)

[0070] In this manufacturing method, the ratio (D2 / D1) of the diameter D1 of the supply port 14 to the inner diameter D2 of the processing container 10 is set to 30 to 3000. This improves the long-term stability of the emulsion through deodorization treatment with pressurized steam. When the ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the processing container 10 is less than 30, a large amount of polymer particle agglomerates are generated, easily leading to reduced productivity and quality. Furthermore, the long-term stability of the emulsion after deodorization treatment decreases, and the quality of the emulsion is prone to decline. On the other hand, when the ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the processing container 10 exceeds 3000, the pressurized steam bubbles become too fine, causing foaming on the liquid surface, which tends to make deodorization treatment difficult. From this perspective, the ratio of the diameter D1 of the supply port 14 to the inner diameter D2 of the processing container 10 is preferably 200 to 3000, more preferably 350 to 3000.

[0071] There are no particular limitations on the configuration used to set the ratio D2 / D1 to the above range. For example, the configuration could be as follows: a pipe with a diameter of D1 that satisfies the above range of ratio D2 / D1 is used as the supply pipe 15, and the pipe is connected to the processing container 10 in its original state without installing any components at the opening of the pipe (see reference). Figure 3 In this configuration, for example, by reducing the diameter of the pipe end towards the downstream side, the diameter of the opening at the front end of the pipe is set to D1, thereby setting the diameter of the supply port 14 to D1. Alternatively, it can be configured such that a metal mesh 18 with a mesh size of D1 satisfying the aforementioned range as D2 / D1 is disposed at the front end of the supply pipe 15, and the supply pipe 15 with the metal mesh 18 installed is connected to the processing container 10 (see reference). Figure 4From the viewpoint that it is easy to design to meet the above range than D2 / D1 and that a sufficient amount of pressurized steam can be efficiently supplied to the emulsion in a short time, it is preferable to set up a configuration in which multiple supply ports 14 are provided in the supply passage, and pressurized steam is supplied from the supply passage to the processing container 10 through these multiple supply ports 14.

[0072] According to the manufacturing method described above, by selecting various conditions and performing a short-term deodorization treatment of approximately 1 to 10 hours, a low-odor aqueous polymer emulsion with a volatile organic compound concentration preferably below 300 ppm can be manufactured. In the emulsion after deodorization treatment using this manufacturing method, the volatile organic compound concentration is more preferably below 100 ppm, further preferably below 50 ppm, even more preferably below 35 ppm, and the closer to 0 ppm, the more preferred. It should be noted that the concentration of volatile organic compounds in the emulsion is a value obtained by gas chromatography according to the method described in the examples.

[0073] In particular, in aqueous polymer emulsions containing (meth)acrylate monomer units as constituent monomers, it is sometimes preferable to reduce the odor of alcohols generated by the hydrolysis of ester bonds in the polymer and unreacted monomers, compared to the odor of the unreacted monomers themselves. To suppress this odor from alcohols, the concentration of alcohols in the emulsion is preferably 100 ppm or less, more preferably 30 ppm or less, and closer to 0 ppm is more preferred.

[0074] According to the present invention, a low-odor aqueous polymer emulsion with low amounts of volatile organic compounds and coagulations and excellent long-term stability can be obtained using a universal device capable of decompression and with simple operation. The emulsion can be widely used in applications with stringent requirements regarding environmental, safety, and quality, such as rubber-like elastomer materials, coatings, coating agents, adhesives, binders, thickeners, cosmetic compositions, and pharmaceutical compositions.

[0075] Example

[0076] The present invention will be described in more detail below through embodiments, but the present invention is not limited to these embodiments. It should be noted that, unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0077] 1. Synthesis of aqueous polymer emulsions

[0078] <Manufacturing Example 1>

[0079] <Emulsion Polymerization>

[0080] Add 45 parts water and 2 parts surfactant (manufactured by Kao Corporation, trade name: NEOPELEX G-15, sodium dodecylbenzenesulfonate, hereinafter also referred to as "G-15") to a flask equipped with a stirrer, thermometer, cooler, nitrogen inlet tube and two dropping funnels, and heat to 80°C.

[0081] A monomer preemulsion 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 obtained monomer preemulsion and 20 parts of a 5% ammonium persulfate aqueous solution (as a polymerization initiator) were continuously added dropwise to a flask over 4 hours using a separate dropping funnel. Emulsion polymerization was carried out while maintaining the liquid temperature at approximately 80°C. After the addition was completed, the liquid temperature was further maintained at 80°C for 2 hours for aging. 5 parts of a 5% ammonium persulfate aqueous solution were added during aging. The mixture was then cooled to 50°C to terminate the polymerization. 0.1 parts of an antifoaming agent (manufactured by SAN NOPCO Co., Ltd., trade name: SN Defoamer PC) were added to the obtained emulsion to obtain an aqueous polymer emulsion (A) with a solid content of 45.0% and a pH of 2.1. The amount of major volatile organic compounds contained in the obtained aqueous polymer emulsion (A) was determined by gas chromatography, and the results are shown below.

[0082] MMA: 211ppm, BA: 277ppm, HA: 104ppm, St: 82ppm, Methanol: 5ppm, n-Butanol: 264ppm, 2-Ethylhexanol: 70ppm

[0083] 2. Deodorization treatment

[0084] <Example 1>

[0085] A steam supply pipe and an exhaust pipe are installed on a cylindrical flask (inner diameter: 120 mm) containing the aqueous polymer emulsion (A) obtained in Manufacturing Example 1 described above. The supply pipe is a 1 mm diameter pipe with a 100-mesh (0.154 mm mesh size) metal mesh installed at the front end. The end of the pipe with the metal mesh installed is inserted from the bottom of the flask. The steam supply port is positioned near the stirring blade (below the stirring blade with a blade diameter of 90 mm, at a distance D3 of 20 mm from the lower end of the stirring blade, and at a position where the stirring blade overlaps with the pressurized steam supply port of the steam supply pipe (hereinafter also referred to as the "steam supply port") when viewed from above and below the stirring blade). (Refer to...) Figure 1 The agitator uses three swept-back blades. It should be noted that... Figure 1The supply port 14 is equivalent to a steam supply port. The diameter of the steam supply port is equivalent to the mesh size of the metal mesh, which is 0.154 mm.

[0086] After heating the liquid to 55°C, the pH was adjusted to 8.0 using 25% ammonia solution with stirring. Pressurized steam at 0.1 parts / min (relative to 100 parts of the aqueous polymer emulsion (A)) was then introduced into the liquid through a steam supply pipe at a pressure of 0.2 MPa. Simultaneously, an exhaust pump was used to vent the steam from the system through an exhaust pipe, thereby reducing the pressure in the flask to 15 kPa and maintaining the system at a boiling state. For deodorization, 25% ammonia solution was added appropriately to maintain the pH in the range of 7–9. A total of 30 parts of steam were supplied through pressurized steam injection over 5 hours.

[0087] <Example 2>

[0088] The steam supply pipe was changed to a pipe with a diameter of 1 mm and a 300-mesh metal mesh installed at the front end (steam supply port diameter: 0.05 mm). Otherwise, the deodorization treatment was carried out in the same way as in Example 1.

[0089] <Example 3>

[0090] The steam supply pipe was changed to a pipe with a diameter of 1 mm and a 50-mesh metal mesh installed at the front end (steam supply port diameter: 0.3 mm). Otherwise, the deodorization treatment was carried out in the same way as in Example 1.

[0091] <Example 4>

[0092] The steam supply pipe was changed to a pipe with a 30-mesh metal mesh installed at the front end of a 1mm diameter pipe (steam supply port diameter: 0.5mm). Otherwise, deodorization was carried out in the same way as in Example 1.

[0093] <Example 5>

[0094] The steam supply pipe was changed to a pipe with a diameter of 4 mm (the diameter of the steam supply port is 4 mm, and no metal mesh is installed). Otherwise, the deodorization treatment was carried out in the same way as in Example 1.

[0095] <Example 6>

[0096] The processing time was changed from 5 hours to 3 hours, and the deodorization treatment was carried out in the same way as in Example 1.

[0097] <Examples 7-10>

[0098] As shown in Tables 1 and 2, the supply of pressurized steam was varied, and deodorization was performed using the same method as in Example 1.

[0099] <Examples 11, 12, 14 and 15>

[0100] The pH was changed during the deodorization treatment as shown in Table 2. Otherwise, the deodorization treatment was carried out in the same manner as in Example 1.

[0101] <Example 13>

[0102] The pH was not adjusted before the deodorization treatment, and no 25% ammonia was added during the deodorization treatment. Otherwise, the deodorization treatment was carried out in the same way as in Example 1.

[0103] <Example 16>

[0104] 3000g of the aqueous polymer emulsion (A) obtained in Manufacturing Example 1 was added to a heating treatment container (internal volume 5L) equipped with a stirrer, thermometer, and cooler. The liquid temperature was raised to 55°C using a three-bladed agitator, and the pH was adjusted to 8 using 25% ammonia. Meanwhile, the aqueous polymer emulsion (A) was continuously supplied from the heating treatment container at a rate of 3.3g / min to a cylindrical deodorization treatment container (inner diameter: 200mm) equipped with a stirrer, thermometer, cooler, steam supply pipe, and exhaust pipe. The steam supply pipe is a 1mm diameter pipe. With a 100-mesh (0.154mm mesh) metal mesh installed at the front end of the pipe, the end of the pipe with the metal mesh installed is inserted into the deodorization treatment container from the top. A steam supply port is positioned near the stirring blades (to the side of the 90mm diameter stirring blades, at a distance D4 of 10mm from the outer edge of the stirring blades, and the steam supply port is located below the upper surface of the stirring blades). (Refer to...) Figure 2 It should be noted that, Figure 2 The supply port 14 is equivalent to a steam supply port. The diameter of the steam supply port is equivalent to the mesh size of the metal mesh, which is 0.154 mm.

[0105] Stirring begins when the liquid volume in the deodorization treatment container reaches 100g (0.5 hours from the start of supply). When the liquid volume in the deodorization treatment container reaches 500g (2.5 hours from the start of supply), pressurized steam at 0.2MPa is blown into the liquid through the steam supply pipe at a rate of 0.1 parts / min relative to 100 parts of aqueous polymer emulsion (A), while the steam in the system is vented through the exhaust pipe using an exhaust pump, thereby reducing the pressure in the flask to 15KPa and maintaining the system at a boiling state. When the liquid volume in the deodorization treatment container reaches 1000g (5 hours from the start of supply), an equal volume of liquid (emulsion) to the supplied volume of aqueous polymer emulsion (A) is extracted from the system, and the deodorization treatment is continuously carried out. It should be noted that 25% ammonia is added appropriately during the deodorization treatment to maintain the pH in the range of 7-9.

[0106] <Examples 17-24>

[0107] As shown in Table 3, the container pressure, container temperature, and the location of the steam supply port were changed during the deodorization process, but the deodorization process was carried out in the same way as in Example 1.

[0108] <Example 25>

[0109] A steam supply pipe and an exhaust pipe were installed on a reactor (inner diameter: 1200 mm) containing the aqueous polymer emulsion (A) of Manufacturing Example 1 described above, and the liquid temperature was raised to 55°C. The steam supply pipe was a 50 mm diameter pipe, and a plate with 30 Φ1 mm holes was installed at the front end of the pipe. The end of the pipe with the plate installed was inserted into the deodorization treatment container from the bottom. A steam supply port was positioned near the stirring blade (below the stirring blade with a blade diameter of 680 mm, at a distance D3 of 150 mm from the lower end of the stirring blade, and at the position where the stirring blade overlaps with the steam supply port when viewed from above). Figure 1 The stirring blades consist of three swept-back blades. It should be noted that the diameter of the steam supply inlet is equivalent to the diameter of the hole in the flat plate, which is 1 mm.

[0110] Next, after adjusting the pH to 8 with 25% ammonia, pressurized steam at a pressure of 0.2 MPa was blown into the liquid at a rate of 0.1 parts / min relative to 100 parts of the aqueous polymer emulsion (A), while the steam was expelled from the system using an exhaust pump. This reduced the pressure inside the treatment container to 15 kPa, maintaining the system at a boiling state. During the deodorization process, 25% ammonia was added appropriately to maintain the pH in the range of 7–9. A total of 30 parts of steam were supplied through pressurized steam blowing over 5 hours.

[0111] <Comparative Example 1>

[0112] The pressure inside the container during deodorization was changed to 20 kPa (water not boiling), and the deodorization process was otherwise carried out using the same method as in Example 1.

[0113] <Comparative Example 2>

[0114] No pressurized steam is supplied during the deodorization process; otherwise, the deodorization process is carried out using the same method as in Example 1.

[0115] <Comparative Example 3>

[0116] As shown in Table 4, the container pressure and temperature during the deodorization process were changed, but the deodorization process was carried out using the same method as in Example 1. However, due to the large amount of foaming and the difficulty in controlling the vacuum, the process was stopped after 1 hour.

[0117] <Comparative Example 4>

[0118] As shown in Table 4, the container pressure and temperature during the deodorization process were changed, but the deodorization process was carried out in the same way as in Example 1.

[0119] <Comparative Example 5>

[0120] The steam supply pipe was changed to a pipe with a diameter of 10 mm (the diameter of the steam supply port is 10 mm, and no metal mesh is installed). Otherwise, the deodorization treatment was carried out in the same way as in Example 1.

[0121] <Comparative Example 6>

[0122] The steam supply pipe was changed to a pipe with a diameter of 1 mm and a 400-mesh metal mesh installed at the front end (steam supply port diameter: 0.034 mm). Otherwise, the deodorization treatment was carried out in the same way as in Example 1.

[0123] 3. Evaluation

[0124] The following measurements and evaluations were performed on the deodorized aqueous polymer emulsions obtained in Examples 1-25 and Comparative Examples 1-6, as well as the condition during the deodorization treatment.

[0125] <Liquid level in the treatment container during deodorization>

[0126] The condition of the liquid surface is evaluated visually during deodorization treatment.

[0127] (Evaluation Criteria)

[0128] ○: Minimal foaming on the liquid surface and no floating condensates (Good)

[0129] △: There are many bubbles on the liquid surface, but no condensation floating (qualified).

[0130] ×: The liquid surface foams violently, making vacuum control impossible, or there are condensates floating on the liquid surface (defective).

[0131] <Quantity of condensate>

[0132] 500g of the deodorized aqueous polymer emulsion was collected and filtered using a 100-mesh (mesh size: 0.154mm) metal mesh [weight of 100-mesh metal mesh = N(g)] whose weight had been measured beforehand. The residue on the metal mesh was washed with distilled water, and the emulsion was left to stand for 1 day in a hot air circulating dryer at 50℃. After standing for 1 day at 23℃ and 50%RH, the mass [M(g)] of the emulsion, along with the 100-mesh metal mesh, was measured. The amount of coagulants in the deodorized aqueous polymer emulsion (A) was calculated using the following formula (4).

[0133] Coagulant content (ppm) = [(MN) / 500] × 10 6 …(4)

[0134] <Contamination status of the container walls>

[0135] After the aqueous polymer emulsion is extracted from the deodorized treatment container, the contamination status of the container walls after rinsing with distilled water is visually observed and evaluated.

[0136] (Evaluation Criteria)

[0137] ◎: Adhesion of aggregates is present on surface portions that constitute less than 10% of the total surface area relative to the emulsion-impregnated area (very good).

[0138] ○: Aggregates adhere to a surface portion comprising 10% to less than 50% of the total surface area relative to the emulsion-impregnated area (good).

[0139] △: Aggregates adhere to a surface portion covering 50% to 70% of the total surface area relative to the emulsion impregnation area (acceptable).

[0140] ×: Adhesion of aggregates (defect) occurs on a surface portion covering more than 70% of the total surface area relative to the emulsion impregnation area.

[0141] <Stability over time>

[0142] Distilled water was added to the deodorized aqueous polymer emulsion to adjust the solids concentration to 20%. 50g of this aqueous polymer emulsion (solids concentration: 20%) was collected into a 100mL glass container, sealed, and left to stand in a hot air circulating dryer at 50℃ for 7 days. The appearance after standing at 23℃ and 50%RH for 1 day was visually confirmed.

[0143] (Evaluation Criteria)

[0144] ◎: No change (Excellent)

[0145] ○: Slight changes such as coagulation and settling occurred, but these were eliminated by shaking (good).

[0146] △: Slight changes such as coagulation and settling cannot be eliminated even by shaking (qualified).

[0147] ×: Coagulation and sedimentation are present (undesirable)

[0148] <Odor from the treatment fluid>

[0149] Collect 80g of the deodorized aqueous polymer emulsion in a 100mL glass container, cover and seal it, let it stand in a hot air circulating dryer at 40℃ for 1 hour, and then take it out immediately. The odor when the lid is removed is evaluated by sensory test.

[0150] (Evaluation Criteria)

[0151] ◎: Almost no odor (Excellent)

[0152] ○: Slightly noticeable odor (good)

[0153] △: Smells foul (Pass)

[0154] ×: Has a strong odor (unpleasant)

[0155] <Concentration of volatile organic compounds>

[0156] The content of volatile organic compounds (unreacted monomers and alcohols) was determined by gas chromatography (GC-2014 manufactured by Shimadzu Corporation, column: DB-1 manufactured by GL Sciences Corporation, carrier gas: nitrogen, detector: flame ionization detector). The concentrations of unreacted monomers and alcohols were then calculated. For the gas chromatography determination, 0.5 g of emulsion, 4.0 g of ethanol, and 0.3 g of 20% calcium chloride aqueous solution were mixed and allowed to stand for 10 minutes. The mixture was then centrifuged at 12000 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 (EDTA) was added to the supernatant as an internal standard. This solution was used as the injection solution for gas chromatography.

[0157] For the aqueous polymer emulsions of Examples 1-25 and Comparative Examples 1-6, the results of evaluating the liquid surface state, amount of condensate, wall fouling of the treatment container, stability over time, odor from volatile organic compounds, and concentration of volatile organic compounds during deodorization treatment are shown in Tables 1-4.

[0158] [Table 1]

[0159]

[0160] [Table 2]

[0161]

[0162] [Table 3]

[0163]

[0164] [Table 4]

[0165]

[0166] As shown in Tables 1-4, according to Examples 1-25, which underwent deodorization treatment using this manufacturing method, low-odor aqueous polymer emulsions with reduced volatile organic compounds to minute amounts can be easily obtained using a general-purpose device capable of reducing pressure, at a relatively low temperature, and for a short time. Furthermore, it was demonstrated that the aqueous polymer emulsions obtained by this manufacturing method exhibit excellent long-term stability, showing little deterioration even during long-term storage. In addition, in Examples 1-25, there was minimal contamination on the inner walls of the containers during and after the deodorization treatment, indicating excellent temperature control and productivity within the treatment containers.

[0167] On the other hand, the reduction of volatile organic compounds in the emulsions of Comparative Examples 1 and 2 was insufficient. In Comparative Example 3, due to the low pressure inside the container (as low as 10 kPa), excessive foaming occurred when pressurized steam was blown in, making vacuum control difficult. In Comparative Example 4, due to the high temperature of 95°C inside the container, a large amount of agglomerates were formed due to emulsion skinning. Furthermore, the excessive heat applied to the emulsion reduced its long-term stability. In Comparative Example 5, a large amount of polymer particle agglomerates were generated. In Comparative Example 6, the ratio D2 / D1 was large, causing the pressurized steam bubbles to become excessively fine and foam from the liquid surface, resulting in fouling of the processing container walls.

[0168] This invention has been described with reference to embodiments, but it should be understood that the invention is not limited to these embodiments. The invention also includes various modifications and equivalent variations. Furthermore, various combinations, methods, and other combinations or methods that include only one element, or more or less thereof, also fall within the scope and spirit of this invention.

Claims

1. A method for manufacturing a low-odor emulsion, characterized in that, The process includes the following steps: An aqueous polymer emulsion is introduced into a depressurized processing container, maintaining the temperature of the emulsion within the range of 50°C to 90°C and the pressure within the container within the range of 12 kPa to 57 kPa. The container is kept at a boiling water state, and pressurized steam is supplied to the container through a supply channel. The water vapor in the gas phase of the processing container and the volatile organic compounds volatilized from the aqueous polymer emulsion are discharged outside the system. The ratio of the diameter of the supply port for supplying pressurized steam from the supply passage to the inner diameter of the processing container is such that, relative to the diameter of the supply port (1), the inner diameter of the processing container is 30 to 3000. The processing container is equipped with a mixer. When the diameter of the mixing blade of the mixer is denoted as d1 [m], the position of the supply port from the surface of the mixing blade is 0.5 × d1 [m] or less.

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 to the processing container is: 5 to 100 parts by mass of pressurized steam relative to 100 parts by mass of the aqueous polymer emulsion.

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

4. The method according to claim 1 or 2, wherein, While maintaining the pH of the aqueous polymer emulsion in the range of 5 to 10, pressurized water vapor is supplied.

5. The method according to claim 1 or 2, wherein, The ratio of the diameter of the supply port to the inner diameter of the processing container is: relative to the diameter of the supply port, the inner diameter of the processing container is 350 to 3000.

6. The method according to claim 3, wherein, The concentration of the volatile organic compounds in the low-odor emulsion is below 100 ppm.

7. The method according to claim 1 or 2, wherein, The alcohol concentration in the low-odor emulsion is below 100 ppm.

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