Method for producing latex, film molded body using the latex obtained by the production method, impregnated molded body, and method for producing a base material for forming an adhesive layer

Abstract

The present invention provides a method for manufacturing latex, which can achieve a good emulsification state in the emulsification process of raw materials. As a result, high-quality latex with less coagulum can be manufactured. The method for manufacturing latex of the present invention includes: an emulsification process of emulsifying a rubber composition containing rubber, an organic solvent, water, and an emulsifier to obtain an emulsion; and a solvent removal process of removing the organic solvent from the emulsion. In the emulsification process, the rubber composition is stirred by a stirring device (3). The stirring device (3) has: a stirring tank (30) for storing the stirred material and a stirring unit (40) rotatably provided in the stirring tank (30). The stirring unit (40) has a structure including flat stirring blades (50). The flat stirring blades (50) have a stirring surface (52) substantially orthogonal to the rotation direction of the stirring unit (40).

Description

Technical Field

[0001] The present invention relates to a method for producing a latex of rubber, and further relates to a method for producing a film molded body, an impregnated molded body, and a base material for forming an adhesive layer using the latex obtained by the production method. Background Art

[0002] Hitherto, a latex composition containing a latex of natural rubber or synthetic rubber has been impregnated and molded to produce an impregnated molded body such as a nipple for a nursing bottle, a balloon, a glove, a bag, or an airbag of a medical catheter, which is used in contact with the human body. In particular, synthetic rubbers such as isoprene polymers are useful as raw materials for latexes for impregnated molded bodies that come into direct contact with biological mucous membranes, organs, etc., because they do not contain proteins that cause allergic symptoms in humans.

[0003] As a method for producing a latex of natural rubber or synthetic rubber, the following production method is known: a rubber solution in which rubber is dissolved or dispersed in an organic solvent and an aqueous solution of an emulsifier such as soapy water are supplied to an emulsifier at a prescribed ratio and mixed to be emulsified (emulsification step), and then the organic solvent in the obtained emulsion is removed (solvent removal step) (see, for example, Patent Document 1, etc.).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent No. 5260738. Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] When producing a latex, in the emulsification step, it is important to make the rubber as a solid component finer and obtain a good emulsified state in which the refined rubber is dispersed in a uniform state. By performing good emulsification, a high-quality latex with few coagulants can be obtained. However, when emulsifying raw materials with an existing emulsifier, sometimes the emulsification is insufficient and relatively large particles of rubber remain, and further, due to this large rubber, the amount of coagulants in the latex after the solvent removal step increases.

[0009] The present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a method for producing a latex, which can obtain a good emulsified state in the emulsification step of raw materials, and as a result, can produce a high-quality latex with few coagulants.

[0010] Means for Solving the Problems

[0011] The manufacturing method of the latex of the present invention is characterized by comprising: an emulsification step of emulsifying a rubber composition containing rubber, an organic solvent, water, and an emulsifier to obtain an emulsion; and a solvent removal step of removing the organic solvent from the emulsion. In the emulsification step, the rubber composition is stirred with a stirring device, the stirring device having a container for storing the stirred material and a stirring unit rotatably provided in the container, the stirring unit being structured to include flat stirring blades, the flat stirring blades having a stirring surface that is substantially orthogonal to the rotation direction of the stirring unit and faces the stirred material. Additionally, all "substantially orthogonal" as referred to in the present invention is defined as: the formed angle is generally 85° or more, preferably 89° or more, and generally 95° or less, preferably 91° or less.

[0012] In the present invention, in the emulsification step, the rubber composition stored in the container is stirred with the stirring blades for mixing, and the rubber composition is emulsified. By using the flat stirring blades of the stirring device of the present invention, a circulating flow that causes the stirred material to circulate in the container in the vertical direction can be generated. Therefore, by circulating the rubber, which is relatively light in specific gravity and floats near the liquid surface and is prone to stagnation, up and down, it can be effectively dispersed in the solution, and an emulsion with the rubber dispersed in a uniform state can be obtained. Thus, according to the present invention, the rubber composition can be emulsified in a good state in the emulsification step, and as a result, a high-quality latex with few coagulants can be manufactured.

[0013] Furthermore, the manufacturing method of the latex of the present invention is characterized by comprising: a primary emulsification step of obtaining an emulsion in a primary emulsified state by mixing a rubber solution obtained by mixing rubber and an organic solvent with an aqueous emulsifier solution; a circulating emulsification step of circulating the emulsion in a primary emulsified state obtained by the primary emulsification step through an emulsifier for further emulsification; and a solvent removal step of removing the organic solvent from the emulsion obtained after the circulating emulsification step. In at least any one of the primary emulsification step and the circulating emulsification step, the emulsion is stirred with a stirring device, the stirring device having a container for storing the stirred material and a stirring unit rotatably provided in the container, the stirring unit being structured to include flat stirring blades, the flat stirring blades having a stirring surface that is substantially orthogonal to the rotation direction of the stirring unit and faces the stirred material.

[0014] In the present invention, by stirring the emulsion using the stirring blades in at least one of the rough emulsification step and the circulation emulsification step, the emulsion can be circulated up and down in the container as described above to obtain an emulsion with rubber uniformly dispersed. Therefore, in the present invention, the emulsion can be mixed in a good state in at least one of the rough emulsification step and the circulation emulsification step. In the present invention, if the emulsion is stirred using the flat stirring blades of the present invention in both the rough emulsification step and the circulation emulsification step, the emulsion can be emulsified into a better state.

[0015] Furthermore, a preferred embodiment of the method for manufacturing the latex of the present invention is: in the above-mentioned solvent removal step, the emulsion is stirred using a stirring device, the stirring device having a container for storing the stirred material and a stirring unit rotatably provided in the container, the stirring unit being a structure including flat stirring blades, and the flat stirring blades having a stirring surface that is substantially orthogonal to the rotation direction of the stirring unit and faces the stirred material.

[0016] In this embodiment, by also stirring the emulsion using the flat stirring blades of the present invention in the solvent removal step, the rubber in the emulsion in the solvent removal is circulated up and down and stirred, so as to be fully mixed. Therefore, the latex obtained after solvent removal becomes a high-quality latex with few coagulants.

[0017] Furthermore, from the viewpoint of effectively obtaining the mixing effect of the present invention, the stirring blades used in the method for manufacturing the latex of the present invention are characterized in that the area of the stirring surface is 10 to 60% of the cross-sectional area of the stirred material stored in the container, and in this range, it is preferably 15 to 50%, more preferably 20 to 40%, and further preferably 25 to 35%.

[0018] Furthermore, the above-mentioned stirring blades of the present invention are characterized in that the stirring blades have a lattice part, and the lattice part has a lattice-like structure.

[0019] According to this structure, using the rotating lattice part, the rubber in the circulating solution is sheared and subdivided, and then the rubber is involved in the fine vortices generated behind the rotation direction of the lattice part and mixed. Therefore, the refinement and mixing of the rubber are promoted, and a good emulsified state can be easily obtained and the coagulants can be reduced.

[0020] Furthermore, in the present invention, in the above-mentioned rough emulsification step, the above-mentioned emulsifier can be used to continuously mix the above-mentioned rubber solution and the above-mentioned aqueous emulsifier solution.

[0021] Next, the manufacturing method of the film molded body of the present invention is characterized in that a crosslinking agent is added to the latex produced by the above-mentioned manufacturing method of the latex of the present invention to obtain a latex composition, and the film molded body is molded using this latex composition.

[0022] Furthermore, the manufacturing method of the dip molded body of the present invention is characterized in that a crosslinking agent is added to the latex produced by the above-mentioned manufacturing method of the latex of the present invention to obtain a latex composition, and the dip molded body is molded using this latex composition.

[0023] Moreover, the manufacturing method of the base material for forming the adhesive layer of the present invention is characterized in that a crosslinking agent is added to the latex produced by the above-mentioned manufacturing method of the latex of the present invention to obtain a latex composition, and this latex composition is formed on the surface of the base material as an adhesive layer.

[0024] Advantages of the Invention

[0025] According to the present invention, a manufacturing method of a latex can be provided, which can achieve a good emulsification state in the emulsification process of raw materials. As a result, a high-quality latex with few coagulants can be manufactured. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of a latex manufacturing apparatus for a manufacturing method of a latex according to an embodiment of the present invention that can be preferably implemented.

[0027] Figure 2 is in Figure 1 a schematic diagram of a latex manufacturing apparatus in which the piping structure of the stirring tank for the rubber solution and the aqueous emulsifier solution is changed in the shown latex manufacturing apparatus.

[0028] Figure 3 (a) of Figure 1 is a side sectional view of the tank body constituting the stirring tank shown in Figure 3 and (b) of

[0029] Figure 4 is a top view of the stirring blade and the rotating shaft of the same stirring tank.

[0030] Figure 5 is in Figure 4 a side sectional view of a stirring tank having a stirring blade according to another embodiment shown in

[0031] Figure 6 is a side sectional view of a stirring tank showing a stirring blade according to a comparative example other than the present invention.

[0032] Figure 7It is a side sectional view of a stirring tank showing a stirring blade of another comparative example other than the present invention. Detailed Description

[0033] Hereinafter, a method for manufacturing latex according to an embodiment of the present invention will be described with reference to the drawings.

[0034] (Embodiment)

[0035] Figure 1 A latex manufacturing apparatus capable of preferably implementing the method for manufacturing latex according to the embodiment is schematically shown. First, this manufacturing apparatus will be described.

[0036] Figure 1 The shown latex manufacturing apparatus includes: a rubber solution tank 1 that prepares a rubber solution; an emulsifier tank 2 that prepares an aqueous emulsifier solution; a stirring device 3 that stores the rubber solution and the aqueous emulsifier solution in a stirring tank 30 and stirs and mixes these rubber solution and aqueous emulsifier solution in the stirring tank 30; an emulsifier 4 that emulsifies the mixed solution of the rubber solution and the aqueous emulsifier solution; a vacuum pump 5 that is used to reduce the pressure in the stirring tank 30 and distill off the organic solvent from the emulsion; and a concentrator 6 that concentrates the organic solvent removed from the emulsion in the stirring tank 30.

[0037] The rubber solution in the rubber solution tank 1 and the aqueous emulsifier solution in the emulsifier tank 2 are directly supplied into the stirring tank 30 from supply pipes 11 and 12, respectively. The solution in the stirring tank 30 can be circulated through a circulation pipe 14 arranged from the bottom to the top of the stirring tank 30. The emulsifier 4 is arranged in the middle of the circulation pipe 14.

[0038] In addition, as Figure 2 shown, it can also be arranged such that the supply pipes 11 and 12 merge with a confluence pipe 13 connected to the stirring tank 30, and the rubber solution and the aqueous emulsifier solution are supplied into the stirring tank 30 from the confluence pipe 13 in a state where they are merged.

[0039] A distillation pipe 15 is arranged between the stirring tank 30 and the vacuum pump 5. Between the stirring tank 30 and the vacuum pump 5 of the distillation pipe 15, a valve 7 and a concentrator 6 are arranged in sequence from the stirring tank 30 side. Each of the tanks 1, 2, and 30 has a heating unit (not shown) that heats the solution stored inside.

[0040] As Figure 1 and Figure 3 shown in (a) of, the stirring device 3 includes a stirring tank 30 and a stirring unit 40. The stirring tank 30 constitutes the container of the present invention.

[0041] As Figure 1As shown, the stirring tank 30 has: a bottomed cylindrical tank body 31 that stores the above-mentioned mixed solution; and a lid 32 that is detachably fixed to the upper opening of the tank body 31 and closes the upper opening thereof. The tank body 31 is arranged such that its axis extends in a substantially vertical direction. The downstream end portions of the supply pipes 11, 12, the circulation pipe 14, and the distillation pipe 15 are connected to the lid 32. In addition, the upstream end portion of the circulation pipe 14 is connected to the bottom of the tank body 31, and the downstream end portion of the circulation pipe 14 is connected to the lid 32.

[0042] As Figure 3 As shown in (a) of the figure, the stirring unit 40 of the present embodiment has: a flat stirring blade 50 that is provided inside the tank body 31; and a rotating shaft 41 of the stirring blade 50. The rotating shaft 41 is coaxially arranged with the axis of the tank body 31 and is rotatably supported via a bearing (not shown). The rotating shaft 41 is rotationally driven by a drive source (both are omitted from the figure) that is connected to its upper end portion via a coupling. This drive source is arranged above the lid 32.

[0043] In addition, the drive source for rotationally driving the rotating shaft 41 may also be arranged below the tank body 31 and connected to the lower end portion of the rotating shaft 41.

[0044] The stirring blade 50 has a rectangular shape and is fixed to the rotating shaft 41 such that the rotating shaft 41 passes through the middle portion in its width direction. That is, the stirring blade 50 has a bilaterally symmetric shape with the rotating shaft 41 as the symmetry line, and has a blade portion 51a on one side of the rotating shaft 41 and a blade portion 51b on the other side. The stirring blade 50 rotates together with the rotating shaft 41, and the stirring blade 50 has a stirring surface 52, as Figure 3 shown in (b) of the figure, which is substantially orthogonal to the rotation direction indicated by the arrow and faces the solution (stirring material) such as the emulsion stored in the stirring tank 30.

[0045] The stirring blade 50 has a paddle portion 53 at its lower part, and a lattice portion 54 is integrally formed on the upper side of the paddle portion 53. The lattice portion 54 has a lattice-like structure. The paddle portion 53 and the lattice portion 54 have the above-mentioned stirring surface 52. In the present embodiment, with respect to the ratio of the height dimension occupied by the paddle portion 53 and the lattice portion 54 to the overall height of the stirring blade 50, the lattice portion 54 is about 6 to 7 tenths, which is larger than the paddle portion 53, but is not limited thereto. In Figure 3 (a) of the figure, the symbol L represents the liquid level of the solution such as the emulsion, and the stirring blade 50 is used in a state where it is entirely immersed in the solution.

[0046] The paddle part 53 has a shape such that its lower end edge generally follows the shape of the bottom surface inside the tank main body 31, and the interval between its lower end edge and the bottom surface inside the tank main body 31 is set as narrow as possible. For example, the interval is set to about 1 to 200 mm, preferably about 5 to 100 mm, and most preferably about 10 to 50 mm.

[0047] The lattice part 54 has a plurality of plate-shaped transverse members 54a and a plurality of plate-shaped longitudinal members 54b orthogonal to these transverse members 54a. The lattice part 54 of the present embodiment has 2 transverse members 54a and 4 longitudinal members 54b, but the number and width of each member 54a, 54b can be arbitrarily set in consideration of the stirring effect and the like.

[0048] The stirring blade 50 rotates together with the rotating shaft 41 to stir a solution such as an emulsion stored in the stirring tank 30. The above-mentioned stirring surface 52 is a surface that faces and contacts the solution to be stirred during the rotation of the stirring blade 50. Therefore, as Figure 3 shown in (b) of, the actual stirring surface 52 is composed of the surface (front surface) of one side of the blade part 51a on one side and the surface (back surface) of the other side of the blade part 51b on the other side. The total area of these stirring surfaces 52 is equivalent to the area of the stirring blade 50 itself.

[0049] Here, the stirring blade 50 of the present embodiment is configured such that its area (equivalent to the total area of the left and right stirring surfaces 52 shown in (b) of Figure 3 ) with respect to the cross-sectional area of the solution such as an emulsion stored in the stirring tank 30, the ratio (hereinafter sometimes referred to as the liquid contact area ratio) is 10 to 60%. This is a ratio that can effectively obtain a mixing effect. Within this range, it is preferably 15 to 50%, more preferably 20 to 40%, and further preferably 25 to 35%.

[0050] In addition, as Figure 3 shown in (a) of, on the inner wall surface of the tank main body 31, a plurality of shielding plates 90 extending in the axial direction of the stirring tank 30 are provided via upper and lower supports 91. These shielding plates 90 are arranged radially such that their width directions are substantially parallel to the radial direction of the tank main body 31. The area and number of the shielding plates 90 can be arbitrarily set in consideration of the stirring effect and the like.

[0051] In addition, of course, each shielding plate 90 ensures an interval from the stirring blade 50 in a manner that does not hinder the rotation of the stirring blade 50, and the interval can be set to about 1 to 200 mm, preferably about 5 to 100 mm, and most preferably about 10 to 50 mm in consideration of the stirring effect and the like.

[0052] According to the stirring unit 40 of the present embodiment, when the stirring blade 50 rotates in one direction, it can stir solutions such as emulsions stored in the stirring tank 30 in the following manner. That is, the solution in the stirring tank 30 generates a vertical circulation flow as follows: the solution in the stirring tank 30 is extruded to the radially outer side by the lower paddle part 53 and collides with the inner wall surface of the tank main body 31. Next, after rising due to the action of the baffle plate 90, it flows from the inner wall surface of the upper part of the tank main body 31 toward the central rotation shaft 41 direction. Next, it flows downward through the rotation shaft 41 and the lattice part 54 and returns to the paddle part 53.

[0053] In the solution that is stirred while circulating like this, using each horizontal member 54a and each vertical member 54b of the lattice part 54, the descending rubber is sheared and subdivided. Furthermore, the rubber is involved in the minute vortices generated behind the rotation direction of these members 54a and 54b and is mixed.

[0054] In addition, since the lower end part of the paddle part 53 is close to the bottom in the stirring tank 30, it can stir the solution without leaving it at the bottom following the circulation flow. In addition, the baffle plate 90 suppresses the solution extruded to the radially outer side by the paddle part 53 from rotating along with the rotation of the stirring blade 50, and plays a role in generating an upward flow. In addition, as described above, the horizontal member 54a and the vertical member 54b of the lattice part 54 play a role in subdividing and mixing the descending solution.

[0055] The emulsifier 4 only needs to be a device that can continuously mix by imparting strong shear force to the solution, and there is no particular limitation. Preferably, for example, a rotor-stator type emulsifier having a plurality of rotor-stator pairs is used, and the above-mentioned rotor-stator pair has a structure in which a rotor having a plurality of slits rotates relative to a stator having a plurality of slits. As such a rotor-stator type emulsifier, commercially available products such as the trade name "TK Pipeline Homomixer" (manufactured by PRIMIX Corporation), the trade name "THRASHER" (manufactured by Nippon Coke & Engineering Co., Ltd.), the trade name "Trigonal" (manufactured by Nippon Coke & Engineering Co., Ltd.), the trade name "Cavitron" (manufactured by Eurotec), the trade name "Milder" (manufactured by Pacific Machine Works Co., Ltd.), the trade name "Fine Flow Mill" (manufactured by Pacific Machine Works Co., Ltd.), etc. can be used.

[0056] In addition, as the emulsifier 4, an emulsifier having a pump function can pump and circulate the solution, so it is preferable. In the case of using an emulsifier without a pump function, a pressure pump can be additionally arranged in the middle of the circulation pipe 14.

[0057] Next, the method for manufacturing latex of the present embodiment will be described.

[0058] The method for manufacturing the latex of the present embodiment includes an emulsification step and a desolventization step. In the above emulsification step, a rubber composition containing rubber, an organic solvent, water, and an emulsifier is emulsified to obtain an emulsion. In the above desolventization step, the organic solvent is removed from the emulsion obtained in the emulsification step.

[0059] In the emulsification step, the rubber composition is emulsified by stirring the rubber composition with the stirring blades 50 in the stirring tank 30 of the above stirring device 3.

[0060] The method for manufacturing the latex of the present embodiment includes a case where the above emulsification step is divided into a primary emulsification step and a circulation emulsification step. In the above primary emulsification step, an emulsion in a primary emulsified state is obtained by mixing a rubber solution in which rubber and an organic solvent are mixed with an aqueous emulsifier solution. In the above circulation emulsification step, the emulsion in the primary emulsified state obtained in the primary emulsification step is circulated through the above emulsifier 4 for further emulsification. In this case, in at least any one of the primary emulsification step and the circulation emulsification step, the case of further stirring the emulsion with the above stirring device 3 is further included.

[0061] Hereinafter, Figure 1 a manufacturing method example of the latex of the present embodiment using the latex manufacturing apparatus shown will be described in more detail.

[0062] [Emulsification Step]

[0063] In the emulsification step, a rubber composition containing rubber, an organic solvent, water, and an emulsifier is emulsified. Here, these raw materials are divided into a mixture of rubber and an organic solvent (rubber solution), and a mixture of water and an emulsifier (aqueous emulsifier solution).

[0064] That is, a rubber solution is prepared by supplying rubber and an organic solvent in a predetermined ratio in the rubber solution tank 1, stirring, and heating to about 60°C, for example, to dissolve the rubber. In addition, after supplying an emulsifier and water in a predetermined ratio in the emulsifier tank 2 and mixing them, they are heated to about 60°C, for example, to prepare an aqueous emulsifier solution.

[0065] Next, the rubber solution is continuously and directly supplied from the rubber solution tank 1 and the aqueous emulsifier solution is continuously and directly supplied from the emulsifier tank 2 into the stirring tank 30 through the supply pipes 11 and 12, respectively. Then, in the stirring tank 30, the mixture of the rubber solution and the aqueous emulsifier solution (rubber composition) is stirred with the stirring blades 50 for mixing to obtain an emulsion.

[0066] From the viewpoint of good emulsification, the rubber solution prepared in the rubber solution tank 1 and the aqueous emulsifier solution prepared in the emulsifier tank 2 are preferably maintained at a specified temperature by heating the respective tanks 1 and 2 as required. The temperatures of the rubber solution and the aqueous emulsifier solution are not particularly limited, and are preferably 20 to 100°C, more preferably 40 to 90°C, and still more preferably 60 to 80°C, respectively.

[0067] In addition, when continuously supplying the rubber solution and the aqueous emulsifier solution into the stirring tank 30, the supply ratio of these rubber solution and aqueous emulsifier solution is not particularly limited. From the viewpoint of good emulsification, the volume ratio of rubber solution : aqueous emulsifier solution is preferably 1:2 to 1:0.3, more preferably 1:1.5 to 1:0.5, and still more preferably 1:1 to 1:0.7.

[0068] [Coarse emulsification process]

[0069] The emulsification process of the present embodiment includes a case where an emulsion is obtained after passing through a circulation emulsification process after the coarse emulsification process.

[0070] The state of coarse emulsification refers to an emulsification state in the previous stage where the solubility of rubber is relatively low and sufficient emulsification has not occurred. In the coarse emulsification process, in the same manner as in the above emulsification process, the rubber solution is continuously supplied from the rubber solution tank 1 and the aqueous emulsifier solution is continuously supplied from the emulsifier tank 2 into the stirring tank 30. In the stirring tank 30, the mixture (rubber composition) of these rubber solution and aqueous emulsifier solution is stirred by the stirring blade 50 for mixing.

[0071] [Circulation emulsification process]

[0072] Next, the emulsifier 4 is operated, and through this emulsifier 4, a circulation emulsification process in which the emulsion in the coarse emulsification state is returned from the stirring tank 30 into the stirring tank 30 through the circulation pipe 14 at least once is performed. In the circulation emulsification process, the emulsion is circulated by the emulsifier 4 in such a manner that it returns from the stirring tank 30 into the stirring tank 30 through the circulation pipe 14. Since the emulsifier 4 is used, the emulsion in the coarse emulsification state is continuously emulsified, and the emulsion is stored in the stirring tank 30. In addition, in the method for manufacturing latex in the present embodiment, it is preferable to include this circulation emulsification process, but it is not essential to include this circulation emulsification process.

[0073] In the case where an emulsion is obtained by performing the circulation emulsification process after the coarse emulsification process as described above, in addition to the case where the emulsion is stirred by the stirring blade 50 in the stirring tank 30 in any one of the coarse emulsification process and the circulation emulsification process, either one of the operation modes of stirring the emulsion only by the stirring blade 50 in the coarse emulsification process and stirring the emulsion only by the stirring blade 50 in the circulation emulsification process can be selected.

[0074] The operation mode of stirring the emulsion in the stirring tank 30 can be appropriately selected according to the state of emulsification and the like. From the viewpoint of performing emulsification well, it is sufficient to stir the emulsion in at least any one of the rough emulsification process and the circulation emulsification process. However, among these, it is more preferable to stir the emulsion in the circulation emulsification process. However, it is most preferable to stir the emulsion in any one of the rough emulsification process and the circulation emulsification process.

[0075] In addition, in the rough emulsification process, it is not necessary to stir the rubber composition, which is a mixture of the rubber solution and the aqueous emulsifier solution, in the stirring tank 30 using the stirring blade 50. For example, as Figure 2 shown, by causing the rubber solution and the aqueous emulsifier solution to merge in the merging pipe 13 and continuously mixing only with the emulsifier 8 disposed in this merging pipe 13, the rubber composition is roughly emulsified and supplied into the stirring tank 30.

[0076] Here, specific examples of the above-mentioned rubber, organic solvent, and emulsifier as raw materials will be described.

[0077] (Rubber)

[0078] Examples of the rubber that can be used in the present embodiment include natural rubber and synthetic rubber. There is no particular limitation on the synthetic rubber, and examples thereof include isoprene rubber (IR), styrene-isoprene-styrene block copolymer (SIS), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-butadiene rubber (SBR), isobutene-isoprene rubber (IIR), and the like. Among these, from the aspect of excellent mechanical properties such as tensile strength and elongation at break when the latex is made into an impregnated molded body, natural rubber, isoprene rubber (IR), and styrene-isoprene-styrene block copolymer (SIS) are preferable, isoprene rubber (IR) and styrene-isoprene-styrene block copolymer (SIS) are more preferable, and isoprene rubber (IR) is further preferable.

[0079] (Organic solvent)

[0080] There is no particular limitation on the organic solvent used to dissolve and disperse the rubber to form a rubber solution, and it can be appropriately selected from, for example, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, or alicyclic hydrocarbon solvents such as cyclopentane, cyclopentene, cyclohexane, and cyclohexene, or aliphatic hydrocarbon solvents such as butane, pentane, hexane, and heptane, or halogenated hydrocarbon solvents such as dichloromethane, chloroform, and dichloroethane.

[0081] There is no particular limitation on the content ratio of the rubber in the rubber solution, and it is preferably 3 to 30% by weight, more preferably 5 to 20% by weight, and further preferably 7 to 15% by weight.

[0082] (Emulsifier)

[0083] As the emulsifier, there is no particular limitation, and an anionic emulsifier can preferably be used. Examples of the anionic emulsifier include: fatty acid salts such as sodium laurate, potassium myristate, sodium palmitate, potassium oleate, sodium linolenate, sodium rosinate, and potassium rosinate; or alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, potassium dodecylbenzenesulfonate, sodium decylbenzenesulfonate, potassium decylbenzenesulfonate, sodium hexadecylbenzenesulfonate, and potassium hexadecylbenzenesulfonate; or alkylsulfosuccinates such as sodium bis(2-ethylhexyl)sulfosuccinate, potassium bis(2-ethylhexyl)sulfosuccinate, and sodium dioctylsulfosuccinate; or alkyl sulfates such as sodium lauryl sulfate and potassium lauryl sulfate; or polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate; or monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate, etc.

[0084] Among these anionic emulsifiers, fatty acid salts, alkylbenzene sulfonates, alkylsulfosuccinates, alkyl sulfates, and polyoxyethylene alkyl ether sulfates are preferred, fatty acid salts and alkylbenzene sulfonates are more preferred, and fatty acid salts are further preferred. From the aspect of being able to more appropriately prevent the generation of aggregates in the latex of the obtained rubber, sodium rosinate and potassium rosinate are particularly preferred.

[0085] The content ratio of the emulsifier in the aqueous solution of the emulsifier is not particularly limited. From the viewpoint of good emulsification, it is preferably 0.1 to 5% by weight, more preferably 0.3 to 3% by weight, and further preferably 0.5 to 2% by weight.

[0086] [Desolventization process]

[0087] The desolventization process is a process of removing the organic solvent from the emulsion obtained by the emulsification process. As the method of desolventization, a method capable of reducing the content of the organic solvent in the emulsion to 500 ppm by weight or less is preferred, and methods such as vacuum distillation, atmospheric distillation, steam distillation, and centrifugation can be adopted. Among these, vacuum distillation is preferred from the viewpoint of being able to appropriately and effectively remove the organic solvent.

[0088] In the present embodiment, a vacuum pump 5 and a concentrator 6 are used to perform vacuum distillation on the emulsion stored in the stirring tank 30 obtained by the emulsification process, thereby performing desolventization. That is, in the desolventization process of the present embodiment, from the state where the emulsion in the stirring tank 30 is heated to about 80°C, the valve 7 is opened, the vacuum pump 5 is operated, and the inside of the stirring tank 30 is depressurized to less than 700 mmHg, for example. Thereby, the organic solvent is distilled from the emulsion in the stirring tank 30, and the organic solvent is discharged from the stirring tank 30 to the distillation tube 15 and recovered by being concentrated by the concentrator 6.

[0089] In this embodiment, in the desolventizing step, while stirring the emulsion in the stirring tank 30 with the stirring blades 50, the amount of coagulates present in the latex obtained after desolventizing is likely to decrease, which is therefore preferred.

[0090] In the desolventizing step using vacuum distillation, it is preferred that the pressure in the stirring tank 30 is reduced to less than 700 mmHg. When the pressure in the stirring tank 30 during the desolventizing step is high, the time required for the desolventizing step is long, and when the pressure is low, there is a risk of excessive foaming of the emulsion. Therefore, from the viewpoint of suppressing the occurrence of these problems, the pressure in the stirring tank 30 during the desolventizing step is preferably 1 to 600 mmHg, more preferably 10 to 500 mmHg, and further preferably 100 to 400 mmHg.

[0091] In addition, the temperature of the emulsion in the stirring tank 30 during the desolventizing step of this embodiment is preferably heated to a temperature above the boiling point of the organic solvent contained in the emulsion. Specifically, it is more preferably controlled to a temperature 5°C or more higher than the boiling point of this organic solvent, and further preferably controlled to a temperature 10°C or more higher than the boiling point of this organic solvent. In addition, the upper limit of the temperature of the emulsion in the stirring tank 30 during the desolventizing step is not particularly limited, and is preferably less than 100°C.

[0092] [Centrifugation step]

[0093] In this embodiment, after performing the desolventizing step, the emulsion from which the organic solvent has been removed is transferred to a centrifuge for centrifugation, thereby obtaining a light liquid with an increased solid component concentration as the latex of the rubber.

[0094] In the centrifugation step, in order to improve the mechanical stability of the obtained latex, a pH adjuster is added to the emulsion from which the organic solvent has been removed in advance to make its pH 7 or more, preferably 9 or more.

[0095] Examples of the pH adjuster include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; carbonates of alkali metals such as sodium carbonate and potassium carbonate; bicarbonates of alkali metals such as sodium bicarbonate; ammonia; or organic amine compounds such as trimethylamine and triethanolamine. Alkali metal hydroxides or ammonia are preferred.

[0096] In addition, the latex of the rubber obtained in this embodiment by performing as described above can also be appropriately blended with additives such as defoamers, preservatives, chelating agents, deoxidizers, dispersants, and anti-aging agents that can be blended in the field of latex.

[0097] In addition, in the case of using natural rubber as a raw material for rubber, when the obtained latex is used as an immersion molded article that comes into contact with the human body, it is necessary to decompose and remove the proteins that cause allergic symptoms in the human body at the latex stage.

[0098] The above is the method for manufacturing the latex of the present embodiment. Starting from the latex manufactured by the manufacturing method of the present embodiment, an immersion molded article such as a rubber glove can be obtained through a latex composition. The immersion molded article is a form of the film molded article of the present invention. Furthermore, by using the latex manufactured by the manufacturing method of the present embodiment, a base material for forming an adhesive layer can be obtained. The base material for forming an adhesive layer refers to a composite material in which a latex composition is formed as an adhesive layer on the surface of the base material.

[0099] Specific examples of the manufacturing methods of the latex composition, the immersion molded article, and the base material for forming an adhesive layer are given below.

[0100] (Manufacture of Latex Composition)

[0101] The latex composition can be obtained by adding a crosslinking agent to the latex.

[0102] Examples of the crosslinking agent include sulfur such as sulfur powder, sublimed sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, etc.; or sulfur-containing compounds such as sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, caprolactam disulfide, phosphorus-containing polysulfide, polymer polysulfide, 2-(4'-morpholinodithio)benzothiazole. Among these, sulfur is preferably used. The crosslinking agent can be used alone or in combination of two or more.

[0103] The content of the crosslinking agent is not particularly limited. Relative to 100 parts by weight of the rubber contained in the rubber latex, it is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 3 parts by weight. By making the content of the crosslinking agent within this range, the tensile strength of the obtained immersion molded article can be further improved.

[0104] In addition, the latex composition preferably further contains a crosslinking accelerator. As the crosslinking accelerator, those that can be used in dip molding can be used, and examples include: dithiocarbamic acids such as diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyl dithiocarbamic acid, dicyclohexyl dithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid, and zinc salts thereof; or 2-mercaptobenzothiazole, zinc 2-mercaptobenzothiazole, 2-mercaptothiazoline, dibenzothiazole disulfide, 2-(2,4-dinitrophenylthio)benzothiazole, 2-(N,N-diethylthiocarbamoylthio)benzothiazole, 2-(2,6-dimethyl-4-morpholinothio)benzothiazole, 2-(4'-morpholinedithio)benzothiazole, 4-morpholinyl-2-dithiobenzothiazole, 1,3-bis(2-benzothiazolylmercaptomethyl)urea, etc. Zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, and zinc 2-mercaptobenzothiazole are preferred. The crosslinking accelerator can be used alone or in combination of two or more.

[0105] The content of the crosslinking accelerator is preferably 0.05 to 5 parts by weight, more preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the rubber contained in the rubber latex. By setting the content of the crosslinking accelerator within this range, the tensile strength of the resulting dip molded article can be further improved.

[0106] In addition, in the latex composition, zinc oxide is preferably further contained. The content of zinc oxide is not particularly limited, and is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 2 parts by weight, based on 100 parts by weight of the rubber contained in the rubber latex. By setting the content of zinc oxide within the above range, good emulsion stability can be achieved, and the tensile strength of the resulting dip molded article can be further improved.

[0107] The latex composition can also be blended with compounding agents such as antioxidants, dispersants, reinforcing agents such as carbon black, silica, and talc; fillers such as calcium carbonate and clay; ultraviolet absorbers; and plasticizers, as needed.

[0108] For example, as antioxidants, there may be mentioned: phenolic antioxidants without sulfur atoms such as 2,6-di-4-methylphenol, 2,6-di-tert-butylphenol, butylhydroxyanisole, 2,6-di-tert-butyl-α-dimethylaminop-cresol, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, styrenated phenol, 2,2'-methylenebis(6-α-methylbenzyl-p-cresol), 4,4'-methylenebis(2,6-di-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), alkylated bisphenols, butylated reaction products of p-cresol and dicyclopentadiene, etc.; or thiodiphenol antioxidants such as 2,2'-thiobis(4-methyl-6-tert-butylphenol), 4,4'-thiobis(6-tert-butyl-o-cresol), 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-triazin-2-ylamino]phenol, etc.; or phosphite antioxidants such as tris(nonylphenyl)phosphite, diphenylisodecylphosphite, tetraphenyldipropyleneglycoldiphosphite, etc.; or thioester antioxidants such as dilauryl thiodipropionate, etc.; or amine antioxidants such as phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonamido)-diphenylamine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, butyraldehyde-aniline condensate, etc.; or quinoline antioxidants such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, etc.; or hydroquinone antioxidants such as 2,5-di(tert-amyl)hydroquinone, etc. These antioxidants can be used alone or in combination of two or more kinds.

[0109] The content of the antioxidant is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the rubber contained in the latex of the rubber.

[0110] The method for preparing the latex composition is not particularly limited. For example, there may be mentioned: a method of mixing a crosslinking agent and various compounding agents as required in the latex of the rubber using a disperser such as a ball mill, kneader, or disperser; a method of preparing an aqueous dispersion of compounding components other than the latex of the rubber using the above-mentioned disperser and then mixing the aqueous dispersion with the latex of the rubber, etc.

[0111] The latex composition preferably has a pH of 7 or more, more preferably in the range of 7 to 13, and further preferably in the range of 8 to 12. In addition, the solid content concentration of the latex composition is preferably in the range of 15 to 65% by weight.

[0112] From the viewpoint of further improving the mechanical properties of the obtained impregnated molded article, the latex composition is preferably cured (pre-crosslinked) before being supplied for impregnation molding. The pre-crosslinking time is not particularly limited and also depends on the pre-crosslinking temperature, and is preferably 1 to 14 days, more preferably 1 to 7 days. In addition, the pre-crosslinking temperature is preferably 20 to 40°C.

[0113] Moreover, after pre-crosslinking and until being supplied for impregnation molding, it is preferably stored at a temperature preferably of 10 to 30°C. This is because when directly stored in a high-temperature state higher than this temperature, the tensile strength of the obtained impregnated molded article may decrease.

[0114] (Manufacture of impregnated molded article)

[0115] The impregnated molded article can be obtained by impregnation molding of the above-described latex composition. Impregnation molding is a molding method as follows: depositing the latex composition on the surface of a mold immersed in the latex composition, then lifting the mold from the latex composition, and then drying the latex composition deposited on the surface of the mold. In addition, the mold before being immersed in the latex composition can be preheated first. Furthermore, before immersing the mold in the latex composition or after lifting the mold from the latex composition, a coagulant can be used as needed.

[0116] As a specific example of the method of using the coagulant, there is a method of immersing the mold in a coagulant solution and then immersing the mold in the latex composition (anodic coagulation impregnation method), and a method of first immersing the mold in the latex composition and then immersing the mold in the coagulant solution (Teague coagulation impregnation method). From the aspect of obtaining an impregnated molded article with less thickness unevenness, the anodic coagulation impregnation method is preferred.

[0117] Specific examples of the coagulant are: halogenated metals such as barium chloride, calcium chloride, magnesium chloride, zinc chloride, and aluminum chloride; or nitrates such as barium nitrate, calcium nitrate, and zinc nitrate; or acetates such as barium acetate, calcium acetate, and zinc acetate; or sulfates such as calcium sulfate, magnesium sulfate, and aluminum sulfate, etc., water-soluble polyvalent metal salts. Among them, calcium salts are preferred, and calcium nitrate is more preferred. These water-soluble polyvalent metal salts can be used alone or in combination of two or more.

[0118] The coagulant is preferably used in an aqueous solution state. This aqueous solution can further contain water-soluble organic solvents such as methanol and ethanol, and nonionic surfactants. The concentration of the coagulant also varies depending on the type of water-soluble polyvalent metal salt, and is preferably 5 to 50% by weight, more preferably 10 to 30% by weight.

[0119] After lifting the mold from the latex composition, the deposit formed in a film shape on the mold is usually dried by heating. The drying conditions can be appropriately selected.

[0120] Next, by heating, the deposit formed in a film shape on the mold is crosslinked. The heating conditions during crosslinking are not particularly limited. As the heating temperature, it is preferably 60 to 150°C, more preferably 100 to 130°C. In addition, as the heating time, it is preferably 10 to 120 minutes.

[0121] The method of heating is not particularly limited, and examples thereof include a method of heating by blowing warm air in an oven, a method of heating by irradiating infrared rays, etc.

[0122] In addition, before heating the mold on which the latex composition has been deposited or after heating, in order to remove water-soluble impurities (for example, remaining surfactants, coagulants), it is preferable to wash the mold with water or warm water. In the case of using warm water, the temperature of the warm water is preferably 40 to 80°C, more preferably 50 to 70°C.

[0123] The crosslinked dip-molded article is detached from the mold. As the detachment method, a method of peeling off by hand from the mold, a method of peeling off from the mold using water pressure or compressed air pressure, etc. can be adopted. If the dip-molded article during crosslinking has sufficient strength for detachment, it can also be detached during crosslinking and then the subsequent crosslinking can be continued.

[0124] As the dip-molded article, it is particularly preferable to manufacture, for example, rubber gloves. In the case where the dip-molded article is a rubber glove, in order to prevent the adhesion of the contact surfaces of the dip-molded articles to each other and to improve the slipperiness when worn on the hand, inorganic fine particles such as talc and calcium carbonate or organic fine particles such as starch granules can be scattered on the glove surface, or an elastomer layer containing fine particles can be formed on the glove surface, or the surface layer of the glove can be chlorinated.

[0125] In addition, as the dip-molded article, in addition to being applicable to the above-mentioned rubber gloves, it can also be applied to: nipples for nursing bottles; medical supplies such as droppers, tubes, water pillows, airbag bags, catheters, condoms, etc.; toys such as balloons, dolls, balls, etc.; or industrial supplies such as bags for compression molding, bags for gas storage, etc.; or various rubber molded articles such as finger cots.

[0126] In addition, the thickness of the dip-molded article depends on the use and the product, and is formed to a thickness of, for example, about 0.03 to 0.50 mm.

[0127] (Adhesive layer-forming substrate)

[0128] The adhesive layer-forming substrate of the present embodiment can be obtained by forming an adhesive layer using the above-mentioned latex composition on the surface of a substrate.

[0129] The base material described in this embodiment is not particularly limited, and for example, a fibrous base material can be used. The type of fiber constituting the fibrous base material is not particularly limited, and examples include polyvinyl alcohol fibers, polyester fibers, nylon, polyamide fibers such as aramid (aromatic polyamide), glass fibers, cotton, rayon, etc. These can be appropriately selected according to their uses.

[0130] The shape of the fibrous base material is not particularly limited, and examples include short fibers, filaments, linear shapes, cord shapes, woven fabrics (such as canvas), etc., which can be appropriately selected according to their uses. For example, the base material for forming the adhesive layer can be adhered to rubber via the adhesive layer and used as a base material-rubber composite. The base material-rubber composite is not particularly limited, and examples include a rubber toothed belt using a linear fibrous base material as the core wire of the fibrous base material, a rubber toothed belt using a base cloth-like fibrous base material such as canvas, etc.

[0131] As a method for obtaining the base material-rubber composite, there is no particular limitation, and examples include the following method: making a latex composition adhere to the base material by impregnation treatment or the like to obtain a base material for forming an adhesive layer, and then placing the base material for forming the adhesive layer on the rubber and heating and pressing it.

[0132] The pressing in the above method can be carried out using a compression molding machine, a metal roller, an injection molding machine, etc. In addition, the pressure of pressing is preferably 0.5 to 20 MPa, more preferably 2 to 10 MPa. In addition, the heating temperature is preferably 130 to 300 °C, more preferably 150 to 250 °C. In addition, the treatment time for heating and pressing in the above method is preferably 1 to 180 minutes, more preferably 5 to 120 minutes. By the method of heating and pressing, the molding of the rubber and the adhesion of the base material for forming the adhesive layer to the rubber can be carried out simultaneously. In addition, it is preferable to previously form a mold on the inner surface of the mold of the compression molding machine used for pressing and the surface of the roller to impart a desired surface shape to the rubber of the target base material-rubber composite.

[0133] In addition, as a form of the base material-rubber composite, a base material-rubber-base material composite can be cited. The base material-rubber-base material composite can be formed by combining, for example, a base material (which can be a composite of two or more base materials) and a base material-rubber composite. Specifically, a core wire as the base material, rubber, and a base cloth as the base material can be overlapped (in this case, making the latex composition appropriately adhere to the core wire and the base cloth to previously form a base material for forming an adhesive layer), and heating and pressing are carried out simultaneously to obtain the base material-rubber-base material composite.

[0134] The mechanical strength, abrasion resistance, and water resistance of the substrate-rubber composite obtained by forming a substrate using the adhesive layer of the present embodiment are excellent. Therefore, it can be preferably used as belts such as flat belts, V-belts, multi-wedge belts, round belts, square belts, and toothed belts. In addition, the substrate-rubber composite obtained by forming a substrate using the adhesive layer of the present embodiment has excellent oil resistance and can be preferably used as a belt in oil. Furthermore, the substrate-rubber composite obtained by forming a substrate using the adhesive layer of the present embodiment can also be preferably used for hoses, tubes, diaphragms, etc. Examples of hoses include single-tube rubber hoses, multi-layer rubber hoses, braided reinforced hoses, and fabric-reinforced hoses. Examples of diaphragms include flat diaphragms and rolling diaphragms.

[0135] Furthermore, in addition to the above uses, the substrate-rubber composite obtained by forming a substrate using the adhesive layer of the present embodiment can also be used as industrial products such as seals and rubber rollers. Examples of seals include seals for moving parts such as rotation, rocking, and reciprocating motion, and fixed part seals. Examples of seals for moving parts include oil seals, piston seals, mechanical seals, protective covers, dust covers, diaphragms, accumulators, etc. Examples of fixed part seals include O-rings and various gaskets. Examples of rubber rollers include rollers as components of office automation equipment such as printing equipment and copying equipment, or fiber processing rollers such as stretching rollers for spinning and drafting rollers for textile, or rollers for ironmaking such as tension rollers, buffer rollers, and turning rollers.

[0136] (Function)

[0137] Next, the function of the method for manufacturing the latex of the present embodiment will be described.

[0138] In the method for manufacturing the latex of the present embodiment, in the emulsification step of the raw materials including the rough emulsification step, the rubber composition (rubber solution + aqueous emulsifier solution) stored in the stirring tank 30 of the stirring device 3 is stirred with the flat stirring blade 50 for mixing.

[0139] According to the stirring blade 50 of the present embodiment, as described above, a circulating flow that circulates the emulsion in the vertical direction can be generated. Therefore, the rubber, which is relatively light in specific gravity and tends to stagnate near the liquid surface of the solution, can be circulated up and down, so that it can be effectively dispersed in the solution, and an emulsion in which the rubber is uniformly dispersed can be obtained. Therefore, the rubber composition can be emulsified in a good state in the emulsification step, and thus a high-quality latex with few aggregates can be manufactured.

[0140] In addition, the stirring blade 50 of the present embodiment uses the lattice portion 54 having a lattice-like structure, and the rubber in the solution circulating up and down is sheared and subdivided. Furthermore, the rubber is involved in the fine vortices generated behind the rotation direction of the lattice portion 54 and is mixed. Therefore, the refinement and mixing of the rubber can be promoted, and it becomes easy to obtain a good emulsified state and reduce the aggregates.

[0141] In addition, since the lower end portion of the paddle portion 53 of the stirring blade 50 of the present embodiment is close to the bottom inside the stirring tank 30, the solution can be stirred following the circulating flow without remaining at the bottom. Therefore, the circulating flow up and down is accurately generated, the rubber is dispersed, and a good emulsion can be obtained.

[0142] In addition, the baffle plate 90 functions to suppress the solution extruded radially outward by the paddle portion 53 from rotating as the stirring blade 50 rotates, and functions to generate an upward flow. Thereby, the circulating flow up and down is accurately generated, the rubber is dispersed, and a good emulsion can be obtained.

[0143] In addition, in the method for manufacturing latex of the present embodiment, by using the stirring blade 50 to stir the emulsion also in the desolventizing step, the rubber in the emulsion in the desolvent circulates up and down and is stirred, and the rubber is sufficiently mixed. Therefore, the latex obtained after desolventizing is a high-quality latex with few aggregates.

[0144] In addition, in the above-described embodiment, the emulsifying step including the rough emulsifying step and the desolventizing step are performed in one stirring tank 30. However, two stirring tanks 30 may be prepared, and the emulsifying step and the desolventizing step may be performed in different stirring tanks 30. In addition, when stirring using the stirring blade 50 is not performed in the desolventizing step, the emulsion obtained in the stirring tank 30 may be moved to a tank dedicated to desolventizing to perform the desolventizing step.

[0145] (Another embodiment of the stirring blade)

[0146] Next, with reference to Figure 4 and Figure 5 , another embodiment of the stirring blade 50 constituting the above-described stirring unit 40 will be described. In the drawings of the other embodiment, the same reference numerals are given to the structural members that are the same as those in the above-described embodiment, and the description thereof is omitted.

[0147] Figure 4A stirring tank (container) 30B with a stirring blade 60 having another embodiment is shown. The stirring blade 60 is generally flat plate-shaped, has a rectangular shape, and has a left-right symmetric shape with the rotation axis 41 as the symmetry line. The stirring blade 60 has: a lower rectangular paddle portion 63 and left and right rectangular blade portions 64a, 64b extending upward from the paddle portion 63. The rotation axis 41 is fixed to the paddle portion 63 so as to penetrate the center in the width direction of the paddle portion 63, and the stirring blade 60 rotates together with the rotation axis 41.

[0148] The left and right blade portions 64a, 64b each have an inner (rotation axis 41 side) edge portion 65, and these edge portions 65 are formed parallel to the rotation axis 41. In addition, the left and right blade portions 64a, 64b each have an outer edge portion 66, and these edge portions 66 are formed in a zigzag shape with repeated concavities and convexities. A predetermined gap is formed between the inner edge portion 65 and the rotation axis 41 and between the outer edge portion 66 and the baffle 90, respectively.

[0149] Regarding the ratio of the height dimension of the paddle portion 63 and each of the blade portions 64a, 64b to the overall height of the stirring blade 60, each of the blade portions 64a, 64b is about 6 to 7 tenths, which is larger than the paddle portion 63, but is not limited thereto.

[0150] The stirring blade 60 has a stirring surface 62 in the same manner as the stirring blade 50 of the above-described embodiment, which is substantially orthogonal to the rotation direction and faces a solution such as an emulsion stored in the stirring tank 30B. The area of this stirring surface 62 corresponds to the area of the stirring blade 60, and the stirring blade 60 is configured such that the liquid contact area ratio of the stirring surface 62, that is, the ratio of the area of the stirring surface 62 to the cross-sectional area of the solution stored in the stirring tank 30B, is 10 to 60%.

[0151] Figure 5 A stirring tank (container) 30C with a stirring blade 70 is shown. The stirring blade 70 has the same shape as the Figure 4 stirring blade 60 shown, but it is a modified example with changed dimensions. Therefore, the same reference numerals are given to the structural members having the same structure as the stirring blade 60, and their description is omitted.

[0152] Figure 5 The modified example of the stirring blade 70 shown has an area, that is, the area of the stirring surface 72, larger by, for example, about 10 to 30% than the Figure 4 stirring blade 60 shown. For example, when the liquid contact area ratio of the stirring surface 62 of the stirring blade 60 is about 15%, the liquid contact area ratio of the stirring surface 72 of the stirring blade 70 is about 45%.

[0153] According to the above-mentioned flat stirring blades 60 and 70 of another embodiment, similar to the case of the stirring blade 50, it is possible to generate a circulating flow in the vertical direction in the stirred solution, and it is possible to circulate up and down the rubber that is relatively light in specific gravity and floats near the liquid surface of the solution and is prone to stagnation, and disperse it into a uniform state. Therefore, it is possible to manufacture high-quality latex with fewer aggregates.

[0154] Example

[0155] Next, examples and comparative examples of the present invention will be described. In addition, the present invention is not limited to the following examples.

[0156] [Example 1]

[0157] (Manufacture of rubber solution)

[0158] After storing 85 parts of cyclohexane (organic solvent) in the rubber solution tank 1 shown in Figure 1 , 15 parts of an isoprene polymer with a weight average molecular weight of 1,300,000 (synthetic rubber: trade name “NIPOL IR2200L”, manufactured by Nippon Zeon Co., Ltd., homopolymer of isoprene, cis-bonding unit amount 98%) was added, and the temperature was raised to 60°C while stirring in the rubber solution tank 1 to dissolve it, and a rubber solution (a) formed from a cyclohexane solution of the isoprene polymer was prepared.

[0159] (Manufacture of aqueous emulsifier solution)

[0160] In the emulsifier tank 2 shown in Figure 1 , 10 parts of sodium rosinate and 5 parts of sodium dodecylbenzenesulfonate were mixed with water, and after preparing an anionic surfactant aqueous solution with a concentration of 2.3% by weight as the aqueous emulsifier solution (b), the temperature was raised to 60°C.

[0161] (Coarse emulsification process)

[0162] Next, the rubber solution (a) formed from the above cyclohexane solution and the aqueous emulsifier solution (b) formed from the above anionic surfactant aqueous solution were supplied to the stirring tank 30 at a weight ratio of 1:1, and then stirred with a stirring blade 50 having a liquid contact area ratio of 30% for 30 minutes for coarse emulsification.

[0163] (Circulating emulsification process)

[0164] Next, while stirring the obtained crude emulsion with the stirring blade 50, the emulsion is circulated in the circulation pipe 14 by the emulsifier 4 in a manner of 2 circulation times for circulation emulsification to obtain an emulsion (c). In addition, the number of circulations is calculated by "the flow rate (L / HR) of the emulsifier 4 ÷ L × HR (L: the amount of the crude emulsion, HR: the operation time)". Further, the emulsifier 4 uses the trade name "Milder MDN310" (manufactured by Pacific Machine Works Co., Ltd.). After the circulation emulsification is completed, the emulsion is allowed to stand in the stirring tank 30 for 20 minutes and the liquid surface is observed, and there are no floating substances.

[0165] (Desolventization process)

[0166] Next, the valve 7 is opened to operate the vacuum pump 5. While stirring the emulsion (c) with the stirring blade 50, the inside of the stirring tank 30 is depressurized to -0.01 to -0.09 MPa (gauge pressure) and heated to 80 °C, whereby cyclohexane is distilled off and removed to obtain an aqueous dispersion (d) of the synthetic isoprene polymer in the stirring tank 30.

[0167] During the removal of cyclohexane, the inside of the stirring tank 30 is observed, and almost no foaming is observed. In addition, after the aqueous dispersion (d) is withdrawn from the stirring tank 30, the solid matter adhering to the inner wall of the stirring tank 30 and the stirring blade 50 is recovered, and the weight of the recovered matter is measured, and the result is 0.01 part or less.

[0168] (Centrifugal separation process)

[0169] Next, the aqueous dispersion (d) withdrawn from the stirring tank 30 is centrifuged by a centrifuge to obtain a light liquid as a synthetic polyisoprene latex (e) having a solid content concentration of 60% by weight.

[0170] (Manufacture of the latex composition for dip molding)

[0171] While stirring the synthetic polyisoprene latex (e) obtained as described above, an aqueous solution of sodium dibutyldithiocarbamate at 5% by weight is added (in terms of the addition amount, 0.4 part of sodium dibutyldithiocarbamate is relative to 100 parts of the synthetic polyisoprene).

[0172] On the other hand, for the styrene-mono-sec-butyl maleate-monomethyl maleate polymer (trade name "Scripset550", manufactured by Hercules), the carboxyl groups in the polymer are neutralized 100% with sodium hydroxide to prepare an aqueous solution of the sodium salt (concentration: 10% by weight) as a dispersant (f).

[0173] Next, a dispersant (f) was added in an amount of 0.6 part in terms of solid content based on 100 parts of the synthetic polyisoprene latex (e) and mixed. While stirring this mixture, an aqueous dispersion of the following compounding agents was added: 1.5 parts of zinc oxide, 1.5 parts of sulfur, 2 parts of an anti-aging agent (trade name: Wingstay L, manufactured by Goodyear), 0.35 part of zinc diethyldithiocarbamate, and 0.3 part of zinc mercaptobenzothiazole based on 100 parts of the synthetic polyisoprene in the mixture in terms of solid content. Then, an aqueous potassium hydroxide solution was added to adjust the pH to 10.5, and then distilled water was added so that the solid content concentration became 40% to obtain a latex composition (g) for dip molding. Then, the obtained latex composition (g) was cured at 25°C for 48 hours.

[0174] (Manufacture of dip-molded article)

[0175] A glass mold (diameter: about 5 cm, length of the frosted part: about 15 cm) with a surface subjected to sandblasting was washed, preheated in an oven at 70°C, and then immersed in an aqueous coagulant solution composed of 16% by weight of calcium nitrate and 0.05% by weight of polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) for 5 seconds and then taken out.

[0176] Next, the above glass mold covered with the coagulant was dried in an oven at 70°C. Then, the glass mold covered with the coagulant was taken out of the oven, immersed in the above latex composition (g) at 25°C for 10 seconds, then taken out, and dried at room temperature for 60 minutes. Thus, the synthetic polyisoprene latex (e) was formed into a film on the surface of the glass mold.

[0177] Next, the glass mold having the synthetic polyisoprene latex (e) formed into a film on its surface was placed in an oven and pre-dried by heating from 50°C to 60°C over 25 minutes and then further dried by being placed in an oven at 70°C for 10 minutes. Then, the glass mold was immersed in warm water at 60°C for 2 minutes and then air-dried at room temperature for 10 minutes.

[0178] Next, the glass mold covered with the synthetic polyisoprene latex (e) formed into a film was placed in an oven and vulcanized at 100°C for 60 minutes. The glass mold covered with the vulcanized film was cooled to room temperature, talc was sprinkled on the surface, and then the film was peeled off from the glass mold to obtain a dip-molded article formed from the synthetic polyisoprene latex.

[0179] [Example 2]

[0180] Using a Figure 4The circulation emulsification process was carried out using the stirring blade 60 (liquid contact area ratio: 15%) shown in place of the stirring blade 50 in the stirring tank 30B. Except for this, the process was carried out in the same manner as in Example 1 to obtain an impregnated molded body.

[0181] [Example 3]

[0182] Using the Figure 5 shown stirring blade 70 (liquid contact area ratio: 45%) in place of the stirring blade 50 in the stirring tank 30C, the circulation emulsification process was carried out. Except for this, the process was carried out in the same manner as in Example 1 to obtain an impregnated molded body.

[0183] [Example 4]

[0184] Using the Figure 4 shown stirring blade 60 (liquid contact area ratio: 15%) in place of the stirring blade 50 in the stirring tank 30B, the solvent removal process was carried out. Except for this, the process was carried out in the same manner as in Example 1 to obtain an impregnated molded body.

[0185] [Example 5]

[0186] Using the Figure 6 shown two-stage paddle-shaped stirring blade 110 (liquid contact area ratio: 5%) in place of the stirring blade 50 in the stirring tank 100, the solvent removal process was carried out. Except for this, the process was carried out in the same manner as in Example 1 to obtain an impregnated molded body.

[0187] Figure 6 The shown stirring tank 100 has a tank main body 101 and a lid (not shown), and has a plurality of baffle plates 109 identical to the aforementioned baffle plate 90. Two stirring blades 110 are disposed in the tank main body 101, and these stirring blades 110 are fixed to the rotating shaft 104 at a prescribed interval in the vertical direction.

[0188] The stirring blade 110 is a stirring blade of a comparative example other than the present invention, and is a plate-shaped one extending from the rotating shaft 104 in the left and right directions, and has a shape inclined at approximately 45° with respect to the rotation direction and with the inclination directions different from each other on the left and right. The above liquid contact area ratio: 5% is the total value of the liquid contact area ratios of the two upper and lower stirring blades 110.

[0189] [Comparative Example 1]

[0190] Using the Figure 6 shown stirring blade 110 in place of the stirring blade 50 in the stirring tank 100, the rough emulsification process, the circulation emulsification process, and the solvent removal process were carried out. Except for this, the process was carried out in the same manner as in Example 1 to obtain an impregnated molded body.

[0191] [Comparative Example 2]

[0192] Using theFigure 7 The double-ribbon type stirring blade 210 shown (liquid contact area ratio of the stirring surface: 15%) is used to replace the stirring blade 50 in the stirring tank 200 to perform the rough emulsification process, the circulation emulsification process, and the desolventization process. Except for this, it is carried out in the same manner as in Example 1 to obtain an impregnated molded body.

[0193] Figure 7 The stirring tank 200 shown has a tank main body 201 and a lid (not shown). The stirring blade 210 is disposed in the tank main body 201 so as to be rotatable by a rotating shaft 204.

[0194] The stirring blade 210 is a stirring blade of a comparative example other than the present invention, and is constituted by a spiral ribbon blade 211 composed of two strip-shaped plates being symmetrically combined point-symmetrically when viewed from the axial direction with the rotating shaft 204 as the center. The two spiral ribbon blades 211 are connected to each other by a bottom frame 221 fixed to the lower end portion of the rotating shaft 204 and a pair of side frames 222.

[0195] The stirring surface of the spiral ribbon blade 211 is a spiral surface and is inclined with respect to the rotation direction. The above liquid contact area ratio: 15% is the total value of the liquid contact area ratios of the two spiral ribbon blades 211.

[0196] The manufacturing methods of the above Examples 1 to 5 and Comparative Examples 1 and 2 are summarized in Table 1, and the evaluations are also included in Table 1. In Table 1, "floaters" represents the observation result of the state of the floaters when the emulsion is left standing in the stirring tank for 20 minutes and the liquid surface is observed after the circulation emulsification is completed. In addition, in Table 1, "coagulants" represents the amount of the rubber component remaining in the emulsion after the desolventization process. In addition, the mechanical strength is the mechanical strength of the obtained impregnated molded body, and is measured in the following manner.

[0197] Based on ASTM D624-00, the impregnated molded body is placed in a thermo-hygrostat chamber at 23°C and a relative humidity of 50% for 24 hours or more, and then a test piece for measurement is punched out using a dumbbell cutter (trade name "Die C", manufactured by Dumbbell Co., Ltd.). Then, the test piece is stretched with a Tensilon universal testing machine (trade name "RTG-1210", manufactured by A&D Co., Ltd.) at a tensile speed of 500 mm / min, and the tensile strength (unit: MPa) at the moment of fracture, the tensile elongation at the moment of fracture (unit: %), and the tear strength (unit: N / mm) are measured.

[0198] [Table 1]

[0199]

[0200] (Evaluation)

[0201] As shown in Table 1, in Examples 1 to 4 where the emulsion is stirred and mixed with flat stirring blades in the emulsification process and the desolventization process, there are fewer floating substances and aggregates compared to Comparative Examples 1 and 2 where the emulsion is not stirred with flat stirring blades. Therefore, it can be confirmed that according to the present invention, emulsification proceeds well, and the resulting latex is a high-quality latex with a small amount of aggregates. Since Example 5 does not use flat stirring blades in the circulating emulsification process, the amount of aggregates is slightly more compared to Examples 1 to 4. Therefore, it is preferable to use flat stirring blades in both the emulsification process and the desolventization process.

[0202] In addition, regarding the mechanical strength of the impregnated molded body, Examples 1 to 5 are more excellent than Comparative Examples 1 and 2, and it can be confirmed that the strength of the impregnated molded body made of the latex manufactured by the present invention is excellent.

[0203] Industrial Applicability

[0204] The present invention can obtain a good emulsification state in the emulsification process of raw materials, and thus is useful as a method for manufacturing latex that can seek quality improvement.

[0205] Explanation of Reference Numerals

[0206] 3: Stirring device

[0207] 4: Emulsifier

[0208] 30, 30B, 30C: Stirring tank (container)

[0209] 40: Stirring unit

[0210] 50, 60, 70: Stirring blade

[0211] 52, 62, 72: Stirring surface

[0212] 54: Lattice part

Claims

1. A method for manufacturing latex, characterized in that, comprising: a rough emulsification step of obtaining an emulsion in a roughly emulsified state by mixing a rubber solution in which rubber and an organic solvent are mixed with an aqueous solution of an emulsifier; a circulation emulsification step of further emulsifying the emulsion in a roughly emulsified state obtained in the rough emulsification step by circulating the emulsion through an emulsifier; and a solvent removal step of removing the organic solvent from the emulsion obtained through the circulation emulsification step, in both the rough emulsification step and the circulation emulsification step, the emulsion is stirred with a stirring device, the stirring device having a container for storing the stirred material and a stirring unit rotatably provided in the container, in the solvent removal step, the emulsion is stirred with the stirring device, the stirring device having the container and the stirring unit, the stirring unit is a structure including a flat stirring blade, the flat stirring blade having a stirring surface that is substantially orthogonal to the rotation direction of the stirring unit and faces the stirred material, the stirring blade has: a lattice part having a lattice-like structure; or an outer edge part and an inner edge part, the outer edge part being formed in a zigzag shape with repeated concavities and convexities, in the case where the stirring blade has a lattice part and the lattice part has a lattice-like structure, the stirring blade has a paddle part at the lower part for extruding the emulsion to the radially outer side in order to generate an upward flow of the emulsion, and the lattice part is larger than the paddle part and has a height of 6 to 7 tenths of the overall height of the stirring blade; in the case where the stirring blade has the outer edge part and the inner edge part, the stirring blade has a paddle part at the lower part for extruding the emulsion to the radially outer side in order to generate an upward flow of the emulsion and a blade part extending upward from the paddle part, the blade part having the outer edge part and the inner edge part, and the blade part is larger than the paddle part and has a height of 6 to 7 tenths of the overall height of the stirring blade.

2. The method for manufacturing the latex according to claim 1, wherein The area of the stirring surface of the stirring blade is 10 to 60% of the cross-sectional area of the stirred material stored in the container.

3. The method for manufacturing latex according to claim 1 or 2, characterized in that, In the rough emulsification step, a step of continuously mixing the rubber solution and the aqueous solution of the emulsifier with the emulsifier is included.

4. A method for manufacturing a film molded body, characterized in that, A crosslinking agent is added to the latex produced by the production method according to any one of claims 1 to 3 to obtain a latex composition, and a film molded body is molded using the latex composition.

5. A method for manufacturing an impregnated molded body, characterized in that, A crosslinking agent is added to the latex produced by the production method according to any one of claims 1 to 3 to obtain a latex composition, and an impregnated molded body is molded using the latex composition.

6. A method for manufacturing a base material for forming an adhesive layer, characterized in that, A crosslinking agent is added to the latex produced by the production method according to any one of claims 1 to 3 to obtain a latex composition, and the latex composition is formed on the surface of a substrate as an adhesive layer.

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