WO2020129765A1 - Latex production method, and methods for producing film molded body, dip molded body and adhesive layer-formed substrate using latex obtained using said production method - Google Patents

Abstract

In order to provide a latex production method in which a good emulsified state can be attained in a raw material emulsification step and a high quality latex having few aggregates can therefore be produced, the present invention is a method for producing a latex, the method comprising: an emulsification step for emulsifying a rubber composition that contains a rubber, an organic solvent, water and an emulsifier so as to obtain an emulsified liquid; and a solvent removal step for removing the organic solvent from the emulsified liquid. In the emulsification step, the rubber composition is stirred in a stirring apparatus (3) provided with: a stirring tank (30) in which a stirred object is stored; and a stirring means (40) provided in a rotatable manner in the stirring tank (30). The stirring means (40) includes a flat plate-like stirring blade (50) having a stirring face (52) that is substantially perpendicular to the direction of rotation of the stirring means.

Description

Method for producing latex and method for producing film molded article, dip molded article and adhesive layer forming substrate using latex obtained by the method

The present invention relates to a method for producing a rubber latex, and further relates to a method for producing a film molded body, a dip molded body and an adhesive layer forming base material using the latex obtained by the manufacturing method.

Conventionally, dip molding of a latex composition containing a latex of natural rubber or synthetic rubber to produce a dip molded body used in contact with a human body such as a nipple for baby bottles, balloons, gloves, sacks, and balloons of catheters. Has been done. In particular, synthetic rubber such as isoprene polymer does not contain a protein that causes allergic symptoms in the human body, and is therefore considered to be useful as a raw material for a latex for a dip-molded product which comes into direct contact with a living mucous membrane or an organ.

As a method for producing a latex of natural rubber or synthetic rubber, a rubber solution in which rubber is dissolved or dispersed in an organic solvent and an emulsifier aqueous solution such as soap water are supplied to an emulsifier at a predetermined ratio and mixed. There is known a production method of emulsifying (emulsifying step) and thereafter removing an organic solvent in the obtained emulsion (desolvation step) (see, for example, Patent Document 1).

Japanese Patent No. 5260738

In producing a latex, it is important to obtain a good emulsified state in which the rubber that is a solid content is finely divided in the emulsification step, and the finely divided rubber is dispersed in a homogeneous state, so that good emulsification is performed. This makes it possible to obtain a high-quality latex with few aggregates. However, when emulsifying the raw material with a conventional emulsifier, the emulsification is insufficient and a relatively coarse particle size rubber remains, and due to the coarse rubber, aggregates present in the latex after the desolvation step There were cases where the amount increased.

The present invention has been made in view of the above circumstances, it is possible to obtain a good emulsified state in the emulsification step of the raw material, as a result, a latex production method capable of producing a high-quality latex with less aggregates. Is intended to provide.

The method for producing a latex according to the present invention includes an emulsification step of emulsifying a rubber composition containing rubber, an organic solvent, water and an emulsifier, and a desolvation step of removing the organic solvent from the emulsion, In the emulsification step, a method for producing a latex, wherein the rubber composition is a stirrer including a container in which a stirrer is stored, and a stirrer rotatably provided in the container. The stirring means is configured to include a flat plate-shaped stirring blade having a stirring surface facing the agitated object substantially at right angles to the rotation direction thereof. It should be noted that all "substantially orthogonal" in the present invention are defined such that the angle formed is usually 85° or more, preferably 89° or more, and usually 95° or less, preferably 91° or less.

In the present invention, in the emulsification step, the rubber composition stored in the container is stirred and mixed by a stirring blade to emulsify the rubber composition. According to the plate-shaped stirring blade provided in the stirring device of the present invention, it is possible to generate a circulating flow that circulates the agitated material vertically in the container. For this reason, it is possible to effectively disperse the rubber, which has a relatively low specific gravity and floats near the liquid surface and easily stagnates, in the solution, and to obtain an emulsion in which the rubber is dispersed in a homogeneous state. be able to. Therefore, 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 aggregates can be produced.

Further, the method for producing a latex according to the present invention, a rubber solution in which a rubber and an organic solvent are mixed, and a rough emulsification step of obtaining an emulsion in a rough emulsified state by mixing an emulsifier aqueous solution, and the rough emulsification step. The emulsion in the crude emulsified state obtained in, a circulation emulsification step of further emulsifying by circulating through an emulsifier, and a desolvation step of removing the organic solvent from the emulsion obtained through the circulation emulsification step, A method for producing a latex, comprising: in at least one of the rough emulsifying step and the circulating emulsifying step, the emulsified liquid, a container in which an agitated material is stored, and rotatably in the container. A stirrer provided with the stirrer is provided, and the stirrer is configured to include a plate-shaped stirrer blade having a stirrer surface that is substantially orthogonal to the rotation direction and faces the stirring object. It is characterized by

In the present invention, in at least one of the coarse emulsification step and the circulation emulsification step, by stirring the emulsion with a stirring blade, the emulsion is circulated up and down in the container as described above to make the rubber homogeneous. It is possible to obtain an emulsion that is dispersed in various states. 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, the emulsified liquid can be emulsified in a better state by stirring the emulsified liquid with the flat plate stirring blade according to the present invention in both the rough emulsification process and the circulation emulsification process.

Further, in the method for producing a latex according to the present invention, in the desolvation step, the emulsion is stirred with a container in which a stirred product is stored, and stirring means rotatably provided in the container. It is preferable that the stirring means is configured to include a plate-shaped stirring blade having a stirring surface that is substantially orthogonal to the rotation direction of the apparatus and faces the stirring object.

In this form, even in the desolvation step, by stirring the emulsion with the flat stirring blade according to the present invention, the rubber in the emulsion being desolvated is circulated vertically and stirred to be sufficiently mixed. .. Therefore, the latex obtained after desolvation has a high quality with few aggregates.

Further, the stirring blade used in the method for producing a latex according to the present invention, from the viewpoint of effectively obtaining the effect of the mixing of the present invention, the area of the stirring surface is the stirring object stored in the container. It is characterized by being 10 to 60% of the cross-sectional area, and in this range, it is preferably 15 to 50%, more preferably 20 to 40%, and further preferably 25 to 35%.

Further, the stirring blade according to the present invention is characterized by including a lattice portion having a lattice structure.

According to this configuration, the rotating lattice part shears and subdivides the rubber in the solution that circulates up and down, and the rubber is entangled and mixed in the fine vortex generated behind the lattice part in the rotation direction. For this reason, miniaturization and mixing of the rubber are promoted, a good emulsified state is easily obtained, and aggregates can be reduced.

Further, in the present invention, in the rough emulsification step, the rubber solution and the emulsifier aqueous solution may be continuously mixed using the emulsifier.

Next, the method for producing a film-molded article of the present invention comprises: adding a cross-linking agent to the latex produced by the method for producing a latex according to the present invention to obtain a latex composition, and using the latex composition, film-forming It is characterized by shaping a body.

Further, the method for producing a dip-formed article of the present invention is a dip-formed article obtained by adding a crosslinking agent to the latex produced by the method for producing a latex according to the present invention to obtain a latex composition. Is molded.

Further, the method for producing an adhesive layer-forming substrate of the present invention is a latex composition obtained by adding a crosslinking agent to the latex produced by the method for producing a latex according to the present invention, and using the latex composition as an adhesive. It is characterized in that it is formed on the surface of the substrate as a layer.

According to the present invention, a good emulsified state can be obtained in the step of emulsifying a raw material, and as a result, a latex production method capable of producing a high-quality latex with few aggregates can be provided.

It is a schematic diagram of a latex manufacturing device which can suitably carry out a latex manufacturing method concerning one embodiment of the present invention. FIG. 2 is a schematic view of the latex manufacturing apparatus shown in FIG. 1, in which the piping configuration for the stirring tank for the rubber solution and the emulsifier aqueous solution is changed. (A) is a side sectional view of a tank main body constituting the stirring tank shown in FIG. 1, and (b) is a plan view of a stirring blade and a rotating shaft included in the stirring tank. It is a sectional side view of a stirring tank provided with a stirring blade according to another embodiment of the present invention. FIG. 9 is a side sectional view of a stirring tank including stirring blades according to a modification of the other embodiment shown in FIG. 4. It is a sectional side view which shows the stirring tank provided with the stirring blade which concerns on the comparative example other than this invention. It is a sectional side view which shows the stirring tank provided with the stirring blade which concerns on the other comparative example other than this invention.

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

(Embodiment)
FIG. 1 schematically shows a latex production apparatus capable of suitably implementing the latex production method according to the embodiment. First, this manufacturing apparatus will be described.

The latex manufacturing apparatus shown in FIG. 1 stores a rubber solution tank 1 in which a rubber solution is prepared, an emulsifier tank 2 in which an emulsifier aqueous solution is prepared, a rubber solution and an emulsifier aqueous solution in a stirring tank 30, and the stirring tank 30 A stirrer 3 for stirring and mixing the rubber solution and the emulsifier aqueous solution therein, an emulsifier 4 for emulsifying the mixed solution of the rubber solution and the emulsifier aqueous solution, and depressurizing the stirring tank 30 to reduce the organic solvent from the emulsion. A decompression pump 5 for distilling and removing, and a concentrator 6 for concentrating the organic solvent removed from the emulsion in the stirring tank 30 are provided.

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

In addition, as shown in FIG. 2, the supply pipes 11 and 12 have a pipe configuration in which they are respectively joined to a joining pipe 13 connected to the agitation tank 30, and the rubber solution and the emulsifier aqueous solution are joined to each other from the joining pipe 13. It may be supplied into the stirring tank 30.

A distillation pipe 15 is installed between the stirring tank 30 and the decompression pump 5, and a valve 7 and a condenser 6 are arranged between the stirring tank 30 and the decompression pump 5 of the distillation pipe 15 in this order from the stirring tank 30 side. Has been done. Each of the tanks 1, 2, 30 is equipped with a heating means (not shown) for heating the solution stored therein.

As shown in FIGS. 1 and 3A, the stirring device 3 includes a stirring tank 30 and a stirring means 40. The stirring tank 30 constitutes the container of the present invention.

As shown in FIG. 1, the agitation tank 30 includes a bottomed cylindrical tank body 31 that stores the mixed solution, and a lid 32 that is detachably fixed to an upper opening of the tank body 31 to close the upper opening. With. The tank body 31 is installed so that its axis extends substantially vertically. The supply pipes 11 and 12, the downstream end of the circulation pipe 14 and the distillation pipe 15 are connected to the lid 32. The circulation pipe 14 has its upstream end connected to the bottom of the tank body 31 and its downstream end connected to the lid 32.

As shown in FIG. 3( a ), the stirring means 40 according to the present embodiment has a plate-shaped stirring blade 50 provided inside the tank body 31, and a rotating shaft 41 of the stirring blade 50. The rotating shaft 41 is arranged coaxially with the axis of the tank body 31, and is rotatably supported via a bearing (not shown). The rotary shaft 41 is rotatably driven by a drive source (both not shown) connected to the upper end of the rotary shaft 41 via a coupling. The drive source is arranged above the lid 32.

The drive source that rotationally drives the rotary shaft 41 may be disposed below the tank body 31 and connected to the lower end of the rotary shaft 41.

The stirring blade 50 has a rectangular shape, and is fixed to the rotating shaft 41 so that the rotating shaft 41 passes through the middle portion in the width direction. That is, the stirring blade 50 has a bilaterally symmetrical shape with the rotating shaft 41 as a line of symmetry, and has a blade portion 51a on one of the left and right sides of the rotating shaft 41 and a blade portion 51b on the other side. The stirring blade 50 rotates together with the rotation shaft 41, and the stirring blade 50 is substantially orthogonal to the rotation direction indicated by the arrow as shown in FIG. ) Opposite to the stirring surface 52.

The stirring blade 50 has a paddle portion 53 at the bottom thereof, and a lattice portion 54 having a lattice-like structure is integrally formed on the upper side of the paddle portion 53. The paddle portion 53 and the lattice portion 54 have the stirring surface 52. In the present embodiment, the ratio of the height dimension occupied by the paddle portion 53 and the lattice portion 54 to the total height of the stirring blade 50 is about 60 to 70% in the lattice portion 54, which is larger than that of the paddle portion 53. It is not limited to this. In FIG. 3A, the symbol L indicates the liquid surface of a solution such as an emulsified liquid, and the stirring blade 50 is used in a state where the whole is immersed in the solution.

The paddle portion 53 has a shape in which the lower end edge thereof is substantially along the bottom surface inside the tank body 31, and the distance between the lower end edge and the bottom surface inside the tank body 31 is set as narrow as possible. It is set to about 200 mm, preferably about 5 to 100 mm, and most preferably about 10 to 50 mm.

The lattice part 54 has a plurality of plate rod-shaped horizontal members 54a and a plurality of plate rod-shaped vertical members 54b orthogonal to these horizontal members 54a. Although the lattice part 54 of this embodiment has two horizontal members 54a and four vertical members 54b, the number and width of each member 54a, 54b are arbitrarily set in consideration of the effect of stirring.

The stirring blade 50 stirs a solution such as an emulsion stored in the stirring tank 30 by rotating together with the rotating shaft 41, but the stirring surface 52 faces the solution to be stirred while the stirring blade 50 is rotating. , And the surface that contacts. Therefore, as shown in FIG. 3( b ), the actual stirring surface 52 is composed of one surface (front surface) of the blade portion 51 a on one side and the other surface (back surface) of the blade portion 51 b on the other side. To be done. The total area of these stirring surfaces 52 corresponds to the area of the stirring blade 50 itself.

Here, the stirring blade 50 according to the present embodiment has the area (corresponding to the area of the left and right stirring surfaces 52 shown in FIG. 3B combined) stored in the stirring tank 30. The ratio of such a solution to the cross-sectional area of the solution (hereinafter, sometimes referred to as wetted area ratio) is 10 to 60%. This is a ratio at which the effect of mixing can be effectively obtained, and within the range, 15 to 50% is preferable, 20 to 40% is more preferable, and 25 to 35% is further preferable.

Further, as shown in FIG. 3A, a plurality of baffle plates 90 extending along the axial direction of the stirring tank 30 are arranged on the inner wall surface of the tank body 31 via upper and lower stays 91. These baffle plates 90 are radially installed so that the width direction thereof is substantially parallel to the radial direction of the tank body 31. The area and number of the baffle plates 90 are arbitrarily set in consideration of the effect of stirring and the like.

Further, each baffle plate 90 is of course provided with an interval with the stirring blade 50 so as not to hinder the rotation of the stirring blade 50, but the interval is 1 to 200 mm in consideration of the effect of stirring and the like. The thickness is preferably set to about 5 to 100 mm, most preferably about 10 to 50 mm.

According to the stirring means 40 of the present embodiment, when the stirring blade 50 rotates in one direction, it is possible to stir the solution such as the emulsion stored in the stirring tank 30 as follows. That is, the solution in the stirring tank 30 is pushed radially outward by the lower paddle portion 53 to collide with the inner wall surface of the tank body 31, and then rises by the action of the baffle plate 90, and then the inner wall surface of the upper portion of the tank body 31. From the center to the center of the rotating shaft 41, then flows downward through the rotating shaft 41 and the lattice portion 54 and returns to the paddle portion 53, thereby generating a vertical circulating flow.

In the solution which is agitated while being circulated as described above, the descending rubber is sheared and subdivided by each horizontal member 54a and each vertical member 54b of the lattice portion 54, and further generated rearward in the rotational direction of these members 54a, 54b. The rubber is entrained in the fine vortex that is mixed and mixed.

Further, since the lower end portion of the paddle portion 53 is close to the bottom portion inside the stirring tank 30, the solution can be placed on the circulation flow without being left at the bottom portion to be stirred. In addition, the baffle plate 90 functions to prevent the solution extruded radially outward by the paddle portion 53 from rotating as the stirring blade 50 rotates and to generate an upward flow. Further, the horizontal members 54a and the vertical members 54b of the lattice portion 54 act to subdivide and mix the descending solution as described above.

The emulsifier 4 may be any device as long as it can apply strong shearing force to the solution and continuously mix the solution, and is not particularly limited. For example, a plurality of slits may be provided for a stator having a plurality of slits. A rotor-stator type emulsifying machine having a plurality of rotor-stator pairs in which the rotor having the above-mentioned structure rotates relatively is preferably used. Examples of such a rotor-stator emulsifier include a trade name “TK Pipeline Homomixer” (manufactured by Primix Co., Ltd.), a trade name “Slusha” (manufactured by Nippon Coke Industry Co., Ltd.), and a trade name “Trigonal” (Japan Use commercially available products such as Coke Kogyo Co., Ltd., product name "Cavitron" (Eurotech Co., Ltd.), product name "Milder" (Pacific Machine Engineering Co., Ltd.), product name "Fine Flow Mill" (Pacific Machine Engineering Co., Ltd.) You can

Further, as the emulsifying machine 4, it is preferable to use one having a pump function because it can pressure-feed and circulate the solution, but when using one having no pump function, a pressure-feeding pump is provided in the middle of the circulation pipe 14. It can be placed separately.

Next, a method for producing latex according to this embodiment will be described.

The method for producing a latex according to the present embodiment is a step of emulsifying a rubber composition containing rubber, an organic solvent, water and an emulsifier to obtain an emulsion, and removing the organic solvent from the emulsion obtained in the emulsification step. And a desolvation step.

In the emulsification step, the rubber composition is emulsified by stirring with the stirring blade 50 in the stirring tank 30 of the stirring device 3.

The method for producing a latex according to the present embodiment, the emulsification step, a rubber solution in which a rubber and an organic solvent are mixed, and a coarse emulsification step of obtaining an emulsion in a coarse emulsified state by mixing an emulsifier aqueous solution, It includes a case where it is divided into a rough emulsified emulsion obtained in the rough emulsification step and a circulation emulsification step in which the emulsion is circulated through the emulsifier 4 and further emulsified. In this case, it further includes a case where the emulsion is stirred using the stirring device 3 in at least one of the rough emulsification step and the circulation emulsification step.

Hereinafter, an example of the latex manufacturing method according to the present embodiment performed using the latex manufacturing apparatus shown in FIG. 1 will be described more specifically.

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

That is, the rubber and the organic solvent are supplied at a predetermined ratio into the rubber solution tank 1 and the rubber is dissolved by stirring and heating to, for example, about 60° C. to prepare a rubber solution. Further, an emulsifier and water are supplied into the emulsifier tank 2 at a predetermined ratio and mixed, and then heated to, for example, about 60° C. to prepare an emulsifier aqueous solution.

Next, the rubber solution is supplied directly from the rubber solution tank 1 and the emulsifier aqueous solution from the emulsifier tank 2 directly into the stirring tank 30 through the supply pipes 11 and 12, respectively. Then, in the stirring tank 30, a mixture (rubber composition) of the rubber solution and the aqueous emulsifier solution is stirred and mixed by the stirring blade 50 to obtain an emulsion.

The rubber solution prepared in the rubber solution tank 1 and the emulsifier aqueous solution prepared in the emulsifier tank 2 are maintained at a predetermined temperature by heating each tank 1 and 2 as necessary from the viewpoint of favorably emulsifying. Is desirable. The temperatures of the rubber solution and the aqueous emulsifier solution are not particularly limited, but are preferably 20 to 100° C., more preferably 40 to 90° C., and further preferably 60 to 80° C., respectively.

Further, when the rubber solution and the emulsifier aqueous solution are continuously fed into the stirring tank 30, the supply ratios of the rubber solution and the emulsifier aqueous solution are not particularly limited, but from the viewpoint of favorably emulsifying the rubber solution and the emulsifier aqueous solution. The volume ratio is preferably 1:2 to 1:0.3, more preferably 1:1.5 to 1:0.5, and further preferably 1:1 to 1:0.7.

[Rough emulsification process]
The emulsification step of the present embodiment includes a case where an emulsion is obtained through a rough emulsification step and a circulating emulsification step.

≪Coarse emulsified state refers to the emulsified state of the previous stage where the solubility of rubber is relatively low and it is not sufficiently emulsified. In the rough emulsification step, similarly to the above emulsification step, the rubber solution is continuously supplied from the rubber solution tank 1 and the emulsifier aqueous solution is supplied from the emulsifier tank 2 to the stirring tank 30, respectively. The mixture (rubber composition) of the rubber solution and the emulsifier aqueous solution is agitated by the agitating blade 50 to be mixed.

[Circulating emulsification process]
Next, the emulsification machine 4 is operated, and the circulation emulsification step of returning the roughened emulsified liquid from the stirring tank 30 to the stirring tank 30 through the circulation pipe 14 is performed at least once. In the circulating emulsification step, the emulsified liquid is circulated by the emulsifying machine 4 so as to return from the stirring tank 30 to the stirring tank 30 via the circulation pipe 14, and passes through the emulsifying machine 4. The emulsion is continuously emulsified, and the emulsion is stored in the stirring tank 30. The method for producing latex in the present embodiment preferably includes the circulating emulsification step, but does not necessarily include the circulating emulsification step.

When the circulation emulsification step is performed after the rough emulsification step as described above to obtain an emulsion, when the emulsion is stirred by the stirring blade 50 in the stirring tank 30 in both the rough emulsification step and the circulation emulsification step In addition, either operation pattern is selected when the emulsified liquid is stirred by the stirring blade 50 only in the rough emulsification step and when the emulsified liquid is stirred by the stirring blade 50 only in the circulation emulsification step.

The operation pattern of stirring the emulsified liquid in the stirring tank 30 is appropriately selected depending on the emulsification situation and the like, and at least one of the rough emulsification step and the circulation emulsification step is selected from the viewpoint of favorably emulsifying. The emulsion may be stirred in step 1, but among these, it is more preferable to stir the emulsion in the circulating emulsification step. However, it is most preferable to stir the emulsion in both the rough emulsification step and the circulation emulsification step.

In the rough emulsification step, the rubber composition, which is a mixture of the rubber solution and the emulsifier aqueous solution, is not stirred by the stirring blade 50 in the stirring tank 30, and the rubber solution and the emulsifier aqueous solution are combined as shown in FIG. 2, for example. The rubber composition may be coarsely emulsified and supplied into the stirring tank 30 by merging in the pipe 13 and continuously mixing only with the emulsifier 8 arranged in the merging pipe 13.

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

(Rubber)
Examples of the rubber that can be used in this embodiment include natural rubber and synthetic rubber. The synthetic rubber is not particularly limited, and examples thereof include isoprene rubber (IR), styrene-isoprene-styrene block copolymer (SIS), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), styrene butadiene rubber (SBR). , Isobutyene/isoprene rubber (IIR) and the like. Among them, natural rubber, isoprene rubber (IR) and styrene-isoprene-styrene block copolymer (SIS) are excellent in mechanical properties such as tensile strength and elongation when latex is used as a dip molded product. Preferred are isoprene rubber (IR) and styrene-isoprene-styrene block copolymer (SIS), and isoprene rubber (IR) is more preferred.

(Organic solvent)
The organic solvent for dissolving/dispersing rubber into a rubber solution is not particularly limited, and examples thereof include aromatic hydrocarbon solvents such as benzene, toluene, xylene, and fats such as cyclopentane, cyclopentene, cyclohexane, and cyclohexene. It can be appropriately selected from a cyclic hydrocarbon solvent, an aliphatic hydrocarbon solvent such as butane, pentane, hexane and heptane, or a halogenated hydrocarbon solvent such as methylene chloride, chloroform and ethylene dichloride. ..

The content ratio of the rubber in the rubber solution is not particularly limited, but is preferably 3 to 30% by weight, more preferably 5 to 20% by weight, and further preferably 7 to 15% by weight.

(emulsifier)
The emulsifier is not particularly limited, but an anionic emulsifier can be preferably 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 sodium dodecylbenzenesulfonate and dodecylbenzenesulfone. Alkylbenzenesulfonates such as potassium acid salt, sodium decylbenzenesulfonate, potassium decylbenzenesulfonate, sodium cetylbenzenesulfonate, potassium cetylbenzenesulfonate, etc., or sodium di(2-ethylhexyl)sulfosuccinate, di(2-ethylhexyl) Alkyl sulfosuccinates such as potassium sulfosuccinate and sodium dioctyl sulfosuccinate, alkyl sulfate ester salts such as sodium lauryl sulfate and potassium lauryl sulfate, or polyoxyethylene salts such as sodium polyoxyethylene lauryl ether sulfate and potassium polyoxyethylene lauryl ether sulfate. Examples thereof include ethylene alkyl ether sulfate ester salts and monoalkyl phosphates such as sodium lauryl phosphate and potassium lauryl phosphate.

Among these anionic emulsifiers, fatty acid salts, alkylbenzene sulfonates, alkylsulfosuccinates, alkyl sulfate ester salts and polyoxyethylene alkyl ether sulfate ester salts are preferable, fatty acid salts and alkylbenzene sulfonate salts are more preferable, and fatty acid salts are More preferably, sodium rosinate and potassium rosinate are particularly preferable from the viewpoint that generation of aggregates in the latex of the obtained rubber can be prevented more appropriately.

The content ratio of the emulsifier in the aqueous solution is not particularly limited, but from the viewpoint of favorably emulsifying, it is preferably 0.1 to 5% by weight, more preferably 0.3 to 3% by weight, and 0.5. It is more preferable that the content is up to 2% by weight.

[Desolvation step]
The desolvation step is a step of removing the organic solvent from the emulsion obtained in the emulsification step. As a method of desolvation, a method capable of controlling the content of the organic solvent in the emulsion to be 500 ppm by weight or less is preferable, and for example, a method such as vacuum distillation, atmospheric distillation, steam distillation, and centrifugation is adopted. can do. Among these, vacuum distillation is preferable from the viewpoint of being able to remove the organic solvent appropriately and efficiently.

In the present embodiment, the decompression pump 5 and the concentrator 6 are used to depressurize the emulsified liquid obtained in the emulsification step and stored in the stirring tank 30 to desolvate it. That is, in the desolvation step of the present embodiment, the valve 7 is opened and the decompression pump 5 is operated from a state where the emulsion in the stirring tank 30 is heated to, for example, about 80° C., and the inside of the stirring tank 30 is, for example, less than 700 mmHg. Depressurize to. As a result, 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 pipe 15, concentrated by the concentrator 6, and collected.

In the present embodiment, it is preferable that the desolvation step is performed while stirring the emulsion in the stirring tank 30 with the stirring blades 50, since aggregates existing in the latex obtained after desolvation tend to be reduced.

In the desolvation process by vacuum distillation, the pressure in the stirring tank 30 is preferably reduced to less than 700 mmHg. If the pressure in the stirring tank 30 is high in the desolvation step, the desolvation step may take a long time, and if the pressure is low, the emulsion may foam excessively. Therefore, from the viewpoint of suppressing the occurrence of these problems, the pressure in the stirring tank 30 in the desolvation step is preferably 1 to 600 mmHg, more preferably 10 to 500 mmHg, and further preferably 100 to 400 mmHg. ..

Further, the temperature of the emulsion in the stirring tank 30 in the desolvation step in the present embodiment is preferably heated to a temperature equal to or higher than the boiling point of the organic solvent contained in the emulsion, but specifically, It is more preferable to control the temperature to be 5° C. or higher than the boiling point, and it is more preferable to control the temperature to be 10° C. or higher. The upper limit of the temperature of the emulsion in the stirring tank 30 in the solvent removal step is not particularly limited, but it is preferably less than 100°C.

[Centrifugation process]
In the present embodiment, after performing the desolvation step, the emulsified liquid from which the organic solvent has been removed is transferred to a centrifuge and centrifuged to obtain a light liquid with an increased solid content concentration as a rubber latex. ..

In the centrifugation step, in order to improve the mechanical stability of the obtained latex, a pH adjusting agent is added in advance to the emulsion from which the organic solvent has been removed, and the pH is set to 7 or higher, preferably 9 or higher.

Examples of the pH adjusting agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, and alkali metal hydrogen carbonates such as sodium hydrogen carbonate. Examples thereof include ammonia, organic amine compounds such as trimethylamine and triethanolamine, and alkali metal hydroxides and ammonia are preferable.

Further, as described above, the rubber latex obtained in the present embodiment is added with an antifoaming agent, an antiseptic, a chelating agent, an oxygen scavenger, a dispersant, an antiaging agent or the like which is blended in the latex field. You may mix|blend an agent suitably.

Further, in the case of using natural rubber as a raw material of rubber, when the obtained latex is used as a dip-molded body that comes into contact with the human body, it is necessary to decompose and remove proteins that cause allergic symptoms in the human body at the latex stage. is there.

The above is the method for producing latex according to the present embodiment. From the latex produced by the production method according to the present embodiment, a dip-formed article such as rubber gloves can be obtained via the latex composition. The dip molded body is an aspect of the film molded body according to the present invention. Furthermore, an adhesive layer-forming substrate can be obtained using the latex produced by the production method according to this embodiment. The adhesive layer-forming base material refers to a composite material in which a latex composition is formed as an adhesive layer on the surface of the base material.

The following are specific examples of the method for producing the latex composition, the dip molded product, and the adhesive layer-forming substrate.

(Production of latex composition)
The latex composition can be obtained by adding a crosslinking agent to the latex.

As the cross-linking agent, for example, sulfur powder, sulfur flower, precipitated sulfur, colloidal sulfur, surface-treated sulfur, sulfur such as insoluble sulfur, or sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, caprolactam disulfide, phosphorus-containing phosphorus. Examples thereof include sulfur-containing compounds such as polysulfide, polymeric polysulfide, and 2-(4′-morpholinodithio)benzothiazole. Of these, sulfur is preferably used. The crosslinking agent may be used alone or in combination of two or more.

The content of the cross-linking agent is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 3 parts by weight with respect to 100 parts by weight of the rubber contained in the rubber latex. .. By setting the content of the cross-linking agent within the range, the tensile strength of the obtained dip-molded product can be further increased.

Also, the latex composition preferably further contains a crosslinking accelerator. As the crosslinking accelerator, those usually used in dip molding can be used, and examples thereof include diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid. Dithiocarbamic acids and their zinc salts, or 2-mercaptobenzothiazole, 2-mercaptobenzothiazole zinc, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(2,4-dinitrophenylthio)benzothiazole, 2 -(N,N-diethylthiocarbaylthio)benzothiazole, 2-(2,6-dimethyl-4-morpholinothio)benzothiazole, 2-(4'-morpholinodithio)benzothiazole, 4-morphonylyl-2-benzothiazyl Examples thereof include disulfide and 1,3-bis(2-benzothiazyl.mercaptomethyl)urea, and zinc diethyldithiocarbamate, zinc didibutyldithiocarbamate, and zinc 2-mercaptobenzothiazole are preferable. The crosslinking accelerator may be used alone or in combination of two or more.

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 in the range, the tensile strength of the obtained dip-molded product can be further increased.

Further, it is preferable that the latex composition further contains zinc oxide. The content of zinc oxide is not particularly limited, but is preferably 0.1 to 5 parts by weight, and more preferably 0.2 to 2 parts by weight with respect to 100 parts by weight of the rubber contained in the rubber latex. By setting the content of zinc oxide in the above range, it is possible to further improve the tensile strength of the obtained dip-molded article while improving the emulsion stability.

The latex composition further requires an antioxidant, a dispersant, a reinforcing agent such as carbon black, silica, talc, a filler such as calcium carbonate or clay, an ultraviolet absorber, a compounding agent such as a plasticizer, and the like. Can be blended accordingly.

For example, antiaging agents include 2,6-di-4-methylphenol, 2,6-di-t-butylphenol, butylhydroxyanisole, 2,6-di-t-butyl-α-dimethylamino-p-cresol. , Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, styrenated phenol, 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4 ,4'-methylenebis(2,6-di-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), alkylated bisphenol, butyl of p-cresol and dicyclopentadiene Sulfur atom-free phenolic antioxidants such as chlorinated reaction products, 2,2'-thiobis-(4-methyl-6-t-butylphenol), 4,4'-thiobis-(6-t-butyl) -O-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, and other thiobisphenol antioxidants, Alternatively, phosphite-based antioxidants such as tris(nonylphenyl)phosphite, diphenylisodecylphosphite, tetraphenyldipropyleneglycol/diphosphite, sulfur ester-based antioxidants such as dilauryl thiodipropionate, or phenyl- α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamide)-diphenylamine, 4,4′-(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N- Amine-based antioxidants such as isopropyl-N'-phenyl-p-phenylenediamine and butyraldehyde-aniline condensate, or quinoline-based aging such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline Examples of the antioxidant include hydroquinone antiaging agents such as 2,5-di-(t-amyl)hydroquinone. These antioxidants may be used alone or in combination of two or more.

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

The method for preparing the latex composition is not particularly limited, but for example, using a dispersing machine such as a ball mill, a kneader, or a disperser, a rubber latex is mixed with a crosslinking agent, and various compounding agents to be mixed as necessary. Examples of the method include a method of preparing an aqueous dispersion of compounding ingredients other than the rubber latex using the above disperser, and then mixing the aqueous dispersion with the rubber latex.

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. Further, the solid content concentration of the latex composition is preferably in the range of 15 to 65% by weight.

The latex composition is preferably aged (pre-crosslinked) before being subjected to dip molding from the viewpoint of further enhancing the mechanical properties of the obtained dip molded product. The time for pre-crosslinking is not particularly limited and depends on the temperature of pre-crosslinking, but is preferably 1 to 14 days, more preferably 1 to 7 days. The temperature of pre-crosslinking is preferably 20 to 40°C.

After pre-crosslinking, it is preferable to store at a temperature of 10 to 30° C. until it is subjected to dip molding. This is because the tensile strength of the obtained dip-molded product may decrease if it is stored at a temperature higher than this.

(Manufacture of dip molding)
The dip-molded article can be obtained by dip-molding the above latex composition. Dip molding is a molding method in which the latex composition is deposited on the surface of the mold immersed in the latex composition, then the mold is pulled out of the latex composition, and then the latex composition deposited on the surface of the mold is dried. .. The mold may be preheated before being immersed in the latex composition. In addition, a coagulant can be used if necessary before the mold is dipped in the latex composition or after the mold is pulled up from the latex composition.

Specific examples of the method of using the coagulant include a method of immersing the mold in a coagulant solution and then immersing the mold in a latex composition (anode coagulation dipping method), or a method in which the mold is first immersed in the latex composition. After that, there is a method of immersing the mold in a coagulant solution (Teag coagulation dipping method) and the like, but the anode coagulation dipping method is preferable from the viewpoint that a dip molded body with less thickness unevenness can be obtained.

Specific examples of the coagulant include metal halides such as barium chloride, calcium chloride, magnesium chloride, zinc chloride and aluminum chloride, nitrates such as barium nitrate, calcium nitrate and zinc nitrate, barium acetate, calcium acetate and zinc acetate. And water-soluble polyvalent metal salts such as calcium sulfate, magnesium sulfate, and aluminum sulfate. Among them, calcium salt is preferable, and calcium nitrate is more preferable. These water-soluble polyvalent metal salts can be used alone or in combination of two or more.

The coagulant is preferably used in the form of an aqueous solution. This aqueous solution may further contain a water-soluble organic solvent such as methanol or ethanol, or a nonionic surfactant. Although the concentration of the coagulant varies depending on the type of the water-soluble polyvalent metal salt, it is preferably 5 to 50% by weight, more preferably 10 to 30% by weight.

After pulling up the mold from the latex composition, heating is usually performed to dry the deposit formed into a film on the mold. The drying conditions may be appropriately selected.

Next, by heating, the deposit formed as a film on the mold is cross-linked. The heating conditions at the time of crosslinking are not particularly limited, but the heating temperature is preferably 60 to 150°C, more preferably 100 to 130°C. The heating time is preferably 10 to 120 minutes.

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

Also, before or after heating the mold on which the latex composition is deposited, the mold should be washed with water or warm water to remove water-soluble impurities (for example, excess surfactant or coagulant). Is preferred. When using warm water, the temperature of the warm water is preferably 40 to 80°C, more preferably 50 to 70°C.

After cross-linking, the dip-molded product is removed from the mold. As the desorption method, a method of peeling from the mold by hand, a method of peeling from the mold by water pressure or compressed air pressure, and the like are adopted. As long as the dip-molded article during crosslinking has sufficient strength for desorption, it may be desorbed during the crosslinking and then the subsequent crosslinking may be continued.

As the dip molded body, for example, rubber gloves are particularly preferably manufactured. When the dip molded product is a rubber glove, organic particles such as talc, calcium carbonate, etc., or starch particles, etc. are used to prevent the dip molded products from sticking to each other at their contact surfaces and to improve the slippage when they are put on and taken off from the hand. Fine particles may be dispersed on the surface of the glove, an elastomer layer containing fine particles may be formed on the surface of the glove, or the surface layer of the glove may be chlorinated.

In addition to the above rubber gloves, the dip-molded article may be a medical item such as a baby bottle nipple, a dropper, a tube, a water pillow, a balloon sack, a catheter, a condom, a toy such as a balloon, a doll, a ball, or It can be applied to industrial products such as pressure molding bags and gas storage bags, and various rubber moldings such as finger cots.

Also, the thickness of the dip molded body depends on the application and product, and is molded, for example, with a thickness of about 0.03 to 0.50 mm.

(Adhesive layer forming base material)
The adhesive layer-forming substrate according to the present embodiment is obtained by forming an adhesive layer formed using the above latex composition on the surface of the substrate.

The base material in the present embodiment is not particularly limited, but a fiber base material can be used, for example. The type of fibers constituting the fiber base material is not particularly limited, and examples thereof include vinylon fibers, polyester fibers, nylon, polyamide fibers such as aramid (aromatic polyamide), glass fibers, cotton, rayon and the like. These can be appropriately selected according to the application.

The shape of the fiber base material is not particularly limited, but examples thereof include staples, filaments, cords, ropes, woven fabrics (sailcloths, etc.), etc., and can be appropriately selected according to the application. For example, the adhesive layer-forming substrate can be used as a substrate-rubber composite by adhering it to rubber via the adhesive layer. The base material-rubber composite is not particularly limited, but for example, a rubber toothed belt with a core wire using a cord-shaped fiber base material or a base cloth-shaped fiber base material such as canvas is used. Examples thereof include rubber toothed belts.

The method for obtaining the base material-rubber composite is not particularly limited, but for example, the latex composition is adhered to the base material by dipping treatment or the like to obtain an adhesive layer forming base material, and then the adhesive layer forming base material. Is placed on rubber, and heating and pressurizing it.

The pressurization in the above method can be performed using a press molding machine, a metal roll, an injection molding machine, or the like. The pressure applied is preferably 0.5 to 20 MPa, more preferably 2 to 10 MPa. The heating temperature is preferably 130 to 300°C, more preferably 150 to 250°C. The heating and pressurizing time in the above method is preferably 1 to 180 minutes, more preferably 5 to 120 minutes. Depending on the method of heating and pressurizing, the molding of rubber and the adhesion of the adhesive layer-forming base material to the rubber can be performed simultaneously. In addition, it is preferable to form a mold for imparting a desired surface shape to the rubber of the target base material-rubber composite on the inner surface of the mold of the press molding machine used for pressurization or the surface of the roll. ..

In addition, a base material-rubber-base material composite material can be mentioned as one embodiment of the base material-rubber composite material. The base material-rubber-base material composite can be formed, for example, by combining a base material (which may be a composite of two or more kinds of base materials) and a base material-rubber composite. Specifically, a core wire as a base material, rubber and a base cloth as a base material are stacked (at this time, a latex composition is appropriately adhered to the core wire and the base cloth as an adhesive layer forming base material), A base material-rubber-base material composite can be obtained by applying pressure while heating.

The base material-rubber composite obtained by using the adhesive layer-forming base material according to the present embodiment is excellent in mechanical strength, abrasion resistance and water resistance. Therefore, the flat belt, V belt, V It can be suitably used as a belt such as a ribbed belt, a round belt, a square belt, and a toothed belt. Further, the base material-rubber composite obtained by using the adhesive layer-forming base material according to the present embodiment has excellent oil resistance and can be suitably used as an in-oil belt. Further, the base material-rubber composite obtained by using the adhesive layer-forming base material according to the present embodiment can be suitably used for hoses, tubes, diaphragms and the like. Examples of the hose include a single tube rubber hose, a multi-layer rubber hose, a braided reinforcing hose, and a cloth wound reinforcing hose. Examples of the diaphragm include a flat diaphragm and a rolling diaphragm.

Furthermore, the base material-rubber composite obtained using the adhesive layer-forming base material according to the present embodiment can be used as an industrial product such as a seal or a rubber roll, in addition to the above-mentioned applications. Examples of the seal include a rotating part, a swinging part, a reciprocating part, and a fixed part seal. Examples of the moving part seal include an oil seal, a piston seal, a mechanical seal, a boot, a dust cover, a diaphragm, an accumulator and the like. Examples of the fixed part seal include an O-ring and various gaskets. As the rubber roll, a roll that is a part of OA equipment such as a printing machine or a copying machine, a fiber processing roll such as a drawing roll for spinning, a draft roll for spinning, or a steelmaking roll such as a bridle roll, a snubber roll, or a steering roll. Are listed.

(Action)
Next, the operation of the method for producing latex according to this embodiment will be described.

In the method for producing latex according to the present embodiment, the rubber composition (rubber solution+emulsifier aqueous solution) stored in the stirring tank 30 of the stirring device 3 in the emulsification step of the raw material including the rough emulsification step is performed by the flat stirring blade 50. Stir to mix.

With the stirring blade 50 according to the present embodiment, it is possible to generate a circulation flow that circulates the emulsion in the vertical direction as described above. Therefore, it is possible to effectively disperse the rubber that has a relatively low specific gravity and floats near the liquid surface of the solution and easily stagnates in the solution in the vertical direction. Can be obtained. Therefore, since the rubber composition can be emulsified in a good state in the emulsification step, it is possible to produce a high-quality latex with few aggregates.

In addition, in the stirring blade 50 according to the present embodiment, the rubber in the solution that circulates vertically is sheared and subdivided by the lattice portion 54 having the lattice structure, and the fine particles generated behind the lattice portion 54 in the rotation direction. The rubber is caught in the vortex and mixed. For this reason, miniaturization and mixing of the rubber are promoted, a good emulsified state is easily obtained, and aggregates can be reduced.

Further, in the stirring blade 50 of the present embodiment, since the lower end portion of the paddle portion 53 is close to the bottom portion of the stirring tank 30, the solution can be put on the circulation flow without being left at the bottom portion and stirred. Therefore, the upper and lower circulating flows are appropriately generated, the rubber is dispersed, and a good emulsion can be obtained.

Further, the baffle plate 90 acts to suppress the solution extruded radially outward by the paddle portion 53 from rotating with the rotation of the stirring blade 50 and to generate an upward flow. Also by this, the upper and lower circulating flows are appropriately generated, the rubber is dispersed, and a good emulsion can be obtained.

Further, in the method for producing a latex according to the present embodiment, even in the desolvation step, the emulsified liquid is stirred by the stirring blade 50, so that the rubber in the emulsified liquid being desolvated is circulated up and down to be agitated. Because of sufficient mixing, the latex obtained after desolvation will be of high quality with few aggregates.

In the above embodiment, the emulsification process including the rough emulsification process and the desolvation process are performed by one stirring tank 30, but two stirring tanks 30 are prepared and the emulsification process and the desolvation process are different. Alternatively, the stirring tank 30 may be used. When the stirring blade 50 does not perform stirring in the desolvation step, the emulsified liquid obtained in the stirring tank 30 may be transferred to a tank dedicated to desolvation to perform the desolvation step.

(Other embodiment of stirring blade)
Next, with reference to FIG. 4 and FIG. 5, another embodiment of the stirring blade 50 constituting the stirring means 40 will be described. In each drawing of other embodiments, the same components as those in the above-mentioned embodiment are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 4 shows a stirring tank (container) 30B including a stirring blade 60 according to another embodiment. The stirring blade 60 has a flat plate shape and a rectangular shape as a whole, and has a bilaterally symmetrical shape with the rotating shaft 41 as a symmetry line. The stirring blade 60 has a lower rectangular paddle portion 63 and right and left rectangular blade portions 64a and 64b extending upward from the paddle portion 63. The rotating shaft 41 is fixed to the paddle part 63 so as to penetrate the center of the paddle part 63 in the width direction, and the stirring blade 60 rotates together with the rotating shaft 41.

The left and right wing portions 64a, 64b each have an inner side (rotating shaft 41 side) edge portion 65, and these edge portions 65 are formed parallel to the rotating shaft 41. The left and right wings 64a and 64b each have an outer edge portion 66, and these edge portions 66 are formed in a sawtooth shape in which irregularities are repeated. A predetermined gap is formed between the inner edge portion 65 and the rotary shaft 41, and between the outer edge portion 66 and the baffle plate 90.

The ratio of the height dimension occupied by the paddle portion 63 and each blade portion 64a, 64b to the entire height of the stirring blade 60 is about 60 to 70% for each blade portion 64a, 64b, which is larger than the paddle portion 63. However, it is not limited to this.

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

FIG. 5 shows a stirring tank (container) 30C equipped with a stirring blade 70. The stirring blade 70 has the same shape as the stirring blade 60 shown in FIG. 4, but is a modification in which the size thereof is changed. Therefore, the same components as those of the stirring blade 60 are designated by the same reference numerals, and the description thereof will be omitted.

The stirring blade 70 of the modified example shown in FIG. 5 is larger in area than the stirring blade 60 shown in FIG. 4, that is, the area of the stirring surface 72 is, for example, about 10 to 30%. 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%.

According to the flat plate-shaped stirring blades 60 and 70 according to another embodiment, as in the case of the stirring blades 50, it is possible to generate a circulating flow that circulates vertically in the solution to be stirred, and has a relatively high specific gravity. It is possible to circulate rubber, which floats near the liquid surface of the solution and easily stagnates, up and down to disperse it in a homogeneous state. Therefore, it is possible to produce a high-quality latex with few aggregates.

Next, examples and comparative examples of the present invention will be described. The present invention is not limited to the examples below.

[Example 1]
(Production of rubber solution)
After storing 85 parts of cyclohexane (organic solvent) in the rubber solution tank 1 shown in FIG. 1, an isoprene polymer having a weight average molecular weight of 1,300,000 (synthetic rubber: trade name “NIPOL IR2200L”, Nippon Zeon ( Co., Ltd., isoprene homopolymer, cis bond unit amount 98%) 15 parts, and the temperature is raised to 60° C. with stirring in the rubber solution tank 1 to dissolve, and a cyclohexane solution of the isoprene polymer is obtained. A rubber solution (a) was prepared.

(Production of emulsifier aqueous solution)
In an emulsifier tank 2 shown in FIG. 1, 10 parts of rosin acid sodium salt and 5 parts of dodecylbenzenesulfonic acid sodium salt are mixed with water, and an aqueous solution of anionic surfactant having a concentration of 2.3% by weight is added to the emulsifier aqueous solution (b). Then, the temperature was raised to 60°C.

(Coarse emulsification process)
Then, the rubber solution (a) composed of the cyclohexane solution and the emulsifier aqueous solution (b) composed of the anionic surfactant aqueous solution were fed into the stirring tank 30 in a weight ratio of 1:1. Then, the mixture was stirred for 30 minutes with a stirring blade 50 having a liquid contact area ratio of 30% to coarsely emulsify.

(Circulating emulsification process)
Next, while stirring the obtained crude emulsion with the stirring blade 50, the circulation pipe 14 is circulated using the emulsifier 4 so that the number of circulation is two, and the emulsion is circulated to obtain an emulsion (c). It was The circulation number was calculated by “flow rate (L/HR)/L×HR (L: amount of coarse emulsion, HR: operating time)”. Further, as the emulsifying machine 4, a trade name “Milder MDN310” (manufactured by Taiheiyo Kiko Co., Ltd.) was used. After the circulation emulsification was completed, the emulsion was allowed to stand for 20 minutes in the stirring tank 30 to observe the liquid surface, but no suspended matter was present.

(Desolvation step)
Next, the valve 7 is opened and the decompression pump 5 is operated to reduce the pressure in the stirring tank 30 to −0.01 to −0.09 MPa (gauge pressure) while stirring the emulsion (c) with the stirring blades 50. The mixture was heated to 80° C., whereby cyclohexane was distilled off, and an aqueous dispersion (d) of the synthetic isoprene polymer was obtained in the stirring tank 30.

While removing cyclohexane, the inside of the stirring tank 30 was observed, but almost no foaming was observed. In addition, after the aqueous dispersion (d) was extracted from the stirring tank 30, the solidified matter adhered to the inner wall of the stirring tank 30 and the stirring blade 50 was collected, and the weight of the collected product was measured. Met.

(Centrifugation process)
Next, the aqueous dispersion (d) obtained by extracting from the stirring tank 30 was centrifuged using a centrifuge to obtain a light liquid as a synthetic polyisoprene latex (e) having a solid content concentration of 60% by weight.

(Production of latex composition for dip molding)
While stirring the synthetic polyisoprene latex (e) obtained as described above, a 5 wt% aqueous solution of sodium dibutyldithiocarbamate was added (the addition amount was 0 parts of sodium dibutyldithiocarbamate per 100 parts of the synthetic polyisoprene. .4).

On the other hand, a styrene-maleic acid mono-sec-butyl ester-maleic acid monomethyl ester polymer (trade name: Scripset550, manufactured by Hercules) was neutralized with 100% of the carboxyl groups in the polymer using sodium hydroxide. Then, a sodium salt aqueous solution (concentration: 10% by weight) as a dispersant (f) was prepared.

Then, the dispersant (f) was added to 100 parts of the synthetic polyisoprene latex (e) so as to be 0.6 part in terms of solid content and mixed, and the mixture was stirred while stirring in the mixture. 1.5 parts of zinc oxide, 1.5 parts of sulfur, 1.5 parts of sulfur, 2 parts of anti-aging agent (trade name: Wingstay L, manufactured by Goodyear), and zinc diethyldithiocarbamate based on 100 parts of synthetic polyisoprene of 0. An aqueous dispersion of these compounding agents was added so that the amount was 0.35 part and the mercaptobenzothiazole zinc salt was 0.3 part. Thereafter, an aqueous potassium hydroxide solution was further 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. It was Then, the obtained latex composition (g) was aged at 25° C. for 48 hours.

(Manufacture of dip molding)
The surface of the glass mold (about 5 cm in diameter and about 15 cm in length of the ground portion) was ground and preheated in an oven at 70° C., and then the glass mold was treated with 16% by weight of calcium nitrate and 0.05% by weight. % Polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) was immersed in an aqueous solution of a coagulant for 5 seconds and then taken out.

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

Then, the glass mold having the film-like synthetic polyisoprene latex (e) formed on the surface thereof is placed in an oven, heated from 50° C. to 60° C. for 25 minutes to be pre-dried, and then placed in an oven at 70° C. for 10 minutes. Let stand for a minute to dry further. Then, the glass mold was immersed in warm water of 60° C. for 2 minutes and then air-dried at room temperature for 10 minutes.

Next, the glass mold coated with the film-shaped synthetic polyisoprene latex (e) 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 from the glass mold to obtain a dip-molded article made of synthetic polyisoprene latex.

[Example 2]
Dip in the same manner as in Example 1 except that the circulation emulsification step was performed using the stirring tank 30B equipped with the stirring blade 60 (wetted area ratio: 15%) shown in FIG. 4 instead of the stirring blade 50. A molded body was obtained.

[Example 3]
Dip in the same manner as in Example 1 except that the circulating emulsification step was performed using the stirring tank 30C equipped with the stirring blade 70 (wetted area ratio: 45%) shown in FIG. 5 instead of the stirring blade 50. A molded body was obtained.

[Example 4]
Dip in the same manner as in Example 1 except that the desolvation step was performed using a stirring tank 30B equipped with a stirring blade 60 (wetted area ratio: 15%) shown in FIG. 4 instead of the stirring blade 50. A molded body was obtained with.

[Example 5]
Example 1 except that the desolvation step was performed using a stirring tank 100 equipped with a two-stage paddle type stirring blade 110 (wetted area ratio: 5%) shown in FIG. 6 instead of the stirring blade 50. Similarly, a dip molded body was obtained.

The stirring tank 100 shown in FIG. 6 includes a tank body 101 and a lid (not shown), and also includes a plurality of baffle plates 109 similar to the baffle plate 90 described above. Two stirring blades 110 are arranged in the tank main body 101, and these stirring blades 110 are fixed to the rotating shaft 104 at predetermined intervals in the vertical direction.

The stirring blade 110 is a stirring blade according to a comparative example other than the present invention, has a plate shape extending in the left-right direction from the rotating shaft 104, is inclined at approximately 45° with respect to the rotation direction, and the inclination direction is right and left. It has a staggered shape. The liquid contact area ratio: 5% is the sum of the liquid contact area ratios of the two upper and lower stirring blades 110.

[Comparative Example 1]
Dip molding was performed in the same manner as in Example 1 except that the rough emulsification step, the circulation emulsification step, and the desolvation step were performed using the stirring tank 100 equipped with the stirring blade 110 shown in FIG. 6 instead of the stirring blade 50. Got the body

[Comparative example 2]
The rough tank emulsification step, the circulation emulsification step, and the desolvation step are replaced with the stirring blade 50, and the stirring tank 200 equipped with the double ribbon type stirring blade 210 (wetted area ratio of the stirring surface: 15%) shown in FIG. 7 is used. A dip-molded body was obtained in the same manner as in Example 1 except that the above procedure was performed.

The stirring tank 200 shown in FIG. 7 includes a tank main body 201 and a lid not shown. The stirring blade 210 is arranged in the tank body 201 so as to be rotatable by the rotating shaft 204.

The stirring blade 210 is a stirring blade according to a comparative example other than the present invention, in which helical ribbon blades 211 composed of two strip-shaped plates are combined so as to be point-symmetrical when viewed in the axial direction around the rotation shaft 204. It is composed. The two helical ribbon wings 211 are connected to each other by a bottom frame 221 to which the lower end of the rotary shaft 204 is fixed and a pair of side frames 222.

The agitating surface of the helical ribbon blade 211 forms a spiral surface and is inclined with respect to the rotation direction. The liquid contact area ratio: 15% is the sum of the liquid contact area ratios of the two helical ribbon blades 211.

The manufacturing methods of Examples 1 to 5 and Comparative Examples 1 and 2 are summarized in Table 1, and the evaluation is also shown in Table 1. In Table 1, "floating matter" indicates the result of observing the state of the floating matter when the emulsion was left standing in the stirring tank for 20 minutes after the circulation emulsification was completed and the liquid level was observed. In Table 1, "aggregate" indicates the amount of the rubber component remaining in the emulsion after the desolvation step. The mechanical strength is the mechanical strength of the obtained dip-molded article, and was measured as follows.

Based on ASTM D624-00, the dip molding was left in a constant temperature and humidity room at 23°C and 50% relative humidity for 24 hours or more, then punched out with a dumbbell (product name "Die C", dumbbell company) and measured. A test piece was prepared. Then, the test piece was pulled at a tensile speed of 500 mm/min with a Tensilon universal tester (trade name "RTG-1210", manufactured by A&D Co.), tensile strength (unit: MPa) immediately before breaking, tensile elongation (unit: immediately before breaking) :%) and tear strength (unit: N/mm) were measured.

(Evaluation)
As shown in Table 1, in Examples 1 to 4 in which the emulsified liquid was stirred and mixed by the flat plate stirring blades in the emulsification step and the desolvation step, Comparative Examples 1 and 2 in which the flat plate stirring blades were not stirred Less floating and aggregates. Therefore, according to the present invention, it was confirmed that the emulsification was satisfactorily performed and the obtained latex had a high quality with a small amount of aggregates. Example 5 did not use a plate-shaped stirring blade in the circulation emulsification step, so that the amount of aggregates was slightly larger than that of Examples 1 to 4, and therefore plate-shaped stirring was performed in both the emulsification step and the desolvation step. It is preferable to use wings.

Also, with respect to the mechanical strength of the dip-molded article, Examples 1 to 5 are superior to Comparative Examples 1 and 2, and the dip-molded article produced from the latex produced by the present invention has excellent strength. Was confirmed.

The present invention is useful as a latex production method capable of improving the quality because a good emulsified state can be obtained in the emulsification step of a raw material.

3 Stirrer 4 Emulsifier 30, 30B, 30C Stirrer tank (container)
40 stirring means 50, 60, 70 stirring blades 52, 62, 72 stirring surface 54 lattice part

Claims (9)

1. An emulsification step of emulsifying a rubber composition containing rubber, an organic solvent, water and an emulsifier to obtain an emulsion.
   A method for producing a latex, comprising a desolvation step of removing the organic solvent from the emulsion,
   In the emulsification step, the rubber composition is stirred by a stirring device provided with a container in which a stirred product is stored, and a stirring means rotatably provided in the container,
   The method for producing latex, wherein the stirring unit includes a flat plate-shaped stirring blade having a stirring surface that is substantially orthogonal to the rotation direction and faces the stirring object.
2. A rubber solution obtained by mixing rubber and an organic solvent, and a rough emulsification step of obtaining an emulsion in a rough emulsified state by mixing an emulsifier aqueous solution,
   Emulsion liquid in a coarse emulsified state obtained in the rough emulsification step, a circulation emulsification step of further emulsifying by circulating through an emulsifier,
   A method for producing a latex, comprising a desolvation step of removing the organic solvent from the emulsion obtained through the circulation emulsification step,
   In at least one of the rough emulsification step and the circulation emulsification step, the emulsion is provided with a container in which an agitated material is stored, and an agitating unit rotatably provided in the container. Agitating with a stirrer
   The method for producing latex, wherein the stirring unit includes a flat plate-shaped stirring blade having a stirring surface that is substantially orthogonal to the rotation direction and faces the stirring object.
3. In the desolvation step, the emulsion is stirred by a stirring device provided with a container in which a stirred product is stored, and a stirring means rotatably provided in the container,
   The method for producing latex according to claim 1 or 2, wherein the stirring means includes a plate-shaped stirring blade having a stirring surface that is substantially orthogonal to the rotation direction and faces the agitated object.
4. The area of the agitation surface of the agitation blade is 10 to 60% of the cross-sectional area of the agitation product stored in the container, and the latex is produced according to any one of claims 1 to 3. Method.
5. The method for producing latex according to any one of claims 1 to 4, wherein the stirring blade includes a lattice portion having a lattice structure.
6. The method for producing a latex according to claim 2, wherein the rough emulsification step includes a step of continuously mixing the rubber solution and the emulsifier aqueous solution using the emulsifier.
7. A film comprising a latex produced by the production method according to any one of claims 1 to 6 to which a cross-linking agent is added to obtain a latex composition, and a film molded body is formed using the latex composition. Method for producing molded body.
8. A dip characterized by adding a cross-linking agent to the latex produced by the production method according to any one of claims 1 to 6 to obtain a latex composition, and using the latex composition to form a dip-molded article. Method for producing molded body.
9. A cross-linking agent is added to the latex produced by the production method according to any one of claims 1 to 6 to obtain a latex composition, and the latex composition is formed as an adhesive layer on the surface of a substrate. And a method for producing an adhesive layer-forming substrate. 

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